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I Just Absolutely Ruined My GK 700 RB II

Discussion in 'Amps and Cabs [BG]' started by telebassman, Dec 5, 2020.


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  1. telebassman

    telebassman

    May 20, 2008
    Virginia
    I am such an idiot. My beloved 700 RB (the only amp I've ever purchased that wasn't used) has bit the dust by my own doing. It has always made a popping sound when I power it up. It always bothered me a little but I thought it was normal because it did it since the day I bought it 7 years ago. I read that if it was bad enough to move the drivers a little on my cab then I should get it fixed. It is long out of warranty but I contacted GK and found out that replacing two transistors Q11 and Q14 would solve the issue for good so I ordered them. They were super helpful and recommended taking it to a GK authorized service tech but the closest one is 2 and a half hours away and he estimated that it would cost $200. I have a fair amount of experience with a soldering iron and I can read a schematic so I decided to do it myself. Bad idea...Long story short I got the iron too hot and a little dab of solder melted into the board when I tried to get it off the printed circuit peeled up. I am sick to my stomach. Now I either have a parts chassis or I need to buy the main board used. Ugh!
     
    Meaculpa, Riff Ranger and Ricky Rioli like this.
  2. Bloomfield

    Bloomfield

    Jan 21, 2020
    Nova Scotia
    Any electronics repair shop should be able to fix a burnt or lifted trace like that fairly easily, so don't give up on it.
     
    Qlanq, SwitchGear, Bassology and 33 others like this.
  3. JKos

    JKos Supporting Member

    Oct 26, 2010
    Torrance, CA
    Exactly!
     
  4. :(

    This is why so many of use recommend a Service Center to post about amps needing repair.

    Many with good intentions have messed up their amps this way, now the original job has to be done as well as repair what the other person has messed up. Sometimes it is easy, a lot of the times it is not with the multi layer boards, or too much of a headache to figure out all the other person has done to make it back to original.

    Good luck getting it fixed.

    :crying:
     
  5. Redbrangus

    Redbrangus Supporting Member

    Nov 19, 2018
    Under The X In Texas
    I agree with what @Bloomfield said -- it's probably not a particularly big deal for an experienced tech. To that, I'd recommend going ahead and biting the bullet -- take it to the authorized GK service guy unless there's someone local that you absolutely know to be a good tech.

    I remember there was some old adage about fixin' stuff that ain't broke, but I can't recall it at the moment.... :D
     
    Last edited: Dec 5, 2020
  6. telebassman

    telebassman

    May 20, 2008
    Virginia
    :):):)
     
    Last edited: Dec 5, 2020
  7. jeff7bass

    jeff7bass

    Apr 9, 2009
    Ampslaughter. The authorities have been notified...
     
    SwitchGear, Low8, mngnt and 6 others like this.
  8. lowphatbass

    lowphatbass **** Supporting Member

    Feb 25, 2005
    west coast
    Don’t feel bad. When I was a lad I blew a fuse at band practice. I didn’t have a replacement so I wrapped the blown fuse with a foil gum wrapper. It actually said, “POOF” the moment I fired it up and a large cloud of ashy smoke shot out the back...education is not always cheap.
     
  9. Wasnex

    Wasnex

    Dec 25, 2011
    In looking at the schematic, I honestly don't see that Q11 (B5) and Q14 (D5) have anything to do with the described problem.

    Anytime you put a soldering iron on a board there is potential for accidental damage...even if you are an experienced pro. Because of this, it's best to actually troubleshoot and confirm where the problem is before replacing components.

    This is just my amateur and somewhat superficial analysis of the circuit. I could be totally wrong.

    I believe Q21 (CD4) and Q15 (D3.5) sense the current flow in the output devices. I believe there is also an RC time constant associated with this...so the output devices have to reach a target current and stabilize for a certain amount of time.

    When conditions are right, Q15 sends a signal to Q19 and Q18 (D1). Q19 and Q18 drives the trigger of a LM555 timer circuit (U2) (D1.5) that is set up as a fault detector. The circuit starts in a mute condition, and when conditions are right in the output section, the circuit unmutes. However, the circuit reverts instantaneously back to mute condition when the amp is turned off.

