Behringer GMX212

[gm212]

Hi,

I recently bought this amp with the intention of fixing it as a cheap practice amp.

Upon power up with the amp flicks channel 1 then goes onto channel 2 and stays stuck there. The display stays on d2, the fx led is out.

I have verified that the power section is ok. All the voltages are present and where they should be.

+15
-15
+5
+36
-36

etc

In faultfinding process I have removed the rom and this makes the amp power up in channel 1 mode.

This also renders the display inactive and the channel button and fx buttons do nothing as to be expected.

If I refit the rom and remove the ribbon to the main pot board that does all the tonal changes to the input, I get no channel lights and the display lights up the green fx led.

I have checked the obv channel switch is working and it is so it makes me believe it is a problem with the processor board (which also handles channel switching)

I can wire in a switch easily enough to allow me to go from channel 1 to channel 2 by effectively removing the vcc to the rom but thats a bit too boogey a solution in my opinion.

Does anyone have any ideas as to what else I could try?

Cheers,

Aaron.

[gm212]

Here are some pics of the components of the amp in the hope it might help others with problems with this amp.


This is the Rom and channel controller board (rom out)


PSU and Power Amp


Rear panel jack board and speaker connections board


Main tonal front pot board

[Enzo]

Just a thought. Are you plugging anything into the input jack during these tests? The input jack has a ground connection to disable the 4053 ICs. Plug something into the input if not already. Those are IC7,IC8.

The small board is not really a channel board, it is your DSP board. Note the three legged voltage regulator, is that working? The little board regulates its own +5.

[gm212]

Thanks Enzo for that I have not had anything plugged into the input when testing. I will grab a lead and do that now.

The 5v reg is working well, all board voltages seem to be correct, well at the regulators anyway.

There is no sort of water ingress tell tale signs to speak of it just failed.

One other poster had the same problem with their amp when I looked through the archives, but no solution.

[gm212]

Why would the amp need 2 of these triple switching IC's? They are right above each other and right above the soft channel select switch.

I will scope them and see what happens when in operation.

[Enzo]

The 4053s?

Each section is used as a switch to select either a signal path or to switch components in and out. When you switch channels a number of circuits have to change.

[gm212]

Ok excellent thanks I wont know what is going through where without schematics, but I can scope the signals and see what is what and hopefully one will look wrong.

[gm212]

I scoped around and found that:

The soft channel switch goes down to the DSP board then back up to the 4053's.

A B C inputs all come from the DSP board.

One 4053 (top) has inhibit high 5v and when you plug in a lead it drops to 1.2v.
The second 4053 (bottom) inhibit stays at 0v regardless.

The A B C inputs for the top one are all high.
The A C inputs for the bottom one are high.

Pushing channel button does nothing.

The xtal is running on the DSP board.

I will now check where the soft push channel button goes on the DSP board.

Any ideas greatly appreciated.

[gm212]

Ok so the soft switch goes through a little transistor under the display and fires a segment of the display possibly to show ch1 or ch2 when the switch is pressed.

The other line of the soft switch goes through one resistor then to the DSP board to what looks like a philips pic.

p80c32sba4

It is a micro so armed with the datasheet I will watch for outputs changing when I press it. I will also trace back the channel 1 led and see if that leads me to another IC to check.

[gm212]

Reading some threads on here about the GMX212 I have found out 2 things.

1. It has a 5 yr warranty and might be under it still
2. There are service agents for Behringer on this forum.

Now I know you cant give out schematics but am I flogging a dead horse here with this amp?

Everyone talks about recycling before repairing them!

S/N is N0601102211

Im tracing and beeping out tracks to try and sort this problem.

I have found that there is a pair of hc273's on the dsp board that has an output on pin 9 (the TTL side) that goes to a tranny that switches the leds for ch1 ch2.

I cant find where pin 8 comes from (the digital side) other than the two pins are linked but not their outputs.

Is it common for these DSP boards to die?

I dont know im just lost now I think I need a break from staring at the blue boards for a couple hours lol.

Any ideas i should try?

TIA

There is a soft switch channel select line that goes into pin 5 of the philips micro.

[Enzo]

If you think it still has warranty coverage, contact Behringer and ask for a repair authorization and referral. I think the warranty is only 1 year, but I could be wrong. It is about when you bought the amp new, not about when the amp was manufactured. You will need your bill of sale as "proof of purchase." That is for any brand, not just Behr.

Common? Not really. When one fails, I am usually looking to scrounge another board. FInding repair parts for the DSP boards would not be my favorite task.

Pin 8 on the 273s is just a data line from the system - goes to several ICs. D3, IC5-40.

The switches on the panel feed directly into ports on IC5 on the DSP.

If it makes you feel any better, I would consider having to chase this down through that DSP board a pain in the ass.

[gm212]

Hi,

I am very pleased to announce that I have solved the problem.

On the DSP board there are 2 1 meg 4 bit cmos ram chips. One (IC19) was getting slightly warm and so looking it up it is a common as mud chip found on ram for computers etc.

I have now replaced it and the amp works great.

Channels switch as they should, the 24 bit processor is all working again etc.

So if you have a D2 or E2 error and stuck on one channel it is most likely to be a $1 faulty ram chip.

Thanks,

Aaron.

[floydian32]

Hi Aaron,

I have a UBFX1204-PRO with the same fault,all i get on the effects panel is D2 and no effects,i wonder if you have any photo's of the ram chip you replaced as mine could be the same fault.

Thanks

Alan

[floydian32]

If you think it still has warranty coverage, contact Behringer and ask for a repair authorization and referral. I think the warranty is only 1 year, but I could be wrong. It is about when you bought the amp new, not about when the amp was manufactured. You will need your bill of sale as "proof of purchase." That is for any brand, not just Behr.

Common? Not really. When one fails, I am usually looking to scrounge another board. FInding repair parts for the DSP boards would not be my favorite task.

Pin 8 on the 273s is just a data line from the system - goes to several ICs. D3, IC5-40.

The switches on the panel feed directly into ports on IC5 on the DSP.

If it makes you feel any better, I would consider having to chase this down through that DSP board a pain in the ass.

Hi there,im new and from the UK,just wondering if you have any working DSP boards for the UB1204FX mixer ?

[Enzo]

Who, me? No.