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another "BA115 keeps blowing fuses" thread!

#81
Amp is reassembled with new mosfets. I used it at practice last night, performed as fine as it ever did. I'm happy to close the book on this repair.

I'd like to extend a big thank-you to everyone who posted helpful advice, whether in the form of a specific suggestion or general knowledge. You guys make this forum great.

The post was edited by a mod to remove a less than charitable sentiment about the people who did nothing but advise me to take it to a tech. The sentiment still stands, but I have been advised not to repeat it.
 
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#82
Well there you go, you worked a little for your reward and maybe learned something more in the process.

For all the folks who were sure it was the transformer, or the caps, or the bridge rectifier with wild ass guesses, you continue to blame the least likely causes.
 
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#83
agedhorse said:
Well there you go, you worked a little for your reward and maybe learned something more in the process.

For all the folks who were sure it was the transformer, or the caps, or the bridge rectifier with wild ass guesses, you continue to blame the least likely causes.
Click to expand...
For my money, it's always the heat sink grease.
How much heat could a heat sink sink if the heat sink had new grease?
I hope the OP checked the heat sink grease when he replaced the FETs.
IT'S ALWAYS THE HEAT SINK GREASE!

I have heat sink grease for sale on CL.:laugh:
 
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#84
That grease is difficult to get off your hands.

It serves as an interface between the heat sink and the component, elimating air between the surfaces which can deter heat transfer. As such, only a thin layer is required.

Never apply new grease over old grease. The surfaces should be clean, use a solvent such as isopropyl alcohol to remove any traces grease or even fingerprint oil.
 
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#86
BTW, all joking aside, there was a youtube with a tech tracing out the same (common)problem on a ba115 that'd I'd checked out about a year ago, I took a couple minutes to try and find it... but no luck. Might be worth a shot on your part.
 
#88
Good point on the bias adjust for the new mosfets, congrats on the fix, With me it's either really fun to fix my own stuff, or it's really exciting... if you know what I mean. the tech I go to usually charges me double when I tell him I tried to fix it myself :)
 
#90
Execut1ve said:
Hello all,

My BA115 keeps blowing fuses as soon as I power it on. I first notice a problem when it wouldn't power on at a gig. Luckily I was able to scrape by without it on that occasion.

After I opened it up to change the fuse, I did some modifications for convenience - added a twist type fuse holder (so I don't have to disassemble the amp just to change the fuse in the future) and replaced the attached power cord with one that detaches, with a standard 3 prong power jack. I also moved the power transformer inside the chassis.

Put it all back together, along with a fresh fuse and fired it up - fuse instantly goes. Looks like blowing that first fuse wasn't a fluke, apparently there is some deeper issue that needs to be corrected. What is the best place to begin troubleshooting this thing? I have the schematic from Ampeg and have been checking my board against it, so far nothing looks obviously burned out or damaged.
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Can’t find the fuse in the chassis for the life of me... can you post a picture of where it’s located in this stupid amp?
 
#92
agedhorse said:
If you can't find the fuse, maybe that's a sign?
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I doubt that it’s any more of a sign than clear message the tech sent by asking $160 to replace what he diagnosed as a blown fuse. It’s a sign that I should open up the amp and pop in a new fuse myself. I can’t sell this amp for more than $160 even when working.

I take your unwillingness to point out the fuse’s location as a “sign” that you too are ignorant on the subject?
 
#93
Emit_remmus89 said:
I doubt that it’s any more of a sign than clear message the tech sent by asking $160 to replace what he diagnosed as a blown fuse. It’s a sign that I should open up the amp and pop in a new fuse myself. I can’t sell this amp for more than $160 even when working.

I take your unwillingness to point out the fuse’s location as a “sign” that you too are ignorant on the subject?
Click to expand...

Time for some popcorn.
 
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#95
Emit_remmus89 said:
I doubt that it’s any more of a sign than clear message the tech sent by asking $160 to replace what he diagnosed as a blown fuse. It’s a sign that I should open up the amp and pop in a new fuse myself. I can’t sell this amp for more than $160 even when working.

I take your unwillingness to point out the fuse’s location as a “sign” that you too are ignorant on the subject?
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Would you care to suggest WHY the fuse(s) blew?

The $160 isn't only to replace the fuses, there's more to it but you don't understand that (yet).
 
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#96
agedhorse said:
Would you care to suggest WHY the fuse(s) blew?

The $160 isn't only to replace the fuses, there's more to it but you don't understand that (yet).
Click to expand...

You bet, the tech’s diagnosis was blown fuse, excess current at output stage.

Hoping a simple fuse swap would get this amp working so I can sell it. I don’t care to get it working if more is required, not looking to delve deeper into the design flaws of the amp, or to repair the amp myself... If it were my primary amp, I would most certainly let a tech do that

The only thing I see is the “thermal fuse,” which is unlike the fuses I’m used to seeing. Out of the hundreds of ba115 blown fuse threads, none have pictures.
 
#97
So, excess current in the output stage is a FAULT that CAUSED the fuse to open. Your tech has confirmed to me that the $160 is NOT simply for replacing a fuse as you suggested.

Without repairing the CAUSE of the fault, all that replacing the fuse(s) will do is cause additional damage while the new fuse blows. It may also expose you to additional hazards. A qualified tech will have the tools, equipment and diagnostic methods to prevent this while troubleshooting.

This is WHY designers (like me) place fuses inside amplifiers, they are not user replacement items. Your example serves as a good reminder of this imo.
 
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#98
Emit_remmus89 said:
You bet, the tech’s diagnosis was blown fuse, excess current at output stage.

Hoping a simple fuse swap would get this amp working so I can sell it. I don’t care to get it working if more is required, not looking to delve deeper into the design flaws of the amp, or to repair the amp myself... If it were my primary amp, I would most certainly let a tech do that

The only thing I see is the “thermal fuse,” which is unlike the fuses I’m used to seeing. Out of the hundreds of ba115 blown fuse threads, none have pictures.
Click to expand...

Are you not planning on telling the potential buyer of the amp's issues (as diagnosed by your tech)?
 
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#99
I'm a big proponent of "Right to Repair". In cases where the amp is out of warranty, people should be able to find a qualified local tech, and that tech should have access to the schematics and information to determine if they can fix the gear and actually be able to fix it. It doesn't need to be a factory authorized tech as it's not in warranty. The the owner has to accept the risk if they choose to go elsewhere.

In this case Ampeg YGG has actually provided all of my concerns of "Right to Repair". They have schematics online available that any Qualified local tech can review.
Good for Ampeg YGG here!
 
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#100
Here's an Unqualified person trying to repair one
smash-jpg.250015
 

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