another "BA115 keeps blowing fuses" thread!

[Execut1ve]

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.

 

[BassmanPaul]

Following the steps required for a proper diagnosis of the problem is the way to go. You really have no idea whether the problem is pre existing or related to your “modifications.” Why on earth would you move the PT inside the chassis where it’s EM field can propagate into the signal path?

 

[Old Garage-Bander]

Fuses blow for a reason. They are not like light bulbs that wear out from use.
One blown fuse may be a fluke. Two blown fuses means you have a problem.
Hopefully after your homebrew mods, you'll be able to find a worthwhile tech who is willing to work on it.

 

[Execut1ve]

Thanks for the votes of confidence, gang. I doubt very much that changing the power plug or fuse holder is a factor in the fuse blowing. If the transformer does in fact turn out to be causing problems inside the chassis, I will happily return it to its original location - however I tested it with the transformer inside and out, and the fuse still blew.

Maybe it wasn't clear in the original post, but these mods were not intended to diagnose or solve the fuse blowing issue - they were quality of life changes that I desired to ease my use of the amp. I undertook them at this time because I had everything taken apart for the fuse anyway. I had been hoping that the fuse blowing was a one time fluke, possibly caused by a storm surge or what not, and that it would fire right back up with a new fuse. Clearly there is a deeper issue present which caused the fuse to blow, and remains unresolved.

With all that out of the way, does anyone have any constructive suggestions on troubleshooting this thing? From reading other threads about the BA115, it seems the output devices and drivers are common culprits - is there a way to test them with a multimeter? Or do folks generally replace them blindly and the problem resolves itself? I've also read a dim bulb tester can be helpful, I think I have enough misc spare parts around here to fab one up.

I'm perfectly capable of using a multimeter and the schematic to trace the entire thing through, hoping to find a short to ground that would account for the issues. But if there are any commonly known causes I'd love to eliminate them first.

 

[Execut1ve]

Following the steps required for a proper diagnosis of the problem is the way to go.

I'd love to know what these "steps for proper diagnosis" are.

 

[Old Garage-Bander]

Thanks for the votes of confidence, gang. I doubt very much that changing the power plug or fuse holder is a factor in the fuse blowing. If the transformer does in fact turn out to be causing problems inside the chassis, I will happily return it to its original location - however I tested it with the transformer inside and out, and the fuse still blew.

Maybe it wasn't clear in the original post, but these mods were not intended to diagnose or solve the fuse blowing issue - they were quality of life changes that I desired to ease my use of the amp. I undertook them at this time because I had everything taken apart for the fuse anyway. I had been hoping that the fuse blowing was a one time fluke, possibly caused by a storm surge or what not, and that it would fire right back up with a new fuse. Clearly there is a deeper issue present which caused the fuse to blow, and remains unresolved.

With all that out of the way, does anyone have any constructive suggestions on troubleshooting this thing? From reading other threads about the BA115, it seems the output devices and drivers are common culprits - is there a way to test them with a multimeter? Or do folks generally replace them blindly and the problem resolves itself? I've also read a dim bulb tester can be helpful, I think I have enough misc spare parts around here to fab one up.

I'm perfectly capable of using a multimeter and the schematic to trace the entire thing through, hoping to find a short to ground that would account for the issues. But if there are any commonly known causes I'd love to eliminate them first.

First, I never attributed your modifications to being the cause of the amp blowing fuses. It was clear that you made the modifications because you thought doing so might somehow fix the problem. At the very least, you were hoping to get by without blowing fuses long enough so that having an easily accessible fuse meant you didn't have to tear the amp apart every time it happened. That is clearly not the thinking that goes along with someone who has the chops to diagnose and repair this amp as a DIY.

Furthermore, asking if blindly replacing parts is a valid way to diagnose a problem, tells me that you really are in over your head on this. And anyone with the proper skills and knowledge in these types of repairs knows better than to make the mods you did without fixing the real problem first.

So before you get up on your high horse about what others are telling you, please realize that just about everything you've said on the matter is very telling in how much you don't know.

