Need schema for Ashdown Evo 500 with Bipolar ouputs, not Fets

[marku52]

Ashdown 500 pissing me off. Came to me with shorted outputs, Bipolars, SK 1695 and SK 4468. I checked the emitter resistors, and all other bipolar devices, installed new outputs, and brought it up slowly with the variac. All looked good, idling at about .3A, no DC on the output, passes signal. All looked good. So I took it off the variac and powered it up normally.

BOOM. A resistor went up in flames, and 2 of the new outputs shorted. I need a schematic to go any farther with this thing. The only ones I've seen have FET outputs, I guess mine is an early one.

Thanks in advance.

-ss

[The Dude]

My experience is that Ashdown has been quite helpful in the past. I would try contacting them directly.

[marku52]

Oh yeah PCB says APC033 Ver 061218

[Jon Snell]

Always fix the cause of the fault first then power up from the mains.
I suspect the bias is not right, causing rapid thermal runaway.
Output transistors are 2SA1695 or 1294 pnp and 2SC3263 or 4468 npn.
The older version had FETs.

[g1]

This schematic has a couple more outputs than the one Jon posted.

[J M Fahey]

As a side note, where did you get your replacements from?
If EBay/Alibaba/etc. there is a high likelihood they are Fakes.

Which behave exactly as you describe.

[marku52]

Ah yes, fake output transistors. That could be it. And yes, Ashdown was amazingly helpful. Thanks to all.