Berhinger PMP 5000

[e_c_mccollum]

Need to find out why pwr amp is shorting out 1 output at power up. The other output is fine. Amp was over heated since fan circuit died. Not easy since Berhinger will not send schematic.

[e_c_mccollum]

Did find a large smt resitor connecting with the coil and cap with a very small hole in it. Also had a burned wire on the neutrik ouput board.

[Enzo]

If the outputs failed, ALWAYS check the speaker connector board for a shorted triac. Behringer puts the same crowbar circuit that Peavey likes on the output.

[e_c_mccollum]

Any replacement for the irfp205n used on the pwr amp board?

[Gtr_tech]

Its a IRFP250 innit?

[e_c_mccollum]

Sorry, your right. Makes it much easier to find the part now. Anyone got a pair of new eyes?


Thanks

[e_c_mccollum]

Need values for c4, c5, c6, L2 used on the neutrik output board. Do these components only have to do with the bridge circuit? If so, I rather take them off and just redo the dc protection circuit.

[Enzo]

Their schematic set almost never covers that little board. Looking at a similar output board - but one lacking the bridge connector - across the output at each channel is a 47k resistor to the end of the diac away from the triac, and from there a 2.2uf cap to negative out. In other words the +out signal flows through the 47k to the diac, and the cap smoothes it out. We don;t want every tiny peak triggering the thing. SO +out, 47k,2.2uf, -out, with diac branching from the center.

Ther are also for each channel 100nf cap from -out to ground.

I have no idea which numbers are which. I would have to guess the inductor was bridge related, especially if there was only one of them.

[e_c_mccollum]

There are two inductors in one for each channel. One is completely blown off. The board is small enough I can draw out a schematic and compare it to your explanation.

I wonder if Behringer will send me a new board if I give them the board#.

[Enzo]

Very doubtful, they don;t have boards in stock at all. I can;t even get boards.

Have you considered contacting them about the possibility of becoming a service center? Don;t expect any support, but access to schematics is valuable.

[e_c_mccollum]

What value do you think will work for the inductor used on the ouput board? I have a PMP2000 schematic that uses a 3uh.

I believe this PMP5000 uses two in parallel for more current capability.

[Enzo]

Duh, I completely overlooked 2000 board. I focused on the 3000 output board. Sorry.

If you have a copy of the PMX2000 output board, then you are looking at the same drawing I now am. And 3uH it is, with a 22R in parallel.

I have no reason to think the values and circuitry on that model should be much different on another. The bridging is just straight wiring to the jack. All the components are duplicated for the two channels. All the stuff left of the jacks is stability and filtering for the power amp output. I wouldn;t eliminate any of it.

We are talking 3uH here, not mH. That inductor, and the 100nf cap in the zobel nearby are there to squash high freq noise and oscillation. Nothing audible. SO I don;t think the 3uH is that critical. Just get close. The purpose is to keep the amp- from turning into a power oscillator. You don;t need 400 watts of RF melting your voice coils.

If they doubled them up - you have four of them on that little board? - remember coils act like resistors when paralleled. But again, I doubt the difference between 1.5uH and 3uH would hurt.

[e_c_mccollum]

Got a good sub for the 4992 used to trigger the triac? Can't find this on mouser. One of them is cracked.

Instead of fixing this amp I think it's time to get out the blowtorch.

[Enzo]

use whatever PV uses. They used to use the SBS14, their part number 70400014, which you can order from them, if they still have them. Alternate type number would be MBS-4992. Since the Behringer schematic calls out 4992, I tend to think it is the same. ON Semi shows the part as obsolete.

In more recent gear PV has taken to using two SCRs back to back. Probably because the old part was no longer made. I don;t know where Behr gets them. Look at the output of this PV2600 circuit.

[e_c_mccollum]

Any idea why channel four "level set" light constantly lit? No signal applied.

Anyway, testing the pwr amps one at a time. Channel A mutes after moderate volume with a 4 ohm load. Channel B burns out the two 10ohm 10watt resistors in the main pwr supply. No shorts in pwr amp that I can see. Very difficult without a schematic to fix since it does have a muti-layer board. When put up to light, you see them inside the board.

As a stand alone mixer, it works beautifully.

[Enzo]

#4 level set. IC4-1 is where the signal is sampled on its way by. That to top of voltage diviers R145/R146 = 12k/18k mid-point to base of T34, Collector T34 to base T28, which shunts the LED. APparently T28's job is to turn the LED OFF.

COmpare readings to ch3 level set light circuit IC3A-1 to R143/R144 to T33 to T27