Fosgate Prime R500-1 car amp

[northpoint]

I am posting here because I do not know of any good electronic repair boards but badcaps (Not buttering up anyone, Im serious). I was given this amp and its a 'moral imperative' that I repair it. If I am totally off base posting here then please redirect me to somewhere else

Person I got it from said it basically had no output. Ok, So got it on the bench and started testing the mosfets on the amp section. It appears the mosfets on one channel are bad. No physical damage at all anywhere. But the gates appear to be blown. The mosfet is a KTA1962A and I cannot seem to find it in the USA. I found it available on ebay from china and will need about 8 (4 per side, 4 extra just in case I have to replace the other side). Problem is I really would not want to wait a month for these chips. Cannot find a cross reference but do have the data sheet. Its a "Triple Diffused PNP Transister".

Anyone know a cross reference or somewhere in States to get them?

Thanks

[diif]

Re: Fosgate Prime R500-1 car amp

I've used this site in the past. http://alltransistors.com/mosfet/crsearch.php

[budm]

Re: Fosgate Prime R500-1 car amp

'The mosfet is a KTA1962A'
Well, the KTA1962 is NOT MOSFET, so are they bad in which way?
How about uploading good clear pictures of what we are dealing with?

[northpoint]

Re: Fosgate Prime R500-1 car amp

'The mosfet is a KTA1962A'
Well, the KTA1962 is NOT MOSFET, so are they bad in which way?
How about uploading good clear pictures of what we are dealing with?

Im glad you asked. This made me go back and recheck my work and I screwed up. They are bi polar and are PNP not NPN. Makes a bit of a difference in testing.

Testing - I am using a DMM to toggle the gate (base) on and off. Checked the emitter and collector basically the same. Perhaps I have the testing wrong and I will head back to the books too. sorry.

I am learning.

Pics of board and transisters from my cell phone cam:

[budm]

Re: Fosgate Prime R500-1 car amp

So what section of the so called bad Transistors are from?
Do you have the boosted Voltages from the switching power supply section?
BTW, I cannot read what are printed on the power devices.

[northpoint]

Re: Fosgate Prime R500-1 car amp

So what section of the so called bad Transistors are from?
Do you have the boosted Voltages from the switching power supply section?
BTW, I cannot read what are printed on the power devices.

Well, I have retested the transistors and they tested fine. I do not have a power supply for it available until friday when my new one arrives. Then I can get more into it. However, I wanted to kinda get a jump on it by testing the transistors. I incorrectly tested them the first time and thats all on me.

On the origional pic in last post on the right side are the transistors that were in question. I see now that its a push/pull circuit setup. Below is a pic of the transistor I was testing. There are 4 of them and then their compliments on the other side of the board.



There is a bank of 4 of them. Then on the other side of the board is a bank of the 5242's.



To restate: Im sorry this whole thread is premature. I made a mistake in testing the transistors and thought they were bad. I then was having a hard time finding a supplier which I actually did finally find a comparable one at fairchild with a different part number.

I have not really done a lot of board level work but have decided to get into it now so I am learning a lot. I just hate the stupid questions I may ask along the way.

sorry to appear totally stupid here.

Northpoint

[budm]

Re: Fosgate Prime R500-1 car amp

Just a push-pull Class A-B power amp, if the outputs are shorted you would have seen blown fuses, and those white power Emitter resistors would have blown open.
BTW, there is no protection speaker relay to stop the unit from dumping large DC to the speakers if the output circuits shorted out. I would not connect any speakers to the output jacks until you verify that there is no big DC offset present at the output terminals.

[hardwareguy]

Re: Fosgate Prime R500-1 car amp

Most car amps detect DC offset via the PSU rails.

The theory being that if a rail gets dumped into a speaker, one rail will go low while the other will remain high. If this differential occurs, the PWM controller shuts down.

I still prefer cutting the speaker outputs and I would test for offset every time you fix any direct coupled amp. Much over 15mV with the gain at minimum and I start asking questions, 50mV or more and I start changing parts. (What I change/test and in what order depends on the severity of the offset. 2V+ offsets are usually OPS faults, 20-200mV offsets are usually input stage faults. Some (crappy) designs may have high-ish offset naturally.)

[kc8adu]

Re: Fosgate Prime R500-1 car amp

2sa1962 and 2sc5242 are available at digikey.
the big filter caps go open more often than any other failure.
the supply with open cap goes low and the amp stays in protect.