The TS-850S Repair Page

Maintained by Larry “Tree” Tyree – N6TR – Boring, Oregon (N6TR Homepage)
Last updated on 19-March-2019

This page has moved to a new home on after many years on 
RIP “JZap” – K2MM – John M Zapisek
May 25, 1951 – August 18, 2012

Please feel free to link to this page, but please do not copy the information here.  It is updated frequently (well if you measure time with a calendar).

The Kenwood TS850S Amateur Radio Transceiver is a very popular radio. It was in production from 1989 until around 1996 when the TS870 replaced it. This page is dedicated to helping 850 owners keep their radios on the air.  This is starting to become a bigger and bigger challenge as time goes on.

I would like to thank all of those who have provided information used on this page. If you have other information that would be of interest, please pass it along to me and I will add it to the page.  My e-mail address is tree at

First – The BAD NEWS!!

One of the biggest issues with TS850S repair is finding parts.  I am sorry to say that getting new parts is almost impossible now and likely the only way you are going to fix your radio is to find a donor radio that you can swap modules with.  However, there is one part that is really a big problem for those who have some of the first year’s production.  This is the four YM6631 DDS chips on the CAR board.  This is a custom part made by Kenwood for the radio.  If you have these older chips – it is only a matter of time before they will self destruct.  Kenwood realized they had a problem and fixed it in the YM66312 version of the chip.  However, there was no extended warranty for this problem – and sadly – there are no longer any of the new chips available to replace the old ones. 

The net result is that if  you have a TS850 with the older chips – you are going to have a hard time keeping this radio on the air (or getting it back on the air if you have had issues).  Over the years – many people have contacted me via e-mail saying that they are having weird problems with their radio.  My first question is to find out if the serial number starts with the number “2” – and if so – check to see  if they have the old DDS chips.  Often – they will have had one or two of them replaced – but the other ones are now acting up and they are out of options. 

These chips do many different things in the radio – from generating RF frequencies used in the mixers – to even generating the side tone when sending CW. 

It is really sad that Kenwood is not doing a better job standing behind their radios.  It is due to this situation that I will never buy a Kenwood radio again.  You can find people at Kenwood who are sympathetic – but they have been unable to convince management to produce some more of these chips. 

Sometimes – you can find some on ebay.  I think I saw four of the new chips sell for over $300 a couple of years ago.  I have sold a CAR board with four new chips on it for over $300 as well.  The new chips DO NOT FAIL!!  This is a clear indication that something was wrong with the design of the older chips. 

Some people have parted out their TS850 – but often this due to the fact that they have the old DDS chips and have given up.  

NOW – for the good news!!  I was hoping someday, someone would design a replacement CAR PC board that used modern components – and that has finally happened!!  You can find them for sale on ebay.  Hopefully – this link will work for you.

Useful Links

TS850S modifications - A good collection of 850 mods.  Here are some helpful pictures of two mods I have done.  One  is an RX antenna input and the other is enabling the MONI control to adjust the CW sidetone level.

Pacific Parts - You can purchase some parts for your radio on-line.  Please be prepared to pay top dollar for parts however. They do NOT have the DDS chips available any more.

AVVid Kenwood repair - Clif can fix your radio if you can't. Check out reviews here. I am happy to report that rumors of Clif being out of business are now incorrect.

K0BX'S Kenwood  Interface Page - Lots of good information here.

Kenwood e-mail list - a good place to ask questions.

Some pages from the service manual - By request for those who can't get a copy of the service manual.

EB5AGV's Amateur Radio Documents – More service manuals and documentation. 

A Russian web site with a .PDF copy of the service manual (without the board drawings I believe). 7 Megabytes.

A new web resource with .PDF copy of the service manual AND board drawings. (thanks 9H1FQ).


Common Problems with the TS850 and Possible Cures

ALC voltage problems - ALC action seems very unstable (did Kenwood put caps in backwards?).
C1 of CAR unit leaking.
Carrier Balance adjustment.
Carrier setpoint adjustment.
Dead Display
Frequency dial calibration a quick check and adjustment procedure.
Frequency display is all dots - and radio sends "UL" in CW over the speaker.
Low Receiver Sensitivity
Monitor function does not work on SSB and/or CW, or is very distorted.
No transmit audio on FM.
Noise Blanker Performance Improvement.
Passband tuning erratic while on SSB, okay on CW. People tell me I am off frequency.
Poor solder connections.
Prevent Static Buildup (and a warning)
Radio stuck in send mode - no receive.
Raspy signals on some, or all bands. Frequency display all dots or blank.
Receiver dead except on FM.
Receiver overloaded by AM broadcast stations.
Reduced receiver sensitivity and transmitter output as you increase frequency
Repairing the rotary encoder.
SO-2 Replacement
Transmitter power drop off and burning smell when in transmit.
VOX Gain Improvement

