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Old 12th June 2010, 10:32 PM   #1
rumble is offline rumble  United States
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Default (help) behringer mx9000 ps revisited

i know this has been touched upon before, but i seem to have a different (newer?) revision of the pcb in my behringer mx9000 power supply than what has been discussed here and on other forums i've seen about the (dismal) subject.

mine says:

MX9000 EURO 09 Power Supply
PCB210080REVD

it's blue.

the symptoms of my mixer were - i turned it on one day and all the
red peak and green -20 leds lit up across every channel, and no sound was passing through.

the only thing i noticed prior to this was sometimes the light on the power switch did not always come on but it still powered up the mixer ok.

this was about a year after light use and of course just out of warranty, and behringer was no help.

i know there are guys doing upgrades to their power supplies, i was just wondering if there's anything peculiar or noteworthy about the version pcb that i have (rev d) in terms of better parts and part numbers to look for and/or any specific values specific to my revision of the board.

i'm going to try to have someone upgrade it and see if that solves the problem (gets it working again..)

thanks
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Old 14th June 2010, 12:03 AM   #2
Enzo is offline Enzo  United States
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Are ther not two green LEDs uper right on the panel that indicate power supply? And is one of those LEDs now dark? All peak lights lit is a classic symptom of missing op amp rail.

The boards may be different, but the power supplies are probably about the same.

The supplies are VERY conventional, the two 18v rails are based upon 6A rectifers and an LM350 each. I just repaired a 9000 powr supply a couple days ago, and it had a failed 6A diode, but in my experience with Behr mixers, the problem in the power supplies has almost always been a failed three-leg regulator.
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Old 14th June 2010, 12:27 AM   #3
rumble is offline rumble  United States
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hi enzo

i never noticed if the power led on the mixer was dark.
i just hooked the ps back up and the -17 led is indeed out.
i guess that's good news.

i'm fortunate to have at my disposal an engineer friend (former bose engineer) that now works at a laser company and he's offered to have one of his co-workers there who is an amplifier expert repair the unit at their lab.

i'm going to ask them to do a higher quality upgrade on as many components as possible while it's there, such as the electrolytic caps and whatnot.

can you suggest what to replace (besides the rectifiers) on each side of the amp or any mods that might be helpful?

thanks for the reply!

Quote:
Originally Posted by Enzo View Post
Are ther not two green LEDs uper right on the panel that indicate power supply? And is one of those LEDs now dark? All peak lights lit is a classic symptom of missing op amp rail.

The boards may be different, but the power supplies are probably about the same.

The supplies are VERY conventional, the two 18v rails are based upon 6A rectifers and an LM350 each. I just repaired a 9000 powr supply a couple days ago, and it had a failed 6A diode, but in my experience with Behr mixers, the problem in the power supplies has almost always been a failed three-leg regulator.
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Old 14th June 2010, 09:36 AM   #4
Enzo is offline Enzo  United States
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Frankly the thing works well enough as is. I don;t detect any hum issues, so there is not much to blame a cap for. The thing uses an LM350 in this, other similar supplies use LM317 and 337s. The regulator is usually what fails, but if something in that suply is going to go, what else would it be? I guess a higher curreent regulator couldn;t hurt, and maybe more cooling, though you don;t want fan noise becoming a problem. But the little parts are under no stress.

Your failure is probably just a power supply fault, but sometimes the mixer can load it down. Always test the power supply with a load after repair. A bad regulator can still work under no load. The mixer is a sea of op amps, and ther are little tiny powr rail bypass caps for each of them. SO if one of those caps shorts... well, pack a lunch, and start looking.
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Old 14th June 2010, 02:57 PM   #5
rumble is offline rumble  United States
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oh boy...

ok thanks!
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Old 16th June 2010, 01:40 PM   #6
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Quote:
Originally Posted by Enzo View Post
The mixer is a sea of op amps, and ther are little tiny powr rail bypass caps for each of them. SO if one of those caps shorts... well, pack a lunch, and start looking.
If the bypass caps go short on one of the channel it won't load down the entire power supply to the point that the mixer does not work anymore, but it will bring lots of mains hum due to the increased current draw. Easiest way to find it is disconnect the voltage rails to the channels one by one. When the hum stops you found the culprit. Depending on the way the power supply failed, ALL the caps on that rail could be shot, so don't panic if you get lots of hum after you replace the regulator, start replacing caps if that's the case. I can think on only one really important upgrade and that is a larger heatsink for the regulator. Berry mixers are notorious for having really small heatsinks on the vregs.

