Another GK 1001RB devloped randomly occuring Popcorn noise

[nevetslab]

Early in January, I had restored a GK 1001RB that had failure of Q14 PNP Voltage Gain stage driver to the output stage, along with its' emitter resistor R31, companion of Q11's emitter resistor R26 opening up, stressed R20 & R31 of the preceding stage's emitter resistors, along with both adjustable IC regulators U4 & U5 failing, Tweeter amp failed, and all of the op amps on the preamp board failed. I had put it all back together and was again working fine, but, it came back, now going thru randomly occurring Popcorn noise in the LF power amp, same behavior as I had with another recent GK1001RB which had been dropped. I never tracked that down, and it got sent back to GK.

This amp, which I looked at briefly......first time I powered it up, it was making the noise. Following morning, worked just fine, no noise. I went thru powering it up and down repeatedly maybe 10 times, and then it finally began making noise. It had been running for a while before, enough to where the small fan began running. I cooled it down with my dual 110 CFM Fan box until the heat sinks were room temp, along with everything else, though the noise continued, and never got quiet again.

Since I had already invested 17 hrs in it earlier last month, it too got shipped on up to GK. I'm hoping to get a technical report on the cause of these two similar-behaving amps, both in the LF power amp section.

1001RB-II_POWER_AMP_PN_206-0260.pdf

[drewl]

are these prone to oscillation?

I'm rebuilding a fried one.
power it up with the limiter, bulb glows bright, starts to get dim then turns bright again.
Not a full on short, it wants to amplify but there's some nasty stuff on the output that is causing it to draw more current.

haven't fully analyzed it yet, just an initial power up after a major blow up that burned a hole in the board!