    The output is through Q20 (D2) (Mute 1). Mute 1 is fed back to the power amp input section at (B6) and associated transistors are Q1, Q4, Q5, Q6 (B5-5). Q1 drives Mute 2 which controls muting of the tweeter amp (A4). I believe what happens in the woofer amp when the mute is engaged is the signal is stopped on the base of Q2 (C6).

    IMHO, If both the woofer and tweeter amp are popping, the problem is before Q11 and Q14...these two transistors clearly have no affect on the operation of the tweeter amp...the only way I can see that they could impact the mute circuit is if they are somehow affecting the bias of the output section. Bias is set at R28 (BC5) and Q11 and Q14 do appear to have a significant roll in the current flows passing through Q12 and Q13 (BC5). Keep in mind that the fault circuit should be in a mute condition when the amp is turned on, so a problem with Q11 and Q14 would possibly prevent the amp from coming out of fault, but I don't think it would cause the amp to pop when it is turned on.

    Good luck! The amp is probably repairable, but now it's going to cost even more, unless you can pull a rabbit out of your hat.

    For those who don't know, the number and letters, like (B5) are XY grid coordinates on the schematic.

    If you want to look at the schematics and offer help, I found the schematics here: Gallien-Krueger 700RB II schematics - Music Electronics Forum
     
    Last edited: Dec 5, 2020
  10. Killing Floor

    Killing Floor Supporting Member

    Feb 7, 2020
    Austin, TX
    Yikes. Get help. Should be fixable. Take it to a pro electronics shop.
     
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    I see this kind of stuff all the time, a 15 minute repair turned into a much more expensive mess. I post about WHY a QUALIFIED tech is the way to go. Just because somebody learns something on the internet and over-estimates their ability does NOT make them qualified.
     
  12. JKB1957

    JKB1957

    Jul 18, 2015
    Take it to a tech. Get it fixed. Pay the price. Learn a lesson.
     
  13. bbh

    bbh Supporting Member

    Sep 27, 2011
    It’s usually fixable. You could probably out find how to on YouTube. If you go the pro route, make sure they will perform that repair over the phone or better yet email or text.
     
    telebassman likes this.
  14. Mingo Sanders

    Mingo Sanders

    Mar 11, 2008
    Austin, TX
    Sympathies. Call the tech. Your beloved amp will be better than new soon.
     
    telebassman and Roxbororob like this.
  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Right, YouTube is full of videos of people hacking on electronics, with horrible skill level and ruining things in the process.

    How do you propose a tech perform a repair over the phone, email or text???
     
  16. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I have a rule when I do plumbing: "Leak tight on the second try." What it means is that I'm willing to tackle a job if a leak won't damage anything before I discover and fix it. Then I figure my cost as the cost of the repair plus the risk of screwing it up. It's still usually cheaper than calling someone.

    If it's too risky, such as a complicated installation above a drywall ceiling, then I call someone.

    Unfortunately, circuit board damage is a possible side effect of repairs, especially single sided boards, and especially parts with heavy leads and multiple terminals. I've seen repaired traces quite frequently when opening old gear. There's a lot of tribal knowledge about how to do it safely, that isn't written down anywhere.
     
    pcake, WillieB, telebassman and 2 others like this.
  17. Horseflesh

    Horseflesh

    Sep 22, 2020
    Seattle-ish
    I bet the board is salvageable. If it's only a top trace damaged you can solder in a wire to bypass it. Can you post pics?

    It sucks but even if you have to open your wallet, it'll get fixed!
     
  18. This is how situations like in the OP starts.

    Talking or sending messages without an amp in the "Pro's" hands makes repairs?

    You may want to reread what is going on.
     
    Frank77 and agedhorse like this.
  19. You're not an idiot. You've made a mistake. Two very different things.

    Now go find a tech. Don't compound your problem.
     
  20. FrenchBassQC

    FrenchBassQC Supporting Member

    Jul 13, 2011
    Gatineau QC CA
    Yeah how? One thing for sure, it would be faster than by mail at least.
     
    agedhorse likes this.
  21. Primary

    Primary TB Assistant

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    Jan 25, 2021

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