Dead Autocostruire amp?

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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 :rolleyes: 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
 
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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?
 
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 :confused: - any chance you could enlighten me here please?

SSmith - thanks for that link :)
 
johnm said:
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. :rolleyes:
 
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! :dead:

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
 
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
 
johnm said:
Agreed the Autocostruire boards don't seem very DIY friendly at all. Have lifted a couple of traces on this board already

Me too. I replaced the input caps, the output filter caps and the PS caps. Think the thing that did it was the solder they used to put the original parts in had a very high melting point.
No fatal mistakes though, and I'm very happy with the sound. Incredible detail.

johnm said:
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.

Not qualified to say if it is better designed, but the PCB may certainly be higher quality.
did you go for the AMP6 basic, which seems more noob friendly, or the regular Amp6? Both kits look like a bit of a bargain.

Would be very interested to hear of your progress. ;) Do keep us posted on that one. :)
 
Went for the basic, as I'm a believer in less is more, and will be using a Skynet 8080 PSU with it rather than a torroidal and regulator jobbie. It also does look easy to mod as well, though straight off the bat I'll be using Obligatto 2.2uf input caps (the heavy copper tubed version) and Panasonic FCs for any other electrolytics on the board. Going to try the Skynet with, and without a 10k stiffener cap. I know some folk prefer it with, and some without out depending on their speakers. I do know when I was using the PSU with my modded T-amp I actually preferred it without the Cerafine 10k. I also have a second Cerafine cap so can try with 20k as well - jeeez this hobby never ends - hahaha! Always something else to try out :D
 
johnm said:
Went for the basic, as I'm a believer in less is more, and will be using a Skynet 8080 PSU with it rather than a torroidal and regulator jobbie. It also does look easy to mod as well, though straight off the bat I'll be using Obligatto 2.2uf input caps (the heavy copper tubed version) and Panasonic FCs for any other electrolytics on the board. Going to try the Skynet with, and without a 10k stiffener cap. I know some folk prefer it with, and some without out depending on their speakers. I do know when I was using the PSU with my modded T-amp I actually preferred it without the Cerafine 10k. I also have a second Cerafine cap so can try with 20k as well

For my autocostruire on-board PS caps I used Elna Silmic caps ordered from here -- supposedly better than Panasonic and almost as good a Black Gates. Can't say myself as I haven't tried the Panasonics or BGs, though the Elna's were an improvement over the stock cheapo caps -- eliminated some fatigue in the treble.

For the input caps, I'm using 2.2uf Audyn Cap Plus foil caps. Plan on changing these to Obbligatos though (why? just for the hell of it, and that copper body does look nice :D )

For the off-board stiffener caps, I started out with an Elna 'for audio' 10k cap, but just changed to using 3x 1000uf elna Silmic II's. Tried this with a surplus 12v SMPS, the autocostruire linear PSU (13.7v) and an SLA battery. My favourite is now the SLA with the 3x Silmic caps. For some reason I'm getting better bass response with this combination.
my amp is being fed the discrete output of a USB-DDDAC, volume controlled by PC, and playing into frugel horns - no preamp, no crossover, less IS more :) ).

johnm said:
jeeez this hobby never ends - hahaha! Always something else to try out :D

Yep... because now I'm tempted by an Amp6 basic. Would be nice though if the 41hz site had instructions and schematics to download before buying though....
 
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Hi John,
OK, ready to start testing?

Break out the voltmeter and have a look at the following points. See if you have any voltage at all, and if so, is it correct.

Rin L&R 2.5 V
C2-C3 5V
C Bias 2.5V
C4 C7 13V (or your supply voltage)
C1 should have about 13 V, but it'sa sqaure wave, so may not read correctly on your meter.

All these a in reference to power ground.

Pins 11 and 17 should also be tried to ground, if not, the amp will be in sleep and/or mute mode.

Start there, see what you have.
 
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