need Behringer BX1200 Schematics

[Odie]

need Behringer BX1200 Schematics put new chips in, works but distorted. and the fan burnt out, i'm guessing it is a 24 volt DC? Help.

[Enzo]

Schematic doesn;t specify fan voltage, just that it is a controlled speed, running from the V+ of the powr amps, but not dead across it. Look closely at the old fan, maybe there is some tiny print on it.

Have you conbected a different speaker to the amp? HAve you plugged a test signal into the powr amp in jack? Have you put a signal in the regular input and listened to the preamp out signa via some other amp?

Have you verified the +/-15VDC for the preamp? And whatever the power amp IC voltages are. I don;t know what the amps run on, but the positive and negative ought to be about the same voltage.

[Odie]

+/- 39.7 and +/- 15 volts are good, right on the money, I can't tell if there are any transistors or opamps before the output IC's. I think the fan is a 24 volt dc, i can get one from allelectronics.com. does anyone got a schematic, I can't find one anywhere. thanks

[Enzo]

HAve you tried using the patch jacks in the manner I described to isolate your problem to either the power amp or the preamp section? APply a sine wave to see what the distortion looks like, and scope it at the outputs of the various op amp ICs.

You didn;t answer if you had tried a different speaker, this series of amps sometimes has a small crossover board in the speaker area, and parts like to fall off that.

it will only be a stroke of luck if you find a schematic. If you google after one, at least dig down 10 pages, don;t expect it on the first page. Unless you are lucky.

[oc disorder]

The fan is a 24volt 0.11A one.
It doesn't kick in 'till the amp gets hot.
Try testing it on one or two 9v batteries.
Get the amp working and I'm sure the fan will kick in when pushed !
Check what Enzo suggested

Have you connected a different speaker to the amp? Have you plugged a test signal into the powr amp in jack? Have you put a signal in the regular input and listened to the preamp out signa via some other amp?

to make sure the fault is in the power amp area.
As the board is double sided and has some very delicate fine PCB tracks I would use a high powered magnifier
and check all those solder pads and also check for continuity between them and where the tracks terminate.
Check both sides of the board as the "through plating" (where the copper runs through the holes where the output IC's terminate) can be accidently removed when pulling the old chips.
If that's happened they can be soldered both sides but makes it even harder next time to remove should the IC's fail.

[Steve L]

Schematics for BX-1200

Here they are.

Behringer BX-1200 Ultrabass (Rev.H) Schematics.pdf

[Odie]

Thank you

Thanks, you guys are awesome, the other output IC was top open and now I know what fan to order. many grats, problem solved.