Reduced receiver sensitivity and transmitter output as you increase frequency (N6TR)

This is the typical symptom from the most common component failure I have heard of in the 850. The cause is that some of the band pass filters on the RF board are always enabled by the 74LS145 decoder chip. You can verify this by using a voltmeter and seeing if one of the outputs from the chip is always "low" (near zero volts).

I would suggest putting a socket down on the board for this IC - so if it ever fails again, you can replace the part quickly. This will require removing the RF board (which is the one underneath the radio with the shiny shield on it). The IC is under this shield.

I have received a comment that Kenwood often replaces a MI303 diode when replacing this chip (thanks K5TSQ). There is mention of a modification on the Kenwood site that might also help eliminate this failure. Check out the service bulletin for more information.

I believe this failure might be a result of a high RF voltage being presented on the receiver input. I do think one or two of the failures I have seen might have been caused by transmitting with full power with a different radio with antennas that were close. It has also been suggested the 47K ohm DC input resistance of the receiver could easily allow nearby lightening hits to produce a high voltage.

Perhaps putting an inductor on the RX antenna input to ground would help as explained as follows:

Prevent Static Charge Buildup (K0ZL)

Remove the surge absorber tube on the small pc board connected to the antenna connector, (remove top cover of filter unit, top of rig, rear-center, to get to it). Obtain a 1-2 milli-henry pi-wound choke (one of the big oldies-but-goodies), and tack solder the surge absorber across it. Re-install the assembly where the surge absorber was. That's it. You now have 2 ohms to ground DC, and much harder to develop high static voltage. The part number is Hammond 1535B, 2.2 mH, from Antique Electronics ( The surge arrestor is DSA301LA.

9H1FQ warns: “I had an R7 vertical connected to my TS850. On a clear blue sky day, I saw a flash at the back of my rig. At the time , I was unaware that I had a DSA301La gas filled  protection tube. Later I found, that the R7 vertical has a choke, which bypasses the whole matching unit, as a protection. The choke was open circuit! I would think twice, before replacing the gas filled tube with a choke, as you mention on your website.”

Frequency display is all dots - and the radio sends "UL" in morse code over the speaker (N6TR)

The “UL” indicates an unlocked condition with the frequency synthesizer. 

This failure might be temperature related - and possibly show up more often when tuning the VFO in specific places (around 1800 - 1850 kHz is one place I have seen it fail). This is probably the DDS chip on the carrier board that produces the VFO frequency. The CAR board is under the bracket that would hold the voice memory board if you had it (under that door on the top of your radio). Remove the four screws that hold the bracket and find the CAR board with the four big chips on it. You can put a scope on the PLL-1-DL01 output and watch the output voltage as you tune around. On a functioning board, the output level should be pretty constant as you tune the VFO through a 500 kHz segment. If the output changes a lot when the VFO jumps from one frequency extreme to the other, then the failure is probably the IC1 DDS chip. They cost $28 and will require you to have the right equipment to work with surface mount VLSI ICs.

One step you should take first is to make sure all of the connections to the CAR board are good.  Remove all of the cables, and reseat them.  

Raspy signals on some bands - maybe no display or all dots (N6TR – NR1DX)

I had this problem with one of my radios after taking it to Louisiana for the Sweepstakes.  The signals on 20 meters all sounded raspy - and broad.  At first, I thought it was something wrong with the transmitter of the other station, but when all of the signals on the band had the same problem, I knew it was my receiver.  I believe my transmitted signal sounded as bad.  It seemed to be temperature related and in extreme cases, the LO1 output from the PLL board was going away. 

And then Dave, NR1DX, hit the nail on the head with this:

I just finished fixing the second TS-850 in my career with this problem...particularly symptomatic is the raspy sound which gets worse as the unit heats up. In both cases TC1 on the PLL board needed only to be adjusted so that TP2 reads 5.0v. (See the service manual page 98, step 8).  The little trimmer cap TC1 inside the VCO-2 can has been documented as getting flaky with time. On the first radio the problem occurred at about year 7 resetting the cap cured the problem and the radio ran fine for another year without incident before I sold it and upgraded to a TS-950SDX.

