[Kenwood] Flaky YK-88C-1 in TS-950SDX

[Michael Tope]

Hi All,

I am trying to fix a problem with our local club's TS-950SDX
whereby the insertion loss of the 500Hz CW filter in 8.83 MHz
IF (YK-88C-1) gets very high from time-to-time (e.g. 10 to 20 dB
greater than normal filter insertion loss). The problem is very
hard to reproduce, but it needs fixing as it can occur at the most
inopportune times (like in the middle of a CW contest run). When 
it does occur, it doesn't seem to respond to mechanical stimulus
(e.g. banging on the side of the radio doesn't make it go away). 
In fact, if I take the bottom cover off the radio, I CAN'T reproduce
it by poking the IF board in the area around the filters or by
wiggling or tapping the filter. I also tried a heat gun to warm up
the area around the filter. These appeared to work once, but
I couldn't reproduce it, so it was likely a coincidence. 

After I pulled the filter board out of the socket and reseated it the 
problem seemed to stop. I then tried to reproduce the problem by 
letting the radio run for a couple of days and checking 
the filter insertion loss periodically using a signal generator to 
provide a constant level. The problem didn't reoccur, so I put the 
covers back on and brought the rig into the shack. I let it run for
a couple more days with the receiver parked on a local AM 
station so I would have a steady reference signal. After it ran in
my shack trouble free for a couple more days, I began to feel 
confident that I had the problem licked. I then sent an email to 
a friend in the club exclaiming that I had the problem fixed and 
that the radio was ready for action again. I kid you not that within
1 minute of hitting the send button on that email, I looked down 
at the S-meter and noticed that the signal level had dropped
markedly. The problem had reappeared within minutes of announcing
that it was fixed after several days of trouble free operation. Talk 
about classic Murphy's law :):)

In any case, I plan on putting the radio back on the bench for
more troubleshooting. One thought was to swap the optional 
1.8 MHz SSB filter (YK-88SN-1) with the 500 Hz CW filter to 
see if the problem follows the filter or stays with the slot 
selection. Is it possible to do this? The former would indicate
a bad filter whereas the latter would indicate a problem with 
the switching circuits that select the CW slot. If it turns out to
be a bad filter, where can I get a replacement? Does Kenwood
still sell these or is INRAD my only option (INRAD sells a 400
Hz 8.83 MHz filter for the TS-950). 

Thanks,

Mike, W4EF...............................