[TenTec] Omni 6 Plus--Epilogue

[K8mp at aol.com]

Radio Dudes:
 
I figured I'd give you a final (I hope) synopsis on the PLL/Synthesizer  
problems I dealt with recently. The info may come in handy for someone, some  
day. By the way, thanks to those who steered me towards the PLL board.  
Otherwise, my radio might still be broken. (or in Sevierville)
 
Symptoms:
The display reads correctly. It even changes when you turn the VFO.  
However, the received freq doesn't change. How did I know that?   When I changed 
bands to 160, I could hear an AM broadcast station.  Turning the VFO didn't 
change what I was hearing.
 
Fixing it:
It was suggested that I check the 5 to 5.5 Mhz output from the PLL. I  
didn't have a freq counter, so I used a Tektronix 456B, which is a 200 Mhz  
scope. The output showed as 5.8 Mhz and it did not change when cranking the VFO  
or hitting the up/down buttons.   The 2 inputs to the board (10  Mhz clock 
and serial freq data) appeared to be good,  so I  was pretty sure I was on 
the right track.  
NOTE: The output also had what seemed like a low voltage level (1 volt  
p/p). I called Ten Tec about the sig level, but they didn't know what it should 
 be. (More on that later)
 
Another Ham who had PLL board problems strongly suggested that I  re-heat 
suspect connections on the board. I did this (in fact, I  hit every 
connection on the board) and the radio worked for 2  days. While it was in the 
working state, I scoped the PLL output and saw it  change with the up/down 
buttons. The voltage level was 1 volt p/p in the working  state, so I now knew that 
was correct.
 
For the next few days, the radio would work then not work. I tried to "make 
 it fail" with heat and cold, but those didn't seem to make a difference. 
During  this process, I made a few notes and drawings of various waveforms 
and  levels around the board. Unfortunately, 3 weeks have passed and some  of 
those notes don't make any sense to me now. Here are the ones that  do:
 
1) At the junction labeled "Test point" (duh...go figure) on the PLL  
schematic: 
When working, and the rig set to 40 meters, it had a 100 mv  sine wave 
riding on a 325  mv DC level. (I forgot to record the  freq).  When failing, it 
was nearly at ground potential (less than 15 mv),  with no sine wave.
 
2) At U4, pin 5, with the rig working, I saw 775 mv when on 40  meters. I 
didn't record it in a failed state.
 
3) At R11 and R12, with the rig working: You should see a 5 volt level,  
with negative-going spikes to ground, every 100 usec.
 
4) U5, pin 6, with the rig working: 133 Mhz signal. I can't remember if it  
was square or sine.
 
5) U4, pin 7, with the rig working: 2 v DC
 
6) U4, pin 1, with the rig working: 3.5 v DC
 
"Sometimes it's better to be lucky than good"
 
While beating on components to try make it work, I noticed that a  slight 
tap on L12 could make the rig fail or work. I re-heated the connections  to 
L12, (including L12's case to ground on top of the board) and the  radio has 
been fine since. That was over 2 weeks ago. I even got brave enough to  put 
it all back together several days ago and it's still working.  Hopefully, 
it's been put to bed.
 
Later,  Joe