Gallien Krueger 700RB ii Pop Repair
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- Опубліковано 2 жов 2024
- The boom or pop when you start up or shut off the amp is caused by a pair of transistors. In this video I do the repair and show the parts. Bonus: tip for quickly and easily de-soldering multi-pin components.
This was a great help. I got a cheap 700RBii from an online auction but it was almost without sound. The pots were super scratchy but Deoxit did the trick. The pots are almost totally sealed but you can sneak Deoxit in through a tiny slot in the side. Then I reset the bias like you showed. It was a great confidence boost watching how you worked on it. My amp seems to be perfect now - woohoo. Thanks so much!
Awesome Peter! Glad it was a help.
I have exactly the same problem with exactly the same amp.
A technician changed all the pots and some other parts only to arrive back at the same issue. I will this method, because it’s a really good sounding amp.
Do you want some more work? I have an older model Gallien Krueger 800RB that cuts in and out. It works but something causes it to cut out but it will come back but it is useless to use onstage because of it. It is a good sounding amp so i would like to get it fixed.
I really don't have the tools to work on electronics but i could get em if i can't find a audio repair tech willing to work on it. It is probably just bad pot, or bad instrument input, or a bad decibel switch that is used to reduce the instrument input if you have active pickups on your instrument. Because if i cycle that specific switch after it cuts out it comes back. I have dirty pots too.
I use a guitar with active pickups so i always have to have the db instrument input switch set to low, but when it cuts out after a few songs or during the first song, when i cycle the switch to the high it allows more power to run thru into the input stage and could be why cycling this switch brings the sound back because the higher power may cause a loose pot and or whatever it is causing it to cut out, to make connection because the higher power in essence kinda forces it to connect again, so that switch could be good but if so then i would suspect it is the pots and maybe some of the other switches too.
Would it be too expensive if i just paid for all new potentiometers, same grade of quality at least? These lasted for a few decades at least so i would be happy with at least the same quality and get another 20 or more years.
Sorry but I'm pretty full up for work. The shipping alone at this point would make it cost prohibitive.
Kind of sound like some isopropyl for those pots and switches is what's needed to start with. I'd look around inside for any cracked solder joints and any corrosion on jacks or ground points. Sometimes it is cheaper to just replace a set of parts but you need to have narrowed the problem down to that area. Otherwise you're just firing the parts cannon and that can get expensive and you'll still have issues. And new parts do not always equal good parts. Give stuff a cleaning and if it's beyond your diagnostic ability, find a tech more local. Sometimes even a computer repair shop will have someone who does some of this stuff. Best of luck.
Great desodering tip - definitely going to use it.
My 700rb started doing the same thing last night, you just saved me hours of trying to chase the problem around the board.
Great! Glad it helped.
How'd you get the heat sink off? I took out all the screws through the transistors but i'm too worried about pulling too hard and breaking something
Double and triple check you have all the screws out. From there pry and lift from different sides. I forget if they use thermal compound or those gray thermal strips on these but they can really bake themselves to the heatsink. You may be able to dislodge some of the outer transistors with a tool but be careful. Sometimes a light twisting motion of the heat sink can help. I do remember this one not being easy but eventually it will break loose.
Can you talk about the technical reasoning behind swapping these two transistors out ? Their specs appear very similar to those GK installed except the MJE pair have 300V rating instead of 200V rating and the MJE pair has a lot higher collector cutoff current. What makes this swap affect the popping of the amplifier ?
To be honest, I didn't dig that far into it. I found documentation that was the swap being performed at Yorkville service centers. I'd guess it has to do with how they discharge when power is cut, they obviously don't have or cause that spike but, beyond that, I'm not sure.
My only guess would be some spike voltage causing the original transistors to go into the breakdown region and fully conduct for a moment causing the loud pop.