Also, the bypass caps on the channels are small for a reason. Contrary to what one might think, increasing the value of the channels' bypass caps will *increase* hum. Any capacitor upgrades must be done on the main power supply only, before the regulators.

Last edited by Th3 uN1Qu3; 16th June 2010 at 01:43 PM.
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Old 16th June 2010, 11:18 PM   #7
Enzo is offline Enzo  United States
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That is not consistent with my experience with these. When the little bypass cap shorts, it takes down the power rail. The regulator shuts down from excess current.
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Old 13th August 2010, 09:54 PM   #8
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"I can think of only one really important upgrade and that is a larger heatsink for the regulator."

I have an MX9000, and I wonder if most folk's PS problems aren't due to insufficient cooling. My +17V regulator would overheat and shut down after 15 minutes of operation. I was all set to replace with LM338's, but before they came, I simply left the cover off the PS and pointed a fan at it. Runs all day, with every channel operating in that mode. I think I'll still replace the LM350s because I think they're operating right at the edge of their envelope, but I'm also going to add additional cooling for the heatsink.

I do have some board problems that I'd like some opinions on:

1. On several channels, the main inputs are acting up. They act like they're padded, but the pad switch is not activated. Happens to both Line and Mic inputs. The B channel inputs work fine on these channels. Makes me think it's the pad or pad switch since the B channel inputs bypass those. In addition to seeming padded, the pot makes no difference in input level. Weird thing is those channels will work correctly intermittently. Haven't figured out a trigger that makes them work though.

2. My Mix-B left channel is dead. All channels. If I run Mix-B through monitor and press Mono, then I get both channels, but at about half the level of right channel when Mono switch is not pressed.

Any thoughts?

Thanks, Bill
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Old 13th August 2010, 11:02 PM   #9
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Quote:
Originally Posted by wlpearce View Post
"I can think of only one really important upgrade and that is a larger heatsink for the regulator."

I have an MX9000, and I wonder if most folk's PS problems aren't due to insufficient cooling. My +17V regulator would overheat and shut down after 15 minutes of operation. I was all set to replace with LM338's, but before they came, I simply left the cover off the PS and pointed a fan at it.
Well pretty much every problem you can think of is due to insufficient cooling, but that's a different topic. Anyway i'd rather add more metal than use a fan, one less thing to fail in the long run and certainly one less noise source (i hate the whine of tiny fans). I'm a "set it and forget it" type of guy, i'm willing to spend a lot of time in the initial configuration of a device, but then i expect it to perform flawlessly for a number of years.

1. Hardwire the pad switch to the not padded position and see what happens.
2. Probably some shot opamps. Check the outputs of all opamps, wherever you see significant amount of DC (usually almost the voltage of the supply rail), replace them.
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Old 13th August 2010, 11:30 PM   #10
Enzo is offline Enzo  United States
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Clean the insert jacks. Or wire up a TRS plug, shorting tip to ring, and shove in there. ANy help? At least when this happens to a channel, try inputting a signal at the insert jack, and also run the insert send to some amplifier for a listen. If the problem persists either in the send or return, then the mixer channel may have an issue. If both send and return seem OK, then the normal shunts in the jack are dirty.

This is especially likely when multiple channels have the same problem. This is a common problem on ANY mixer with insert jacks, and indeed is the first place I look for such complaints. In fact if some channel is reported as bad but is working at the moment, sometimes probing its insert jack a time or to with some plug will wake up the symptom. I keep a TRS plug configured as an insert bypass parked in my patch bay for just such testing.

Go down the rows. If this scenario seems to be the case for any of the channels, poke the insert on every channel to see if any that have been working are just on the edge of failing. Often as not a squirt of deoxit down the jack then shove a plug in and out a couple tomes is sufficient to cure it, no need to extract the board.


Mix B. If all channels are dead that way, I'd first pull and reseat any involved ribbon cable connectors, then consider the master section.
Look for signal. From the channel bus, Mix B L and R are buffered by IC41a, IC41b. Got signal at those output pins?
VR19 is the level control for Mix B, but is wired directly to op amp inputs, but check for signal at the buffers after that. IC33 for L and IC28 for R. Both sections in use, pin 1 first then pin 7 on each channel.

My main suspects would be the control and IC33.
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