[TenTec] Omni 6 Plus--Epilogue

[John]

Good stuff, Joe....thanks for posting.

John W4II
----- Original Message ----- 
From: <K8mp at aol.com>
To: <tentec at contesting.com>
Cc: <w8sjv at nexgenaccess.com>
Sent: Wednesday, October 28, 2009 4:58 PM
Subject: [TenTec] Omni 6 Plus--Epilogue


> 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
>
>
>
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