What's wrong with this amp? PICS inside

[dB-r 10+ year member]

How does the ground line get driven high to burn out like that on the 494?
Also, the SMPS transformer isolates the drive transistors from the 494.

the SMPS fets might draw more current from their gates than the 494 could handle before those SMPS fets blew.

The drive (pulldown) transistors are directly attached to the 494, pins 9 and 10. The SMPS mosfets gates are attached to the drive transistors via the gate resistors. The 494's only link between the mosfets and itself are the drive transistors, and if they blow or short they can kill the 494. I think it's most likely your amp has a transformer winding short. It's a VERY common problem with these newer amps because the transformers are so much bigger than what was in the old (weak) amps back in the day. They vibrate alot more due to the higher SPL levels too than the old amps could produce so even your average setup these days has enough vibration going to cause a transformer winding to rub on itself until the enamel coating is gone and cause a short which will sure blow the SMPS mosfets quickly when attached to a large source of current like a car battery.

Not sure why you are investigating this so heavily? Just curiousity or because you are trying to get someone else to pay for the damage?

 

[midnightg35x 10+ year member]

The drive (pulldown) transistors are directly attached to the 494, pins 9 and 10. The SMPS mosfets gates are attached to the drive transistors via the gate resistors. The 494's only link between the mosfets and itself are the drive transistors, and if they blow or short they can kill the 494. I think it's most likely your amp has a transformer winding short. It's a VERY common problem with these newer amps because the transformers are so much bigger than what was in the old (weak) amps back in the day. They vibrate alot more due to the higher SPL levels too than the old amps could produce so even your average setup these days has enough vibration going to cause a transformer winding to rub on itself until the enamel coating is gone and cause a short which will sure blow the SMPS mosfets quickly when attached to a large source of current like a car battery.

I guess I haven't seen many amps with shorted transformers, but I don't deal with many high power (1kW+) amps, so I don't have any experience there. I know you deal with these amps 10^10 times more than me, so I'm just trying to figure out how the ground pin on the 494 would fry out instead of the drive pins on the 494 driving the transistors.

Not sure why you are investigating this so heavily? Just curiousity or because you are trying to get someone else to pay for the damage?

It is just curiosity. I have no relation to the OP. Also never dealt with any IA amps before, but the TL494 (besides maybe a SG3525) is about as common of chip as you get in a SMPS //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[dB-r 10+ year member]

I recently had an old SoundStream Reference 300 here, looked to be a simple fix, just replaced the power supply FETs, and the PWM IC.

I replaced it with a SG3525 IC. I could never figure out why it would not work right... was a retardedly simple little amp, hardly anything in it... So I got frustrated and sent it to another shop we use. The guy writes back:

SS Ref 300 - DONE Wrong PWM IC, SG3525, supposed to be SG3524....

LOL... I couldn't believe it, I never even noticed when I pulled the original IC that it was a "24" instead of a "25". He is old school, been doing this a long time, since mid 80's, I am fairly new to amp repair, so I had never recalled seeing a SG3524 before.....

The 494 likely shorted internally and burned the ground pin off itself.... could happen if the right parts inside that IC short. Could have also caused the amp to fail. So it could be the 494's fault entirely, but just not common, those IC's are tanks in the proper circuits, that's why they are so popular, cheap, simple, and they work goooood for an unregulated simple SMPS in car stereo amps with a basic protect circuit.

 

[dB-r 10+ year member]

Are you really a Rockford Fosgate amplifier design engineer? Or does RF mean Radio Frequency (like transmitter amplifiers)? Or are you just being funny?

 

[midnightg35x 10+ year member]

Are you really a Rockford Fosgate amplifier design engineer? Or does RF mean Radio Frequency (like transmitter amplifiers)? Or are you just being funny?

RF = Radio Frequency. I design broadband RF amplifiers (discrete and MMIC).

I'd include the entire word in the signature, but its over the character limit....

 

[dB-r 10+ year member]

Awesome. You must be really good at math. And brave too... I built a few 1kw homebrew rf amplifiers, played around with it for a while, got burned a few times if you know what I mean.... it's like getting beatdown with a car antenna.... welps...

 

[midnightg35x 10+ year member]

Awesome. You must be really good at math. And brave too... I built a few 1kw homebrew rf amplifiers, played around with it for a while, got burned a few times if you know what I mean.... it's like getting beatdown with a car antenna.... welps...

RF burns certainly hurt more than DC burns! Lots of times the FCC can come down on homebrew high power amps... if they don't have spectral control, the homebrews spew RF everywhere. The FCC (and all your neighbors) are not amused //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[dB-r 10+ year member]

I know, I got out of it because it was dangerous and highly illegal.... No filters here...I also blew my TV out once with RFi.... ****** because I had that TV forever too and really didn't want to buy a new one, it was a nice one.