[R-390] R-390A intermittent loss of Diode Load voltage

[Jordan Arndt]

Hello again group, sorry if this is long, but:

Thanks to the advice of Dave, Larry, Thomas, Jacques et al, I tracked the 
problem down to the wiring harness which feeds the front panel just to the 
right of the RF gain control. I could provoke the audio loss by pushing and 
pulling on that bundle, so I pulled the panel again to take a look at that 
bundle.

I found that pressing down on the bundle right it where exits the clamp 
would cause random the DL voltage to drift around, and in one particular 
spot drop dramatically.

I pulled the clamp from the harness and inspected the wiring under 
magnification, and aisde from some abrasion, I couldn't find any breaks or 
cracks in any of the insulation of those wires. No matter how hard I pressed 
and manipulated the bundle, I could not provoke the problem.

Since the rubber insulator of the clamp was disintegrating, I separated the 
shielded lead from the DL to the Limiter control from the bundle, gave it 
it's own wrap of teflon, and then wrapped the rest of the bundle with the 
remaining teflon strip, which is about an inch wide, and re-installed the 
now naked clamp over the wrapped bundle.

No matter how I pushed and prodded that bundle along it's entire length 
could I provoke the problem so I thought that was resolved.

But no...about 15 minutes later the meter on the DL started twitching along 
with the audio output and L:ine meter...

I went back in and looked even more closely at the wiring and again found 
nothing, so I took a nylon brush and cleaned each wire and the shield of the 
DL-Limiter line and then flushed and rinsed the bundle with MG no-residue 
contact cleaner and let it dry for a bit before re-installing the teflon 
wrap and the clamp.

The teflon wrap is from a sheet of .01" teflon that I used to make HV plate 
line capacitors in some VHF'UHF tube amps. The bundle has 2 wraps which 
extend  ~1/4" beyond the ends of the clamp , so the wiring is well insulated 
and won't chafe.

So far, the second treatment seems to have been a success, but I'll be 
keeping a close eye on the metering and the audio going forward on this 
receiver. Maybe there was a very small metal burr or a wire from the 
shielding working it's way through some insulation that the brushing and 
flushing removed, but so far, no mount of poking and prodding results in the 
problem re-appearing...!

I haven't quite completed going through the RF deck yet, but I think any 
problems there are top-side so I won't have to pull it again...Here's hoping 
anyway...!

Thanks again guys and 73...Jordan VE6ZT