Peavey tour series 700

[tdlunsfo]

Does anyone have the schematic for this? Peavey is taking a bit getting back with me. Also, I am halfway through checking main components and have already found 2 blown NPN power transistors but the PNP's check good. Any reason why only NPN's? I am sure the schematic would help me here but don't have it just yet. This is gen 2 which I believe does not have the triac. Came to the bench with a blown mains fuse and the customer stating that "it is acting funny". Dead bulb is brightly lit on power up, clears after pulling transformer secondaries.

[Enzo]

Pick up the phone and CALL customer service at Peavey and ask for it.

Why only the NPNs fail? Why did only the left rear tire go flat on the car? Failures don't always follow a pattern. If one fails on that side, it doesn't automatically kill one on the other side. And if one fails with a short to base, it may also take out others in that row. Usually an EC short doesn't hurt the neighbors.

[tdlunsfo]

Understood. Just wanted to be sure there wasn't another obvious failure that could had taken them out. I will call peavey tomorrow and continue checking parts.

[Enzo]

ALWAYS check all resistors associated with the failed transistors. Especially the power resistors of low value like 0.33 ohm, look for opens.

[tdlunsfo]

I checked them, they are all good. Found one of the PNPs blown as well. 5 out of 8 power transistors blown. Seems a good idea to replace them all to me. I'm still looking around for collateral damage and found a small diode shorted near the power transistors. I am assuming this to be a bias diode? Hard to tell anything about it as it's covered in white goo. So far this is all I have found. Need to see if the customer wants to pay to fix it in this condition. Seems to be a nice amp.

[g1]

It might be a diode, but it might be some kind of thermistor or thermal cut-out too. And maybe it's supposed to be low resistance till it gets hot. I'd wait for the schematic. Whatever it is, if it covered with heatsink goop and mounted to the heatsink, it's sensing temp.

[Jazz P Bass]

Here is the schematic: tour700.zip

[tdlunsfo]

Thank you for the advice and the schematic. The other short is D13 and likely showing shorted as it is in parallel with 61.9 ohm R48. Willing to bet D13 is fine. At this point I simply have shorted output transistors and as Enzo has pointed out...just happens sometimes