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

[DIYGuy]

Uh... I'll have to get out my file again.

Thanks. Pin 9 contact is also damaged

[km6xz]

I found a web site that says they have the schematic for the GM110 but it "reports back, Download failed try again later"
BEHRINGER GM110 manual circuit diagram manual online download - Download enter the address -Service Manual Download,Download the circuit diagram,Manual Download

[DIYGuy]

I found a web site that says they have the schematic for the GM110 but it "reports back, Download failed try again later"
BEHRINGER GM110 manual circuit diagram manual online download - Download enter the address -Service Manual Download,Download the circuit diagram,Manual Download

I tried but have no success. I know someone else who have had no success as well.

[nickb]

I found a web site that says they have the schematic for the GM110 but it "reports back, Download failed try again later"
BEHRINGER GM110 manual circuit diagram manual online download - Download enter the address -Service Manual Download,Download the circuit diagram,Manual Download

I've come across that site before - it did the same for all schematics I tried. I guess it's just a bogus advert-generating shell.

[Enzo]

Pin 10 is grounded. Pin 9 is wired to a pair of 1 meg resistors, R69 and R70. The other end of R70 is pin 8, so it is the feedback resistor. The other end of R69 is the gate of JFET T1.

[DIYGuy]

A little confused by your previous posts regarding the connections hence sending a pic. The contacts under the bottom of 2nd and 3rd pin from the left is damaged (just above and between C32 and C33). Can't see any R69 and R70 resistors closeby. Those said resistors are on the preamp circuit board (where all the control pots are attached)

[Jazz P Bass]

Hey, if you know where the traces are supposed to go & they don't (anymore), then run a wire lead.

Or, if you do this type of repair alot, http://www.soldertools.net/products/...epair-Kit.html

Further reading: http://www.engineeringlab.com/circui...air-guide.html

[DIYGuy]

Hey, if you know where the traces are supposed to go & they don't (anymore), then run a wire lead.

Or, if you do this type of repair alot, PCB Trace Repair Kit for repairing circuit traces | soldertools.net

Further reading: Circuit Board Repair Guide

That is the problem - I do not know where the traces go (schematic not available) and it is not easy to have a visual of the traces. I plan to run a wire lead once someone can tell me to determine the next component in the sequence.

[Jazz P Bass]

Post #20.

Enzo spelled it out.

[DIYGuy]

Post #20.

Enzo spelled it out.

Except that if you had looked at the pic, R69 and R70 is not on that circuit board.

[The Dude]

So find them on the connecting board and see which pin of the connector they go to.

[DIYGuy]

There are also two TL074 on the connecting preamp board so I want to be absolutely sure that Enzo is referring to the right one as I was specific at the beginning.

[DIYGuy]

Pin 10 is grounded. Pin 9 is wired to a pair of 1 meg resistors, R69 and R70. The other end of R70 is pin 8, so it is the feedback resistor. The other end of R69 is the gate of JFET T1.

Hi Enzo,

Would you be kind enough to look at the pic I have posted below re: pins 9 and 10. I suspect pin 9 connects to C33 but not sure where pin 10 goes. Can you please advise. I have been able to trace continuity for the other pins.

[Enzo]

OK, I am terribly sorry, I had a senior moment in post #20, please ignore it. I was looking at the preamp input when I called out the IC connections, however you need IC3-C on the power amp. Sorry, let me try again.

IC3-C
Pins 8 and 9 are tied together, and also to + end of C4. Pin 10 is not ground, pin 10 is tied to R24. There is also diode D5 between pin 10 and 8/9. Cathode to pin 10.

Does that fit the picture better?

[DIYGuy]

OK, I am terribly sorry, I had a senior moment in post #20, please ignore it. I was looking at the preamp input when I called out the IC connections, however you need IC3-C on the power amp. Sorry, let me try again.

IC3-C
Pins 8 and 9 are tied together, and also to + end of C4. Pin 10 is not ground, pin 10 is tied to R24. There is also diode D5 between pin 10 and 8/9. Cathode to pin 10.

Does that fit the picture better?

Hi Enzo, My PCB says IC3 (not IC3-C) and also has markings PCB216100revc/01 on the underside. There is no C4 on the board - can see C3 and C5,C6,C7, C8,C9 (C7 and C8 are the huge 2200uF caps). Also cannot see R24 - seems to jump from R21 to R26. THERE is a D5 connected to pin 8 though. Perhaps it is a slightly different version?

I tested for continuity for each of the pins

Pin1 - R14,R19
Pin2 - R18,R19
Pin3 - C20 (one end)
Pin4 - C20 (other end)
Pin5 - C29, R17
Pin6 & Pin7 - R15

Pin8 - D5
Pin9 - ???
Pin10 - ???
Pin11 - C32 (one end)
Pin12 - C32 (other end) , C34, R28
Pin13 - R29, R26
Pin14 - R28

Can you please recheck?