Peavey 1.3K amp smoked... board testing - diyAudio
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Old 29th August 2008, 07:28 PM   #1
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Default Peavey 1.3K amp smoked... board testing

Hi
We recently blew a Peavey 1.3K. There is a number of burned resistors on one of the preamp boards, the two npn and pnp transistors are toast and I suspect the output drivers are gone as the path of destruction leads through them. The other preamp board seems perfectly OK. I have sourced the parts I need to fix the preamp and it should be relatively easy to fix.

Testing the power stage is bothering me though. There is a small 1/4 or 1/2- Watt resistor on the board nestled between two of the three banks of the big 5Watt resistors and this little guy has burned right through. I do not know what would cause that, but more importantly I do not know what other damage might be involved, either before or after this blew. I am not inclined to plug this monsterous PSU back in just to smoke the power stage a bit more, which will surely happen if only because of this little 1/4-Watter already being shot

In one of the main banks of resistors there is one that looks like a leg could be a bit brown and it could be burned, but hard to tell. This thing had no fan cover for years and when I took it apart everything was covered in a 1/4 inch of dust. Ii suppose that in itself might have caused a problem. But it could be that what I think is soot damage (at least) on these big resistors could be ground-in dirt.

I actually thought it was me, because I didn't notice that it was in Bridge mode and I just plugged in a regular 1/4-inch jack to one channel instead of doing the funky "hot from one channel, cold from the other" wiring you need to do for bridging. But, guys on a different list say it would not have caused this damage.

So, can you offer some advice please?
I would especially like to know the value of this solitary dead resistor on the power board as it will have to be replaced before any power gets applied.
Thanks a lot everybody
Phil
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Old 29th August 2008, 07:45 PM   #2
Netlist is offline Netlist  Belgium
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Clean up the dust and dirt that piled up for years thoroughly.
Measure critical components twice, use fuses about half the rating they should be and use a light bulb in series with the mains when powering up the first few times.
All this, along with original components will save you a lot of trouble.

/Hugo
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Old 30th August 2008, 12:11 AM   #3
jaycee is offline jaycee  United Kingdom
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Location: Norwich, UK
Peavey's seem to really let go when they break. I had a friend who salvaged one from a holiday park his brother worked at. Several small signal transistors had exploded so that all that was left was the leads sticking up out of the pcb, resistors had fried and all of the output transistors were dead short across all terminals.

The staff had no idea why this went (and took the speakers with it!) - it wasn't mistreated in any way, it was operating normally one day, then it simply blew up with a loud bang. My friend asked me for advice and i told him that it was a write off.
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