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The Stereo 80

S

SFM-Ptgal

Well, it's almost one after a another...
A few weeks ago I got my Stereo 80 console MON output module card fixed, using equivelent transistors, so to speak. The only drawback after fixing was a slight warmth on the heatsink. It runned ok.
Now I'm getting random "pops" on the speaker corresponding to the fixed module, the output level is becoming lower, I'm having crosstalk (that's wierd) and when I tap on the heatsink I can hear the tapping on the speaker, just like tapping on fm exciter shield (sounds like a spring reverb). Swapping the card from MON to PGM causes the problem on the PGM output, swapping to the other channel too.
Should I replace the capacitors, or might it be something else? The heatsink is still warmth, no difference from "day 1"
 
Some types of caps can introduce microphonic noise. Some types of ceramic caps and film types have been known to do it. Take the eraser end of a pencil and tap around on the caps (gently). Maybe you can find the problem that way.
 
I took care of a few Stereo 80s back in the '80s. The tantalum capacitors Harris used on the amplifier cards (tubular style with red ends) were a constant source of trouble. One is in series with the negative feedback loop of the program amp -- so as it dried out the gain would increase, frequency response would get funny, and distortion would rise. So you might start by checking the condition of those tantalums.
 
Those same tantalum caps were used in the gain control loop of the Statesman series limiters, and as they started to fail, the audio would start to pop and spike in level.

Play Freebird said:
I took care of a few Stereo 80s back in the '80s. The tantalum capacitors Harris used on the amplifier cards (tubular style with red ends) were a constant source of trouble. One is in series with the negative feedback loop of the program amp -- so as it dried out the gain would increase, frequency response would get funny, and distortion would rise. So you might start by checking the condition of those tantalums.
Click to expand...
 
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