KR-3090 Popping

I don't have the bottom off so pin 1 was obscured. Following the trace R1 has 6.3V and R2 has 9.6.

That's bad.

I'm going to stare at the schematic and diagram some more to self-smarten.
 
it is on one of the edges. here is a pic of the foil side from page 18 of the SM:

kr-3090-pins.png
R and L channel in should be 0v.
 
So, all of the DC measurement possibilities are before C56 and C57. From that point on DC is bad, so C56 and C57 are not doing their jobs.

In electronical genius school (North Dakota State College of Science, class of 1988) I was taught how the components (instruments) worked but I failed to grasp how the symphony came together.

Better late than never, brain don't fail me now.
 
it might be here ( don't own one and google images is kind of a hard way to find this)
kr-3090-board.png

don't forget avionic says the audio amp is part of the pre for the tuner only.
 
Capacitors block DC voltage and pass AC signal.

Right, their job is to keep DC out of the rest of the circuit.

How do both fail? And I thought caps usually failed open?

I'm having fun now, my Expedition job looked easy on YouTube...not so much in my world, see: Production Variables.
 
I don't have the bottom off so pin 1 was obscured. Following the trace R1 has 6.3V and R2 has 9.6.

That's bad.

I'm going to stare at the schematic and diagram some more to self-smarten.
What source do you have selected? If it was FM/AM then the coupling caps are leaking.(Cg72&73) Select AUX and remeasure.
 
It's a mess.
R1
AM 9V
FM 6.2V
PHONO 5.8V
AUX 7.4V

R2
9V-10V for all.

TAPE source button makes all voltages zero.
 
If it was FM/AM then the coupling caps are leaking.(Cg72&73)
This is about the only logical source for the stray voltages. But the input selector switch would need to be the conduit. ie. really fouled internally or shorted at the solder connections.
 
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If I'm going to order two I might as well recap all the electrolytics. I paid $30 for it (very nice shape) so it's got some headroom as an educational aid.

Stay tuned for the results.
 
if you are planning to order new caps, I'd suggest posting what you plan to get. guys like hopjohn might have some recommendations.

for example, i'd probably use 505-MKS4B041002CJF00 for the 1/50v Cg72,Cg73. just need to verify lead spacing.
 
if you are planning to order new caps, I'd suggest posting what you plan to get. guys like hopjohn might have some recommendations.

for example, i'd probably use 505-MKS4B041002CJF00 for the 1/50v Cg72,Cg73. just need to verify lead spacing.

Ah, yes, the Mouser capacitor wormhole of infinite possibilities. I hate it. Any recommendations are greatly appreciated.
 
Well that escalated quickly..

I pulled the blocking caps and they measured good, both traces popped in the process (I've never had a trace pop up like that) and in an unconnected event the power/speaker select switch will only work on both channels with some decent windage applied.

Tossing it to Barter Town to see if anybody needs parts, I've got other projects to move on to.
 
Well that escalated quickly..

I pulled the blocking caps and they measured good, both traces popped in the process (I've never had a trace pop up like that) and in an unconnected event the power/speaker select switch will only work on both channels with some decent windage applied.

Tossing it to Barter Town to see if anybody needs parts, I've got other projects to move on to.

I do have exactly the same issue with mine
Have
you figured it out?
 
I do have exactly the same issue with mine
Have
you figured it out?

No, I let it go. That was my first, I was clueless, a little better now. I bulldog things until they're fixed and learn valuable lessons every time (usually that I'm not very good at remembering valuable lessons).

Time to bulldog! Avenge my failure.
 
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