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Old September 25th 06, 04:02 AM posted to rec.radio.amateur.homebrew
[email protected] KC2PIH@gmail.com is offline
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First recorded activity by RadioBanter: Sep 2006
Posts: 6
Default Kenwood TS-940 Power Supply Voltage Regulation

Hi,

My 940 was working good for while, but now the S-Meter lights and the
VFO display have started to flicker. They flicker at random times very
quickly (all at once). The LCD display bulbs don't flicker, but they
have both burnt out now. And I just replaced them less than 2 years ago
(with Kenwood factory replacements).

I checked the voltage to the power amp and it reads 28.6 volts. The
S-Meter (lights) read 13.6 volts and when the flicker occurs the
voltage very quickly varies from ~6 to 13 volts - never above 13.6
volts. Is this some kind of voltage regulation issue? I can't get it
to do this by moving wires around and pushing on things. It does only
seem to effect the lights the are controlled by the dimmer switch.

On a side note, I've been reading several posts about the 2N5885 that
regulate the 28v supply for the power amp failing and wiping out the
MRF-485 transistors that are no longer available. Does it make sense to
preemptivly change the 2N5885 transistors to help prevent damage to
those MRF-485? I use my 940 daily - and its on most of the day.

-Scott,WU2X