Need help identifying component from power amp circuit board

bhuckabee

Member
2013-03-03 4:38 pm
Any idea what this component is (says R1 on circuit board)???

the long story...
I bought a damaged PV900 power amp from ebay to try and repair it. Looks like considerable shorting on the toroidal transformer (plastic tape melted and some wire sheathing) along with a short on the cb from the toroidal lead that was shorting. I removed outer plastic tape wrap, followed electric leads down to where winding begins and re-taped where sheathing had melted against the toroidal copper windings. I then repaired the fried spot on the cb by bridging the small burnout with wire. Everything seemed to be working and then this thing burned up. and what some possibilities for why it's overheating?

Long time lurker first time poster, thanks for all the help
 

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Looks like a thermistor. Could be a SL32 2R025 (or 10015), but because the photo was most likely taken with a potato (I kid!) I could be very wrong.

Best to check the numbers that on there and compare.

SL32 2R025 - AMETHERM - NTC THERMISTOR | Newark

and if you are in the UK, Farnell...

SL32 10015 - AMETHERM - THERMISTOR, SERIES SL32 | Farnell United Kingdom

Important to make sure you have the right number so you can limit the initial voltage until it gradually heats up and drops to lower resistance (some to 2 ohms or so) allowing for everything to go in.
 

bhuckabee

Member
2013-03-03 4:38 pm
really blurry printing on thermistor

yeah it looks like the camera was out of focus but it's actually the crappy printing on the part. I think you're right about it being a thermistor. I'm trying to figure out if it was damaged before my attempt to repair the transformer. WHen I plugged everything in, the original short seemed ok but then this thermistor got very hot and cracked. I can't find any method described on-line to test the actual toroidal transformer.
 

bhuckabee

Member
2013-03-03 4:38 pm
sorry for previous post I see in the description of each that they are rather different. 10ohm or 2ohm. The amp goes to 2 ohm but I imagine that has nothing to do with this component.

Thanks so much for pointing me in the right direction. Only wish I knew what to do now...
 

bhuckabee

Member
2013-03-03 4:38 pm
Any notion how to go about testing a toroidal transformer to see if it's shorting or something on the board?

I'm wondering if someone had hooked it up to too many speakers reducing the load to under 2 ohm thus overloading the amp. Thing is, I'm a novice and am not sure if the transformer would fry or another component when this type of load scenario occurs.
 
I am assuming that is a Peavey PV900 amp. It shares the schematic with the PV1500. COntact them - customerservice@peavey.com - and ask for the schemtic.

Is there a second one of these parts right next to the bad one, called R2?

Schematic identifies them as a 1 ohm 30A for 120v mains and 2 ohm 15A for 240v mains. The 1 ohm 30A one has a Peavey part number of 70250123, and I am sure they could provide the number for the other one.

If you are in the USA, you can call Peavey and order th exact part direct from them at a reasonable cost. Otherwise any inrush limiting thermistor of similar characteristics will work.
 

bhuckabee

Member
2013-03-03 4:38 pm
thanks DF96 for the suggestion. Built one tonight and about to see what happens.

DigitalJunkie and ENZO seem to be right about the part being the 1R030. It's just really hard to read but I'll look into getting that schematic. On the PV900 the R2 insert on the cb is just bridged with no thermistor in that spot.

Thanks for all the help. Even if I don't get it going, I'm learning a good bit. I'll post a pic of the lamp test.
 

bhuckabee

Member
2013-03-03 4:38 pm
lamp test and toroidal transformer

so I hooked the lamp test directly to the transformer.
(pics wouldn't upload for some reason)

the bulb stayed off and it was definitely getting voltage, no over heating no funky smell, nothing but measured voltage at 117.8

I'm planning on ordering the thermistor (or 2 or 3) and putting everything back together then run the lamp test. If it fails then (most likely it will) I suppose it's probably toast without a new circuit board.

history to this point: I had to remove the transformer to check out the damage. Wire leads were melted to the copper. dug these out and temporarily taped so there was no contact. (It's lame but I was just planning on butt splicing it back into the board instead of fooling with resoldering everything to find out it still doesn't work) removed circuit board and repaired small short with a wire bridged (learned solder doesn't stick to plastic, duh) hooked it back up and it seemed to work for a few seconds and then breaker on amp tripped. Tried it one more time, because I'm brilliant, and saw the heat fry through this thermistor and crack it.
 
Well, the thermistor is there to sort of gently let things warm up (it is still pretty quick though) instead of having this massive blob of voltage go through to your transformer and parts downstream. You might be able to use it without a thermistor to see if the amp is going or not as the value of the resistance goes down dramatically as the thermistor heats up.

Other than that, wow, did the transformer look like that before or after the incident?
 

bhuckabee

Member
2013-03-03 4:38 pm
great, thanks for the tips. The transformer came with some serious tape melting and I removed about half of it to get access and see if it had a short. Unfortunately, the center of that trans is filled with epoxy and a metal tube to receive the bolt through. The trans could still be shorted but the lamp test did not reveal that.
 
The transformer came looking like that before the blow up? Wow... I have touched many a toroidal transformer and they most of the time run much cooler than the big iron. I am sure you have checked it properly and been very careful about it, but the possibility of an intermittent short? Who knows? I would be careful.

Check the outputs for a short like Enzo recommends. If this doesn't happen to be the case and none are found then take care with that transformer.

One doesn't usually see that in a normal working transformer (Chinese or Canadian made). How much would it cost to replace a like transformer from Piltron or going with big iron from Edcor USA or Lundahl in Europe?
 

bhuckabee

Member
2013-03-03 4:38 pm
I'd be into replacing it if it's not crazy expensive. I haven't been able to find one like this one but I don't know the exact specs but I'm hoping it'll be in the schematics. I'll check the companies you mentioned and see what the cost is.

I ordered a new thermistor.
Then I suppose I'll figure out how to test outputs with Speakon connectors.

After that it's the scrap heap.