What's wrong with this amp? PICS inside

[Lakota 5,000+ posts]

Oh man, I know what amp that is...

 

[Ignatowski 5,000+ posts]

great close up shots,my camera wouldent even get close

 

[midnightg35x 10+ year member]

The pin that fried on your TL494 chip was the ground pin (Pin 7). I think that should be a big hint. Ground doesn't just disappear very often //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif I agree with earlier comments that the SMPS went poof

 

[shizzzon 10+ year member]

would u believe it came from my cell phone? gotta love technology.

this electric guy i been talkin to strongly believes it was due to ESD when packaged.

i know it sucks for the guy who owns this amp... we were just curious what happened.

i guess i'll stick to that conclusion

 

[rumblebee2 10+ year member]

and the amp is?

 

[midnightg35x 10+ year member]

would u believe it came from my cell phone? gotta love technology.
this electric guy i been talkin to strongly believes it was due to ESD when packaged.

i know it sucks for the guy who owns this amp... we were just curious what happened.

i guess i'll stick to that conclusion

ESD when what was packaged? Automotive/Industrial grade components generally are the most robust components outs there (minus military spec). I have a really hard time believing ESD did that unless you hooked up a Van de Graaff generator to the ground line while it was running full tilt...

 

[SicAudio 5,000+ posts]

and alot of new amps are MIL spec PCB now.

 

[Louisiana_CRX 5,000+ posts]

it should be a fun fix for someone

 

[ngsm13 5,000+ posts]

The pin that fried on your TL494 chip was the ground pin (Pin 7). I think that should be a big hint. Ground doesn't just disappear very often //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif I agree with earlier comments that the SMPS went poof

This. What amp is it already?

nG

 

[shizzzon 10+ year member]

IA20.1

It was an idea that the amp may have been damaged by styrofoam while being packaged when it was sold by a member here several months ago.

I am not saying, yea, ok thats the answer nor am i saying that's not the answer.

What i am saying is it was outputting a clean signal, nothing wrong with the wave, only reached 28.7v output, the gain was completely down, we didnt even have a chance to turn the gain up yet because the volume to be reached on the head unit never happened...

The volume was being increased from vol. 10 to 27 before tuning commenced...

The head unit was being turned up about 1 notch a second monitoring the scope very carefully.

When it hit around vol. 22, a "click" inside then an immediate poof, smoke all on the power\gnd side.

No reason except some sort of part failure due to whatever reason.

An amp was immediately swapped to test other signals input and output and measured nothing out of the ordinary.

 

[dB-r 10+ year member]

I would say either an output failed and shorted and for some reason the protect circuit didn't shut the amp down and the power supply, now running into a dead short (the bad output is a dead short) went Poof!

That's the most likely scenario. This has to be an OLD IA 20.1, not the new one, the new one uses TO-220 mosfets, the one in your pics uses TO-247AC mosfets. Only other LIKELY scenario is a shorted power supply transformer. We deal with this stuff on a daily basis and those are pretty good guesses. Have rebuilt plenty of older model IA 20.1's. They are great amps, really, If I had one I'd run it in my setup. If a power supply transformer shorted, which is pretty likely too that may have happened instead of a bad output, it would also make the power supply go poof!

Check the outputs to see if any of them read as a dead short. Something that most people don't understand about repairing an amplifier is that you have to TEST the parts, visible damage will only occur on the parts that were still good when the other parts went bad, which likely won't have a hint of smoke or anything on them, they will look good as new until you test them.

 

[dB-r 10+ year member]

As far as the chip blowing, if the drive transistors failed when the power supply mosfets failed, that failure could have caused the 494 to burn up like that too.... But I would really check the power supply transformers for shorts. Rebuild the amp, then with a dinky power supply, not a big one, power the amp up, and wiggle the transformers around if it sparks and starts drawing massive amounts of current from the little power supply then you know you've got transformer winding shorted somewhere.

 

[dB-r 10+ year member]

NOTE: If you use a big power supply to power up the amp and you end up with a transformer short you will get instant smoking and exploding mosfets again. This is most amp repair shops biggest mistakes, they use a massive power supply to power up an amp that may have a transformer short or some other major problem and it just goes poof on them again, wasted parts... We can power them up here on our small power supply without ever risking damaging the mosfets, even if the board is out of the heatsink. No, our power supply is not a store bought, it is home-made/custom built here and is not for sale....

 

[midnightg35x 10+ year member]

As far as the chip blowing, if the drive transistors failed when the power supply mosfets failed, that failure could have caused the 494 to burn up like that too.... But I would really check the power supply transformers for shorts.

I guess to me that still seems a little less likely to me. How does the ground line get driven high to burn out like that on the 494? If the drive transistors along with the output fets failed, then all the power should be handled along the normal ground plane and the ground wire hooked up to the amp, not through the 494. To go through the 494's ground pin (like in the picture), the resistance of the +12V to ground internal to the 494 would have to be lower than the resistance of the direct short (due to blown transistors) between +12V and ground on the FET's. Also, the SMPS transformer isolates the drive transistors from the 494.

Now if all transistors blew and the smps transformer saturated (broke) I could maybe believe it would do that because the SMPS fets might draw more current from their gates than the 494 could handle before those SMPS fets blew. I think its much more common for a ground to be loose or a bad connection somewhere compared to the above scenario happening. It is POSSIBLE, but I say start with the more probable option.

I agree with your posts about using either a small supply to test it or a supply with a good overcurrent protection.

 

[eutechnyx 10+ year member]

man,that looks nasty,I was running my mmats d300hc modded to 0.5 ohm and only blew about 4 fets at most and it was smokin like a champ lol.That thing looks real bad.