frozen amp...need help

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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?
 
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
 
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
 
Re: maybe...

Stuart Easson said:
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.

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?:confused:
 
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
 
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.
 
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.
 
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.
 
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.
 
even if u got -40c outside i dont think that the amp that is inside a car will be that cold .
i think the problem is not the temperature , we=hen the weather is that cold + humidity = ice , maybe theres a thin ice layer inside :D = short circuit :rolleyes:
never had those problems over here :)
 
symptoms...

Hi,

Can you tell us what exactly happened just before the amp started behaving badly, then can you tell us what happens now?

For instance, with the amp on, if you plug an otherwise unconnected rca cable into the amps input and then touch the pin at the centre of the other end, do you hear anything through your speakers? perhaps a pop, buzz or plop?

do both channels behave the same?

Stuart
 
Not much in there...

This one's pretty easy. Does the amp get hot even without the 'remote' wire activated? Or does it get hot after being on for a couple minutes? If it's the first, the MosFets in the power supply are blown. If it's the latter, one or more output transistors are shot. The MosFets are probably IRFZ34 or IRFZ44. Replace them both with IRFZ44 if they aren't already. They can be checked in circuit by using a meter with diode check function. Place the negative lead of the meter on the third pin and the positive lead on the second pin (count left to right facing the part as it is read). If you read anything like 0.000 or 0.020, the thing is shot and must be replaced. If it reads 0.450 or so, it's fine - you are reading the voltage drop of the internal avalanche diode.

The output transistors can become leaky and activate the protection circuits. If they are blown "a certain way", they will get really hot without blowing the fuse. They are probably 2SB688 and 2SC718 - easily gotten from MCM Electronics. They are checked similarly to MosFets except we are looking for a dead short from the first pin to third pin or across all three pins. You can also do this in-circuit. For example, the output transistors for one channel are Q210 and Q211.

In fact, from the look of the burnt glue on that big white ceramic thing (emitter resistor) - I would bet that Q211 is shorted and is making the amp heat up big time. Replace output transistors like those in pairs. In fact, if you could replace all the transistors for $10, since there are so few. The other two transistor-looking things are high-speed rectifier diodes. I can count on one hand that I've had to replace the diodes - and that's out of many hundreds of amplifier repairs.
 
Re: symptoms...

Stuart Easson said:
Hi,

Can you tell us what exactly happened just before the amp started behaving badly, then can you tell us what happens now?

For instance, with the amp on, if you plug an otherwise unconnected rca cable into the amps input and then touch the pin at the centre of the other end, do you hear anything through your speakers? perhaps a pop, buzz or plop?

do both channels behave the same?

Stuart

Must i check this with the power on or off?
 
more info

The amp needs to be powered and switched on via the remote turn-on. If there is a sensitivity knob (I don't see one) you'd adjust it so the amp is at it's most sensitive, indicated by the lowest voltage. As you touch the end of the plug the speaker for whichever channel you are touching should make noise.

If you hear something with the basic test, you could then try some sort of battery powered device, like a walkman, mp3 player or the like. Connect it's headphone output to the input of the amp, play something and slowly increase the volume of the player to see if you can hear an undistorted signal.

If the amp, or the cables connecting it, get hot, don't leave it on too long, and allow it too cool completely between tests.

If you don't get any sort of output from the speakers based on the test I mentioned, then you will need to disconnect and power down the amp and follow the protocol envisionAudio descibed to test the power supply transistors (Q33, Q34) followed by the output transistors (Q110, Q111, Q210, Q211). To do this you will need a multimeter, and depending on what you find, you may have to replace one or more of the transistors.

If you don't have any soldering experience or any of the tools, it might be a good time to get someone involved who does.

The individual transistors are not expensive, somewhere between $1 and $5, depending on what you find under the metal blocks that clamp them to the heatsink. When you know what you need, I'd go post a want to buy (WTB) ad in the trading post, there are people here who have plenty of these things and will sell them to you at a good price...if you get really lucky they may just give them to you.

Stuart
 
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