HW-101 puzzlement

[Edward B Richards]

Hi guys;

I had a request for more info on how I found the low output from the VFO
that was causing low power and no loading. Below is my answer to him. I
thought others might be interested.

Yes, I meant VFO. I am including below, the original message that you
accidentally deleted.  I did a lot of ghost chasing. What I did was to
measure all of the voltages and resistances in accordance with the
manual.  I replaced several out-of-tolerance resistors, but that did not
help.  I thought for a while I had a bad driver board, because the input
to the driver board seemed low, looking at the signal with a scope. I
replaced the driver board, but that was no help. Then I thought the
bandpass filter might be at fault, because it seemed to have excessive
loss.  That didn't help either.  At this point, I synced the scope to the
signal and discovered that what I was seeing was 120 cycle ripple on the
B+ line, which was masking the signal.  Then I turned to measuring the
signal levels with an RF probe and a VTVM.  I found that the input to Pin
2 of V5A was OK, but the input to Pin 7 of  V5A (from the VFO) was only 1
volt and was supposed to be 2 volts.  The output on Pin 6 of  V5A was low
and so were all measurements from there on.  I retuned T941, the VFO
output transformer, which raised the output from 1 volt to 3.5 volts.
This raised all of the drive levels to their prescribed values, and the
output and loading are now correct.  I did not find, in the alignment
procedure, any mention of tuning T941.  I hesitated to tune this
transformer, because it has to cover 1/2 MC. and I thought it might be
factory swept aligned and not to be messed with.  I peaked it at 3750 KC
and checked the band ends, which were down less than 1 S-unit.  I tried
stagger tuning the coils, which did not help.  I left it peaked at 3750
KC.  I now have full power across every band, and the loading works
correctly.  Lessons learned:  1.  Check signal levels with a RF probe
first.  2.  Sync your scope to the signal so that you know what frequency
you are looking at.

I am posting this to the reflectors as others might be interested.

73, Ed Richards K6UUZ

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