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, K4EAA
|Soft Bandswitch Operation
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,
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 for:
The slug in the coil form in the
lower right (pink) is cracked.
The one 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
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 pseudo-fuses.
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.
Tuning 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 years.
You can see the plate
held by two phillips head screws on the side of the VFO can
Forget those Variable RF Amp, Mixer, and Driver Capacitors
Less 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
DG-1 Access for Repair
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
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.
yellow circle shows the DG-1 with cover removed, being probed.
Some Additional K4EAA Site Links
Please Note: The above address is a
GIF image, to foil spammer robots.
You will have to type that address into your email client. Thanks
for your understanding, Ken.
Photos and content copyright 2005, K4EAA, Ken Kemski.