[TenTec] Buzzing OMNI VI caused by 962 power supply problem

[Zivney, Terry L.]

Jeff Kelly, KT2K,  wrote:

>>Woke up this morning to a problem with my OmniVI Opt/1 and 962.
On startup there is a buzz (brrrrrr) for a few seconds form the rear center
to left of the radio and the display comes up a half brightness.  I then
tried
feeding the radio with 12v from a astron supply and while I don't hear the
buzz the display was still at low brightness.

I then reseated all the molex connectors/etc. in the radio with no luck.
I then tried a clear reset and a master reset and while the brightness
returned
now some of the display digits are gone or intermittant.  The buzz is still
there
with the 962.

The receiver functions fine.  Didn't transmit.

I guess a trip to TT will be in order but wondering if anyone has any
suggestions?

*****

I had a problem with an OMNI VI+ (964) and 962 combo this past CQWW CW
contest.  The buzzing had been happening at power up from time to time
for a year or so.  But, after the second or two of buzzing, things always
worked ok, even with 48hour duty cycle.  So, I ignored it.  Well, right
at the beginning of the contest, every time I tried to transmit,
the rig would go bonkers (technical term), the power supply would buzz,
rig lights would dim, etc.  This happened for at least 15 minutes.  I
couldn't figure out an easy answer, so I powered down and used the other
OMNI VI for the remainder of the contest.    

After the contest I called TT service and asked some questions.  I
thought my trusty rig had given up the ghost.  But, no, it was the
power supply!  To demonstrate this, I used an analog voltmeter on
the accessory +12v at the back of the supply.  With just the power
supply on, it reads a solid 13.8v.  But, when the on/off switch on the
964 was turned on, the buzzing from the rig was accompanied by the
voltmeter shown a large overshoot in voltage, past 16v!  So, the
rig was doing it's thing and protecting against overvoltage from
the power supply.  TT service indicated that some, but not all, 962s
have this problem.  The fix is to put a few components on the PC
board on the back panel of the PS.  This is not recommended for
home repair.  Apparently the regulation circuitry in the negative
lead has some instability potential.

I swapped the 962 PS with the 961 PS on the other rig.  Both appear
to be happy now.  I can't get the buzzing to show up at all.  But,
if (when) the problem reappears, I know to swap out power supplies.
Round trip shipping and repair doesn't make economic sense to me.

Terry Zivney, N4TZ/9