Peavey Combo 210tx questions

[nosaj]

I've got a Peavey combo 210tx with shorted outputs. I've found Q209 and q207 shorted.
Somewhere I'd read that with shorted outputs you should check the drivers and surrounding resistors.
Would Q100 and q104 be considered the drivers? If so then I'll check r200, r205, r112, r114 and r136, r139, r129, r127.
Schematic attached outputs are near end of pdf
Thanks for any help,
nosajCOMBO_115_210_96.pdf

[The Dude]

It couldn't hurt. I normally check anything connected to the outputs and/or associated circuitry that might have been damaged when the output transistors shorted. It takes a few minutes to verify that no other transistors/diodes/etc. are shorted. It can save you lots of trouble and frying a new set of output transistors. It goes without saying (maybe), the initial fire up should be done on a LBL and with no speaker attached. Verify no DC on the output before firing up normally (without limiter and with speaker) . And, yes those transistors are drivers.

[Jazz P Bass]

Don't forget to check the output 'flyback' diodes.

CR200 & CR201.

[The Dude]

...... and that SAC187 triac.

[nosaj]

It couldn't hurt. I normally check anything connected to the outputs and/or associated circuitry that might have been damaged when the output transistors shorted. It takes a few minutes to verify that no other transistors/diodes/etc. are shorted. It can save you lots of trouble and frying a new set of output transistors. It goes without saying (maybe), the initial fire up should be done on a LBL and with no speaker attached. Verify no DC on the output before firing up normally (without limiter and with speaker) . And, yes those transistors are drivers.

Resistors and Drivers ok. and output 'flyback' diodes ok.
What part number is this SAC187 triac? I looked in the parts list but didn't see it listed.

thanks,
nosaj

[The Dude]

It's CR116.

[nosaj]

It's CR116.

That is part of what they call the crowbar circuit correct?

This all I could find for testing a triac would this apply to this triac?

Thanks,
nosaj
Testing triac using a multimeter.
A multimeter can be used to test the health of a triac. First put the multimeter selector switch in a high resistance mode (say 100K), then connect the positive lead of multimeter to the MT1 terminal of triac and negative lead to the MT2 terminal of triac (there is no problem if you reverse the connection).The multimeter will show a high resistance reading (open circuit).Now put the selector switch to a low resistance mode, connect the MT1 and gate to positive lead and MT2 to negative lead. The multimeter will now show a low resistance reading (indicating the switch ON).If the above tests are positive then we can assume that the triac is healthy. Anyway this test is not applicable triacs that require high gate voltage and current for triggering.

[The Dude]

Yes, crowbar. It's Peavey's "patented speaker protection". Great for speakers- not so much for amps. If the amp develops a DC offset, the triac turns on and shorts the output terminals so that DC doesn't reach the speaker. Normally, but not always, they are either shorted or good.

[Jazz P Bass]

If that triac is bad, you will be blowing fuses.

Agreed, when they fail, they are either shorted or blown off the board.

The SAC187 is long discontinued.

I use these: BTA16-700BWRG

http://www.mouser.com/ProductDetail/...FQdLDQodkkAE4w

[nosaj]

If that triac is bad, you will be blowing fuses.

Agreed, when they fail, they are either shorted or blown off the board.

The SAC187 is long discontinued.

I use these: BTA16-700BWRG

http://www.mouser.com/ProductDetail/...FQdLDQodkkAE4w

Well when first powered it would be a loud hum till the fuse blew. So far all I have found bad were 2 output transistors(one NPN and one PNP).
Lookin at the ratings for your replacement being a 16amp would pretty much ensure that the fuse blows before it does.
nosaj

[Enzo]

Well first thing to do is disconnect the speaker or other load from the amp until it is stable and nopt producing DC.

[The Dude]

And, FYI, the triac doesn't need to be there for the amp to function. It is protection only. So, If you find it's bad, you can leave it out while you troubleshoot the amp. Just don't hook up a speaker until you verify no DC out.

[nosaj]

And, FYI, the triac doesn't need to be there for the amp to function. It is protection only. So, If you find it's bad, you can leave it out while you troubleshoot the amp. Just don't hook up a speaker until you verify no DC out.

It'll be a little while till I get the replacement transistors. Then I'll check the DC. The triacs are cheap so I'll add a couple to inventory.

Thanks,
nosaj

[nosaj]

The Triac can be tested by looking for a short across the output connector.

Jazz P Bass said this in another thread.

Does this apply in my case?

Now the output board is disconnected and putting a meter on the speaker terminals(on the Drive board. shows roughly 5k. The amp is not plugged in.

nosaj

[The Dude]

Yep. It does apply. Look at the schematic. the triac is across the output from L1 to ground. The 5k seems a little odd, but I haven't checked that way for many moons. I usually use diode check across the terminals and if all is good, it will not show a junction or short.