Behringer Europower PMP1280S Mixer power supply failing?

[Boffosteve]

Howdy -- just joined the forum. My brother's Behringer Europower PMP1280S Mixer is starting to show symptoms of what I believe will be power supply failure. Randomly it will "tick tick tick" from both sides (I believe); sounds like classic "motorboating." Also, I was not able to download the schematic from another thread on this forum -- nothing happened (using Chrome browser). Is it blocked or otherwise disabled by Behringer or others? Available anywhere else? In any event, I will certainly appreciate any wisdom provided before I go in and randomly replace large caps (carefully discharging them first, of course) ...

Thanks!
Steve

[Enzo]

No blocking on the downloads, the forum software had a glitch and wiped out the stored files. SO they are now empty. Best we can do is request them again and whoever posted them the first time might post them again.


When switching power supplies tick rick tick, it means they are trying to start but are shutting down as soon as they do. That cycles them. It usually means a problem on the secondary side. That could mean the circuits it powers are bad - blown power amp channel for example - or it could be the power supply itself. A couple tests: Unplug the power amps from the power supply. There is probably a small wire 6-pin connector also, pull it too. Does the supply still tick? If not, check the output voltages. I forget, but I think the main power amp supplies are like 80v.

If it still ticks or won;t make power, check the rectifier diodes on the secondary side - any shorted?

It is also possible the soft start is bad. On a lot of the Behr power supplies, there are a couple power resistors in series with the mains, and a relay to short across them after a second or two. Make sure they did not open.

These switchmode power supplies are DANGEROUS to work on. 340vDC with all the current your wall outlet can provide, just waiting to stop your heart, or burn up a scope with teh ground probe clipped the wrong place. Be careful.

[Boffosteve]

Behringer Europower PMP1280S Mixer power supply failing?

Enzo --thanks for quick response. I should have made clear that (I believe) the whole mixer/amp seems to work just fine other than this occasional random tick tick out the mains -- the switching power supply would restart fast enough to appear to operate normally? Also, I'll have to listen again (later this eve) as I recall there was random, possibly rhythmic white noise. Both symptoms seemed to "go away" if we slapped or jiggled the unit (classic TV fix, eh?). Again, thanks for info and safety tips.

I did find a schematic on line, made a small donation, downloaded. Attached it here -- wait, tried twice, this site failed to accept, how come? Sorry.

Cheers!
Steve

[km6xz]

Adding the term "rhythmic white noise" changes everything. What is the noise like, is it hiss or sharp click or ? What amplitude and do and level controls change the level or frequency of noise?

If it goes away the jarring the unit, disassemble it where you can safely have access to the modules and try to isolate an area that is more mechanically sensitive to vibration or wiggling of cables, pc board or mountings.

[Boffosteve]

Have now run the unit several hours, driving it with my CD player in attempt to stress it similar to our rock band practice last week during which the symptoms were heard (during a couple quiet breaks). Monitoring both main outputs with speakers in parallel with a load bank of 600-watt resistors (total DC resistance measured at 8.1 ohms/channel), only once did I hear a short play of random 'whooshing, not clicking' white noise suggesting a noisy connection (internal?). Have not reproduced the other original symptom, the "tick tick tick" (at about 150 ticks/sec, I'd guess...). Wondering now if that might have been an external influence (radiated or power line?) picked up by the amp. (My shop and the original unit location are a long distance apart.) Master volume would control the level; didn't think to try individual channel controls; frequency not affected. Perhaps tapping the unit was merely coincidental in making the noise(s) 'go away' though this occurred 3-4 times mid-way through the session. I will continue testing after >carefully< re-seating internal connections where I can. Ultimate test will be later this week with another rehearsal then a gig on the weekend. Thanks for your support! Steve

[km6xz]

This one might be hard to track down because there is a good chance it is not even in the mixer but its operating environment. If it can't be reproduced on be bench, anything you do might or might not change the cause so you will not know if you corrected it or not. Don't change anything or clean anything, limit you checks to probing mechanically with an insulated prod or for vibration sensitive intermittents, I use an electric toothbrush with the bristle shorted just a little. It is safe to use, and can track down connections, solder joints, microphonics, broken leads etc in very short order. The brush end can be used to touch any part or just the whole pc board or surround a part with the bristles and if there is any mechanical defect, the brush vibration will find it.

If you are using the amp in a rehearsal hall or venue and it happens but not on your bench taken apart, and the newly clarified symptoms, there is a good chance it is being induced by other equipment or the AC mains. I would attempt to find out if that is the case before spending a lot of time on finding a noise that does not occur on the bench. If it is AC mains or induced by RF or electric fields, it might be time of day dependent, weather influenced(like when cold, a heater is used that has a thermal switch that could be buzzing due to pitted contacts as an example), or lighting. If in a club or rehearsal hall, there are other tenants who might be using industrial equipment that is on the same mains branch. I would not even take it apart until you can reproduce it and isolate the mixer as the cause or not the cause. I am betting on the mixer as not being the problem.

[saj888]

Howdy pilgrims. How are you all? I have one in the shop that came in with the two 22ohm discharge resistors missing. Could someone please tell me the wattage of these resistors? These would be R11 and R12.
Thanks.

[Jazz P Bass]

SPS 1000 Schematic

I would call R11 & R22 the 'soft start' resistors.
Whatever, they are 10 watts.
If they are blown open, check the amplifier outputs for shorted transistors.

[saj888]

My mistake.

I would call R11 & R22 the 'soft start' resistors.
Whatever, they are 10 watts.
If they are blown open, check the amplifier outputs for shorted transistors.

My mistake. Its 'slow charge' or better yet 'soft charge' resistors. T3, T4 and T9 were blown.
Could you explain the audio output configuration. There is t22 and t23 in parallel. and t25 by itself.
Anyone? Enzo?

[saj888]

Thanks Jazz

[Enzo]

Disconnect the power amps, including the small 6-pin cable. Does the SMPS work by itself? Once you have stuck new resistors in it? Or is that the T3,4,9 you have blown? Always check the rectifiers on the secondary side for shorts. And those main power amp supplies can remain charged a LONG time once power is removed and the amps are not connected. Don't give yourself an 80 volt surprise, VERIFY the supplies are discharged.

I have no idea in the world why they used a pair of 9640 on the V+ side and a single 250 on the V- side. But that is just a detail, it is still a push pull output. See R138? 0E03? That is 0.03 ohms - 30 milliohms. They can burn open when the amp blows and goes to DC.

I don't recall on this one, but a lot of the Behr amps in this series use a crowbar triac on the output like Peavey does. If the amp goes to DC, the triac shorts the output to prevent speaker fires, but it often gives its life. SO check the posts on the speakon board where the power amp wires would go, see if either channel reads shorted. If so, you likely need a new triac.

The amps are digital, the big IC sends drive to the push and pull through IC2. Then the output of the MOSFETs runs through all that stuff to the right, which is a low pass filter to screen out the digital hash and leave only audio.