[Collins] Collins 32S-1 Problem

[Dr. Gerald N. Johnson]

On Thu, 2008-07-03 at 16:04 -0500, Gary H. Harmon, Jr wrote:
> The 32S-1 I have is experiencing the following problem.
>  
> There is no output in TUNE or CW but there is normal output in LOCK KEY.  In
> LOCK KEY the bottom relay holds but when you move it to TUNE or CW the relay
> falls out.  In CW, closing the key has no effect.  Tubes all check good.  No
> voltage checks yet.
>  
> Thoughts?
>  
> 73, gary   
>  
> Gary H. Harmon, Jr. / K5JWK
> 6003 Archwood
> San Antonio, TX 78239-1504 
> 210.884.6926
> gharmon at idworld.net
>  
>From studying the schematic, I don't see anything easy that would make
it do exactly as you describe. Though there are several switch sections
on the mode switch with multiple poles wired together, particularly to
key the VOX relay. If there was a bad solder connection to the bus wire
around the switch and the wire to the VOX circuit was connected to the
switch pole for lock key, that would explain your problem. That seems to
me to be a stretch.

I'd look at the four resistors in the VOX relay tube cathode. Especially
the 68K 2w are prone to drifting from running too hot and that limits
the bias on the tube. Those four are R87, R88, R89, and R112.

I'd also check the -70 volt bias. It's rectifier in the power supply was
originally a selenium diode in a little rectangular package. Today is
well beyond the expected life of that diode and it would be best
replaced by a three terminal solder tag strip and a silicon diode,
1N4004 or higher voltage rating. Since that bias is used to control
stages, if its low the rig works oddly. That's worst in a KWM-2. And if
its low the PA idling current will be high.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer