Behringer GM110 permanent low volume but surge in volume on switching off power

[Enzo]

IC3 is a TL074, which is a quad op amp, four sections. The four sections are A, B, C, and D. I suppose that is less than helpful if you lack the schematic, th ABCD are not printed on the board.

I am looking at the schematic in front of me, GM110 rev B. They often put small parts under the jacks, which would be on the other side from your photo. But other numbers are not making sense either. And thanks for the board number, but that does not appear on the schematics. I wouldn't think one revision step - to C - would be a wholesale change of board, but perhaps.

Does your GM110 say V-tone on the panel or elsewhere? Or does it say Vintager anywhere? Those could be two versions. ANy date codes on it?

[DIYGuy]

IC3 is a TL074, which is a quad op amp, four sections. The four sections are A, B, C, and D. I suppose that is less than helpful if you lack the schematic, th ABCD are not printed on the board.

I am looking at the schematic in front of me, GM110 rev B. They often put small parts under the jacks, which would be on the other side from your photo. But other numbers are not making sense either. And thanks for the board number, but that does not appear on the schematics. I wouldn't think one revision step - to C - would be a wholesale change of board, but perhaps.

Does your GM110 say V-tone on the panel or elsewhere? Or does it say Vintager anywhere? Those could be two versions. ANy date codes on it?

Hi Enzo,

I have gone through both sides of the PCB with a magnifying glass and looked underneath the jacks. It appears that this is Revision C. Here are the markings:

On the Power amp PCB - it says (in addition to what I have given you) Behringer model Gm110/01. Also has UCP5 94V-0 and 03 10 underneath the words "PCB216100REVC/01". You can also see the words"C33" hand-stamped in the middle of the panel on the pic. This also appears on the preamp PCB. Perhaps it is meant to represent version C with 33 alterations?

On the panel it says Vintager (no SS) GM110 with a date code of "1103")

The serial no is L0311090145 and it doesn't say "V-tone".

[Enzo]

C33 is more likely a production line code.

My schematic is for the Vintager version, but clearly does not match your board. Again, all those board numbers do not appear on schematics, so I appreciate the effort but they don't help me, other than the REVC within the one number.

I'd wager the amp was made in November of 2003. Sound reasonable?

[DIYGuy]

C33 is more likely a production line code.

My schematic is for the Vintager version, but clearly does not match your board. Again, all those board numbers do not appear on schematics, so I appreciate the effort but they don't help me, other than the REVC within the one number.

I'd wager the amp was made in November of 2003. Sound reasonable?

Yes - that appears to be what the date code says. I agree that it is unlikely that a revision from B to C would be that great. It is also interesting that several components from removed between B and C. However, I am guessing that the functions of ABCD as to where they feed into should be the same. So if you have a pic of the B circuitboard, perhaps I can to a visual comparison.

[Enzo]

Um, no, I haven't seen one in a long time, let alone have photos.

For your benefit in the future, look up "Chip Quik" and consider getting some. That will cut down on tearing up the pads when removing surface mount ICs. Places like Mouser and Digikey sell it as well as most general electronics suppliers.

[DIYGuy]

Um, no, I haven't seen one in a long time, let alone have photos.

For your benefit in the future, look up "Chip Quik" and consider getting some. That will cut down on tearing up the pads when removing surface mount ICs. Places like Mouser and Digikey sell it as well as most general electronics suppliers.

Thanks. I am still pretty determined in fixing this one, perhaps using logic. Can you briefly tell me what each of the ABCD opamps services or leads to (eg external speaker, phones)?

[gui_tarzan]

DIYGuy, I applaud your tenacity and drive to get this amp to work, as well as Enzo's (and others) willingness to help, so don't take this the wrong way please. You need to be more proactive in determining where the leads go from the chip to their partner components. Since you have a magnifying glass, and I assume you have paper and a pencil, take the time to draw the individual traces from the chip outward. You will not only learn more about how that part works in the circuit, but you will also save the others a bunch of time.

I say this because at one time I had to do the same thing, and when I run into something I haven't seen before I still do it today. Right now I have an old Peavey with a burned circuit board that I repaired and have to lay down wire from the connector to its related parts. Before I repaired it, I drew where the traces were on the board with a marker so I don't have to guess. You obviously have a lot more patience than I do when it comes to solid state components, I will not work on SMD parts anymore. My hands aren't as steady and my close-up vision is not as good as it was when I was younger and it's too easy, as you have found, to make a mistake and ruin (the trace connection) something.

So my respectful advice to you is take some time, draw out the circuit of that chip and where the traces go, and you'll be much further ahead for yourself and the others.

[DIYGuy]

DIYGuy, I applaud your tenacity and drive to get this amp to work, as well as Enzo's (and others) willingness to help, so don't take this the wrong way please. You need to be more proactive in determining where the leads go from the chip to their partner components. Since you have a magnifying glass, and I assume you have paper and a pencil, take the time to draw the individual traces from the chip outward. You will not only learn more about how that part works in the circuit, but you will also save the others a bunch of time.

I say this because at one time I had to do the same thing, and when I run into something I haven't seen before I still do it today. Right now I have an old Peavey with a burned circuit board that I repaired and have to lay down wire from the connector to its related parts. Before I repaired it, I drew where the traces were on the board with a marker so I don't have to guess. You obviously have a lot more patience than I do when it comes to solid state components, I will not work on SMD parts anymore. My hands aren't as steady and my close-up vision is not as good as it was when I was younger and it's too easy, as you have found, to make a mistake and ruin (the trace connection) something.

So my respectful advice to you is take some time, draw out the circuit of that chip and where the traces go, and you'll be much further ahead for yourself and the others.

Hi Jim, thanks for your comments - no offence taken. That's exactly what I am also doing but very slow and patiently (in addition to using some logic and studying diagrams how opamps are wired up to caps and resistors. Have also been putting the PCB under bright light to see where the traces go - some are obvious (and checked subsequently with multimeter) and some not. I have worked my way through a few amps with success but this is the first time I have worked with SMDs. I have also observed that traces on PCBs with SMDs are less obvious than those with through-hole components. Hence I asked Enzo what each of the ABCD opamps do. Obviously that are 4 sub-circuits. If I can isolate the one that perhaps I can work out how to wire it. About not working with SMDs, I am tending that way too. However as I am only starting to learn about electronics (in my 50s - never too late), I scrounge around for cheap faulty amps to play with. Whilst the simple bit is to replace like with like and get it to work, I am hoping to learn some theory along the way too while working on the components.