I recently came on a bargain ($550) TS-850SAT (10 years old) which was too good to pass up (including the a 500HZ and 270 Hz CW filters and a DRU ).  It had this same problem only worse in that after setting the cap the unit would play fine... for a while, then drift back into the same old problem.  I then replaced the cheap Kenwood trimmer cap with a glass piston trimmer cap which so far after four hours is stable as a rock.. Ill send you a picture of the mod ( if you want it) as I had to drill a hole in the side of the VCO-2 can to mount the new trimmer cap.

So check your problem radio's PLL - TP2 when it gets raspy, I'll bet it is no where near 5Volts, the setting is quite critical.

When I checked the voltage on TP2 (located near the front of the board right next to the smaller shiny box), it was around 4 volts.  I adjusted it up to 5V, and things sounded worse...  that was until I removed the lead to the DVM (it was acting like an antenna and picking up all sorts of junk).  After that, the radio sounded like new.  When I thanked Dave, I got this in response:

Don't thank me ... thank Cliff at AVVID he is the one that clued me in the first time three years ago. The guy is amazing Here is the picture of the modification and the PLL board afterwards.

You will see the little piston cap on the left of the VCO2 can. The little melt from the soldering iron on the edge of the little blue plastic thingy was an "aw- $#!^", in trying to clear the holes in the board. Didn't hurt it electrically...

To do this you have to remove the whole VCO2 enclosure there are about 5 places where the can is soldered to PLL board plus three wires. If you have never used solder wick now is a good time to learn. Removing the can is almost as difficult as brain surgery but still not as bad as changing one of the DDS chips.

Pass-band tuning is erratic while on SSB, but seems okay on CW. People also tell me I am off frequency.  (N6TR)

This happened to one of my two TS850Ss. The culprit was IC4 on the CAR UNIT (DDS chip) that generates the CAR signal (on the bottom of the CAR UNIT schematic page). They cost $28 and will require you to have the right equipment to work with surface mount VLSI ICs.

The SSB and/or CW monitor functions do not work - or is very distorted on SSB. (N6TR)

Another DDS chip on the CAR unit (IC3) produces both the RF frequency used to demodulate the SSB for the monitor function (MCAR) and also the audio tone used for the sidetone (STON). If this chip isn't working correctly, it would explain these failures. They cost $28 and will require you to have the right equipment to work with surface mount VLSI ICs.

Receiver overloaded by AM BC stations (N6TR)

This could be the 74LS145 failure mentioned above. It could also be the diode mentioned in the Service Bulletins (thanks KS4XG). I also had this problem in spades on one of my radios - but it turned out to be a pair of back-to-back diodes I had installed when adding the external RX antenna modification. Removing this cured the problem.

ALC voltage problem (NB1B)

The problem manifested itself as varying power output; if you close the key and watch the power meter, it will go from zero to full output and then back to zero output on about a 5 second cycle. What is happening is easy to see by using an external wattmeter and putting the 850 meter on ALC; the ALC goes from zero to max as the power goes from max to zero. This was explained to me by the guy that diagnosed and fixed the problem. The circuit that is bad is one that has resistors, transistors, and capacitors all on a multi-legged component. It is a multivibrator that develops a voltage that is then rectified and amplified and is used as the ALC voltage.

Something goes bad and it causes a very slow oscillation, and the ALC voltage swings from zero to max and back again, causing the power to oscillate in step. I don't know how much the part cost, but the guy spent 8 hours on the radio (not a Kenwood Factory Rep) before he could figure out what was going on. Since then, I have seen probably a dozen postings from hams that have had the identical problem that have sought an explanation for it.

K0BX reports the same problem: The DC-DC board X59-1100-00 fails and causes the power output to go up and down. First time I had Kenwood replace it for a total cost of $150.00. This past December I replaced it my self for a cost of about $14.00 with shipping. I have a detailed description on how to do this repair on my webpage and then go to TS850S ALC/TX PROBLEM.

And this from K2UT:   One of my 850s had the DC-DC board replaced about 18 months ago after experiencing the usual problem: output power oscillating back and forth.  Had it repaired and the rig was working great.  Then, about 4 months ago, a new problem appeared. I had a couple DC-DC boards on-hand for repairs, but this didn't seem to fit the usual pattern.

When the rig was on for a while but not transmitting, the first SSB transmission would peg the ALC meter for a couple seconds with no output. It would then drift back down to a normal level, and output power would rise.  Transmitting again within 10 seconds would work fine; no ALC problem. After about 15 seconds, the cycle would repeat.

