[Collins] Problem with a KWM-2

[Dr. Gerald N. Johnson]

On Tue, 2006-12-26 at 23:15 -0500, Robert Mazzullo wrote:
> Hello all,
> 
> Before I start tearing into my KWM-2, I would like to present this
> problem and find out from the more knowledgeable folks on this list if
> there are specific areas I should troubleshoot first. The problem is
> that I am picking up a strong RTTY signal on the exact same place of the
> dial no matter which position the bandswitch is in. The bandswitch is
> switching from position to position cleanly, and the detents are clearly
> being felt. On the other bands, I am heading signals that do not
> duplicate themselves elsewhere.  I am going to start looking  at the
> bandswitch itself, but in case I may be going off in the wrong
> direction, I thought I'd ask here in case the cause (and hopefully,
> cure) is more obvious (or more devious) than I am aware of.
> 
> Thanks,
> 
> Bob Mazzullo

KWM-2 and 75S receivers are essentially tunable 2.955 to 3.155 MHz
receivers with crystal controlled converters in front. So you are seeing
IF leak through. With the low sun activity, many commercials are running
such low frequencies this year. Tuning the preselector should reduce the
strength of that IF leak through as you tune to higher frequencies. That
RTTY signal should get stronger if you tune to the lowest frequency
range.

I thought there might be a service bulletin on the topic, but I don't
find it in my collection that I've downloaded.

Things I'd check include bypass capacitors and their grounds in the RF
section. Switch shield grounds. Slugs. Is one broken and sitting in the
bottom of the coil? Then I'd search out KWM-2 service bulletins as well
as Amateur Service Bureau service bulletins for further hints.

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer