A few days ago my bands PA blew at practice and kept blowing fuses. I took it apart and I found a Metal Oxide Varistor (MOV) was fried, or at least I think its a MOV. I took the part out and there aren't very many marking on it. The only thing it says is 'TL08' and below that '020'. I took it to a local part store and they said it was a varistor and gave me a replacement but said they weren't sure if they were the same rating; why they didn't check that I have no idea. Does anyone know of any website I can go to to check this? I can't test the part because the one is fried so I need to find out the rating from a data sheet.
[ The only thing it says is 'TL08' and below that '020'. I took it to a local part store and they said it was a varistor and gave me a replacement but said they weren't sure if they were the same rating; why they didn't check that I have no idea. Does anyone know of any website I can go to to check this? I can't test the part because the one is fried so I need to find out the rating from a data sheet.[/QUOTE]
hello.
can you make a foto of the bad part?
where was it built in (at the primary side of the transformer,....or secondaries........or.......)?
greetings..........
hello.
can you make a foto of the bad part?
where was it built in (at the primary side of the transformer,....or secondaries........or.......)?
greetings..........
The first image is the part. I know its chipped because when I saw it fry a spark shot out of it and it melted some of it so it became brittle.
The second image is where it is on the board the empty spot with the resistor symbol.
Third image is more of a wide view where it is on the board.
Fourth image is the whole board itself.
The second image is where it is on the board the empty spot with the resistor symbol.
Third image is more of a wide view where it is on the board.
Fourth image is the whole board itself.
Attachments
In my opinion, this is rather a NTC limiting the charging current of the the filter caps:
http://www.gesensing.com/downloads/datasheets/920_325a.pdf
It is easy to know which category it belongs: if it's in series, , it is a NTC. If it's in parallel, it is a MOV.
http://www.gesensing.com/downloads/datasheets/920_325a.pdf
It is easy to know which category it belongs: if it's in series, , it is a NTC. If it's in parallel, it is a MOV.
If your photographs weren't so awful...
You should take the part out in direct afternoon sunlight and photograph it there. Smaller aperture = greater depth of field.
It appears the damaged part is next to a relay, so I'll guess its an NTC for the switch-on surge limiting.
TL08 will be the size: 8mm (your part should measure 9mm diameter)
20 will be the cold resistance.
edit: a bad inrush limiter is not going to blow a fuse. So I guess you have another failed part further down the line.
You should take the part out in direct afternoon sunlight and photograph it there. Smaller aperture = greater depth of field.
It appears the damaged part is next to a relay, so I'll guess its an NTC for the switch-on surge limiting.
TL08 will be the size: 8mm (your part should measure 9mm diameter)
20 will be the cold resistance.
edit: a bad inrush limiter is not going to blow a fuse. So I guess you have another failed part further down the line.
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sorry about the pictures...I don't have a camera besides what is on my phone. I will take more in sunlight once these clouds go away.
so if this NTC is bad it wouldn't cause it to blow fuses? see what I did was I plugged the board is as shown in the pictures trying to narrow down where the short could be. when I did that and flipped the power a spark shot out of the NTC. I instantly knew that was a problem but does this mean that something else could be shorting out on the same board?
so if this NTC is bad it wouldn't cause it to blow fuses? see what I did was I plugged the board is as shown in the pictures trying to narrow down where the short could be. when I did that and flipped the power a spark shot out of the NTC. I instantly knew that was a problem but does this mean that something else could be shorting out on the same board?
This is probably the first thing you should do. (To definitively establish if its an NTC or a MOV.)
Because if its an MOV you'll be off on a wild goose chase checking the bridge and the caps.
Thanks. I will check those...I just don't know where on the board the filter caps or rectifier bridge is. If anyone can tell by the (crappy) pictures let me know.
It looks like an inrush limiting thermistor to me, and those are common enough in the industry. They fail and they open, leaving the amp dead. In that regard it is like a power switch, so it won;t cause any further damage. Generally the amp doesn;t cause the thermistor damage either, unless some extremely heavy overload occurs that the fuse can;t handle.
Enzo,
Thanks for the info. I still don't know what rating the part is. However, the amp was blowing fuses. I blew 3 fuses the moment I turned it on but the internal fuses are fine. I am hoping that it is just this one part but I guess I just have to replace it to find out....that and hope that it doesn't fail again
Thanks for the info. I still don't know what rating the part is. However, the amp was blowing fuses. I blew 3 fuses the moment I turned it on but the internal fuses are fine. I am hoping that it is just this one part but I guess I just have to replace it to find out....that and hope that it doesn't fail again
If the internal fuse didn't blow then the fault is narrowed down to something between that fuse and the NTC.
Looking at the last photograph, that eliminates pretty much everything except the 2 capacitors in the filter. (The big green cubes.) (Which should have been X1/2 capacitors are therefore should not have failed short.)
However, I'm scared by your declaration that you don't know what a bridge looks like.
If that is true, you shouldn't be messing around with mains voltages.
Give the amp. to someone else to fix.
I just need to look up what it is again. its been a few years since I was in school for it and I don't deal with it everyday. I just need to look it up online.
There are 4 internal fuses and none of them blew. The only fuse that blew was the main power one. The part that went bad was off of one of the main power legs as well. Could it be possible that because the part failed it was causing the main fuse to blow? I have heard that it can and then it can't.
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