Ron,
Yes, I see that your padding attempts were not successful, and the
proper conclusion is that you have something other than the crystals
that is incorrect.
The BFO is similar to any VXO - and the components involved are the
crystals, the inductor and the capacitors. In this case, the varactors
D36 and D37 are the variable capacitors, so check to be certain they are
the correct type - the body on the iSV149 is the smaller of the 2
varactor types used in the K2. If they are the correct type, check the
voltage swing on the VBFO signal line (check at Control Board U10 pin
14). Enter CAL FCTR and tap BAND+ (the voltage should go to almost 8
volts), then tap BAND- and the voltage should be near zero volts. If
those are correct, tap BAND+ again and check the voltage at RF Board RP6
pin 1 - it should be the same as the voltage at CB U10 pin 14, if not
check soldering on all VBFO points. Also check the soldering at all
pins of RF board RP6.
If that did not correct the problem, then I would arbitrarily replace
D37, D38 and L33.
73,
Don W3FPR
Ron Hahn (EI2JP) wrote:
Don,
Updated data below. No real progress with the padding. :-(
A B 10pf 20pf 47/122pf
BFO Hi 4917.62 4917.63 4917.11 4916.8 4917.39
BFO Lo 4913.59 4913.49 4913.3 4913.16 4913.02
Range 4.03 4.14 3.81 3.64 4.37
A is the original set of BFO crystals
B is the replacement set of crystals
Try 1: 10pf from pin 3 - 6 of U11
Try 2: 20pf from pin 3 - 6 of U11
Try 3: 47pf across C174, 122pf across C173
As you can see by the data padding the junction of the crystals only
reduced the upper range.
So I then tried the recommended padding across C173 and C174, and, as
you can see, it still fails to bring the lower range into spec.
Where to go from here?
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