Behringer mixer DSP crash fix

21st October 2012

Th3_uN1Qu3

Gear addict

Joined: Oct 2010

Location: Bucharest, Romania

Posts: 315

Thread Starter

Behringer mixer DSP crash fix

Just a heads up if anyone stumbles upon one of those. I received a Behringer Eurorack UB1222FX-Pro mixer with a bad effects processor. Sometimes it would work, sometimes it would crash making weird noises, but most of the time it wouldn't start at all. When trying to select an effect the FX display would just go out and there was no more response until power cycling the unit. And you would power cycle it only to have it crap out again. You get the idea.

The failed parts were the memory ICs. They are 1Mx4 DRAM chips. No idea where Berry got them, but i can tell you those parts are dinosaurs. I found some on a 4MB 68-pin SIMM memory from the 386 days, i still had some of those in a drawer. I don't even remember where i got them, i'm lucky to have found them.

Also, it didn't work first time. It's likely that the some of the chips on the SIMMs i had were bad too, they've been sitting for god knows how long in improper conditions. First pair of chips i tried worked for a few minutes then started making loud noises. Second pair worked but would click and pop on some effects, and sometimes have trouble starting up. Third pair started up fine but all the reverbs were consistently borked, flangers and delays consistently worked. Likely a bad area. Fourth pair of chips i pulled from the SIMM module work perfectly. I've been messing with it for 3+ hours with no signs of trouble.

Attached is a schematic i found on the internet. It doesn't have part values besides the main ICs, but that was enough for me to find the culprit.

Attached Files

behringer_dpm5m_schematics_rev_a[1].pdf (66.0 KB, 86 views)

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27th November 2012	#2
Th3_uN1Qu3 Gear addict Joined: Oct 2010 Location: Bucharest, Romania Posts: 315 Thread Starter	Status update: It came back in with the same fault. This time i tried all the RAM chips i had around with no luck, it would, at most, work for 1 minute or so and then shut down. Replaced the main DSP chip. Fired up first time and working perfectly, no misses. Along with the capacitor upgrade i've given it first time around, should serve well until the faders go bust. Now i need to get around to fixing that DJ console of mine, as i found the USB audio IC that's gone south, available from the same seller i got this DSP from. On both counts, the failures are due to design issues. The power supplies are designed in such a way that if capacitors fail, one or more sections will go way overvoltage, and stuff will fry. Another reason to steer clear from Behringer, but if you have one in for repairs, now you know what do do.

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