Metropoulos Forum

Well I finally did it and fried one of my '76 Bud Box's. You can smell "the smell"

I am heavily bummed, but have high hopes.
Unless there's a NOS IC (or used) chip that is obtainable, I'm going to properly repair it, sell it, and then pay to get another exact replacement... Which means only '76 Script Logo. Yes, I would consider a '74, but anything other than is futile with me...
I apologize if this seems anal in this particular department, but I have my shit dialed in to this.... and like it !

How it happened ??? IHNFC ?
I can tell you that it sits on my pedalboard connected to a battery clip. I cannot fathom what actually happened, but I have to ask if these chips fry like that with just a battery ? Is that rare that it happens ? ? Never in over 30 years, that this happened, man.

Sorry just a little pissed walking down vintage lane... The price and the sacrifice are worth it to me... Tuff to part or try a modern replacement since the vintage MXR stuff is what I grew up on. These are some of the sounds in my head. I use it with the Vol. all the way up and then dialing in unity gain. Used more as a boost that Distortion...

you'd probably know it if the chip died... the only time ive ever seen one fried it literally smoked and made noise.

most likely a cap went bad, they only last x amount of time, the resistors and chip are far more durable. if you had an audio probe this would be a cinch to figure out since the cicuit is so simple. these are based around the 741 chip, they are as common as they are useful. if you have trouble finding one i may not be able to help as that would mean you live in fiji or some inaccessible part of the world... they a literally everywhere.

check your caps over thoroughly, if you see any bubbling or strange residue, you found the culprit. the green ceramic towards the top of your photo looks a bit weird.

I agree. Fix it and see what you got, tonewise. You may be pleasantly surprised. I think it would be 'harder' to replace the 'sound' of your particular unit by getting another of the same vintage. Replacing a componant here or there may be the better option.

IIRC, that pedal has a 741 opamp chip. Basic opamp chip, later pedals went to the 4558 variation, those are actually dual opamp chips with better noise specs. But you want the 741.
I remember seeing some of those in Radio Shack a few years ago. You might luck out and have one sitting around in the bottom of one of those parts bins that keep getting smaller every year.

Like the guys have said above, you're highly unlikely to have fried the opamp.

Build yourself a signal tracer and see where the signal dies. You want a 0.1uF cap (value doesn't matter too much) connected to the 'hot' of your amp and a ground clip to attach to the pedal. Just probe from the input and follow the signal path through the pedal. You'll find that where the signal stops is likely your bad component.

What about voltages? - take some voltage measurements and post them here, you'll get help for sure.

Thanks guys. I GREATLY appreciate the help here. I am totally up for this learning curve.
......the only time I've ever seen one fried it literally smoked and made noise. Unfortunately this did happen...
You can smell it.
but firtst, I will take some voltage measurements on my Beckman and report back A.S.A.P. with readings...
Then the signal chaser.

Oh... what year is this 4558 chip, from '78 ?
If it sounds like my '76 then I will investigate. Subtleties cannot hide with me.

I really appreciate all youz guyz help

http://www.mouser.com/ProductDetail/Tex ... ah0f4VM%3d" onclick="window.open(this.href);return false;

No way... Says *New* item ?! Looks a different, though.
Ordered a couple and will report back upon arrival...
Readings shortly to follow.

http://www.jameco.com/webapp/wcs/stores ... 1_24540_-1" onclick="window.open(this.href);return false;

http://www.ti.com/lit/ds/symlink/lm741.pdf" onclick="window.open(this.href);return false;

The smell will likely be the cap from the voltage divider going to pin3 or the 100ohm resistor in line with the supply. I doubt very much that your opamp is fried, there are other things that would smoke first.

Removing an opamp isn't a job for the faint-hearted if you're inexperienced at stuff like this and you could easily fuck up your PCB and/or a perfectly good opamp.

Take it one step at a time, measure voltage from the supply (i.e. the battery) then trace it through and annotate a schematic with your findings.

JimiJames wrote: No way... Says *New* item ?! Looks a different, though.
Ordered a couple and will report back upon arrival...
Readings shortly to follow.

I'd get a 8-pin socket and solder that in. So you can swap out chips and see if there's a difference.
Seriously though, a 741 is a 741. The pinout will be the same, it will work the same.
A 741 opamp chip is ubiquitous. It's been around forever.

I've fixed more than a few pedals, and opamp chips DO die. It's not uncommon and you usually don't smell anything burned, they just stop working.

The 4558 chip will not work, it has a different pinout than a 741. A 1458 is a dual 741 inside but still the same pinout as a 4558 which won't work on this PCB. Just get an actual 741.

Steve Mavronis wrote:The 4558 chip will not work, it has a different pinout than a 741. A 1458 is a dual 741 inside but still the same pinout as a 4558 which won't work on this PCB. Just get an actual 741.

Right. I suggested using a socket to try 741s from different manufacturers, if one is inclined to do that. Judging from your avatar, I see you did the same. I was in a pedal building phase a while ago and always used sockets for chips.

Mouser came in today. I'll get to those readings A.S.A.P...