Some Common Problems and Solutions
|There are many facets to a
Kenwwod Hybrid Transceiver. It is virtually impossibe to go through
all possible problem areas that might turn up in a page or two, but I've
included several common areas that need attention on many rigs. This
should help to give you an idea of things to look for if you are
performing your own restoration on one of these wonderful Kenwood
rigs. I hope you enjoy the photos. 73, Ken,
You have to wiggle the bandswitch to get a
selected band to respond properly. This is most often caused
by a cracked coupler between the front panel control and the final cage
bandswitch. Easy to identify, sort of hard to get at. It
will restore perfect bandswitching if you do, however.
The arrow points to the guilty culprit, a broken
plastic coupler that Kenwood used on later rigs
|How do I fix
it? I replace that plastic coupler with a bronze coupler with 4 setscrews
that will last for the next 100 years . . . It's all at ground
potential, no need for an insulator at this juncture . . . Hard to
reach, but well worth the effort. A much closer view
appears in the picture below.|
Here you can clearly see the crack in the coupler, it
will never again work properly.
Even though the Kenwood owner's manuals explicitly
warn about using metal tools to try tweaking the tuning cores, some people
have to learn for themselves. During an alignment, any time my
plastic wand won't budge a core means there's a cracked slug. The
slug is nearly impossible to remove without damaging the fragile and
brittle coil forms, so I have to stop and change the entire coil.
Here's some pictures showing what to watch
slug in the coil form in the lower right (pink) is cracked.
just to the left of it has already been removed, as it too was cracked.
The shield has been removed for access.
Here's a close-up showing the cracked (and immovable)
If a rig appears to load up properly, with
sufficient plate current and good high voltage, but suffers from low
output, the answer is many times the cathode resistors. Kenwood uses
these resistors as fuses, to protect the finals and power transformer if
the rig is mistuned for any length of time. The resistors will
overheat, start to climb in resistance, and maybe even burn and
rupture. In the picture below, the larger 1W 10 ohm resistors are in
series with the cathodes of the 6146B's. In a rig that's been
abused, these resistors may look fine, but actually be high in value from
being overheated. The only way to tell is to measure them.
Being in parallel, they should measure a total 5 ohms to
ground. The plate current metering is derived from these R's,
and will read much higher than it's actual value if the resistors are
damaged. I replace them with 10 ohm 1W metal film units, to maintain
the safety that they provide as
These cathode resistors look and measure fine.
They do not need replacement.
Note the bandswitch section (bottom center)
that has been revealed by removing the shield plate.
It is important to clean
and lube these contacts as well.
Capacitor Noise & Dropout|
After 25 to 35 years of use,
or certainly after a few years of storage, the VFO capacitor will become
noisy, intermittent, even quitting all together because the mechanical
sliding contact has tarnished and corroded. The picture below shows
the access door on the side of the VFO unit on a 520S. A right angle
screwdriver, plenty of light, and a steady hand allow me to remove this
cover for access to the sliding contact area on the VFO capacitor. A
health dose of contact cleaner, working the cap between its extremes
several times, followed by a quality lube applied to the contacts will
prepare this important cap for the next 25-35
You can see the plate held by two
phillips head screws on the side of the VFO can
those Variable RF Amp, Mixer, and Driver Capacitors|
obvious than the VFO cap, these 3 units for peaking the receiver and
driver circuits require cleaning and lubing as well. Each sliding
contact must be sprayed and the capacitor worked between its extremes to
allow smooth operation and tuning.
The arrow points to one of 3 clean & lube points
on the Driver control
TS-820 DG-1 Access for
One of the most common, yet the
most difficult problems to diagnose on a TS-820 concerns problems in the
digital display. The Mixer and Counter boards are housed in a metal
box next to the IF board, and troubleshooting it can be hard. The
picture below shows the digital unit with its cover removed and laying on
an insulating piece of cardboard while being troubleshot.
In this case, the mixer board passes the test, showing
strong output and stable frequency on all bands. That means the
problem HAS to be on the digital board, which has been known for it's
questionable plated through-holes.
circle shows the DG-1 with cover removed, being probed.
Some Additional K4EAA Site Links
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All Photos and
content copyright 2005, K4EAA, Ken Kemski.