The BOSS GEB-7 Bass Equalizer is a convenient, compact 7-Band graphic EQ solution for bass guitarists. In this post, I cover the troubleshooting process taken to repair a faulty GEB-7.
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The Faulty BOSS GEB-7
In this issue, we experienced intermittent cutting-out of the pedal’s output signal. For some time the pedal would play fine, however if nudged or moved in the slightest way the signal would either drop, become squashed, or attenuate too low to be heard at the output. If the pedal was nudged again you might be able to redeem the signal, but it wasn’t long until it was sent back to a quiet place.
Initial Inspection
The slide pots are mounted on a separate daughter board which connects to the main board via a ribbon cable. On the main board these wires are soldered through-hole, but on the daughter board they are done in a surface-mount fashion. To protect the cables from getting strained there was glue present on the surface-mount termination.
Once I removed the PCBs from the enclosure I gave a quick visual inspection. The problem wasn’t immediately apparent: nothing was damaged and there were no marks on the board or components. I reworked the solder on some questionable areas but when retesting the pedal the same issue kept creeping up.
Troubleshooting the BOSS GEB-7
I injected a sine wave into the input and moved the daughter board to see if the ribbon cable connections were the issue. I heard the signal both cut-out and cut-in while moving the daughter board. That forced my attention to reflowing the ribbon cable connections. To do so, I had to remove the glue on those terminations.
Removing the glue was a challenge, I managed to use a combination of isopropyl alcohol and a small exacto knife to chip away the glue. After spending some time doing that I reflowed the ribbon cable connections, but unfortunately I wasn’t able to relieve the issue.
A Deeper Look at Signal Flow
The input signal flows into the main board, is routed to the daughter board for “Level” control, and then heads back to the main board.
It then travels to the op amp circuits that are responsible for the rest of the equalization. During the equalization, the signal makes trips back and forth to the daughter board for each of the graphic EQ controls.
The Solution to My BOSS GEB-7 Repair
I was able to probe a healthy signal all the way up to the EQ section. After this section the signal flows into a capacitor.
I found that one of the solder joints on the capacitor was sensitive – passing signal only when pressed down with the probe. There was a blatant cold solder joint on one of the legs of this capacitor! I reflowed this joint and the pedal came back to life.
When the bad solder joint was uncovered it didn’t take much to recreate the problem. Earlier on, while moving the daughter board, the main board was probably moving against the lab bench just enough to simulate the intermittent signal.
Another thing I should mention: during initial testing I was able to bring the signal back to life by striking a chord with an excessive amount of attack and with the level control at max or near max. This must have produced enough voltage to push the signal through the bad joint and off to the output. After that initial push the signal cut right back out.
Meet the Author:
Hi, I’m Dominic. By day, I’m an engineer. By night, I repair and modify guitar effects! Since 2017, I’ve been independently modifying and repairing guitar effects and audio equipment under Mimmotronics Effects in Western New York. After coming out with a series of guitar effects development boards, I decided the next step is to support that community through content on what I’ve learned through the years. Writing about electronics gives me great joy, particularly because I love seeing what others do with the knowledge they gain about guitar effects and audio circuits. Feel free to reach out using the contact form!
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