Which component is fried?

[steveyraff]

Hey all,

I built someone a 2-in-1 stomp box. It has a Tubescreamer on one side, a Blues Breaker on the other. They didn't have a power supply so apparently they grabbed the first one at hand which unfortunately turned out to be a Modem power supply which is 12v , 1.5A.

I got it back to repair today. As luck would have it, today is also the day my multimeter decided to not work. I did notice the first 100uf 16v cap the 9v supply hits was blown, so I replaced it, but still no joy. The Bluesbreaker side works fine, its just the TS side thats not doing anything.

I also tried replacing the two transistors, still nothing.

Just by looking at the layout, would anyone hazard a guess what else is most likely blown? I'm just gonna replace anything I can until I get it at this stage...

Many thanks as ever,
Steve.

[Juan Wayne]

I don't know what you're powering it with now, but 12V won't do that. A modem PSU with a positive inside instead of outside, probabvly will. That would most certainly kill the op amp on the TS side, so if I had no multimeter, I'd throw any compatible one you have laying around there and check for sound.

Quick edit: if it was indeed reverse polarity, you got lucky it didn't kill the bluesbreaker as well.

[R.G.]

Add my vote for the opamp(s). The power supply was likely reversed, and >may< have been an AC type. I would also replace any reverse-polarity protection diodes. If the reverse polarity diode is dead, that would mean it was almost certainly an AC-power-supply disaster.

[R.G.]

Last thought hit me as I hit "post".
If you don't have a spare multimeter, get one. An auxiliary multimeter can be under $10, sometimes as low as $5 on sale at Harbor Freight. Cheap insurance.

[steveyraff]

Cheers dudes. Whats confusing me, how come the first 100uf 16v cap at the 9v supply had its entire bottom blown out? (that sounds weird  )

I was thinking the OP amp, but when I seen that first cap doing that, and I knew it was 16v rated, I started to wonder was it the other electrolytic caps too, so I replaced them all and still nothing.

I have a spare Op Amp of the exact same kind - I'll try it now. It's gonna be so awkward getting it out of there now  Part of the reason I was putting off replacing it first lol.

I'll let you know how I get on.

P.S
I had a spare multimeter. The one thats not working for me right now as the replacement. I live very rural, so I tend to order this stuff online.

Thanks all!

[GibsonGM]

Cheers dudes. Whats confusing me, how come the first 100uf 16v cap at the 9v supply had its entire bottom blown out? (that sounds weird  )

12V, 1.5A is likely an unregulated power supply.  Unloaded, I have zero doubt you will read in excess of the 16V cap rating, so the cap likely died to to over-voltage.   

You could read over 20V unloaded with a brick like that!  What the spec tells you is that "If you draw 1.5A from this supply, it's going to be about 12V output".   So, drawing what, 20mA including the LED....you will be far, far in excess of the 12V rating. 

Even worse if it was an AC supply....

You can use your audio probe to trace the signal, find out where it dies, if you like. I vote opamp too, tho...most of the rest should be 'resistant' to over-voltage problems.     You had the IC socketed, right?   

[steveyraff]

Cheers dudes. Whats confusing me, how come the first 100uf 16v cap at the 9v supply had its entire bottom blown out? (that sounds weird  )

You had the IC socketed, right? 

Thanks man. You know, I used to always socket my IC's. Then a few regulars here started to tell me I should just commit when I know its the right one and do it properly. For months after that, I'd post pictures of my builds and everyone would be all "Hey whats the socket still doing there!". I eventually removed myself from the habit of it when I was sure about what IC I was using. Now, I am not so sure why people advised me against socketting lol. I really wish I had, that was a pain in the ass trying to remove. Got it eventually. Gonna solder in this new IC now and see what happens.

Cheers all!

[steveyraff]

ITS ALIVE!

....Finally. Thank you guys so much. That was a bit of a nightmare replacing that IC. I called it all the names of the day - my wife asked me who I was speaking to lol.

I've a new multimeter ordered!

Cheers all! Phew!

[Juan Wayne]

Noice!

Yeah, some people don't like sockets, I don't particularly either because it sort of feels like I haven't decided to declare de the job as finished, but I still use them anyway because they make life easier in some cases, and if enough time goes by I forget they're in there.

I've gone as far as socketing resistances and caps. Don't do that. Only sick people do that and then others look at you funny.

[PRR]

> how come the first 100uf 16v cap at the 9v supply had its entire bottom blown out? (that sounds weird

Grab a few small 16V electrolytic caps and some power supplies.

Go outside! Heavy shirt, glasses.

Stretch the power cords out so you can connect the cap, then step back 6 feet to plug-in the supply.

Connect 16V cap to 9V-15V DC power *reverse polarity*. It gets hot, boils, blows the seal. Smoke, spews damp paper, stinks.

Connect 16V cap to 9V-15V AC power either way. It gets hot, boils, blows the seal. Smoke, spews damp paper, stinks.

Connect 16V cap to DC power the right way, but 20V DC or more. It gets hot, boils, blows the seal. Smoke...... (This may take longer, even hours-weeks; try 24V on a 6V cap.)

A large low-Volt e-cap in a 120V outlet *may* spray boiling copper before the damp paper explodes. Do not try this at home.

[bluebunny]

Connect 16V cap to 9V-15V DC power *reverse polarity*. It gets hot, boils, blows the seal. Smoke, spews damp paper, stinks.

This all happens faster than it took Paul to write it - POP!    I had a reversed cap on a synth module due to a bad silkscreen...    It popped and spewed its fluffy guts all over the other components.  Nothing left apart from the leads and a tiny part of the case.   

[ElectricDruid]

Aah, the infinite wonders the learning process. Isn't it beautiful. folks?

T.

[Tony Forestiere]

Aah, the infinite wonders the learning process. Isn't it beautiful. folks?

T.

Absolutely agree. Omelette = Break some eggs. Many times. Adjust process. Break more eggs. Fewer times. Adjust process. Break only the eggs you want. Process works for you. Omelette comes out the way you want it. Every time.