If you want to simply explain that your amp is blowing fuses and has anyone experienced that before with this amp and do they know what it took to fix their's, well that's fine. And if what it took was to take it to a qualified technician and all you learn from that is that the bill was $100, then you're that much further ahead of the game.

We can tell what you don't know by what you did and what you are saying. The only dim bulb around here is the one you're using to look at this problem in the proper light.

 

[Old Garage-Bander]

I'd love to know what these "steps for proper diagnosis" are.

Most of us who do this kind of stuff have gone through formal electronics repair schools and have many years of experience. It ain't like asking someone how to mix up a pitcher of frozen lemonade.
If your car is broke down on the highway and oil leaking badly out of the engine, do you first rotate the tires and then call a mechanic and tell him you have a Chilton's and lug wrench and ask him what's wrong so you can fix it yourself?

 

[12BitSlab]

I have a BA115 (V1) and have never had a problem.

Which version is yours?

 

[Slevage]

I'd love to know what these "steps for proper diagnosis" are.

It’s a blend of learning theory and getting some real life experience—- just like playing the bass.

 

[BogeyBass]

If i remember correctly that amplifier has no output short circuit protection. Or kinda...basically the main fuse is the protection. So a blown driver could possibly blow fuses.

Likewise a known issue with that amp is the speaker output is routed through the headphone jack. And the contacts on the jack are known to oxidize/ burn up and cause problems. The jack needs replacing if so since the contacts will be heavily discolored and have little to no contact.

Often grunted against on here is the classic..." Its the capacitors" lol

But if the output transistors dont show obvious damage or burning. Check the main power supply capacitors for swelling or leakage since damaged caps arent always obvious.

Likewise without going through a huge write up on how voltage checks and isolating areas of the amplifier to see where a possible damaged component excists. A bad or damaged bridge diode is a likely candidate. Or any large ceramic resistor dropping large amounts of current for the opamp preamp section. Or a possible damaged zener diode used to regulate the +/- 15 volt preamp power supply. Bad zener is not always obvious as well. And likewise ...huff huff puff puff lol check the low voltage 15 volt caps for swelling in the preamp as well

This of course is all internet guessing game cause as mentioned a full run through is the only way to fully tell whats going on. Aside from cracked or bad solder connections from vibration that arent obvious could be a problem. Not likely but a close inspection dont hurt

Just throwing guesses cause bad bridge diodes. Zener diodes and headphone jack failures are relatively common with this amp.

Id check the driver as well with ohm meter or test signal. Or simple push on it since a melted voice coil would definitely be obvious and toast fuses.

 

[bobba66]

It was a happy day indeed when I dragged my BA-115 out to the curb and left it for the scrappers.

 

[Execut1ve]

I was gearing up for a salty and sassy rant to respond to all this condescension, but after sleeping on it I think it would be better if I didn't.

Thank you BogeyBass for the constructive suggestions - I will be sure to check those items first.

The rest of you, please feel free to continue being unhelpful. But if there's not a big altar call after all this preaching I'll be very disappointed

 

[Slevage]

If i remember correctly that amplifier has no output short circuit protection. Or kinda...basically the main fuse is the protection. So a blown driver could possibly blow fuses.

Likewise a known issue with that amp is the speaker output is routed through the headphone jack. And the contacts on the jack are known to oxidize/ burn up and cause problems. The jack needs replacing if so since the contacts will be heavily discolored and have little to no contact.

Often grunted against on here is the classic..." Its the capacitors" lol

But if the output transistors dont show obvious damage or burning. Check the main power supply capacitors for swelling or leakage since damaged caps arent always obvious.

Likewise without going through a huge write up on how voltage checks and isolating areas of the amplifier to see where a possible damaged component excists. A bad or damaged bridge diode is a likely candidate. Or any large ceramic resistor dropping large amounts of current for the opamp preamp section. Or a possible damaged zener diode used to regulate the +/- 15 volt preamp power supply. Bad zener is not always obvious as well. And likewise ...huff huff puff puff lol check the low voltage 15 volt caps for swelling in the preamp as well

This of course is all internet guessing game cause as mentioned a full run through is the only way to fully tell whats going on. Aside from cracked or bad solder connections from vibration that arent obvious could be a problem. Not likely but a close inspection dont hurt

Just throwing guesses cause bad bridge diodes. Zener diodes and headphone jack failures are relatively common with this amp.

