Re: {Collins} 75S-3 with an Issue



Do you have a frequency counter?  That would tell you if the BFO was on frequency.  You insinuate that it works fine on USB is that correct?  If bad on both and BFO is on frequency ,as I suspect it is, then you may have a bad mechanical filter.  I know that the 75-S3C has a tune-able BFO oscillator, does the 75-S3B?  If so you should be able to use that instead of the crystal BFO and see if that works.
73 Jim

James C. Owen, III K4CGY 

    On Thursday, August 8, 2019, 10:49:48 PM EDT, Chuck Curran via Collins <collins@xxxxxxxxxxxxx> wrote:  
 
 Hello to All:

This morning I received a 75S-3, 32S-1, 30L-1, and a 312B-4 for repair.  This group of equipment was purchased from the family of the original owner, 20 years ago.  Has been in storage ever since.

The owner also has several 32V series transmitters and 75A receivers that he is working on, and I have volunteered to repair the S-Line gear.  He simply has too much work to address all of it.  75S-3 receiver was used 1-2 years ago and worked

OK, tested all the tubes in the 75S-3, found three weak ones and replaced them.  Took bare chassis, and without tubes, applied 40 AC and let it cook for 5+ hours.  Just trying to give the electrolytics a chance!  Replaced all tubes and hooked up an antenna and tried to tune in stations on 75 meters.

Receiver was responding better than expected.  Had a strong Calibration signal on 80/40 and 20, however another issue.  

No station had a legible LSB signal.  All sounded like Donald Duck, or worse.  Got out the Deoxit D5 and sprayed the AM/LSB/USB/CW switch wafers and worked the switch about 20 times, since I was suspecting a missing LSB Crystal Y15 signal from the V8B oscillator.  I have recapped and aligned four other 75S-3 receivers, with good results.  Never had this issue.

Checked manual, no RF output voltage is listed for the LSB or USB crystals from oscillator V8B.

Here is the question:  With nothing but garbled signals being received, am I on track for suspecting an issue with the LSB crystal oscillator?  Any comments will be appreciated, Thank You in advance!

Chuck W9KR
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