park G10 gone bad

[remmelt]

hey there!

i own a park g10 (my first amp ever!)
the pots were crackling so hard i opened it up to clean them, but i must have touched something to somewhere because now there's  just a large hum and hardly any signal.

also there are sparks coming from the cooling fin when i touch it to ground, which in my opinion would be a bad thing.

i tried audio-probing it, but couldn't get any further than the first opamp. after that, the sound is kind of soft and whirly.

any suggestion as to what may have gone bad?

any voltages i should be reading? i'd love to have this thing up and running to test and debug effects with, rather than fire up the bluesbreaker every time.

[niftydog]

but i must have touched something to somewhere because now there's just a large hum and hardly

are you saying it was switched on while you opened it up?

You don't need the power on just to clean the pots you know!!!  

also there are sparks coming from the cooling fin when i touch it to ground, which in my opinion would be a bad thing.

um, yes. bad, bad, bad. So bad in fact that the fuse probably should have blown... bad design, bad sound, just generally bad from what I'm reading here lately!

any suggestion as to what may have gone bad?

It's likely that the output transistors have blown. They're probably short circuit, and that could be why you're getting those sparks.

Are you sure you put everything back as it was?

[Steben]

It should be quite nice to throw out as much as you can and replace the parts. I recently gave mine a go.

You can replace the power chip TDA2030 with another one.

Change the JRC4558DD chips with other 4558's (as the KA4558 or RC4558) or even TL072's. Change the diodes D1 and D3 as I explained recently in this forum.
Of course you can start tweaking the cap values etc...

Doing this you put in an extra $10-15, but get a much better sounding "cheap" amp.

[remmelt]

bad sound, i know i know. it's cheap.

i did not have the power on when i was cleaning the pots, but i must have done something wrong. i can't really remember now, i must have wanted to test before closing it all again. the pots were VERY VERY crackly. it was a while ago.

after some time passed i decided i was going to fix the little bugger and turned it on again: poof, no more fuse. i looked, the fuse didn't even have the right value! it was a 200mA where a 125mA should have been. thank you for the eye for detail, mr Park!

i did put everything back the way it was, ofcourse. there is a TDA2030 in there, on the cooling fin. there are no transistors, just two opamps (JRC4558DD).

should i just forget it and make a new one from scratch and salvaged parts? the speaker is pretty horrible, but the case is alright. it would be fun to make this thing work again though.

[remmelt]

i saw your thread, Steben, i was about to post all this in there but thought it deserved its own post.

i was wondering if you could maybe post some voltages i should be getting on a couple of key points in the circuit? that would be of great help!

[niftydog]

it was a 200mA where a 125mA should have been. thank you for the eye for detail, mr Park!

that was probably intentional. as I said, bad design.

there is a TDA2030 in there, on the cooling fin

desolder that and check it with a multimeter, chances are that it's dead short.

When you say you "turned it on again and poof" do you mean it was sitting out of it's case for a while? Something may have landed on the circuit and made a short. Give the board a good dust off and check for foreign objects.

[remmelt]

talking about debugging eh? unfortunately (or not, depends on how you look at it) i kept the board boxed up. i checked, there aren't any ufo's on there.

i found the datasheet for the tda2030.
the pins go:
1) non inverting input
2) inverting input
3) V-
4) output
5) V+

what should not be connected to what when i check?

on a related note: i checked with my audioprobe, but the sound is already very weak after the first couple of components in the pre-amp, so straight after the input. this is especially the case after the op-amps. i have no idea what the sound should be, straight after the oa. is this right?

the tab on the tda2030 is connected to V- (3rd leg) and that has a screw to  the cooling fin. my guess is that V+ and V- should not be connected (don't laugh at me, i'm learning here! ). so when i take out the ic, these pins should have no connection. checking with my dmm, an R of NaN.

any suggestions what i can replace that chip with? is the LM1875 a good replacement?

[niftydog]

is the LM1875 a good replacement?

proabaly ok. It's in fact a better device, but since the circuit is designed for a 2030, you should try to replace it with same.

Measure the ± voltage rails and take a note of them. Then pull the 2030 and measure them again. You should also find (if the voltage rails have come back to where they're supposed to be) that with the 2030 out of circuit that all the audio has come back to life around the op amps etc.

I think you'll find that a simple continuity test of the 2030 will reveal all. I can't say what resistances you'll find, but in this case I'm willing to bet that you have a dead short between at least two of the pins.

[remmelt]

I'm willing to bet that you have a dead short between at least two of the pins.

which should not be the case? i'm in the dark with these IC's. i'm going to try this tonight and post the results here. thanks a lot so far!

[niftydog]

yes, short circuits are generally bad news, especially when you find them in ICs.