Sergimm
Active Member
No I haven’t. I thought that dirty switches can cause scratchiness but not loss of sound quality. I haven’t noticed much scratchiness, except for a bit on the loudness button. I guess that I should do that next huh.
Sparks and a volatilized transistor
- Thread starter Sergimm
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Dirty controls and switches will do both.
That looks good..LED should be working unless you have a broken wire.Or it is indeed bad.
Sergimm
Active Member
I just did. It was quite out of whack, now perfectly adjusted. Distortion and muffling still there, perhaps a bit less. Will try to clean the pots next.
Sergimm
Active Member
So, I cleaned up switches and pots (except for the two faders...sounds easy to mess those up) with contact crc cleaner + 2 26 lubricant...and it’s now quite worse. I don't hear the left channel unless I have “loudness” activated, and the distortion is worse, especially with the low tones.
It really does sound terrible, nothing hi-fi about this machine yet
. Time to let it rest for today and try again tomorrow!
Sergimm
Active Member
Ok some progress. I found out that if I jiggle the bus that goes from volume pot to the loudness pot I can get my left channel back, but it doesn’t stay that way. It’s a bad contact. I guess that when I detached the volume from the case something moved, although the bus (photo attached) seems well attached and I don’t see anything clearly wrong. I guess I’ll resolver all the pins.
but that has made me suspicious of whether either the volume or the loudness board are sabotaging me. Is there a way to defeat these controls, even if temporarily? I’m not good enough at reading the schematic to be able to do that.
but that has made me suspicious of whether either the volume or the loudness board are sabotaging me. Is there a way to defeat these controls, even if temporarily? I’m not good enough at reading the schematic to be able to do that.
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I would go over all the solder connections on that board.
Sergimm
Active Member
I did go over all the connections on these boards. I have the left channel back and perhaps a bit more fidelity. It still sounds a bit muffled and it distorts like crazy when I turn up the volume, especially on the bass.
I was tired (I can only work on this late at night) and I started randomly testing resistors...and the second one I tested, R806, is completely shorted. It's a 220Ω resistor connected directly to one of the main filter caps (C809). I won't have a replacement for it until tomorrow, but I wonder what's the effect that this shorted resistor is causing. I'm surprised anything works at all!
I was tired (I can only work on this late at night) and I started randomly testing resistors...and the second one I tested, R806, is completely shorted. It's a 220Ω resistor connected directly to one of the main filter caps (C809). I won't have a replacement for it until tomorrow, but I wonder what's the effect that this shorted resistor is causing. I'm surprised anything works at all!
Resistors don't short.. They go high resistance " open".. Were you measuring this resistor in circuit ? If so, take it out of circuit and remeasure it.
Sergimm
Active Member
Right! When I took it out of the circuit it would still give me “0L” in the meter, so there is something definitely wrong with it.
Similarly, R809 should be 10Ω but measured 30Ω...and checking it’s band colors it’s officially a 22Ω one. I will replace it by the canonical 10Ω too. It’s interesting because both resistors are connected to the filter caps. When I opened this amp, the first wrong thing I noticed was that main filter caps were 6800uF/43V instead of 50V as it should be. I wonder if that hurt the resistors.
