Wednesday, October 16, 2013

Zoom G1 guitar effects pedal repair

I got this unit essentially for free a few years back after getting rid of my VooDu Valve which was too expensive/overkill.
It's a nice little unit great for practicing guitar and has the added bonus of foot switches (the two big knobs at the bottom):

This unit has seen better days and it kept switching itself off or resetting once in a while whenever the cables were moved. Also, it didn't want to work on battery power.

The back is pretty simple, just input, output, expression pedal input and power.

The battery compartment is completely removable without any wires. The designers chose an interesting solution of sending the power via some springy wires that are sandwiched between the battery compartment and the board.

To get the front panel off the two knobs from the digital pots need to be removed...

... as well as the two plastic stand-offs keeping the board in place. Another nice mechanical touch.

It's a full digital effects processor so there's not much to see. A big ASICs labeled ZFX-3 that is probably a derivative of a 32-bit DSP. I suspect the same chip is used in several products of the time, with this one being the entry-level.

  • WM8734 CODEC chip that provides a 96kHz ADC and DAC solution.
  • 1Mx16 SDRAM chip from Etron that's probably used for the echo/reverb buffers.
  • small chip labeled Zoom MPU-1 - probably a small uC that provides the glue logic and coordinates the DSP, CODEC and LCD
  • small chip from TI labeled 68J771k. Probably a 68000 uC derivative, though I cannot figure out what it's supposed to do, it seems to only be connected to the right digital potentiometer. If that's the case, it's quite overkill
  • the small chip marked 7082 8615 JRC might be an headphone amplifier

Well, there's nothing wrong with the board and it looks in perfect condition. The soldering on the I/O sockets is also good and without play.

Aha! The input jack is quite corroded and the other sockets don't look so well.

Some rubbing with the brass wire brush and a bit of Isopropyl alcohol on a Q-tip cleans the stuff easily.

The case is given a rub with hot water in the sink and a small blow with the aircan.

Oh, the the power-on on battery works only when the input jack is connected. Still, it's intermittent, even after cleaning, and it only works by pushing the jack well into the socket.

Well, that's quite stupid, I thought TRS (?) jacks are standard by now. The culprit is obviously shorter by a couple of millimeters.

Since the guitar was also in the need of some love, I did a temporary fix to the output socket that was hanging around. One of the ears from the cover broke off and the cable kept plugging itself out.
The cover is curved and from a brittle yet slightly elastic material, not easy to get hold off. I'm thinking ebonite, but a 3D printed part from PLA or ABS might work just fine.
In the meantime some steel wire will have to do.

For anyone having the same problems: the unit does not need to be opened.
Rubbing all the contacts with alcohol and a small wire brush cures the symptoms.


  1. hello dear sir this zoom i have problem sometime its work properly sometime its doesn t work
    for xample if you put conect the adapter you will wait for second than the machine will on but...often hang no on ...then i cut the conect adapter and conect again this sometime ok sometime truble its mean regulator or something problem but if you using for long time problem will begin again please help for solution
    nyoman /bali

  2. Hello, I have a G1XNEXT, circuit is the same but I have problem with patch switch (left switch from PLAY to DECAY)), it turn free and is not possible to select the different patches. I have no idea which type of component to buy. I read only ALPS and CC503 but I didn't find the component via internet with these specifications.
    Can you help me?

    1. It's probably a rotary encoder made by Alps. I cannot find the product code but you might want to check their website, see if this might narrow the search:
      Search for something without a push-on switch.
      It might be possible to add a different brand of encoder but I would not rely on that.

      But first, you might want to check the soldering on that encoder and reflow the solder. Otherwise, try to spray some WD40 or something inside it and see if it starts working.

    2. As an update, it's indeed a potentiometer, it has 15-16 detents and varies from 0 to ~20k on the middle pin. I don't know how a 270 degree potentiometer with detents would be called.

