Dead Autocostruire amp?

[johnm]

Hi!

A few months back I stupidly fried the TA2020 chip in my Autocostruire amp by accidently applying the dreaded reverse DC polarity stunt!

A few months later I finally replaced the chip with a new one - tonight in fact. I also installed a fresh pair of Panasonic FC 2200uF caps. Result, the amp is still dead silent No life at all...

Everything appears fine on the main board - all neat and tidy and all flux residue removed.

My question is does anyone know if any of the other components on the main board would have suffered when I reversed the polarity? It was only for 2-3 seconds tops. Could the two smaller caps (1uF/100v and 10uF 16v) be damaged by this and result in no sound from the amp?

Any help gratefully received.

Cheers,

- John

[Pano]

2 or 3 seconds should not have killed the caps, but I don't know why else it wouldn't be working. Have you checked all the traces to see if any broke, like a fuse?

I don't have the schematic for the amp, but if you point me toward it I or someone else here should be able to give you a few things to test.

You checked mute and sleep, right? Power supply is good?

[ssmith]

The schematic is in the PDF instructions here

[johnm]

Hi yes checked the rest of the circuit and all appears to be fine. There was a lifted circuit trace on the upper boards which leads from the positive leg of C7 to the negative leg of Cpump which I instead made underneath the board - that appears to be fine.

I don't know how to check the mute/sleep functions alas - any chance you could enlighten me here please?

SSmith - thanks for that link

[ssmith]

Originally posted by johnm
SSmith - thanks for that link

No problem, sorry though cannot be much more help.

One thing can suggest though -- if you have a multimeter with continuity testing, try that on all the solder points on the board.

I have one (ordered pre-built), and did some mods to it, and found the traces were not that resistant to my sloppy soldering skills.

[johnm]

Agreed the Autocostruire boards don't seem very DIY friendly at all. Have lifted a couple of traces on this board already and I'm very careful... er reversing polarity aside! Haha! Unsoldering the dead TA2020 chip and trying several times to rid the remaining holes of solder using a thin tip iron and de-soldering braid was a complete nightmare!

I've gone and ordered an AMP6 as this appears to be better made and designed. At least if I have no luck resurrecting the Autocostruire kit I can try out the air-core inductors in the AMP6 to see if they're better or worse than the supplied torroids.

Cheers,

- John

[Lostcause]

Hi John,
Best bargain: Maplin's do a solder sucker really cheap...and you get a soldering iron for free!!!! Those sucker jobbies certainly get the solder out of anything.

[Pano]

I'm amazed that you managed to get the chip off the board. You're a better man than I, Gunga Din.

Will have a look at the schema to see if we can find your problem.

What sort of measurement tools do you have?

[Lostcause]

I'm wondering if the 1uf Cpump cap is toasted?
That's gone on a couple of dead sonics I've had in the past.....

[johnm]

I found it easier to remove by wiggling the ship several times back and forth which snaps off quite easily, then heating the remaining legs quickly and removing them while heated with a pair of pliers. Yep... this is chip torture haha!

Doh! A solder sucker! I should have thought of that would have saved me alot of time and stress! Gahhhh!

Thanks for your help - I'll try replacing the 1uF as I think I have a spare somewhere. Only meauring tool I have as just a bog standard digital multi-meter I'm afraid.

- John