I called Kenwood and suggested the DC-DC board, but the repair tech didn't think it could be the problem. Rig went back to Kenwood for repair. The problem? The f***ing DC-DC board! $135 and six weeks spent when I could have repaired it myself.

Design Mistake? (ON4CAF / PA0LBN): This problem may be caused by a DESIGN MISTAKE on the part of Kenwood.  This DC to DC converter creates a NEGATIVE voltage output and is filtered by two capacitors (33 uf).  They are C626 and C628.  D605 is a Zener diode to prevent the voltage from going too far negative.  If you look at the schematic, these components are shown with the + side of the capacitors connected to the negative voltage.  

Click here to look at the schematic.

Only a schematic error (ON7GO)

However, ON7GO reports that the parts at least on his PCB seem to be okay, and only the schematic has the caps reversed. He also found a way to improve the operation of the board:

My TS850 developed the ALC problem about 3 years ago, but I did buy a new rig and the TS850 was put in reserve status. Then I found on your website information about this problem. I checked my TS850 and it had still that problem. So I removed the PCB with the dc-dc convertor and put it on the testbench at work. I checked C626 and C628, they were wrong on the schematic but they are OK on the PCB. I fed the DC-DC convertor with 12.5 V at L605 and it worked fine, output was -6.2v. But when I lowered the input voltage strange things began to happen. At an input voltage of 12.43v, the output voltage started to go down and up. When I checked the oscillator signal on C625 (output of oscillator) it fell regulary out and started up again . The problem got worse with lower input voltage and the dc-dc convertor stopped working at about 11.9V. So I concluded that my PCB was working ok, but that the input voltage in my TS850 was low (maybe got lower with aging). I was at my work and my TS850 at home, so measuring the voltage was out of the question.

So I tried the following: I changed resistor R2 and R3 (on the dc-dc pcb) from 22k to 18k and checked again. What I found now was that the dc-dc convertor worked fine from 12.5v down to 9.5v. Back at home I then put the PCB back into the TS850 and now have again a rig that is working fine, ALC and output are stable now.

Well, there you have it... change a couple of resistors and perhaps your board will start working again.

+12V Regulation Root Cause (N6TR)

I was having problems with the output of my radio starting off okay when I started transmitting, but would quickly go WAY down and after a second or two, build back up to full power. I finally decided to dive into this and did a bunch of probing on the RF board to see if I could figure it out.� After considering the effect of the -6.1 volt supply (created by the DC to DC converter discussed above), I found that the supply was indeed going out of regulation when I started transmitting, but would recover in sync with my power coming back up.

Changing the resistors is not easily done, so I first replaced the 33 uF caps in the circuit - thinking that maybe they had dried up. That really did not impact the problem. Then I checked the +12V input on the back of the radio and found 13.8 volts in receive - but only 12 volts when I went key down at full output. I checked the power supply and it was solid - so that voltage was being lost in my +12V power distribution! A few years back, I installed the RigRunner power distribution box. I removed the RigRunner from the equation and hooked the radio's power cord up directly to my power supply.  Now, when I transmit, I see 13.4 volts at the back of the radio with full power and there is no longer any hint of the original problem.

It could be that changing the resistors that ON7GO mentioned would have fixed the problem as well, but I don't really want to have 30 some watts of power being lost in my DC power cabling.

Low Receiver Sensitivity (K7FR)

The only failure that I had on either of my 850's was that one of the switching transistors that muted the receiver during xmit went sour and wouldn't go all the way to cut-off in receive. This had the effect of putting about 20dB of pad into the receiver. This happened on both. The first one went out to be fixed the second one I did myself. 

N6TR adds: Low receiver sensitivity could also be related to the first item on this list (74LS145 part).

No receive except on FM (from W9PL/7)

My 850 was purchased new in 1993. It was repaired twice under warranty for the same symptoms. The symptoms (to make a long story short) involved an inoperative receiver in all modes other than FM. The initial failure occurred after a few months of use, in 1993. The second failure occurred after only 5 hours of operation following the first repair action. However, since the second repair action, it has worked just fine and I am very happy with the radio. The first time they repaired it, Kenwood replaced a VMI308 diode and a 3SK131(M) FET (Q15) on the IF Unit. Q15 is the last of stage of IF AMP preceding the SSB Demod. The second time they repaired it, they replaced the same FET (Q15) on the IF Unit. I suppose they had a "bad" run of Q15 FET devices at that time. 

