Behringer PMH518M Amp Dead After Running Only One Speaker Side

[Sean T]

I have a Behringer PMH518M powered mixer (basically, it’s a power amp w/five lines in).

I've had this amp for a few years and only used it sparingly. The amp has two mono line outs, and I normally used it to push two 8 ohm cabinets via 1/4" TS cables. One night however, while attempting to be as quiet as possible while practicing, I deactivated one of my speakers by leaving one of the 1/4" TS cables only halfway-inserted into the rear of the speaker. Within minutes the amp stopped working and will no longer power up at all.

The amp has that "burnt electrical parts" smell to it, so I'm sure that some electrical component was damaged. I opened up the unit but see no black soot to indicate which component may have burned out.

Questions

1. Which part have I likely damaged that causes the unit to no longer power up?
2. Can I repair the amp myself?
3. If so, from where can I purchase the replacement parts?

Can anybody help?

P.S. - I’ve got more time than I have money, so I’d prefer to repair the problem myself instead of taking it to someone else.

Thanks in Advance,
Sean

[J M Fahey]

By

I deactivated one of my speakers by leaving one of the 1/4" TS cables only halfway-inserted into the rear of the speaker.

you very effectively deactivated that side's power amp, by shorting its output cable plug (that's what they do when you plug them half way).
It *might* have survived, if it had a fool-proof short protection, but it does not seem to be the case.
Definitely there are burnt/shorted/failed parts, the problem is finding *which* ones.
You should have fully removed the plug at the amp's end and nothing would have happened.
Sorry.

[Enzo]

Agre3ed, you burnt out the power amp for that channel. WIll need transistors and resistors replaced at very least.

[Sean T]

you burnt out the power amp for that channel.

Guys, thanks for your responses.

If I burnt out only one of the two output channels, why does that prevent the amp from powering on at all? It would seem that it should power up and that at least one side would work (right?).

I failed to mention that it is a mono, not stereo amp. Does this make a difference?

[J M Fahey]

Well, in that case you burnt its only power amplifier.
For all practical purposes, it means the same: dead Behringer.
*Maybe* you just burnt the fuse, replace it with one with the same value (same Amperes).
Good luck.

[Jazz P Bass]

How to Change a Behringer PMH518M Fuse

.Difficulty:EasyInstructions

1
Unplug the device's AC power cord from the wall.

2
Remove the fuse holder from the rear of the device, located above the power cord.

3
Remove the fuse from the fuse holder and insert the replacement that features the exact power ratings of the old fuse. Versions that require a 100/120-volt power connection use a "T 6.3 A H 250 V" fuse, while 220/230-volt devices require a "T 3.15 A H 250 V" fuse.

4
Install the fuse holder back into the rear of the device. Connect the power cord to an available wall outlet to finish the process.



Read more: How to Change a Behringer PMH518M Fuse | eHow.com How to Change a Behringer PMH518M Fuse | eHow.com

[Enzo]

On any system that fails, usually only one part fails. Your car may get a flat tire, but not usually all four go flat, along with a dead battery, and run out of gas. But any one of those things is enough to leave the car undrivable. The power supply can be affected by a blown power amp stage in an amplifier. If the +40v power is burnt out, that means the +15v for the preamp may come up missing as well, since it is derived from the +40. That is the sort of interconnectedness we have.

[Jazz P Bass]

Guys, thanks for your responses.

If I burnt out only one of the two output channels, why does that prevent the amp from powering on at all? It would seem that it should power up and that at least one side would work (right?).

I failed to mention that it is a mono, not stereo amp. Does this make a difference?

Sean.
The amp only has one output amplifier.
There are two jacks.
One amp.

[Sean T]

Thanks to everyone who has replied.

1. I just popped the fuse out and it still has the white coating on it. I presume that the fuse would be blackened if it had burned out, right?

2. How can I test the power supply?

3. If the power supply has burned out, can I simply buy a replacement and install it myself? If so, what's a good source for Behringer replacements parts.

4. If I find that I have in fact destroyed the power amplifier, is it possible or feasible to attempt a replacement? Or, at that point should I simply abandon this amp and look for another?

Again, I have more time than I have money, so my preference is to buy replacement parts and perform my own labor whenever possible. I'm not very electronics-savvy, but I will learn for the purpose of fixing this amp!

Thanks guys.

[Enzo]

White fuses have a ceramic body instead of glass. They look no different blown or not blown. You have to remove them from the clips and check them with a meter.

Power supplies are tested by getting out the volt meter and seeing if they are present.

Potential replacement:
Behringer Q05 26500 05736 PCB LPA1180 PMP518M | Full Compass

[J M Fahey]

1. I just popped the fuse out and it still has the white coating on it. I presume that the fuse would be blackened if it had burned out, right?

Not necessarily, it may be open close to one of the endcaps , not easily visible.
To be certain either measure it with a multimeter or pop in a known good new one.
It might blow again, of course.

2. How can I test the power supply?

You'll need a multimeter, plus knowing how to use it.

3. If the power supply has burned out, can I simply buy a replacement and install it myself? If so, what's a good source for Behringer replacements parts.

Probably not, but let Behringer Authorized Technicians around answer that.

4. If I find that I have in fact destroyed the power amplifier, is it possible or feasible to attempt a replacement?

I know you can buy replacement boards for the *big* ones, dunno on these small ones though.

Or, at that point should I simply abandon this amp and look for another?

It's up to you.
Economy wise, a new one costs less than U$200, and Uncle EBay might provide a used one or an equivalent for *much* less.

Again, I have more time than I have money, so my preference is to buy replacement parts and perform my own labor whenever possible. I'm not very electronics-savvy, but I will learn for the purpose of fixing this amp!

It's up to you.
To fix *one* amp and forget it, I have my doubts; if you want to get into something new, you are welcome.
It will take some $$$ and time+commitment.
Good luck.
PS: anyway a Behringer is not quite beginner-friendly, they don't supply schematics easily, parts may be tiny SMT ones, or custom made for them, etc.
Now, if you had, say, an old Kustom or Peavey, and similar classic amps, your life will be *much* easier, and a lot of people will be able to help.

[Sean T]

Well, I finally acquired a replacement fuse with the same amperage and voltage. However, Radio Shack did not have a ceramic fuse like the original one in my amp. Can I use a regular glass fuse instead? The package describes it as a "slow-blow" fuse.