Behringer PMH1000 pwr amp

[drewl]

Or is it PMX1000??

Anyway, got one with a blown IRF640 FET in the output amp, replaced it and now the power amp seems to power up normally, or at least it's not in protect mode.

I've got signal on the inputs of IC4 (HCA4001) but no output A or B.

Does Behringer sell replacement boards, or the whole module?
I really don't feel like screwing around with this as it's a favor for a friend of a friend.

[km6xz]

How are you measuring the output of the Class D driver IC. It is constant amplitude pulses. There is a muting circuit that you need to check as to whether it is shut down. The power amp is not a conventional analog amp, the signal does not become the normal waveform expects of a A or AB amp until this pulses are integrated by the output filter.
There still might be a problem in the power output stage that is causing the amp to be turning off the signal path in IC1.
What test equipment do you have available. An oscilloscope with 10meg or 100meg probes and fast rise time is the bare minimum for working on a Class D amp.

[drewl]

Looks like the correct digital signals coming from HCA4001.
I'm guessing IC1 is the output filter?
So far both output amps "seem" okay, but not amplifying.
The proper voltages come up and it's not blowing itself apart.
I need to check the shutdown circuit.
It's just a real pain as everything is crammed in there really tight.
Even with microscopes, digital scopes and the other equipment here in the lab.

That's why I asked if anyone had replaced the whole module, it's not my dime and that would be alot easier.

[km6xz]

IC1 is a two section gate. When turned on, the same signal appearing at the input is seen at the output of each section. It shuts down the path from driver to output power transistors when the gates are opened by the shutdown circuit. Are you getting the same signal on in and out of the IC1? If not, the protection circuit is triggered.
The output filter is an LC network at the output of the amp.
The output transistors do not really amplify anything, they switch on or off at very quick rise time pulses that have the same amplitude. The pulse duration determines the power generated, that is controlled by the driver IC (IC4). The out put is either full positive rail, full negative rail or 0, with sub-microsecond transition times. In many ways they are far simpler than conventional AB amps and MUCH more efficient, which is why those small power devices run cool had high power out to the load.

[Jazz P Bass]

Thankyou Stan.

After much head scratching & believing it was the HAC4001, I found this post.

IC1 was indeed in Shutdown.
The 0.1 ohm resistor (R1) & the 1K resistor (R44) took a hit & where open.

At first, all that I could find was one shorted mosfet (T2).

Cheers.

By the way, the HCA4001 is really a ZXC D1000.

zxcD1000.pdf

[Enzo]

Too late to call back the dead ones, should be at your door tomorrow.

[drewl]

Too late to call back the dead ones, should be at your door tomorrow.

????

[Jazz P Bass]

Inside joke.
Enzo was kind enough to 'unload' some of his junk.

No foul. No harm.
The parts alone will be worth the freight.

[Jazz P Bass]

Hmm.
It appears that the speaker protect triac also took a hit.
Usually they test shorted when bad.
This one didn't.
The briefest signal, into a load, would trigger it, thus no signal.
It was fine without a load. (suprise!)

Whar a treat it is removing the speaker connector board.