Amp repair??

[pregunta]

Does anyone know anything about amp repair? I have a Phoenix gold QS 900.1 and as soon as the radio comes on the fuses blow. I checked the ground and the power both were fine. So I figure it is the amp I don't want to send in the amp for repair because the repair cost +$100= New amp. So does anyone have any amp repair knowledge. Feel free to school me if you want . Thanks -Pregunta

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[Rycechyk]

Sorry, I don't have an answer for you, I just wanted to say that I love your username!

[pregunta]

Thanks I thought that name would be alittle different. You know, I like to throw people curve balls. I guess there are no ELE majors out there.

[SiClone]

I don't think we have any amp repair guys here.....

[fastball]

Originally posted by SiClone
I don't think we have any amp repair guys here.....

Here's one! If your amp is blowing fuses, here's a simple way to troubleshoot without tearing it appart:

Completely disconnect the amp and remove it from your car. Replace the fuse with the SAME EXACT rating (probably 25 amp). Now you will need a digital volt meter. If you don't have one, you can't troubleshoot the amp, but I'll explain anyway incase you do. Set the meter to diode or continuity check (or you can set it to impedance check but you will need to read the display instead of just listening for the beep). Check accross the 12v constant and ground taps on the amp. If it beeps or reads 0.00 ohms, you have a direct short in the amp, most likely two or more mosfets are blown. If you don't have electronic training, I don't recomend or encourage you do attempt servicing. If done wrong, bad news. If you have any more questions, please post and I'll be happy to answer.

[pregunta]

When this first happened I took the amp appart and used my volt meter to check the circuits. I noticed that I didn't get a current over some of the mosfets chips. So I am assumig about 3 of them blew. Where can I buy mosfets and are they really expensive. I am not an electronics genius but I have a general idea. Is this something I can tackle or should I get beat for the 175.00

[fastball]

Originally posted by pregunta
When this first happened I took the amp appart and used my volt meter to check the circuits. I noticed that I didn't get a current over some of the mosfets chips. So I am assumig about 3 of them blew. Where can I buy mosfets and are they really expensive. I am not an electronics genius but I have a general idea. Is this something I can tackle or should I get beat for the 175.00

Hmmmm...... MOSFETS aren't "chips", they are transistors (Metal Oxide Semiconductor Field Effect Transistor). Don't try to troubleshoot with it powered on..... I can tell right off the bat you don't have the experience for that. Set your meter to diode check and test the legs of the big transistors that are screwed directly to the heatsink. If it beeps long, that output is shorted. Now, they must be replaced in pairs, and alot of times the emitter resistor is open, so you need to check those as well. Not to mention there may be a blown ground trace on the other side of the circuit, and the trigger sense line may be blown as well (usually a 2sb1243 or similar switching transistor). If what I just talked about is greek to you, I don't recomend you go any further with it. It can get complicated very fast if you aren't a trained electronic technician. I've been in the business for over 5 years, and including tech school, I've been working on 12 volt and 120 volt electronics for 7 years. And I will say I still don't know all there is to know (relatively). It's fun, but you need to understand alot of circuit theory.

[pregunta]

I used the wrong terms in my last post. I did check the mosfet transistors with the power off. I used the setting on the volt meter that allows you to test if there is a closed circuit or not. I could get a circuit on all but three (If I remember correctly.).
What you said is not greek to me it is just tracing it. I took some ELE courses in college and the borads were alot simpler. Where could I got to buy the parts I would need? I don't think these are average everyday Radio shack parts.

[fastball]

Well, if you know what you are looking for, you need to go to an electronic repair and supply shop. Find one who caters to electronic technicians, because you are correct...... Radio Hack won't cary what you need. There should be a big 4 digit number on each of the MOSFETs along with a letter. If it says C4120, you need a 2sc4120 output. If it says D1861, you need a 2sd1861. Now, like I said before, they must be replaced in pairs. So if you only find three shorted, replace the other good one in that channel. There are 2 in each channel (one for the B+ and one for B-, usually around 40 volts for 12 volt power supplies). They should be no more than 20.00 each. Did you check to see if the emitter resistors are open? Those are the big white ceramic resistors on each channel, should be .22 ohm or equivalent. Those are exactly the opposite of transistors. If they measure short, they are good, and if the measure open they are bad. You should double check them to be sure before replacing the outputs. If an emitter is bad, it will blow your new outputs the second you power it up. They don't open all the time, but I always check them because they do open occasionally.