[DEMI] 144-28K problems

[George Fremin III - K5TR]

I want to thank everyone who offered advice on my sick transverter.

It is still sick.

To recap the problems:

It is deaf on receive - sort of like if a 20 or 30 or more db pad
was in place.  When truned on the RX noise floor comes up only 
very very slightly.

It does not put out much power - like less than 1 watt.

All of the (there are four in the manual) RX voltage test points
check out ok.

All of the TX test points check out ok.

The T/R relay seems to be working.

I called DEMI today and got some other places to check.
the suggestions were:

1. PIN diodes CR3 and CR4.
   I am not sure how to check them but the look and act the same
   as the ones in my 222-28 transverter when checked with my volt meter
   when the transverter is not powered.

2. Check the inductors in the LO signal path - they all seem
   to conduct - I might need to double check them.

3. R28 - near F1 - should see a votage drop across this - I do.
   It has 13v on the 13v side and about 6-7 volts on the other side.
   The only thing that I notice is that this resistor is getting 
   almost too hot to touch.  I powered up the 222 transveter and 
   the same resistor gets warm as well but I think the one in the 
   144 box is getting a bit warmer.
   Could this mean that IC7/MAV11 be drawing too much current?

4. The junction at R15 / C22 peak the voltage with C24.
   I can do this and the voltage does change and I can peak it up
   just fine.

5. And then something in my notes that says R3 - TX.
   I am not sure what he wanted me to check here but maybe it 
   was to see the voltage drop on TX across this resistor and I 
   think it is doing the right thing.

I have also heated up some of the solder joints in the LO chain 
that looked like they might have problems.

Comments?




-- 

George Fremin III                 
Johnson City, Texas             "Experiment trumps theory." 
K5TR (ex.WB5VZL)                            -- Dave Leeson W6NL
geoiii@kkn.net                             
830-868-2510                      
http://www.kkn.net/~k5tr