Peavey Studio Pro 112

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Carlosraj

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Joined 2010
#1
Hi,

I am trying to fix this amp. When I turned ON the amp at first there was a loud humming sound. I opened up the amp and realised that it is using a power IC (LM3886T). Before replacing the IC, I checked all resistors, diodes, caps and the thermistor (U72) on the power amp board and they all tested OK. The thermistor shows a low ohms reading. After replacing the IC with a (LM3886TF), I turned ON the amp but there is totally no sound. I resoldered the board and tested the components again but there is no differences. I checked at pin 10, which is the input pin for the IC and there is signal present. At pin 3, which is the output, there is no output. All the components on the power amp board are OK, but no sound. Can the power IC which is new I replaced can be faulty. Please assist.

Thanks

Carlos
 
#2
Peavey is a very helpful Company, ask them for the schematic so you can repair it and post it her for member suggestions.

If the chip amp was bad and you replaced it with a good one, fine, but you may still have other problems.
For example if whild de/re soldering some track cracked/split, sound might not reach the speaker out, and many other similar possibilities.
We can suggest you what voltages you "should" measure on different IC pins, but we still want the schematic so we all talk the same.
 
#4
Enzo said:
Wwhen you get the schematic, look also at the mute pin on that IC, and the circuit that controls it.

factory contact:
customerservice@peavey.com
Click to expand...

Thanks, Fahey and Enzo, The problem was the power IC. It was a LM3886TF. This has a plastic mountig tab. The originalwas LM3886T and this has a metal tab mounting. I guess the IC I bought was fake, I suspected this by looking at the print quality of the part number on the IC. The printing was poor quality and fading off. I managed to get the original from another supplier and now it is working fine.

Thanks again

Carlos
 
#5
The part may have been fake, but the plastic versus metal thing is legit. The F suffix means insulated tab. Peavey never relies on a metal tab for electrical connections so you can use an insulated one if you like. To replace a insulated tab with a plastic tab, you need to use a mica washer, and a plastic step washer in the screw hole to insulate teh tab from the heat sink.
 
#6
Enzo said:
The part may have been fake, but the plastic versus metal thing is legit. The F suffix means insulated tab. Peavey never relies on a metal tab for electrical connections so you can use an insulated one if you like. To replace a insulated tab with a plastic tab, you need to use a mica washer, and a plastic step washer in the screw hole to insulate teh tab from the heat sink.
Click to expand...


OK Thanks Enzo
 
#7
Sorry, I stated that backwards. If it was originally a metal tab, you can bolt a plastic one right in its place. If it was originally a plastic tab, you can replace it with a metal tab, but you then must have the mica washer plus the plastic washer around the screw.

In other words, the tab has to be insulated from the chassis - either by being a plastic IC or by using insulators.
 
#8
Enzo said:
Sorry, I stated that backwards. If it was originally a metal tab, you can bolt a plastic one right in its place. If it was originally a plastic tab, you can replace it with a metal tab, but you then must have the mica washer plus the plastic washer around the screw.

In other words, the tab has to be insulated from the chassis - either by being a plastic IC or by using insulators.
Click to expand...

Noted, Thanks Enzo

Carlos
 
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