lagasse@biomed.UUCP (Robert C. Lagasse) (10/22/85)
........As the proud owner of a Kenwood TR-7950 I have experienced
several intermittent type problems, most of which I believe I have
permanently fixed. It would be interesting to see if other people have
experienced identical failures:
1) All of a sudden, the transmit power (which is displayed by a bar of LEDs)
drops from a full set of LEDs (7 I believe) to one or two which flicker.
The hi-lo power switch has no effect. The antenna VSWR was checked and this
was not changing. Smacking the radio brought back a full set of LEDs and
also full output power on an inline wattmeter. After tapping on the
transmit board with a non-metallic diddle stick and unplugging and plugging
several pc board connectors, and checking the RF drive to the final amp with
a scope and also the hi-lo switch logic, it was determined that the problem
was poor grounding of the final amplifier board to the aluminum heat sink.
Scraping some flux residue away from the mounting hole locations and also
scraping the contact area of the cast mounting bosses for the final amp
board has cleared up the problem, hopefully forever.
2) When the radio is just sitting there, turned on, squelched receive mode,
without the automobile engine running, scratchy noise comes and goes from
the speaker. The sound is like someone turning a dirty volume pot back and
forth. This problem was cleared up by playing with all of the connectors
when looking for problem 1. It has not occured since.
3) When transmitting, the people listening at the other end would complain
of haering my first few words loud and clear, and then my audio would fade
out to about 30 percent in about three or four seconds. DTMF tones would
also fade out and become distorted and unusable for an autopatch. Again,
this problem has not occured since looking for problem 1.
All three problems used to come and go independently, which made things
difficult. They all occured within six months of being a new set. I did
not send it to the factory for repair since I already felt guilty for buying
a ready made store bought set, never mind not trying to fix the problem
myself first. (That's what ham radio is all about, isn't it?) All systems
are GO now, and I would be curious to hear if others have had the same
problems.
P.S. I just remembered, when first looking at the rear heat sink
assembly, there is a strange phillips screw about 1 to 2 inches long,
screwed in from the rear of the heat sink. The shaft of this screw is
threaded for only about a half inch and the rest of the length is smooth.
On the inside of the radio a solid wire, #16 I believe, soldered at the DC
power connector minus terminal, was just WRAPPED around this smooth screw,
obviously trying to provide a ground from the DC power connector to the heat
sink assembly. This wire was promptly soldered to the screw, but it did not
seem to make any difference when searching out the problem in #1 above. I
assumed that somone forgot to solder this solid wire at the factory. Maybe
they did not want it soldered, by I can see no reason why.
Bob Lagasse N1/ALG