Oberheim OB-MX LCD Repair & Unit Reassembly (finally successful!)

[@bak4320]

Great news and thanks Alloy!! Thanks for keeping the long, lost, art of repair alive.

[@paulcottingham241]

Wonderful to see some real bench engineering!

[@sonovoxx]

02:00 The silk screen should have a notch, a corner angled, a dot or a 1 to indicate where pin 1 goes (red stripe).

[@Lantertronics]

"Should" being the operative word there. ;) I think the part label was trying to play that role but I didn't trust it.

[@johnmeroney2007]

Who else is holding their breath that Oberheim and Buchla will revisit this? I’d love to have one. There was a 8 voice for a low proce a while back that I maybe should have jumped on. Also heard these don’t always cooperate with you.

[@Lantertronics]

I wouldn't hold my breath on that, alas. Don is no longer with us, and he and Gibson had a tumultuous working relationship. It is a very quirky beast.

[@Lantertronics]

The source code for the voice cards was made available by Lynx Crowe, who maintained ownership of it after a long protracted legal battle with Gibson: github.com/jkmaxwell/oberheim-ob-mx So, that's there if anyone wanted to try recompiling it and fixing it up. Basically it was released before Don and Lynx were happy with it. I should state that Gibson is under new management now.

[@NaudioElectronics]

When I started watching this video, I realized that the problem is not the zebra strip connection. It's all about brightness. You can disconnect the brightness pin and add a single trimpot where you can select your desired brightness. Otherwise, there could be an issue with the brightness control, it could be PWM from the microcontroller?

[@Lantertronics]

Interesting... cleaning the zebra strip did seem to help a little bit, though. It was more readable after cleaning it than before cleaning it. I will keep that in mind about the trimpot if it goes on the fritz again.

[@Lantertronics]

By brightness, you mean the darkness of the LCD segments and not the backlight, right? (Because the backlight looks fine). Just making sure I understand...

[@NaudioElectronics]

@@Lantertronics True. those type of displays have a pin to control how much are visible the segments. It is necessary based on the angle of view.

[@alloy2754]

Good deal.

[@andywlala]

I bet that display menu setting provides a variable voltage to pin 3 of the lcd unit, often called “contrast”. Scope out the pin while you change the menu, then look backwards to see what kind of DAC is driving it, you may find a fault upstream….

[@Lantertronics]

It's working OK for now, but I will keep that in mind if it goes on the fritz again.

[@AnalogDude_]

a thought, maybe you should have used the opportunity to swap the capacitors. Ask some student to help you decode the LCD for the worse, so you can put in a Oled on a later date witch an additional mcu.

[@Lantertronics]

I'm generally not a fan of willy nilly recapping unless there's a specific reason to do so -- to easy to accidentally damage something in the process.

[@Lantertronics]

But yeah, in old equipment bad caps are usually a thing to look for.

[@AnalogDude_]

@@Lantertronics Well, source good ones, like Panasonic electrolytic at Mouser, there is another Japanese brand. not sure if the have these type or values, but they have high end variants for sound. "Nichicon" Aluminum Electrolytic Capacitors, they even have non polarized variants. Just take it easy, breath in between. : ) Use a "leg" for the camera. This is definitely a device that should be preserved. although many circuits can create cool sounds. even if you build a VCO on virtual ground as you can see at my profile.