mx9000 PSU repair how to when -17 or +17 is droppping

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Member Since: Dec 20, 2008

Thought I pass along some DIY info on repairing your behringer mx9000 PSU, when the -17 or the +17 goes out.

I just rebuild my mx9000 PSU circuit board rev B ( Green) when the -17 was dropping . After some testing and actually trying to cause it to drop I found the following will most likely repair the majority of the users PSU issues when -17 or +17 fails. First , you need to fix both sides at the same time. Just fixing one side exploits the weakness of the other side and it will drop. With out going into all the details do the following:

Tools needed:
Phillips #2 Screw driver
15/64 wrench to remove ground nut from heat sink and VR nut on bottom of the board
20-30 Watt soldering Iron
Soldering wick also called desoldering braid
Solder sucker
Solder 62/36 .022-.025 Dia.
Heat Sink paste


1)Remove PSU lid cover
##NOTE make a cable connection diagram so you know exactly what plugs back to where. I actually left them connected and just flipped the board after a few trail & error runs.####

2) remove the circuit board
3) replace the lm350T with a lm338T
##Note: get new mica insulators and to-220 bushings on both and heat sink compound Also inspect your your soldering on the x3 pins. If it looks like the solder joints may touch, use you solder wick to remove a little .
4) replace the x3 resistors on both
150 ohm 1/4 watt 2% ( Replace with 1%) 1.91K ohm 1/4 watt 1% 2.21K ohm 1/4 watt 1%
4) replace 1n5204 diode ( its in front of the lm338T's)

Total repair is less than $20 with shipping. Not bad compared to the Behringer auth repair centers starting at $65 and hour plus parts.

Some times just replacing the VR (lm350T) works, but component failure usually has a domino effect. Mine had the -17 VR fail that also cause the 150 ohm & 1.91K ohm resistor to short after they got warm. The board would work fine for about 10 minutes and drop. I replaced the lm350T with the lm338T and still the same. Basicaly if you have +17 or -17 drop, you have to replace the VR, for just a few bucks more you eliminate alot of the troubleshooting and hassles in 1 attempt. Trust me I learned this repair by trial and error. I'm not a electronics tech, just a DIY'r that got part of the info from this site and the rest from playing , just trying to pass along the info to help someone else out with this known issue .

All these parts can be bought online at digikey. or most on ebay.

I actually have x2 mx9000's, one PSU (older) is REV B (green PSB)the most common with issues, the other is REV F (Blue PSB) newer less issues.
The older Behringer date code 0604 with PSU Rev B works flawless. The new mx9000 board , date code 0609 (PSU Rev F) has some bad channel issues across the x3 8 channel boards. I purchased this as aparts mixer, but after playing around with it I'm look at rebuilding it with quality components and see if the preamps and EQ can be modified for greater improvement. I will update in the future as I get time to do this.

I'll update later with PSU +5 fix for No solo or mute function at a later date .

Hope this helps someone and keeps you up and recording.


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Czar of Midi
Since: Apr 04, 2002

Dec 20, 2008 01:15 am

Thanx very much for the info. I know Walt just went through this. I thankfully have not had issues with my PSU yet.

Since: Dec 20, 2008

Dec 20, 2008 01:25 am

There are at least x2 different revisions of the PSU

REV B Green circuit has 6a4 recifier diodes with Moterola LM350T VR's and 1n4802 Diodes

Rev F Blue circuit has 6a2 recifier diodes with Fairchild LM350T VRs and 1n4007 diodes.

the older Rev B, from research appears to have the -17 +17 drop issues the most , and the REV F appears to have the +5 issues. I basically rebuilt my Rev B with all new Caps 2000Hr 105C.

The difference between the x2 REVs is rectifier diodes 6a4 vs 6a2, 1n4802( no longer avail)vs 1n4007 diodes, and Motorola LM350T vs Fairchild LM350T's , the rest is the same. The Rev F does look like a better build board though.

Since: Dec 20, 2008

Dec 20, 2008 04:39 pm

Just an update, my PSU burn in ran 22hrs straight with phantom power on and used .. No issues .. not bad for .55HP or 400W's

Czar of Midi
Since: Apr 04, 2002

Dec 20, 2008 06:44 pm

I would be guessing here as I have not opened mine up, but it must be a newer rev.

Mine runs an average of about 50 hours per week, and that would be on the low side most weeks. With no issues in the last 5 years or so.

Nicely done then bp.

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