[TenTec] Omni VI Logic board

[chacuff]

I'll probably get beat up as many may consider this either a sore subject or 
a dead horse or both, but I need to ask. (use your delete key as needed 
please)

I have been working a bit this afternoon on a VI Option 3 that I acquired as 
a spare to my working VI Option 3.  It's too nice a radio not to try to fix.

Has anyone gone as far as to determine what seems to be the common failure 
on these logic boards.  This one has already been worked on by someone.  U21 
has been replaced with a like part number chip but in a different package 
with half the leads in the board and the other half wired in with wire wrap 
wire.  U20 shows signs of being replaced as well.  All else appears to be 
factory.  I have checked the battery and performed system resets with no 
effect.

As I understand the radio was sent to Ten-Tec and deemed unrepairable and 
the owner sent it to someone else who took a shot at it with no luck.

I haven't begun that task of tracing signals around on the board to 
determine if there are proper voltages, clock signals, chip selects and any 
data moving about but will soon.

The tuning encoder causes the display to count up and down as normal but all 
other buttons functions are frozen.  Another strange symptom is the RF gain 
adjusts the noise level up and down but the AF gain control has no effect.

I do have a working rig but am not willing to risk it by swapping the logic 
cards at this point.  I will use it for making measurements of what is 
normal as a point of reference.

I know there was quite a bit of discussion as recently as a year ago on this 
subject, based on a search of the archives, but never any indication of a 
solid determination of the pattern failure.  I'm sure what is failing on the 
boards is common to most all of the routine failures...those not related to 
lightning or other external factors.

Any info you would be willing to share would be much appreciated...

Thanks

Cecil Acuff
K5DL