Good evening good people,
I just bought a secondhand GK mb 112 ii. It had the pink/purple led (instead of the normal blue) on the power button, which indicates a fault, but it still worked fine and sounded good, so I took a gamble on it (I got it for around 150$). I'm trying to troubleshoot the amp and hopefully make it as good as new. So far what I know:
- The amp's manual states : "Smart Protection Circuitry: The MB Series protection circuitry constantly monitors for unsafe operating conditions such as short circuits, miswired speaker cables, blown speakers, improper ventilation, and incorrect speaker configurations. In addition, protection is provided during power up/down. If the MB Series senses any unsafe operating conditions, the output signal is immediately muted and the power light changes from Blue to Red. The amplifier will remain muted until the fault is removed. Be sure that you are not exceeding the maximum recommend load described in this manual. If the problem persists, contact GK directly for technical advice."
No info about purple light, or if it can still work if the protection circuit detects a fault.
- When I plug a bass, turn the amp on, I get sound. When no bass is connected, there's a very low hum, that is (very) slightly affected by the gain button and the -10db pad and moderately affected by the treble control.
- I tested the speaker on my guitar amp too and it works perfectly fine.
- The phones output is not working. I wonder if the purple light can be caused by a faulty headphone circuit ? If it’s the case, I can totally live with that.
- The DI output does work, but I can hear some static on the recording.
This is my first attempt at repairing an amp. I think it would be a good learning experience. If all fails, I'm gonna turn it into a cab. Any help would be appreciated.
Thank you
I just bought a secondhand GK mb 112 ii. It had the pink/purple led (instead of the normal blue) on the power button, which indicates a fault, but it still worked fine and sounded good, so I took a gamble on it (I got it for around 150$). I'm trying to troubleshoot the amp and hopefully make it as good as new. So far what I know:
- The amp's manual states : "Smart Protection Circuitry: The MB Series protection circuitry constantly monitors for unsafe operating conditions such as short circuits, miswired speaker cables, blown speakers, improper ventilation, and incorrect speaker configurations. In addition, protection is provided during power up/down. If the MB Series senses any unsafe operating conditions, the output signal is immediately muted and the power light changes from Blue to Red. The amplifier will remain muted until the fault is removed. Be sure that you are not exceeding the maximum recommend load described in this manual. If the problem persists, contact GK directly for technical advice."
No info about purple light, or if it can still work if the protection circuit detects a fault.
- When I plug a bass, turn the amp on, I get sound. When no bass is connected, there's a very low hum, that is (very) slightly affected by the gain button and the -10db pad and moderately affected by the treble control.
- I tested the speaker on my guitar amp too and it works perfectly fine.
- The phones output is not working. I wonder if the purple light can be caused by a faulty headphone circuit ? If it’s the case, I can totally live with that.
- The DI output does work, but I can hear some static on the recording.
This is my first attempt at repairing an amp. I think it would be a good learning experience. If all fails, I'm gonna turn it into a cab. Any help would be appreciated.
Thank you
I suggest you get a circuit diagram of the preamp from GK? Here is the address I have used. Tech01 <Jose@gallien.com>
You will need to supply the actual part number on the preamp board as the design has changed over time (which I found out for a similar model).
The purple or pink light indicates there is a problem somewhere in either the main amp or the preamp. The preamp board has the power on switch plus a relay which will turn the amp off if the main ICE amp board identifies a problem. I am working through the issue of identifying where the "problem" lies.
You will need to supply the actual part number on the preamp board as the design has changed over time (which I found out for a similar model).
The purple or pink light indicates there is a problem somewhere in either the main amp or the preamp. The preamp board has the power on switch plus a relay which will turn the amp off if the main ICE amp board identifies a problem. I am working through the issue of identifying where the "problem" lies.