Car amplifier(Polk Audio PA660) question

[jakdedert]

Re: Car amplifier(Polk Audio PA660) question

I've opened a few of these now that I had marked as defective back when. Also got a few more that were in the batch and overlooked; two PA330s and another 880 and 660.

I've limited myself so far to testing outputs, drivers and smps MOSFETS with a meter. I ordered a quantity of each, as each of the four amps I've looked at so far has a problem with one or more of the above. Until I get some new parts, I'm going to swap some parts around and see how many I can get going that way; then replace the defectives when new parts arrive.

This is getting fun...may even get lucrative.

[tibimakai]

Re: Car amplifier(Polk Audio PA660) question

The PA660 failed again.
Found a final transistor 2SB668, shorted. After I have removed it, and powered it up, the Red LED turned on, for like 7 seconds and then went off. I'm wondering what that means? The Blue LED(power) does not turn on at all. It could be, that one of the transistors is missing and the amp is not ready?
It is hard to work on these things, without a SM.

[Piotr07]

Re: Car amplifier(Polk Audio PA660) question

How you want to run the amplifier without one final transistor, you should unsolder both final transistor to check the amp. What about the DC voltage at the power outputs ?

[tibimakai]

Re: Car amplifier(Polk Audio PA660) question

Makes sense, thanks.
Hopefully, today I will pick up some transistors. I will replace both and I will report back, with the result.

[tibimakai]

Re: Car amplifier(Polk Audio PA660) question

OK, I have replaced both transistors and the protection LED is off. But the blue LED is not on either.
I measure -27V, but only +1.4V on the other rail, if I measure it the right way.
It is hard without a schematic.
I would appreciate any help. I can't listen to my stereo in my car, because this amp supplies my door speakers. I drive over an hour each way to work and without it, it is very bad.

[R_J]

Re: Car amplifier(Polk Audio PA660) question

There are liklely two large caps for the + and - supplies, see if they are correct, if they are, then check for bad/open component supplying that side, If there is no positive voltage on the cap, search components toward the power supply

[tibimakai]

Re: Car amplifier(Polk Audio PA660) question

There are actually 4 big capacitors.
I believe, that I have the proper voltages, I'm just not measuring, from the right ground.
I'm having a hard time, to find the proper grounds to measure. I'm in a hurry and I'm not able to think clearly.
Here are some pictures taken, with my phone.

[R_J]

Re: Car amplifier(Polk Audio PA660) question

This should be the ground and plus minus marked.

[tibimakai]

Re: Car amplifier(Polk Audio PA660) question

I may have made a mistake, when I have removed the two double diodes. I thought that they are the same, but the last three letters makes them different and I did not pay attention to that.
1FB2CCA /1FB2CAI

[R_J]

Re: Car amplifier(Polk Audio PA660) question

One would be common cathode, one would be common anode, those are strange numbers

[tibimakai]

Re: Car amplifier(Polk Audio PA660) question

The amps is powered by + GND - power supply, right?
Why I'm getting only - at both amps? It seems like one of the rails is way to low(-1.3V)
What would happen, if I would revers these double diodes?

[R_J]

Re: Car amplifier(Polk Audio PA660) question

Check the connections on that dual diode, also did you check it to make sure you did'nt blow it when you reversed it
If you reverse the diodes you will blow up the amp. What do you think happens if you put negative voltage to the positive of a capacitor... pufff
You likely damaged a trace taking them out

[tibimakai]

Re: Car amplifier(Polk Audio PA660) question

R_J, you are awesome. Thank you very much!!!!
To me it did not seem like there is any bad soldering there(maybe, the center pin on the left double diode, it was a bit suspect), but I went over all 6 joints and the blue led has turned on.
The Red LED turns on, for like two seconds and then turns off. Than the Blue LED turns on.
Now I have +27V as well.
YEAHHH!!!

[R_J]

Re: Car amplifier(Polk Audio PA660) question

Check that the voltage at the speakers is near zero volts, run it for a while checking the temperature of the transistors to make sure one or two are not over heating

[andy_nz]

Re: Car amplifier(Polk Audio PA660) question

Another attempt to dredge up an old thread.
I also have a PA660 amp - it was working, but experiencing very bad noise when installed in the car. I checked all earth points in the car, to no avail, and one day the left rear channel 'popped' and stopped working. All other channels had around 27v, the left rear had around 1.5v.
I since replaced the amp with a new one, and all noise etc has gone - and I am now attempting to repair this amp.
No components appear to be blown up - there is no visible signs of damage...but if anyone could point me in the right directions as to where to start looking that'd be great.
I am going to replace all the caps initially on the power supply (C30, C31, C1 and C4) followed by the larger caps (C18, C19, C28, C29)

[mark97564]

Re: Car amplifier(Polk Audio PA660) question

Prolly bad transistor on that channel, my pa660 has issues with that same channel. Since it was new it would sound shorted with the car was cold in winter, bumps in the road would affect it also, but after warning up it would work fine for years that way. But now that channel sounds like it's shorting out, no bass, no volume compared to the other 3 channels.. its been running this way for a few months and hasn't gone into protection mode at all, one of these days I'm going to pull it out of the car and see what I see with a scope, busy since the amp works fine besides that channel and it's not going into protection, im thinking there is a bad transistor or solder joint.. post back if you get yours fixed, be nice to have a starting point with my amp.