SB-101 Crystal Nightmare!

[Pat Bunsold]

I had Mike N6IEFs SB-101 almost working!  It received and transmitted great on all bands except the 28.0-28.5 segment.  Since that is the most important part of 10 meters, I really wanted it to play.  But for some reason, the 36.895 Mc xtal wouldn't oscillate!  I played with the Het osc coil and watched the V19 output with no response.  The Crystal may have been bad!!! So I tore one out of a HW-101 in the pile and installed it.  STILL no output!!!  Measuring the correct voltage on the coil and seeing proper continuity through all the switches and wires, it was a hair tearer!  I removed the wire coming from the xtal switch and installed a HC-6 Xtal socket from V19 pin 7 to ground.    Plugging in the HW-101 xtal, it now worked!! That told me something was fishy about the rotary switch.  But it worked fine on all other bands.  I tried the original xtal and no response.  Unsoldering it open, I found the quartz disk boke in half.  OK, that Xtal has had it!  I had read on here that someone openned the xtal and was able to mouse around with the disk and make it play again, but today was not  the day.  TOUGH to get those open!!  Anyway, I clipleaded the xtal to the socket and found with one end connected to the switch contact and the other connected to ground, the xtal would oscillate.  But soldering it into the board made it stop.  I experimented with different ground locations and tried buss wires to run grounds to that xtal pin, but it still wouldn't work!!  Something about that Crystal doesn't like being where it should.  I soldered on crystal leg to a ground pad on the PCB just below it (carrier Oscillator PCA) and ran a wire from the 2nd pin up to the switch.  NOW it worked!!! I have no idea why, as ground is ground, and my liberal use of additional grounding wires made no difference.  Also, the other 3 xtals in that range have no problem!!  What in the world??  I did notice that the coil is now very touchy for proper oscillation, while the norm is a very broad tuning slope.  But the xtal is oscillating on the proper freq and 10M now works, so I closed it up.  Obviously, the Mickey Mouse mounting method is not shock protected and very poor installation techniques, but it was the only way I could get it to work!  The best I can figure is that this xtal is very marginal and it is lucky it oscillates at all!  So I am looking for more 36.895 Mc xtals now, one to replace in the HW-101 and one for the SB-101.  Also need a 12.395 Mc xtal for 75 Meters also robbed at one time.  I see these on Ebay now and then, but they command unreasonable and outrageous prices.  Anyone have a lead to these without having to order factory replacements?  And anyone have an explanation as to why this xtal would not oscillate in the PCB yet works  fine outboard??  These radios can be tough to fix!
73
Pat
--
Pat Bunsold WA6MHZ
San Diego Section Manager
Curator, Crest Radio Museum

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