Suzuki Omnichord OM-84 Repair - Diagnosis Tips & Dunce Moment
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- Опубліковано 8 лют 2025
- Got my 1984 Omnichord back from the studio to do some work on a project and... it broke down. I fixed the first fault, caused another, wasted almost a month on the fault I'd caused like a total berk, but but did get it going again. This might be of use to anyone looking to diagnose a faulty Omnichord, as I cover a few pointers here, and in fairness I didn't hide my dumb mistakes.
Note: a couple of minor corrections:
Early on I mention the amplifier being on the smaller circuit board. Doh. The amplifier is on the main (big) board, not the smaller switchboard!
The 2007 date on the new amp chip is dubious. The chip sheds black stains when given the acetone-on-a-swab test. I think it's been sourced from China and while it works, I think it's been recycled, re-surfaced, laser etched and dressed up. Not an uncommon practice nowadays but this can reveal fakes or duds. It's frustrating. I could've put the old chip back in but didn't want to stress the pads on the board further. I will keep that chip though.
The hex inverter chip for the master oscillator is legit though.
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Bro this helped me go down a rabbit hole to ultimately realize I can't just use a random 12v adapter just laying around the house... which I did... then upon closer inspection, quickly learned what that little diagram means on the side of the adapter that refers to the center pin being positive or negative lol
I made the same mistake today. How did you fix it?
Fantastically helpful walkthrough-- exactly what I needed to get my bearings for a board level repair on a friend's OM-84
watch out for those solder blobs!
Hey James; thanks so much for this video. I have a OM-36 experiencing the same symptoms you describe at the beginning. I replaced the TC40H004P chip like you did, and it did not fix the problem. I tested with a multimeter, and the chip is receiving 5 volts. I also reflowed connections between the board.
Oddly, right as I was about to give up hope, I accidentally shorted Q3 and VSS on the 4556 (the two upper, left pins on that IC chip). When I did this, the Omnichord immediately started to function. I can control the drums, the premade chord backing tracks, volume, tempo, etc. But, it appears most of the note / scale buttons do not work. Also, oddly. when I hit the 'square' touch-sensitve pad on the top, right - OR - when I hit the 'chord hold' button, the Onnichord 'dies' again and exhibits the same issues mentioned in the beginning of your video. It will not play anything until the 4556 IC is shorted again. Shorting the 4556 also only works when the device is powered on. When shorted, you only have to short the pins briefly -- not install a jumper between them. It almost works like a 'on' switch.
Any hunches as to what might be causing this?
sent you an email!
Awesome video. Thank you. Can I just ask you to let me know what settings you had your scope on when checking the timer output? Thank you.
Had to watch the video back to check! You should be able to see it on the screen there. DC coupling, 2v/div and 500ns horizontal sweep
Nice one@@jamesbennettmusic thank you for the quick reply.
hey james! wonderful video! i’m currently struggling with a weird issue that noone online seems to have. my omnichord has a strange glitch where it will only play different chords once i’ve pressed down all the buttons at the Chord Memory Interface, otherwise it just locks onto one chord and stays there. the auto bass sync has completely stopped functioning. the sonic strings are still perfectly fine. any idea on what could be causing this?
Like anything else I would say make sure you've resoldered the joints between the boards, and cleaned the switches, the usual stuff. Look really carefully for dry joints on the board. Reflow anything that looks at you funny
on my om 27 I have the exact same problem with the sound, but with the only diffrence that the drum machine works and that only two notes work on the strumming plate.
Do you think replacing the sound chip you replaced is going to fix it, because my problem is very simmilar to the one in this Video.
Nothing would work at all with a faulty master clock, and the OM-27 has quite a different circuit to the OM-84
I have video of my om-84 malfunctioning in a few interesting ways, would love to get your read on the issue. Has the rumbling sound on the strumplate sometimes and at that point the chord buttons won't change. Also the rhythm will quit playing. This happens anywhere from 30s to 5 minutes after turning it on - sometimes it has a good day and will work for a few hours. Turning it off and on again often fixes it for a while, but sometimes its bad for a while and will need to sit. I have found unplugging it and turning it on will light the power and the speaker for about a tenth of second and this is sometimes followed by a period of functional operation.
Any ideas on what might be happening?
The first port of call is usually to re-solder anything that looks suspicious - I would do both sides of the connector between the two boards (and try not to bridge any joints!) Try powering it on and pressing both boards, see if you can find a pressure point that makes it work / not work. Without putting it on a meter or scope, it's hard to pinpoint specific components that could be causing it, but someone else in the comments here potentially has a bad 4556 decoder chip... you'd need to look on a scope to confirm that though. Good luck!
@@jamesbennettmusic oh so new development. The big black capacitor under the AC port smokes when I put in the OCA1 plug OR batteries.
Might that be the only problem causing my other issues? And do you know what type of capacitor it is and where I can get a replacement?
I have one. It hums when I plug it in.
Can i contact you? I bought one and it's been broken for 3 years. I cannot find anyone that can fix it
feel free to drop me an email!
@@jamesbennettmusic what is your email?
go to my channel page and look on the channel description and there's a 'show email address' button there - it only works from computer though... youtube doesn't show it from mobile
@@jamesbennettmusic okay, will do that