No receive (N6TR)

I had a friend send me his radio with this symptom.  I noticed when I turned the radio on, there was an oscillation that I could hear coming from the RF board.  I found it on a bunch of signals - and measured it around 11 kHz.  I looked at the 3rd mixer of the receiver (which is on the IF board) and saw the 455 kHz signal going into it just fine - and nothing coming out of it.  You could inject an audio signal there if you wanted to see if the audio chain was working okay.  I also didn't see anything going into the mixer. 

My attention shifted back to the front end - where I saw all of the strange oscillations.  I looked for the signal coming into the first mixer - which is a pretty high frequency from the LO1 signal - buffered by Q28.  I couldn't find it.  I checked the two diodes that steer the output of Q28 to either the receiver or the transmitter - and saw it working FB for the transmit condition, but not so good for the receive condition.  The bias for the diode comes from the signal RXB - which should be around 8 volts when in receive.  It wasn't.  This is generated on the IF board on one of those little modules that stand vertical on the board.  Without this voltage - there is no way the receiver is going to work.  I could jumper the RXB signal to 8 volts and make the oscillation go away.  My next step is to see if doing this makes the receiver function again.  I will probably replace the components on the little pc board to fix the problem as Kenwood probably wants too much money for the replacement board.  Three is only about 10 components on the board - and they should be cheap to replace from DigiKey or Mouser.

Well, it turns out the little board is probably okay.  I found that the problem was the TXB signal was not going all the way to ground when in receive - which kept the RXB signal from turning on all of the way.   If I grounded the TXB signal, the receiver came to life.  I removed the module - and found that both RXB and TXB were at ground.  However, if I pulled RXB up to 8 volts, TXB came up to about two volts...  NOT GOOD!  There is obviously something leaking RXB voltage over to the TXB signal.  My next step is to try and find where the leakage is taking place.  Probably a diode somewhere has turned into a short circuit. 

I swapped RF and IF boards with a good radio and isolated the failure to the RF board.

I checked all of the diodes on the RF board with a meter. There were a few that had funny readings, but they were the same as my good RF board.  I started removing various inductors and resistors to isolate the TXB and RXB signals and eventually found that removing the series inductor (L5) that biases D3 during receive stopped the leakage.

This narrowed it down to either D3 or D31 (the path back to TXB) - and it was D31 that was bad (RLS135).

PA0RLS adds: Note that there may be other causes to make TXB not 0V during receive such as D30 on the RF-unit.

More information provided by Grant, K1KD:

22-04-2000 TS-850S Low/no Receive sensitivityReports of low or no receive sensitivity accompanied by a lack of audio
from the speaker during CW or SSB modes might be caused by improper RXB voltage levels. Normal RXB voltage is +8 Vdc during receive and 0 Vdc during transmit. If you find approximately + 2 Vdc during receive you might suspect a problem with a leaking diode, D31 on the RF unit (X44-3120-00).

Cause: D31 is used as the transmit switching diode. Leakage of this diode id most probably caused by electrostatic surge or discharges from the antenna.

Parts required: D31, MI204

Procedure: A temporary cure for units that have already been manufactured is to replace D31 with an MI204 diode. Future production radios will change D31 to an LFB01 diode and incorporate a change in the printed circuit foil pattern to allow addition of a series diode. D103 (LFB01).

Poor solder connections (N6TR)

It is possible that one of my DDS chip failures was really due to a poor solder connection. I noticed when replacing the chip that there wasn't a lot of solder on the IC pins. I was able to reuse this chip on another board and it came up and worked fine. The following comments are from an ex Kenwood service person: The history we were given regarding the solder quality is that amateur gear is a very low priority, low quantity production run at Kenwood. The PCB blanks are all made at a plant at one time for the estimated life production run of the rig. Then they are shipped to a plant where maybe 6 months or even years later the PCBs are used for a small run of the units. This plant is on a coastline and the boards suffer from salt air corrosion problems, so the solder does not wet properly. I can believe that story, but they still suffer from very poor QC with regard to insufficients, cold solder, and lack of eyelet properly done before soldering on the older PCBs. Kenwood has service bulletins out on some boards, where they point out 30 to 60 feed through for shotgun re-soldering of eyelets with a bare wire fed through the eyelet hole when re-soldering and then clipped off.

