Gallien Krueger 700rb volumen problem

[Carlos Nash]

Hi
I have a gk 700rb combo.
I play it with a 1*16 speaker.
My problem is that It felt down, and now It doesn't raise nor decrease the volumen; I mean the volumen knob doesn't work.

I don't know what could be happening. I checked if the volumen potentiometer works or its joins are broken, but everything there is okey. So I don't think it shouldn't be the problem.
All other functions of the amp works (all voice filter, eq, tweeter, woofer... etc)

By the way, I'd like you to pass the schematic.
PD: I'm learning, but I know basic knowledge.

[nevetslab]

This should help. Most of the 1001RB/700RB documents I have are too large to load, without pulling them apart in Adobe Acrobat to make them smaller. Hopefully this will load. The 700RB and the 1001RB are nearly the same....less power, so I think it's a smaller power transformer and less output xstrs.

1001RB-II_POWER_AMP_PN_206-0260.pdf

See if you get output level variation when you plug into the Return jack at the far right end of the front panel. Form that Return jack, you should have the Boost, Woofer and Tweeter levels working. I gather the Volume Control at the other end of the panel is NOT working. It's possible the knob took a hit, and fractured the resistive track on the control, which breaks the pot. In which case the preamp PCB has to be removed, the pot unsoldered from the PCB and raplaced

[Carlos Nash]

This should help. Most of the 1001RB/700RB documents I have are too large to load, without pulling them apart in Adobe Acrobat to make them smaller. Hopefully this will load. The 700RB and the 1001RB are nearly the same....less power, so I think it's a smaller power transformer and less output xstrs.

[ATTACH]47311[/ATTACH]

See if you get output level variation when you plug into the Return jack at the far right end of the front panel. Form that Return jack, you should have the Boost, Woofer and Tweeter levels working. I gather the Volume Control at the other end of the panel is NOT working. It's possible the knob took a hit, and fractured the resistive track on the control, which breaks the pot. In which case the preamp PCB has to be removed, the pot unsoldered from the PCB and raplaced

Hi, thanks for answer. I really appreciate.

Look, I checked again the volumen pot with my ohmmeter and It marks 47 k (I think It's good, taking account that the pot ohms are 50 k)

So, I don't think the pot would be the problem. Anyways, I bought a new pot. I'll replace but I don't know how to remove it without to damage, It seems to be soldered in both sides and I haven't never remove a pot . But I'll looke for help.

In case, changing the volumen pot, doesn't work, What would be the problem? I plugged into return jack, as you say, and anything is okey. The tweeter, woofer and boost work terrific (as you predicted).

I saw the schematics, and all point that the pot is broken. But I don't know, It works great...

[52 Bill]

Have you tried plugging a guitar cord from the FX send into the FX return?

Is the back side of the pot still solidly mounted to the wafer section?

[Carlos Nash]

Have you tried plugging a guitar cord from the FX send into the FX return?

Is the back side of the pot still solidly mounted to the wafer section?

Hi, Yes
I just try your what you said and still the problem, everything works except the volumen pot.

And yes, the pot seems to be mounted solidly. I must try changing the pot for a new one. But If the problem is there, could the amp still sounding ?



Thanks for answer

[nevetslab]

Google Desoldering Techniques, and you'll find numerous sources, on YouTube, tutorials, and the like. These are basic skills we all need to and have learned in order to build, modify and repair our equipment, all being soldered & connected together in forming working circuits. Cheapest are the solder sucker and solder wick, both which make use of a soldering iron in the process. Double-sided PCB's are more difficult as solder want's to cling to the plated-thru holes occupied by the component leads...and aggressive application of heat can lift traces and break the thru-hole continuity.

Trouble-shooting the pot....meaning following a test signal flowing to and thru the pot on the 700RB is tricky due to parts density and finding the components on both sides of the circuit that may be how you get to probe it. It can be done with a DMM in AC Volts mode. Easier if you have an oscilloscope, though I assume you don't. A steady-state signal is best for a signal source.

[Carlos Nash]

Google Desoldering Techniques, and you'll find numerous sources, on YouTube, tutorials, and the like. These are basic skills we all need to and have learned in order to build, modify and repair our equipment, all being soldered & connected together in forming working circuits. Cheapest are the solder sucker and solder wick, both which make use of a soldering iron in the process. Double-sided PCB's are more difficult as solder want's to cling to the plated-thru holes occupied by the component leads...and aggressive application of heat can lift traces and break the thru-hole continuity.

Trouble-shooting the pot....meaning following a test signal flowing to and thru the pot on the 700RB is tricky due to parts density and finding the components on both sides of the circuit that may be how you get to probe it. It can be done with a DMM in AC Volts mode. Easier if you have an oscilloscope, though I assume you don't. A steady-state signal is best for a signal source.

Hi, I start to looking for videos about soldering technics. Thank you so much for your advices. Actually, I'm in first year of electrical engineering, so I'd better learn

Look I measured the AC voltage in the pot, even I don't have a oscilloscope (I put my finger on the tip of the input cable so I think it makes a constant signal, doesn't it?). I measured it with the third terminal and the wiper ( I saw the schematics and the second therminal is grounded) and I notice when a scroll the pot, the voltage change. So, I think the pot is not the problem. I don't know what else could be

[g1]

Finger on the tip will not give a constant signal, any slight change in pressure will cause the voltage to change.
Turn the amp off. Set meter to measure resistance. Put one probe on ground and the other probe on the wiper terminal of the volume pot.
What is the meter reading when volume set to 0 ? What does the meter say with volume half way up? What about when volume turned all the way up?