  3. Hey there. I have a Zoom G1 effects pedal. I'm having a problem with pedal, where the lcd blinks with the code 'bt'. I tried resetting it by holding the store button, turning it on and pressing the store button twice but the problem was persistent. If you have a fix on this, please let me know. Thanks! :)

  4. Hi, I also have a zoom g1n processor and my battery cover is lost. Can somebody post images of battery cover in high def so I can design and 3d print. Thanks

    1. I hope it's not too late, here are some details pictures next to a ruler:

  5. Hi Ligius, thanks for the info on the G1. My 2 cents here: On the list of relevant chips that the G1 has, you mention an unknown one from TI, if you view more carefully it says "HCU04" on the bottom line which is a CMOS high speed family derivative of the TTL Hex Logic Inverter 7404 (like S, LS, AS, ALS and so on) and is related to the main clock generator portion of the circuit.
    I have one of those G1's that unfortunately is totally dead by now, received as a gift for donor parts. I've examined the unit carefully but can't figure out yet which part or parts is/are the main culprit, it only dies abruptly yet using the correct power supply for about two years aprox.
    I thought that this blog would make explanations of a major repair of this unit, but saw with a little sadness that it only talks about of a regular maintenance and overview of the internals of it. Great article BTW!!

    1. Hi David, I'm sorry to hear about that. I initially started the article thinking there is something to repair, but it turned out to be just maintenance. On my former Zoom 9001 I had to reflow the board and change the IC that generated the negative rail.
      If there is anything that I can help you with - voltages, signals - just give me a shout.
      I would check first if the supply voltage reaches all the parts, as there might be SMPS ICs that have died or have capacitors with a high ESR.
      The large regulator (IC3) receives the input voltage (4XAA) and supplies 3.3V on the pin on the left. The small regulator (Q301) generates 1.27V on the large pad/tab. There are various test points on the board. I would start with voltages first.
      The unit requires a MONO jack on the input in order to start.

  6. hai im sherlan, i do have a friend whos left potentiometer, whos broken, i think its on the rythm i dont im not guitarist, what do you call that b50k potentiometer? is it detent?

    1. Hi Sherlan. The left 'potentiometer' is a rotary encoder made by Alps with 15-16 detents. The only marking on it is CC503.
      It seems pin 1 is connected to ground, second pin varies from 0-19kohms (at 12 o'clock) and then to 10k at 5 o'clock.

      Edit: I've measured it while powered on and indeed it's a potentiometer, I think 20k. The middle pin is the wiper, the other ones are GND and 3.3V.

  7. As soon as connecting my G1XN, after just 2-3 seconds , it is followed by a loud noise/disturbance (like shhhhhh) throughout on very patch, until i put it on bypass.
    Showed it to 3 shops, just by hearing the issue, the people in the shops said its a problem in the motherboard and cannot be repaired.
    Can a problem in the motherboard of this processor be repaired??....
    should i search in some other places as well with the hope of getting this processor repaired ? , plz reply....

    1. I had a similar problem with a Zoom 9000, but could not fix it. I suspect it might be power supply related, so if you have access to an oscilloscope check all the rails (especially the negative supply) for the correct voltage and noise. Let me know if you need waveforms, but I'm not sure that it's identical.

  8. My zoom g1 just died ...
    And I don't know if its gonna work again...i need help
    'When i plug the adapter it doesnt work,

  9. Hi, I'm Carlos. I have a trouble with mi G1u. I don't know if it is a firmware issue or anything else, but when I plug the adapter (both USB or DC), system appears to initiate fine, until it shows an "u" code. Since that, it does not work. Just that "U". It's been around one month and I couldn't find a solution to this. Do you know what could it be?

    1. Don't know, I would try first plugging it into a computer via the USB cable.
      Other than that, a factory reset might help:
      "To restoring the factory settings of Zoom G1XN, first power on while simultaneously holding the STORE button until “AL” appears on the display. Finally, press STORE again to start initialization of the program. The Factory Reset procedure is complete."
      Try updating the firmware next. If it was a firmware update that killed it in the first place the unit might be bricked. I don't have access to one to know if it can be recovered.

    2. I am very interested in trying to hack/mod my G1N up to the G1u or just adding USB capability. Could you please share a couple of hi-res photos of G1u PCBs?

  10. I also have a problem with my G1xn. When I put delay in the patch, or maybe a reverb, it sounds like a robot. It's awful. It only happens when i put delay and reverb in the patch.

  11. I have the same problem with the left potentiometer. So there's any way to fix it?

    1. Try to see if you can clean it first, otherwise search for a similar potentiometer, I think the value is 20k but I have measured mine in-circuit.

  12. how to fix the left rotary? it's not clicking anymore.

  13. how to fix the left rotary? it's not clicking anymore.

    1. The only option I can think if is taking it apart completely and see what became broken. That's because I don't know of any replacement parts so the best bet is to try to fix the existing one.