Radio Fails in FM Transmit mode – microphone amplifier not working (CT2HMX)

I saw the Board X59-3000-03, FM mic amp and all components were okay. I put a 1 kHz tone, 5 mv, into the the mic input on the front of the radio and saw the signal on C630 on the RF board (X44-3120-00). I did not see the signal on the collector of Q609 however. The hfe (beta) of this transistor was very low and I replaced Q609 (2SC2912A) on RF board and the problem was solved. The old transistor wasn't bad - but the hfe gain was very low and caused the failure.

Replacing Rotary Encoder (DJ3TZ)

I recently had a problem with my 850 which I could fix myself and would like to share this information. It concerns the rotary encoder that transforms any movement of the main frequency dial into digital pulses. The part in question is a COPAL RMS20 encoder.

For a long time, my Kenwood TS-850 had the problem that while turning the main frequency dial, the frequency would stop changing with the last digit jittering. For several years, the problem occurred so rarely that it did not really hinder operation, and I saw no chance to locate the problem.  Recently, however, the problem became more serious, making the radio almost useless. Using the 850's service manual, I was able to locate the encoder and its connection to the radio's main data bus.

The encoder has two data outputs, A and B. Both carry digital signals at 5V level. Its frequency depends on the rotation speed and the signals differ in phase to allow for clockwise/counterclockwise detection. Together with my friend Theo, DJ9PK, I observed these signals with an oscilloscope. One of them vanished whenever the the frequency stopped changing.

Taking a look into the encoder, we tried to locate any kind of mechanical problem, perhaps a little bit of dust, but there was none.  The encoder consists of a magnetized wheel and an magneto resistive Hall sensor, in addition with some electronics. Checking the signals from the sensor revealed that is analogous. It consists of a voltage of approximately 2.5 V DC plus approximately 80 mV AC when turning the shaft.

We found that the amplitude of the AC voltage strongly differs while turning the shaft. The reason is perhaps that the magnetic field produced by the wheel is not constant, but seems to depend on its position towards the Hall sensor. The amplitude seems also to depend on other, unknown factors.

The PCB inside the encoder has an IC that obviously works as a comparator and digitizes that input. Checking its 8 pins revealed that two carry the input coming from the sensor, two carry the digital output, and two pins are connected to reference voltages. These reference voltages can be adjusted with two variable resistors on the left and the right of the IC.

Turning one of the resistors fully into one direction causes the digital output to become constantly low or high, respectively, because the reference voltage then is always higher or lower then the sensor signal. Within a range of 10 or 20 degrees, the comparator works as intended. I suspect that the reason for the occasional failure was that the amplitude of the AC signal was sometimes below the comparator's reference voltage, thus causing the output to stay high or low.

Rotating the shaft by hand but at a constant speed and observing the digital output on the scope allowed us to adjust both resistors so that encoding now works fine.

Here is the pin layout of the IC:

1 Output B
2 Reference voltage B
3 Input B from sensor
4 Gnd
5 Input A from sensor
6 Reference voltage A
7 Output
8 + 5

I hope this information will be helpful to you and others.

C1 of CAR unit leaking (PA0RLS)

Beware of C1 on the CAR-UNIT: If it starts leaking (I mean fluid coming out of it) then you may expect all sorts of crazy things.  Most common are: RX is deaf and/or the TX led is on during receive. Monitor the TXB line during receive: It MUST be 0V. If not the problem above may be the cause, as the + from this cap. leaks to TXB ! Replace C1 by a normal (not SMD/metal can) electrolytic capacitor: 100 uF / 25V will do. You may see that the fluid from the old C1 is etching the PCB and in one case I had a hole burnt in the PCB just under C1. Replacing ALL other 10 uF elec.caps is strongly advised, as they ALL start leaking fluid that ruins the PCB. Remove them all and CLEAN the PCB before putting new caps on.


1. Open the little hatch on top of the radio. Locate VR501, VR502.
2. While depressing F. LOCK, turn the transceiver ON.
3. Click the M. CH. control until MENU 00 is displayed.
4. Select LSB
5. Turn the power control all the way down.
6. Push the SEND switch.
7. Make a slight adjustment to VR501 to make your voice higher or lower while speaking into the mic, listening to yourself in the monitor.
8. Put the radio in USB.
9. Make a slight adjustment to VR502 to make your voice sound higher or lower while speaking into the mic, listening to yourself in the monitor.
10. Put the SEND/RCV switch back to RCV, and then press CLR.
11. Listen to on-the-air signals on both USB and LSB to see if additional adjustment is required.

