A GK 2001RB came in last week from our rental inventory with the note (No OUTPUT). After pulling the cover for initial scrutiny, I found all of the main Bridge Rectifiers fine, and three of the four 15A Pico Fuses intact. But, F4 fuse was open. That's connected between the +38V LV Buss cap and the + output of the LV Bridge Rectifier.
So far, I've not found any of the output stage xstrs shorted, lower tier output stage emitter resistors all intact. Drivers all measure ok, flyback diodes as well as large high current diodes (MUR410's) ok. The 50W Tweeter Amp doesn't measure short, nor do the +/- 15V regulator IC's (LM317T, LM337T). Now just going further to see what else may have shorted.
I checked for bad buss caps, using a 5khz 30V P-P square wave across each of the filter caps, which will show ESR character, and all of the buss caps measure the same.
I've yet to cobble any fixture to power these up outside the chassis, using the main power xfmr. Though I do have a dual +/-120VDC/0-1.7A Lamda dual tracking supply that could be pulled down from the shelf to see what I get slowly running up the rails.
2001RB_Power_Amp.pdf
The LV bipolar supplies (+/- 15V) are derived from the left Channel, which is where F4 is. If either/both F3/F4 fuses open, no output from either channel is the result.
I did just find solder joint voids on the outside pins of the 7-pin power xfmr header, repaired both.
So far, I've not found any of the output stage xstrs shorted, lower tier output stage emitter resistors all intact. Drivers all measure ok, flyback diodes as well as large high current diodes (MUR410's) ok. The 50W Tweeter Amp doesn't measure short, nor do the +/- 15V regulator IC's (LM317T, LM337T). Now just going further to see what else may have shorted.
I checked for bad buss caps, using a 5khz 30V P-P square wave across each of the filter caps, which will show ESR character, and all of the buss caps measure the same.
I've yet to cobble any fixture to power these up outside the chassis, using the main power xfmr. Though I do have a dual +/-120VDC/0-1.7A Lamda dual tracking supply that could be pulled down from the shelf to see what I get slowly running up the rails.
2001RB_Power_Amp.pdf
The LV bipolar supplies (+/- 15V) are derived from the left Channel, which is where F4 is. If either/both F3/F4 fuses open, no output from either channel is the result.
I did just find solder joint voids on the outside pins of the 7-pin power xfmr header, repaired both.
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