kb/a100

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damopinn2
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kb/a100

Post by damopinn2 » Tue Jun 13, 2017 5:42 am

Hi,
I need to replace 2 blown transistors. On the schematics it says SJE5331 SJE5332 but the parts I removed were H669a and H649a. Can I still replace them with MJE243 and MJE253 like some people said on the web.
I have to replace some resistors too but thats not as mysterious to me.

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Enzo
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Re: kb/a100

Post by Enzo » Tue Jun 13, 2017 10:06 am

I don't know those H numbers, but the factory might use any number of oddly marked parts. You can order the 5332 and 5331 directly from Peavey, and they will either send parts marked that way or their current part equivalents. Otherwise the MJE243 and 253 should work, just make sure the leads are the same, not all TO126 are in the same order. Those are generally drive transistors, so if they blew, and some resistors, I would be HIGHLY suspicious of the power transistors they drive.

damopinn2
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Re: kb/a100

Post by damopinn2 » Tue Jun 13, 2017 10:40 am

You are right about the other transistors At least one is blown too an MPS6533. the resistors I took out have 0 resistance so I'm expecting some more damage in there. The local repair shop quoted 180euros and couldn't guarantee that it would be fixed so I'm looking at it. It's for a local school and they were going to throw it out. I'll probably need more help, so Thanks for your advice

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Re: kb/a100

Post by damopinn2 » Tue Jun 13, 2017 1:25 pm

What kind of capacitors are used on this board? they are tiny yellow axial things. I've never seen them before could ceramic disc be an OK replacement. On the parts list it is 100pf-10%-50vdc-T/C-t&R. What does T/C mean?

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Enzo
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Re: kb/a100

Post by Enzo » Tue Jun 13, 2017 4:19 pm

Offhand, not sure, but are these bad? I can't recall ever having to replace a small ceramic cap on a Peavey amp. If they are parallel a blown transistor, the transistor will make them appear shorted, and if so, remove the transistor and then recheck the cap.

Tubular ceramic comes to mind. A 100pf cap is likely to be ceramic.

Seriously, check the two large power transistors for shorts. That is the most likely thing to blow the 5331/5332 ones, plus the little MPS dudes really don;t fail much other than when the big ones short. Especially when the resistors burn open. I mean the 0.33 ohm 5 watt resistors. Also find R171, a small 180 ohm resistor - is it open?

damopinn2
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Re: kb/a100

Post by damopinn2 » Wed Jun 14, 2017 2:16 am

r171 is the one that's open. I don't think the caps are broken but I want to get all the parts I could possibly need. I live in Spain and it's difficult and expensive to get parts from here the cheapest company charges 12euro delivery so if I need some more part later it will get very expensive.

damopinn2
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Re: kb/a100

Post by damopinn2 » Wed Aug 16, 2017 4:41 am

Hi, I need more help with this amp. I finally fixed it and it worked for about 5 minutes. It made a very loud buzzing noise. much louder than usual. and then resistors 171 and 187 seem to have blown again. I had replaced all the 6 transistors in that part of the circuit and checked all the resistors. so I'm out of ideas. Any advice where to go next will be very appreciated.

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Re: kb/a100

Post by damopinn2 » Sun Sep 10, 2017 3:11 am

I don't mean to be cheeky. Can anyone offer me any more advice with the kba100 I've been trying to fix?

Some other people advised me to replace the whole amp board with a modern amplifier.

Thanks in advance

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