[Kenwood] TS-930S digital board glitches

[Vladimir Ljubojevic]

Recently I obtained an TS-930S with 4xxxxxx serial nr. As soon as I got it, 
I made the W6NL modification of the power supply, and mounted a mutch 
stronger 12V computer fan for cooling the power supply instead of the 
original fan. The new fan runs continuously, and can be switched off. It is 
powered from the 28V line, with 7812 dropping it to 12V.

The problem is that I have "glitches" in the digital board from time to 
time. Sometimes once a week, sometimes every time the rig is switched on. 
The previous owner did not complain about any problems with the digital 
board. Since the problem might be originated in the power supply, in the 
digital board or the PLL board, I will give the simptoms in detail 
(appologies for the length):

1. In almost all of the cases, the display goes blank and there is no 
reception. Sometimes, the display and the reception are OK, only some of 
the additional symptoms appears (the RIT wents ON for instance).

2. The normal operation of the display is restored after a slight movement 
of the dial knob. It is not necessary to switch off the rig to resume 
normal operation.

3. This seems to happen during the first 15 - 45 minutes since the rig is 
powered, and happens only once since the rig is powered.

4. There might be only one brief glitch, or several pulses during a couple 
of seconds.

5. Additional symptoms (not always): a beep tone is heard; the RIT goes on; 
the band switches are "selected" (followed by relays clicking) and the 
frequency is changed (to other band, or the beginning of the same band); 
the working memory is changed. Second VFO and other memories are not altered.

6. I have the impression that the "glitches" are a regular thing if the new 
PS fan is left ON when the rig is powered off (thus draining the big 
capacitors). Since I started to turn it off before switching off the rig, 
the glitches appear approx. once in a week.

7. Maybe this is related: While I had the original PS fan connected 
continuously to the 8V line (for a short time), once (but only once) a 
couple of stations informed me that I have a chirpy cw signal during a 
contest. Since then the PS fan has changed and a couple thousands of cw 
qsos were made, and nobody told me that again.
==============

These symptoms do not correspond to any of the known problems with through 
holes on the digital bord. Besides, this serial nr. should not have 
problems with the digital board at all. PLL board should produce different 
symptoms (or not?). Most of my suspitons lie on the power supply - maybe 
something is wrong there and the voltage supplying the digital board is 
dropping? W6NL mentions (regarding the Q6 and Q3 in the PS circuit): "As 
the pass transistor is failing the radio will typically exhibit unusual 
operation, such as chirpy signal or intermittent display". My voltage 
reading are OK, but maybe some component in the PS circuit makes a problem 
for a moment while being heated.

Since problems with the power supply are common in TS-930S, I supose that 
somebody already experienced the same symptoms.

73
YU1WC Vladimir Ljubojevic "Fric"