Precision Power PDX-10K

[caraudioguy2100]

Amp has no output .

Amp has both positive and negative rail voltage and has both positive and negative regulated voltages .

Relays click on but no output.

Amp also has rail to rail oscillation on the outputs

Any ideas ?

 

[Perry Babin]

Switches/potentiometers?

Are you getting audio to the board with the DC offset pot?

 

[caraudioguy2100]

I got it working it had bad solder connections on the preamp board .

 

[caraudioguy2100]

This amp just blew the outputs while playing on the bench.

The outputs are IRFP4242 but no one has stock .

Is there a good sub for these outputs ?

The outputs I posted are expensive is there a better choice for replacements

 

[seankane]

IRFP4242 MOSFET IR 300V 46A .059Ω PDF PDP N-CHANNEL (25 PCS) USA SELLER | eBay


This Ebay seller has them for a good deal. I'm not sure if they are real or counterfeit but he has good feedback.

 

[jkrokenberger]

The newer version may be a better option as even though it will cost more it is available through an authorized seller of genuine items. It will be less costly to buy once. Everything has an entry fee. If you aren't paying what it actually costs, you aren't getting what you actually want.

 

[jkrokenberger]

I have purchased on Ebay before. I've got good parts and non-good parts, you never know until you have the parts in hand. I've also purchased from Digikey - I've always received exactly what I ordered, genuine. For obsolete/vintage Ebay is good if the seller has GOOD photos of the actual item and you can make your decision that way.

 

[caraudioguy2100]

Replaced the outputs and driver ic’s in this amp along with the driver ic’s.

I get pulsing DC on the outputs it goes as high as 5 volts then drops to 0 and reparations this over and over .

Any ideas on what to looks for

 

[Perry Babin]

Have you tried installing only one driver board at a time?

 

[caraudioguy2100]

I think the preamp board has issues .

The 47 ohm 2 watt resistors that connect to the rca shield ground are way out of tolerance they read in the mega ohms .

Do you happen to know what might cause these to go bad ?

If I unplug the rca’s the voltage remains at 0 on the outputs

 

[Perry Babin]

Have you replaced them and they burned again?

They are in series with the shield ground. They generally burn when there is a shorted transformer or if an active speaker wire shorts to ground.

 

[caraudioguy2100]

I replaced them and as soon as I try to power the amp up they pop and burn again

 

[Perry Babin]

Does it burn them with no RCAs plugged in?

Does it burn them with only B+ and ground connected?

You don't have to keep burning them for testing. If you have a 120v incandescent lamp (12v may work if the problem is a primary to secondary short), that would allow current to pass without burning resistors.

 

[caraudioguy2100]

Do you happen to know the value of this resistor this is also burnt up and I can’t make out the value from the pic but it connects between the main ground terminal and the preamp board

 

[Perry Babin]

Probably 1k. I only have one photo that shows just the top of it.

 

[caraudioguy2100]

Ok I replaced the 1k resistor and the 2 47 ohm resistors .

Amp powers up and the resistors don’t burn anymore .

Now the problem I’m having is I get no output I just get a what do I da like a wind storm out of the test speaker and the test speaker flutters off and on .

Any ideas on where to go from here what to check

 

[caraudioguy2100]

The original outputs in this amp are IRFP4242

I ordered them off from eBay I know a big mistake .

That was the only place I could find them and I believe I got fake parts since the problem is the outputs heatup within seconds .

I’ve checked everything else and all tests fine but the outputs get to hot to touch within 3 secs .

Do You know what this pot is for ?

Also if it has nothing to to with the outputs getting hot do you happen to know of a sub for the outputs I can try ?

 

[Perry Babin]

Do you have rail-rail oscillation at the output transistors?

Probably DC offset.

The DC offset pot is simply to allow the offset at the speaker terminals be adjusted as close to 0v DC as possible.

 

[caraudioguy2100]

Yes I get rail to rail oscillation on the outputs .

Problem is the outputs get very hot within a few seconds

 

[Perry Babin]

Do you have a capacitance meter? If so, you could compare the gate capacitance of the old FETs to the new.

Have you tried installing a couple of banks of the old FETs to see if they run cooler than the new ones?