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Old 28th December 2004, 12:19 AM   #1
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Angry frozen amp...need help

My amp froze. It's a MTX RT2200X. It was working fine until a few days ago. Now, when I apply power to the remote terminal, the amp pulls tons of power, stops, pulls more power, stops again. It does that a few times a second. It pulls so much power that all the lights in my car dimmed. It didn't blow the fuses though. I checked the ps fets with a dmm, and they seem fine. The chip controlling the ps is a TL494CN which should be operated from 0 to 70 deg. C. The temperatures around here have been at around -10 C. Could the tl494 be bad because of this?
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Old 28th December 2004, 01:25 AM   #2
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Default maybe...

Sounds to me like the power supply is working and you have some sort of short in one or both of the amps. The power supply circuitry is shutting down every few seconds because it is trying to supply so much power. Try using your multimeter to measure the resistance of the output transistors, chances are one or more of them are dead, and shorted.

As to how it happened, sorry, your guess is as good as mine, never had an amp frozen before, so I have no clue what it could do to the circuitry. If it was cold and you started and warmed the inside of the car perhaps condensation formed in the amp and screwed up the bias somehow...

Stuart
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Old 28th December 2004, 01:33 AM   #3
tool49 is offline tool49  Canada
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I've had my amp running very cold for years and it is still alive and kicking! Around here we get ~5 months of sub 0 temperature and I've tried and tried to blow my amp without success, so I think it is an unfortunate event. Sorry not to be of more help as to how to repair though.

Sébastien
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Old 28th December 2004, 02:21 AM   #4
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Default Re: maybe...

Quote:
Originally posted by Stuart Easson
Try using your multimeter to measure the resistance of the output transistors, chances are one or more of them are dead, and shorted.
Yep. Output fets on one channel are gone. I should've checked those first.

Quote:
If it was cold and you started and warmed the inside of the car perhaps condensation formed in the amp and screwed up the bias somehow...
I drove the car, and the amp was fine. I didn't even play it loud, so i'm sure that it wasn't hot. Then I left the car out in the cold for an hour, and when I started it back up, the amp was going crazy (right away, not after the car warmed up).

I replaced those fets before. I had the amp running all summer, in the heat, and it was fine. Now, when it gets cold and I don't even play it loud, and it blows the output fets. How is that possible?
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Old 28th December 2004, 02:51 AM   #5
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Default static?

Not a clue really, but...Fets are static sensitive devices, perhaps the dry air in the cold weather allowed some charge to build up that hadn't occured before...the, presumably longer and unshielded, speaker cables could have been zapped somehow, exposing the outputs, but not the power supply fets.

One amp I worked on didn't have any overvoltage protection, so using one of the huge charger/starter boxes sent >17v into the SMPS and made the internal voltages exceed +/-50v, fried drivers, bias transistor and all the outputs.

At the temps you were seeing, it obviously wasn't an overheating failure...

Stuart
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Old 28th December 2004, 03:03 AM   #6
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I know you figured it out and all, but I figured I would share my own experience. I had a Rockford amp doing the exact same thing. It would turn on... shut down... turn on... The problem was traced to a loose connection in the wiring from the amp. The amp would begin to draw current, the voltage would sag, it would shut off, and repeat. After a few seconds the amp would stay on, I guess the capacitors in the power supply charged up. But as soon as a signal was applied, it would die again.
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Old 29th December 2004, 07:10 AM   #7
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semiconductors have a specified operating and storage temp. storage temp is usually wider than the operating temp which means that the devices could survive the extreme cold if they are not being used.
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Old 29th December 2004, 03:33 PM   #8
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All that I can say is that a car amplifier that cannot survive -10 C storage could never be sold here.

Currently, the temperature is -17C outside. I expect that I can USE my amplifier in these temperatures without problems.

New Year's Eve, the forecast is calling for -30C. I wouldn't be surprised at all to have a few nights getting close to the -40 mark in January. I expect that when I start my car, the amplifiers will just work. Now, I don't plan on playing the music loud, but I'm planning on having the radio or CD player ON.

IMO, any commercially made amplifier ought to be able to survive any temperature that it is possibly going to be subjected to. Around here, that means that it had better be able to take anything from -40 to about +70C or so, as it can still get very hot in a closed car in the summertime. (Well, it might not get that hot in my car here, but it well might in places that I might drive to!)

I am looking at making a DIY amplifier, and power supply. I bought the ICs with an operating temp down to -40, and considered the ones which are supposed to be able to take -55C, though the extra cost was a deterrent.
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Old 22nd January 2005, 07:05 AM   #9
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This is the EXACT same thing that is happening to my Amp right now. However i am not Amp litterate, at least to the terminology, so im hoping someone can point me in the direction of what to test in my amp in order to get this thing working again.

Is there a specific page i should look at? Or a section.

I did a search, this came up, and its exactly whats happening to me. The only difference is im using a VERY Cheap Jensen 250w Max amp.

Please help me out. Thanx.

~anthony

On a side note: My amp was doing this, and last night it got REALLY hot, so i disconnected the Ground. Now it doesnt do anything.
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Old 22nd January 2005, 09:01 PM   #10
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Well, i took pictures. Hopefully someone can circle the part/s i need to check, and point me in the direction on HOW to test them. Ive also noticed, that it only freezes when i have a speaker hooked up to the bridge. If speakers are hooked up to either channel, no sound comes out. When i flip the Bass Boost switch back and forth, the speakers make a "thump" sound.

Here are the pictures.

https://home.comcast.net/~ort8ga/DSCN0572.JPG
https://home.comcast.net/~ort8ga/DSCN0575.JPG
https://home.comcast.net/~ort8ga/DSCN0576.JPG
https://home.comcast.net/~ort8ga/DSCN0577.JPG
https://home.comcast.net/~ort8ga/DSCN0578.JPG
https://home.comcast.net/~ort8ga/DSCN0579.JPG
https://home.comcast.net/~ort8ga/DSCN0580.JPG

the pictures are HUGE.. give them a sec to load.
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