Id check the driver as well with ohm meter or test signal. Or simple push on it since a melted voice coil would definitely be obvious and toast fuses.

Output transistors often “ look” good.
I’ve replaced enough to fill a couple of 5 gallon buckets.

 

[Execut1ve]

Most of us who do this kind of stuff have gone through formal electronics repair schools and have many years of experience. It ain't like asking someone how to mix up a pitcher of frozen lemonade.
If your car is broke down on the highway and oil leaking badly out of the engine, do you first rotate the tires and then call a mechanic and tell him you have a Chilton's and lug wrench and ask him what's wrong so you can fix it yourself?

I'm afraid the joke's on you, my friend... I literally taught myself basic auto repair, with a Chilton's manual being my primary source of information. I've been doing all the mechanical maintenance on my vehicles ever since. In fact I have a set of new valve cover gaskets ready to go into the wife's car just as soon as I get some free time and the weather is tolerable. So your choice of analogy is ironic.

Bottom line, all I asked for was the most likely failure point given the symptoms - just to eliminate the most probable causes first. I did this because while I've tinkered with plenty of electronics over the years, I haven't tinkered with this particular one. So I had hoped someone with experience on this particular amp might be able to point me in a good direction and save me time and effort in the long run. Instead, you felt the thing to do was preach at me and waste your time and mine - thanks for that.

 

[Execut1ve]

Output transistors often “ look” good.
I’ve replaced enough to fill a couple of 5 gallon buckets.

Thanks John - I'll check those first when I get some free time and can get back to work on this thing

 

[MultiScaleMale]

“Not what I want to hear” does not equal “not helpful”.

 

[Roland GR 88]

The rest of you, please feel free to continue being unhelpful. But if there's not a big altar call after all this preaching I'll be very disappointed

You're asking a question that can't be properly answered without having the amp on a bench and an experienced tech looking at the insides. These 'diagnose my problem' threads are rarely solved because the average TB'r will give you poor/wrong or just ill-informed advice and most of the engineers amongst us are smart enough not to guess and will encourage you to go to a qualified tech.
Getting upset and trading insults will simply kill this thread just as dead as your amp.

 

[Execut1ve]

Thanks for weighing in, Rich and Roland. As explicitly stated previously: I am not looking for someone to DIAGNOSE the problem for me. I am looking for known common failure points of this amp so as to find and correct the issue faster. Thankfully a couple of more helpful posters above have provided some good starting points for my testing.

Seriously, how hard is it to say "these amps are known to fail here, here, and here"? If you have that information, what do you lose by sharing it? If you don't, why do you feel the need to speak up at all?

My plainly stated goal is to diagnose and repair this thing myself. I am not going to consider taking it to a tech until I am satisfied that fixing it myself is completely out of the question. Things like advising me to take it to a tech, admonishing me about all the years of experience that are required, or scoffing at my knowledge/abilities are by definition not helpful - they do not aid me in achieving my stated goal. They just provide a soapbox for the poster to promulgate his/her views and belittle me.

 

[BassmanPaul]

I'd love to know what these "steps for proper diagnosis" are.

Meaning no offence but if you don’t know the steps perhaps you should take the unit to a tech.

 

[beans-on-toast]

Go here Link Removed, type in BA-115. If you have an older model, you can obtain the schematic from Loud. They don't provide schematics for current models.

There's a short somewhere, it needs to be located.

The amp needs to be methodically checked out from the power cord, through the power transformer, to the power supply. There are DC reference voltages on the schematic that can help you determine what is working and what isn't.

I would start with a visual inspection looking for any obvious signs of distress. As mentioned, look for swollen or leaking electrolytic power supply capacitors.

If none are found, disconnect the primary of the power supply transformer. Test the power coming into the chassis to the power supply primary connector with a volt meter set to AC volts. If the fuse blows, there is a short between the wall and that connector.

If no issues to that point, reconnect the power supply primary and disconnect the secondary. Test the voltages at the power transformer's secondary.

Progress through the amp, one step at a time.