[Kenwood] TS940s HELP needed

Tue Jul 27 20:56:46 EDT 2004

Only a guess, but suggest you look at the power regulator board (it is on
top, in the back left-center of the receiver). It is notorious for failed
solder connections. Your receiver symptom was similar to mine before I
removed the board and resoldered virtually every printed-circuit connection.
I also had frequency stability problems which were solved by resoldering
almost all the connections on the VCO board located underneath the set.
Examine each connection pad with a high power magnifiying glass. Look for a
fine circular crack around each lead. If found, resolder the connection.
The solder has cracked and likely oxidized, providing a high resistance
electrical connection. Look at the large tab connectors, if they are like
those in the receiver here, they have all broken loose and need to be
resoldered.
Very important: remove rosin with denatured alcohol, a paper towel and a
toothbrush. Wet the board with the toothbrush saturated with alcohol, rub
the toothbrush around to loosen and disolve the rosin, then place a towel
over the boad and rub the toothbrush over the towel to wick up the liquid
into the towel. Visually examine the board and use a pick to break up the
hard spots. Repeat until the alcohol in the towel is clear.
Keep track of where plugs go on the regulator board as you remove them.
Some of the 2-pin plugs look like they could be interchanged. I took a
number of pictures of the board with a digital camera before I removed
anything, and was very happy I did so.
Hope this helps.
73 de Bill, AB6MT
billsmith at ipswest.com
----- Original Message ----- 
From: Cleeve
To: kenwood at mailman.qth.net
Sent: Tuesday, July 27, 2004 5:33 PM
Subject: [Kenwood] TS940s HELP needed
I would appreciate any help and guidance with the problems I am experiencing
with a late model TS940s. Having performed perfectly for a considerable
time,
the following faults appeared, in sequence, over a period of a week or so.
Fault 1. At switch on the receiver gain appeared low, but then, after about
30 seconds it came up to the normal level......this situation lasted for a
couple of days, every time the rig was switched on.....then, the problem
disappeared.
Fault 2. During Qsk operation on CW, whilst in the receive condition,
tapping
the rig cabinet, or gently thumping the desk brought the rig into the
transmit
mode ......then, again, after a couple of days, this problem disappeared.
Fault 3. Now, the output from the transmitter section will not achieve more
than 50 - 60 watts, maximum into a Bird dummy load, the front panel power
control being at "4 oclock" whereas the rig always provided 50 watts with
the
power control at "12 oclock" and 100 watts with the power control at "4
oclock". The exception being that on 28 Mhz, the power output and power
control are behaving normally. This problem is still ongoing.
My question to the group is, has anyone had a similar experience, do I have
three faults, or are the faults described, symptomatic of a common cause ? I
have looked through all the International Radio data sheets for the TS940s,
but can find nothing which matches the symptoms. I would be most gratefull
for
any assistance to resolve this situation.....sincerely, John Cleeve. G3JVC.
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