Rat Build Emergency!!

[zwound]

Oh my god...i think i just messed up my rat build, but i wanna know how badly...

basically, the symptoms:

No guitar signal is let through the thing (although the output pot and output do work, so the problem is somewhere in the input).

One of the diodes was heating up immensely, after which i shut everything down. nothign else was hot though.

I'm asking now...the Chip..the LM306...do i need to buy a new one? is there a big chance anything got damaged? it would really suck if i needed to buy a new chip cause it costs loads...however it did not heat up at all.

Thanks! Im waiting for quick replies...im in dispair 

EDIT: I have a small theory, that i might had exposed one of the diodes to too much heat...

LINK: http://www.tonepad.com/getFile.asp?id=89

the ones i have in mind are D1 and D2. no clue which one, but one of them....

[slacker]

which diode was getting hot? If it was D3 then you've probably either put the diode in the wrong way round or you've got the power connections reversed. That diode is there so that if you plug the power in the wrong way round you don't damage the opamp so hopefully it's done its job and nothing else is damaged.

[Mark Hammer]

1) It's an LM308 not 306.  My guess is that this is simply a misprint on your part rather than an error in terms of which chip you bought.  An LM306 is also an 8-pin chip, but boy oh boy is it different.

2) The number of ways it is possible for a FET to have different pinouts than you thought it had appears to defy mathematical possibilities.  Whenever I see someone have difficulty with a project involving a FET, it is often a case of mistaken assumption about pinout.

3) If it is one of your first handful of builds, there is all the usual stuff that tends to get in the way of getting it to work, quite apart from any fatal flaws that are specific to this circuit or that one.  A lot of that is in the FAQ.

[zwound]

yeah, that was my typo...mine has 8 pins...and 308 written on it

and the D1 OR D2 were getting hot...hence that they are next to each other and connected. everything else was fine though...

where should i look for the problem?

[zwound]

which diode was getting hot? If it was D3 then you've probably either put the diode in the wrong way round or you've got the power connections reversed. That diode is there so that if you plug the power in the wrong way round you don't damage the opamp so hopefully it's done its job and nothing else is damaged.

D3 was absolutely cool. i checked that

[dschwartz]

you mean LM308?
maybe thats wrong.....

i think you have a short circuit if the power diode y getting hot

[zwound]

do you think the diodes wouldve still protected the rest of the components from the lethal blow ?

[soulsonic]

It's hard to judge anything without seeing a picture first.
Any potential damage done by overheating while soldering wouldn't cause this problem.
I'd look for a short on the circuit board.
Is the chip in a socket? If it is, yank it out and power the circuit up and see if you can find anything more.... that way you don't have to worry about potentially hurting the chip.

[zwound]

It's hard to judge anything without seeing a picture first.
Any potential damage done by overheating while soldering wouldn't cause this problem.
I'd look for a short on the circuit board.
Is the chip in a socket? If it is, yank it out and power the circuit up and see if you can find anything more.... that way you don't have to worry about potentially hurting the chip.

it's in a socket allright ...

ok, ill power it up now and see what happens....i'll be back in a jiffy.

[zwound]

Ok...

ive found something...the battery clip and the battery dont connect properly because the clip is slightly broken and cant properly bond with the battery. Only one side of the battery is taken in, whilst the other one is jerking about and is not properly connected. now that i pressed the clip against the battery properly (it doesnt 'attach' itself to the battery properly), it seemed to me that the diode stopped heating...could this be the problem??

EDIT: there was also a distinct hum when i ran the rat with the chip (and it was present when i ran it without the chip). but when i pressed the battery and the clip together properly, the hum stopped...

[zwound]

Ok...

ive found something...the battery clip and the battery dont connect properly because the clip is slightly broken and cant properly bond with the battery. Only one side of the battery is taken in, whilst the other one is jerking about and is not properly connected. now that i pressed the clip against the battery properly (it doesnt 'attach' itself to the battery properly), it seemed to me that the diode stopped heating...could this be the problem??

EDIT: there was also a distinct hum when i ran the rat with the chip (and it was present when i ran it without the chip). but when i pressed the battery and the clip together properly, the hum stopped...

ignore this. the battery clip kinda came off the rat itself...its kind of unstable on the outside right now coz im testing it (just whacked the pots and jacks on).

otherwise, everythign else is now connected...and still the same thing. i ran the thing without the chip, and STILL D1 or D2 heat up immensely. When i noticed that they didnt heat up before, that was probably an accident

[soulsonic]

Something has to be shorting somewhere.

[zwound]

ok...im gonna scan this big ball of wire tomorrow...but are the diodes fine if they heat up..or i need to replace them? can you tell the approximate whereabout of the mistake by where the diode heats up?

[nooneknows]

A diode heating up is at 99% a problem concerning some short circuit. Double check solder drops between traces, electro caps connected backwards, etc.
Once I lost 2 hours with a simple boost not working looking for the problem, it was a tenth of a hair of solder shorting out two traces...

[dschwartz]

yes i definetly looks like a short..maybe 9 volts are going thru the clipping diodes and warming it up...fix it fast, your batt will die soon that way..

and USE A VOLTMETER...measure the voltage across the diodes.. it should be near 0 volts..anything different means something´s wrong

[GibsonGM]

Trace the power wires from where they go into the board...follow the path looking for shorts.  If you find nothing, measure the voltages at the IC socket (keep the IC out for now! If it isn't dead yet, you'll be happy you debugged with it not installed!).   Post the voltages present at each pin of the IC socket so we can see what it looks like. 

Check each ground point, and be sure you didn't accidentally connect something to "+" that should be going to "-", a very common error....sometimes it takes more time in checking at circuit than it did in building it!  Don't worry, you'll find the problem.
 
The diodes may or may not be dead.  Check their resistance - in the circuit, all I know to do this way is to measure resistance and if it's very high, the diodes are probably still good.  Very low, and they're toast.   You can disconnect them for this (best way to test).