Gallien Krueger 1001rb schematic FOR PREAMP

[rockman627]

I had to change the volume and master volume pots. The old ones were difficult to remove and I may have nicked the pcb doing so. I can get sound out of the fx send jack, but nothing when I plug into the fx return. I would like to verify signal passes thru the master volume to the fx return. But although I can find plenty of schematics for the power amp, I can't find anything for the preamp.
Can anyone point me in the right direction?

[Kaz Kylheku]

Try including the preamp board part number "206-0251-A" in quotes when searching.

Another Gallien-Kruger amp uses the same preamp, evidently:

https://elektrotanya.com/gallien-krueger_700rb-ii_sch.pdf/download.html

Assuming that is correct, I can see that, as I suspected, the Return is a switched jack. If you are getting signal through the amp with nothing plugged into Return, that means signal is flowing through the connection in the jack. If you can't insert signal by plugging into the jack, something is wrong there. 

Like if the Return jack's switch is somehow not opening as it should, then your input has a low impedance path back to the output of the U5-A op-amp that drives Send.

Or do you mean that there is no sound out of the amp: but the last confirmed externally observable output where signal is seen is the Send jack?  I.e. the Return jack worked before, but you only touched volume pots; so the jack is probably fine.

[rockman627]

The amp made sound but the pots were noisy. Cleaning them did nothing, and the shafts on both pots moved in and out a little, so I changed them. I had to desolder, then really pry them out. Then there was no sound. I plugged a bass to the input and from the fx send to a Roland microcube . I got sound. Then I plugged straight to the fx return, no sound. I didn't touch the power board so I figure the problem is in the preamp board around the master volume area. The pot itself tests ok.

[Kaz Kylheku]

If you remove as much solder as you are able, there is usually still enough solder to hold a component to the through hole and pad. If you pry it out when cold, you risk damaging the board, so if that happens, you have to identify what is wrong and make a repair.  (Even if you are careful, you can damage things: on some circuit boards, pads and traces lift if you just look at them with the wrong attitude.)

Check the connectivity between each solder lug of the pot: follow the trace from it and use first solder blob you can find in every direction.

When removing components, don't worry about removing solder up-front. That is actually counterproductive because the presence of solder helps to transmit heat. Ideally you want to heat all the solder blobs at once and pull the part out. There are tools for that like special soldering iron tips for heating all the pins of a DIP IC at once.

Sometimes you can use a regular soldering iron tip to heat both solder blobs of a small part like a capacitor at the same time.

If you can't heat all solder joints of the to-be-removed device at once, the next thing to consider is: do you need to keep the device, or is it going to be discarded? If it is going to be discarded, then what you can do is cut its terminals, remove the device and then remove the pins from the board one by one. Removing individual pins is easy peasy: just heat the solder, and tug on the thing very gently with with a pair of pliers; when the solder liquefies, it will pull out with next to no force. If you feel resistance, it means the solder hasn't melted: more heat is needed, not a stronger tug.

If you have to keep the device, what you may be able to do is heat the pins one by one and nudge them out a little bit at a time, rotating among them. Only try to move the part when the solder is liquefied.

I sometimes thread a loop of wire underneath a part. That lets me tug on the part while applying heat, kind of like pulling a tooth out with a string. Pliers are not as good; it's clumsy to keep pliers on a part while working the iron with the other hand, especially since these two activities are on opposite sides of the board with through-hole components.

Once the part is out, including all of its pins, that's where you bring in the vacuum pump and wick to get the solder off the pads and out of the through holes. Until you reach this point, the solder has been helpful.

If you vacuum out solder from a through-hole joint, it becomes harder to heat up the solder that is down in the through hole, and may have to add solder to make better progress. In fact, it can paradoxically help to add solder anyway: flood the existing joints with solder to help desoldering.
 
Electronics craftspeople such as boutique amp or stompbox builders like to scoff at board-mounted jacks and pots as an earmark of cheap mass production. Now you know part of the reason why: these things use the circuit board for physical support and transmit stresses to it, especially if they are not adequately screwed to a chassis.  If you are designing something new, have your pots and jacks mounted the external case / chassis / panel, using hookup wires to connect them to the board. So much easier to remove a pot, when you have three separate hookup wires to desolder. and even if that pot loosens from the panel and is abusively used, it will never transmit forces to the circuit board.

When replacing jacks or pots in an existing mass produced device, it's often possible to rework things so that the new jacks or pots are mounted only to the panel and hooked up to the original board footprint with wires, rather than trying to replace the parts with matching board-mounted ones.

[rockman627]

Yes, thanks for The info. You are correct about The 700rb using the same preamp. My board says 206-0251-A2. Any schematic I find only say A or B. Which would be more accurate?
Furthermore, I found a 2001rb schematic in my download folder instead of my GK folder, and I will upload it. When I find the upload button.