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GSRM20 MIKRO BASS
Danpoet
#1 Posted : 5/12/2015 5:31:01 PM

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The wiring diagrams that I have found on the Ibanez site don't exactly match the passive Mikro Bass that I have.
The closest wiring I have found to my bass is on the Ibanez site, and is listed as WB040009 on the schematic for a GSR 190. My Mikro GSRM20 is a passive system with only 2 volume controls, and a tone control. The schematic does differ as to the tone control as to what was on my Mikro GSRM20. I had a bad neck pickup dual pickup assembly, and it was replaced with factory pickups.

Each individual volume control for both the bridge and neck work fine individually. However,if I max out the volume control on the bridge pickup, then increase the volume on the neck volume control - when I get to maximum volume, the neck pickup volume drops to zero output. The same thing happens when I start with max volume on the neck pickup - when I get to max volume on the bridge pickup, the neck pickup volume drops to zero output. Just short of either pickup volume before maximum gives full output from both pickups.

When I describe the volume potentiometer left, center and right connections, it is looking in the back of the bass cavity. The volume controls are mounted with the center connections at 12 o'clock. The volume pickup potentiometer connections are:
Ground is on the left side, the center is the hot side of the pickups, and the right side connects the two pickup assemblies together through the grey cable with the white hot wire. The grey shield wire is soldered to each potentiometer case.

Looking at the tone potentiometer from left to right from the cavity side, it is not vertically positioned as the volume controls are, but turned to the left 90 degrees.The center connection is at 9 o'clock.

The tone control potentiometer diagram has ground on the right side. Mine is on the left side, and the right side is open. The other two connections are where my wiring differs from the schematic.


The tone control diagram shows the capacitor with one end tied to the left end of the potentiometer , and the other side going to case ground. The center of the potentiometer is tied to the neck and bridge hot wires. The right side of the tone potentiometer is ground.

My Mikro bass has the right end connection as open, and the center(9 o'clock) connection soldered to the right side of the capacitor, and the left side of the capacitor is soldered to the right(hot) side of the bridge pickup potentiometer that has the grey cable white wire soldered to it. The left connection is grounded to the tone control case. A black wire is also soldered to the tone control case at this point, and runs to the bridge volume potentiometer case ground, along with the bridge ground wire(black).

I tried lifting one side of the capacitor that went to the center of the tone control, but it had no effect on the volume problem.

The neck pickup connections are red and white. The red wire is soldered to the center of the neck potentiometer. The white wire is soldered to the potentiometer case.

The bridge pickup connections are yellow and red. The yellow wire is soldered to the center of the bridge potentiometer, and the red wire is soldered to the potentiometer case.

The output jack white(hot) wire is soldered to the neck volume right side terminal. Another white wire(hot) that is in the grey shielded wire cable is also soldered to this terminal. The cable shield is soldered to the neck volume potentiometer case. The other end of the grey shielded cable goes to the bridge volume control. The white wire is soldered to the right side of the bridge potentiometer, and the cable shield is grounded to the bridge potentiometer case.

The output jack black(ground) wire is soldered with the bridge ground to the bridge potentiometer case. All grounds read zero resistance with each other. I would appreciate any assistance that you could give with this problem.
Thanks!

Bill@Ibanez
#2 Posted : 5/12/2015 8:18:43 PM
Bill@Ibanez


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That diagram is the closest I have as well.

After reading your post a few times to get my bearings straight, I'm wondering if the neck pickup's volume pot is properly connected to the ground. Not only should the neck pickups ground wire be connected to the left lug, that left lug should also be connected to the casing of the pot.

If this isn't the problem, I'm honestly not sure what could be going on. Hopefully someone else here can offer some more advice for you to try. Otherwise, I would consider replacing the entire pot(or both volume pots) to see if that fixed the problem.

Hope this helps,
-Bill
Tracy Dae
#3 Posted : 5/13/2015 2:00:42 AM
Tracy Dae


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Originally Posted by: Danpoet Go to Quoted Post
The wiring diagrams that I have found on the Ibanez site don't exactly match the passive Mikro Bass that I have.

You do not need a diagram that matches your bass exactly. The important thing is to use a diagram that matches your configuration, in this case 2-pickups, 2-volume controls and one tone control. Since the diagram you have found matches that configuration, you can use that digram to re-wire your guitar and see if doing so will resolve your problem. It just might. If not, you can use any diagram from any brand that has the same configuration to see if one wiring scheme works better for you than another.
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