CARLSBRO GRX7 MIXER PA AMP INTERNAL FUSE BLOWS Help Please

[sim]

Hello

I have a Grx7 that blows an internal fuse T 6.3a I have read posts on the Carlsbro forum ( now seems to have ended) about this amp and they say to replace the MJ15024 all four. Mine has 2 MJ15024 and 2 SJ63438 I assume this to be incorrect.

my question is should I replace them all with 4 MJ15024 or are there versions of this with the above
I would be very grateful for a little guidance and or a schematic

[J M Fahey]

Not in principle.
Amp circuits vary overtime, you must believe the one you have on your bench, not what "Internet says", *unless* it has previously bein "repaired" by a soldering iron armed chimpanzee.
SJ63438 rings no bells , please post all codes written on them, case type, etc.
A couple sharp close-up pictures would help.
EDIT: I see you got into a Carlsbro Forum, did you contact Carlsbro Company for info?

[Jazz P Bass]

Carlsboro GRX7

I believe the SJ number is a factory issued number.
Rather than just throwing transistors at the amp, why not find out what is wrong.
After removing the output transistors use the diode check function on your meter to test the transistors for shorted leads.
If any are shorted you should also check the transistors before these. The drivers.

There are many things that can take out a fuse.

[sim]

Not in principle.
Amp circuits vary overtime, you must believe the one you have on your bench, not what "Internet says", *unless* it has previously bein "repaired" by a soldering iron armed chimpanzee.
SJ63438 rings no bells , please post all codes written on them, case type, etc.
A couple sharp close-up pictures would help.
EDIT: I see you got into a Carlsbro Forum, did you contact Carlsbro Company for info?

I think the SJ 63438 number is Peavey I am fairly certain it should have 4 MJ15024. I am going to do some testing with my limited knowledge. The Carlsbro co is now finished thanks for quick reply

[sim]

I believe the SJ number is a factory issued number.
Rather than just throwing transistors at the amp, why not find out what is wrong.
After removing the output transistors use the diode check function on your meter to test the transistors for shorted leads.
If any are shorted you should also check the transistors before these. The drivers.

There are many things that can take out a fuse.

thanks for reply I think the SJ number is Peavey . I'm going to do some testing with my limited knowledge

[Enzo]

SJ6343 is a Peavey number, but I have no idea what SJ63438 might be. Sure it is not SJ6343B?

In any case, it is likely that whatever they were, the parts in there used to work. They are two different types most likely because a repair was done at a previous time.


I agree with Jazz, don;t just throw parts at it, find out what is wrong.

If the power transistors are blown, it is not uncommon for the driver transistors to be damaged, and associated resistors could be bad as well.

[sim]

SJ6343 is a Peavey number, but I have no idea what SJ63438 might be. Sure it is not SJ6343B?

In any case, it is likely that whatever they were, the parts in there used to work. They are two different types most likely because a repair was done at a previous time.


I agree with Jazz, don;t just throw parts at it, find out what is wrong.

If the power transistors are blown, it is not uncommon for the driver transistors to be damaged, and associated resistors could be bad as well.

yes you are correct the 2 power transistors are sj6343B eyesight not as good as it use to be. I have removed all 4 power transistors and diode tested them on my meter all seems ok I am going to test diodes next

[Steve Conner]

Well, according to the Peavey cross reference guide, SJ6343 says "NPN 180V Output" and "Field Replacement Number: MJ15024"

So you can replace a SJ6343 with a MJ15024 in a Peavey product, but is it OK to do the opposite?

[J M Fahey]

Hi Steve.
I *guess* that in this particular case , it might have happened the other way (with the same end result)
The MJ15024 might have been the original part, and this amp has before visited the bench at some authorized Peavey service shop; the technician there might be stocked on SJsomethings and just grabbed his little parts box and used them, knowing their being equivalent.
I would have done the same.
I can find no other explanation to find Peavey parts there.

[Enzo]

If I wanted to get a repair out the door, and I was out of MJ15024, and I had some SJ6343 PV parts, I would indeed install them confidently.

The PV cross-ref is not like the NTE book, their chart is pretty much telling you what the parts really are under the house numbers. They didn't have Motorola design them all new transistors.

[Steve Conner]

Well, except the MJ15024 is a 250V transistor, so why does the Peavey guide say 180?

That suggests to me the SJ6343 was some older, less powerful part, and they list the MJ15024 as the field replacement so that techs don't have to stock so many parts.

So what I'm asking is, is it OK to sub this into some other circuit that was designed around the "actual" MJ15024? Could the SJ parts have failed because they have a smaller SOA than the protection circuit was designed for?

It's academic anyway, if they're dud you'll be replacing them with MJ15024s. We established that the SJ numbers are Peavey house numbers, so there's no way they'd be fitted at the Carlsbro factory.

[Enzo]

Because as used, the gain is specified at certain current levels, and they also derate the parts to watch for SOA. These are the parts PV uses for their 180v applications.

[sim]

Hello

I have a Grx7 that blows an internal fuse T 6.3a I have read posts on the Carlsbro forum ( now seems to have ended) about this amp and they say to replace the MJ15024 all four. Mine has 2 MJ15024 and 2 SJ63438 I assume this to be incorrect.

my question is should I replace them all with 4 MJ15024 or are there versions of this with the above
I would be very grateful for a little guidance and or a schematic

Hello all thanks for all your replies I have found a large resistor that has burnt the circuit board I think I will replace it anyway when I get a schematic, but could this be the problem?

[gw3xjc]

Carsbro grx7

Hello

I have a Grx7 that blows an internal fuse T 6.3a I have read posts on the Carlsbro forum ( now seems to have ended) about this amp and they say to replace the MJ15024 all four. Mine has 2 MJ15024 and 2 SJ63438 I assume this to be incorrect.

my question is should I replace them all with 4 MJ15024 or are there versions of this with the above
I would be very grateful for a little guidance and or a schematic

I wonder if you were fortunate to obtain a circuit diagram????
I am also looking for the same.