TS-850 Carrier Balance Adjustment (K6LL)

1. Open the bottom hatch of the TS-850.
2. On the IF unit, locate VR8 and VR9 (near the little Murata filter).
4. Construct an RF voltmeter by sticking a silicon diode, such as 1N914 into the antenna socket. Connect a sensitive DC voltmeter between the diode and ground.
5. Push the SEND switch on the TS850 and adjust VR8 and VR9 for minimum indication on the voltmeter.
6. Make sure that BOTH of these controls are going through minimums. It is possible to get so far off on VR8, that VR9 has no effect.
7. Check that LSB is ok also.
8. For the best final measurement, take a piece of insulated wire, bare one end, and stick that end into the antenna socket of the 850. Bring the insulated wire NEAR the receive antenna connection of a second receiver tuned to the carrier frequency, and make fine adjustments to the null, with the POWER control set at MAX. Of course, do not connect the second receiver directly, in case your hand slips while you are making the adjustment! I just wrap the insulated wire around the center pin of a PL-259 connected to the second receiver.

Radio stuck in send mode - no receive (I7ALE)

The problem was that when you switched the radio on, in would go in "SEND" status, in any band or any mode. The set was perfectly working, in the "Send" condition, but no way to have it go back to "receive".

After checking out all the most likely "areas" for this problem (microphone port, SEND/REC push button, keyer input, etc.), further analysis of the digital unit X46-3080-A4 and in particular of the IC2 processor revealed that pin 5 of IC2 was LOW, as it should be when the rig is in the SEND condition. This pin is also connected to the SS line, going from IF UNIT to the digital unit and to other boards, among which the BK SW, which is an interface between the CW KEY port and the IF UNIT. It was discovered that the problem was due to a short between the collector and emitter of the "digital transistor" Q3 in the BK SW board, which short forced the SS line to LOW. Replacing the damaged transistor (DTC 124EK) solved the problem.

Noise Blanker Performance Improvement (WA3REY and KI6MZ via N3US)

There was a lot of interest about the noise blanker mod posted here a week or so ago so I'm passing along my results. After performing the mod (copied below) the noise blanker in my TS-850 reduces line noise from an S8 on 10 meter AM to S3 or less. This is much better than before the mod. On SSB, the noise blanker reduces noise several S units, but not as dramatically as on AM. The mod is "simple": Remove C618 and C619 from the circuit. But finding the chip caps is next to impossible without using the Service Manual. List member Rick, KN3C, located the chip caps - they are on the solder side of the board - then removed them for me. Again, don't try the mod without the Service Manual because the two caps are unmarked. -  73, Tom, WA3REY

---Mod follows---------
Hi Dave When I took delivery of my TS850 and used it along side of my TS940...the 850 was noisy and turning the noise blanker on had no effect...some of the noise was radio noise and some was power line noise ...the noise blanker in the 850 had no effect on the power line noise...I sent the radio back to Kenwood...they said it operated as they wanted it to...i.e. no trouble found... I compared the noise blanker of the 940 (works very good) schematic to the 850...electrically they were the same except for a bypass capacitor in the output of the noise pulse detector...I guessed this bypass capacitor was slowing the noise gate down and it was not blanking the leading edge of the power line noise (very fast rise time noise)...I cut the bypass capacitors) out of the circuit (surface mount capacitors) and now my 850 noise blanker works as good as the 940 noise blanker.

On the schematic you got in the operators the RF UNIT at the bottom of the RF unit schematic is the noise blanker schematic...the circuit symbols are in the 600 range i.e. R601...C601 etc...the bypass capacitors to cut out are C618 and C619 (0.01 mfd)...the noise blanker board is located in the upper compartment on the left hand side (approximately under the speaker) is about 2inches by 3 inches and can be removed for the cutting of the traces to the capacitors.... The service manual has a much better readable schematic and also a drawing of the board...the drawing will not copy and remain if you have any trouble locating these capacitors, try to locate a service manual. Hope this helps. -  Jim KI6MZ

SO-2 Replacement (N3BA)


The SO-2 unit is no longer available, or at least is really expensive. I have been able to make an aftermarket SO-2 from commercially available parts, and the performance has been astounding. It really settled down my drifty 30 mil s/n TS-850, and I made one for a friend who swears by it. I've built and sold 6 more of them for $75 apiece. If you want to post a link to me on the page, I would build one for anyone who needs it. You can reach Bob, N3BA at robertan at cfw dot com.


Sudden drop-off in transmitted power (K6LL)

Along with a terrible burning smell coming out of the fan vent whenever the radio is in transmit. When the top cover is removed, the smell seems to be coming from the left front side of the radio. The following failure occurred on both of my TS-850's within a six month period.

