Crate GX2200H Excaliber Schematic needed

[fredcapo]

I hope everyone had a great holiday season. Work picking up from December slowdown.

I need a schematic to figure out the problem on a Crate GX2200H.

Preamp section isolated is OK except some intermittent channel switching issue.

Power section sounds OK then after about 30 seconds breaks up with static and hum then extremely loud noise. I removed speaker and connected load resistor (8 ohm 200 Watt) while monitoring AC across load...AC seemed "normal" 15 to 20 vollts when driven, then load started overheating and smoking after about 5 minutes. Thinking perhaps electrolytics, but need to see schematic before I start probing.

Thanks

[Jazz P Bass]

Crate GX2200 Schematic

I can upload the schematics, on one condition.

Please let us know how you make out with stuff.

Dangling, unfinished threads do nobody any good.

[fredcapo]

Great. Thanks. Will troubleshoot it tomorrow.

I agree with you re the dangling threads. I don't think I am an offender... I think they should be deleted.

[fredcapo]

Made an initial measurement at test point 6 at L1. After about 30 seconds it goes from 0 volts, jumps a bit then to 33 vdc, which is the positive rail I believe. I will test the transistors in and/or out of circuit tomorrow. Thinking one could be shorting... Want to guess which one?

[fredcapo]

I removed the two pair of output transistors and tested out of circuit with my B&K. They all test good but the NPN pair identify as Ge while the PNP pair id as Si. And with the transistors out I dont see the 33VDC at TP6.

Also with the power transistors removed i see +/-44VDC for the 35 volt rails.

I need some advice on taking the next step on this. Thanks.

[Enzo]

If a silicon transistor tests "good" as a germanium, that should be a clue that it ain't good.


The germanium junction drop is about half what a silicon junction is. That is how a tester knows if you have a silicon or a germanium transistor. So when you have a silicon transistor with a junction drop of .2v, that doesn't mean it is secretly germanium, it means it is breaking down.

[fredcapo]

I replaced the NPN pair of power transistors (the ones that tested questionably )today, and the amp was fine for bout a minute then I heard popping. I was monitoring the DC on the center rail of the output stage...it was 0 as expected. I powered down immediately before i could notice a voltage change. The TO3s were still cool. I did not have my current limiter bulb at this location so will retry when I have it.

The theory here was that the power transistors were breaking down, though no idea of what caused the breakdown...just perhaps spontaneous device failure.

If the center rail stays near 0 vdc, can I assume the output stage is not frying?

Would monitoring the center rail give me the best indication if th

[fredcapo]

Ran with bulb limiter for 10 minutes...center rail hanging at 0 vdc...maybe it's fixed.