Kenwood TS-440SAT s/n 9010598
Feb. 09 -- symptoms - cruddy sound, as if it was receiving on several frequencies, but not well anywhere.
These have 2 common problems that give that or just muddy sounding audio.
1. One of several VCO's (Voltage Controlled Oscillator) has a glue installed around the components for some reason, and that glue is hygroscopic. It loses any electrical insulating properties it may have had, and becomes somewhat conductive, thus placing some resistance between all the various components, and causing the VCO to quit. That means the PLL (Phase Locked Loop) can't lock on any frequency, and the unit doesn't know where it is.
2. The band select circuitry uses diodes for selection of the proper band. These diodes fail and become "leaky". This can also cause strange frequency responses and poor reception, if any.
The first is relatively easy to cure, the second takes some more analysis to determine the faulty diodes, and then close, detailed, work to replace them. Since the first will eventually raise it's head if it hasn't already, I attacked it first.
this is the top ckt board, the IF, which must be flipped up to gain access to the next board which has the VCO's on it.
this is the type of glue, on a different area that's not so sensitive to the problems.
the rectangular box is a shield around the VCO ckt in question, teh white substance is some of the glue that's been chipped away and is ready for removal.
this is the VCO with most of the glue removed.
After cleaning out the area, resetting the proper voltage at a test point in the VCO, and retesting, the rig was working properly. It wasn't necessary to go to the band selection area.
The transceiver was operated on the air, a SSB voice contact made on the Maritime Mobile Net frequency, 14.300mc, and a long contact on CW was made on 7.056mc with a station in New Jersey. All bands were tested for proper reception and power output, as was the Automatic Antenna Tuner. All systems are working, output power of 100 watts is possible with a properly matched antenna.
Well, Chapter 2 -- (and the final one, hopefully)
After the rig had been shut down for a few hrs and the shop cooled off after I shut off the heat, I went back and turned the rig on. It didn't work, same old non-freq. problem. The next AM I tried again, same problem. I opened it up and held a hair drier over VCO-5, the problem one, and it came to life again. I thought maybe it was moisture still in the remains of a little of the glue/wax. After the heat was off of it for 6-8 minutes, it died again. warm up, OK, cool off, dead, several cycles. OK, there's gotta be a mechanical problem there. Pulled the PC board out to inspect it, particularly the bottom, trace, side, and found 2 component leads that looked suspect at the solder pad. One was cracked all around, and would move very slightly under pressure. The other was cracked, maybe not all around. I re-soldered all the pads in that area, and looked very carefully at the whole board, but didn't find any other suspicious places.
I couldn't get a good closeup pic with decent focus/resolution to show the bad items.
I left the rig under power overnite, after making a contact or 2 with it. We'll see tomorrow if it's OK.
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