Problem: The problem is that C1 on the Carrier Unit, X50-3140-00, has failed. This board is the second board down in the 3-stack of boards on the left top side of the radio.

Solution: Unscrew and remove the shield that covers the board. Access to the underside of the board is not necessary. Inspect C1 for signs of burning. C1 is labeled, and is the largest of the electrolytic caps on the board. If damage is verified, remove C1 by heating its two small mounting tabs to unsolder it from the board. After C1 is removed, make sure that the circuit board trace that runs underneath C1 has not been blown open. If so, repair it by jumpering with wire. Replace C1 with a conventional 47uf 35vdc radial lead electrolytic capacitor. I used one from Radio Shack. Mount the capacitor in a couple of convenient copper holes that are adjacent to where the old capacitor leads were connected. The plus side of the cap attaches to the trace that goes to L1 (looks like a resistor, it's labeled), and the negative side goes to ground.

Dave Hachadorian, K6LL
Yuma, AZ


TS-850 Quick Dial Calibration Check (K6LL)

1. Tune the radio to 10Mhz, so you can hear WWV.
2. Press the "tune" button on the radio (keypad #7).
3. Set vfo A to 10000.10 KhZ.
4. Set vfo B to 9999.90 Khz.
5. Flip back and forth between vfo A and B. On both, you should hear a low tone of about 100Hz, just off zero beat of the WWV carrier. If the tones are not equal in frequency, adjust TC-5 on the PLL Unit, as follows:

TS-850 Quick Dial Calibration

6. Remove the TS-850 top cover.
7. There is a three-stack of boards on the left side of the radio. On the left side of the lowest shield, there is an elliptical cutout. Peek inside, and you will see the screwdriver-adjustable pot TC-5.
8. Make small adjustments to TC-5, and repeat step 5 above until the two tones are exactly equal in frequency.

Dead Display (N6RA)

Thanks to KH6DV who pointed me in the right direction, I fixed my TS-850's dead display.

The problem was a bad 470 microfarad 16 volt electrolytic associated with an inverter that powers the LCD display.� The cap leakage was not apparent until the cap was removed.� In my case, the cap damaged a circuit board trace, so I also had to install a jumper. The damage to the trace was not visible, so it was hard to find.� The damaged trace interrupted the power to the inverter.

Oddly, the cap (labeled C18 on my board) is not on the service manual schematic (page 173), but it is in the "pictures" on page 174. For good measure, I replace the other two electrolytics on the board (two 100 microfarad 16 volt electrolytic caps).

I still think the 850 is one of the best radios ever made.

And this from G3LVP:

I'd just like to say thanks for running the TS850 site. I just had an intermittent display fault on my TS850S and using the information supplied by DL6NAA saved me much time in locating the cause of the problem which was caused by a burnt out (!) plated through hole on the PC track carrying the clock signal to the display. (Why did the PTH 'burn' out? I have no idea but it does worry me a bit!).

Having successfully fixed the problem I was alarmed when the display then failed completely! I traced this to another track which had failed under electrolytic C18 this supplies the 8V to the display inverter. There was apparently nothing wrong with the capacitor, no sign of leakage etc. The 8v supply for the inverter is fed via L3 but this isn't shown on the diagram on my copy of the service manual.

Apart from this fault the only other repair which I've had to do since I bought the radio (in San Antonio) back in 1996 was to cure the ALC instability problem by changing two SMD resistors in the -6v generator circuit, not bad for a radio which is at least 15 years old & gets used most days & sometimes in contests. The only thing which it lacks is the dual RX capability which would be very useful for contesting & DX pile-ups.

Vox Gain Improvement (N3BA)

Bob, N3BA offers this modification to improve the VOX gain:

I have a link to another great mod that applies to the TS-850. I've been using a Heil HC-5 mic cartridge on my '850 that sounds great but has too little drive to trip the vox properly, even with vox gain all the way up. I performed this easy mod on the vox daughter board (located on bottom of rig, right rear side with knobs facing you) marked 1080-01 on the non-component side. Same vox board is used in the TS-950, and the mod posted at has great pics showing how to do it. Now I have plenty of vox gain for the Heil, and you can always turn it down enough to use an MC-60 or other mic.

Intermittent Display (WB6TMH)

I discoverd a spot of black "goo" on the front (LCD) side of the LCD unit.  After cleaning off the goo, it was apparent that the goo had corroded away the trace that carries the serial data (LDA).  Replacing the bad trace with a wire fixed the radio.