Ibanez DM2000 Digital Delay Needs Service

[tylerpenn]

My DM2000 has recently gone on the fritz.

Basically everything works fine except for the HOLD feature, which I have used extensively so I'd really like to figure out a fix

Symptom:
-Set delay time to max 1023ms
-Get a phrase going, hit HOLD button. (Normally this feature would just loop the first 1023ms of the phrase indefinitely.)
-Here is where the issue comes in: The repeat will immediately start crackling and breaking up and eventually fade to nothing.
-In addition, if I continue playing my guitar, the delay will continue to build on new sounds, when it shouldn't be. Pressing HOLD should disengage any new audio coming into the delay portion.

There have occasionally been times when the hold does work properly for a few seconds, but then the crackling starts and it goes into a crackled fade out.

Does anyone have any contacts who still service these models? I'm in NY state in the Hudson Valley and can ship anywhere in the US

Thanks for any help on this!

[The Dude]

Here's a link to the service manual.

https://music-electronics-forum.com/...1&d=1472317075

[tylerpenn]

Yeah I'm guessing it's a bad RAM module that is malfunctioning, unfortunately the service manual isn't very descriptive as to what each component does what in the schematic. I'll see if I can find a service technician in the area who can at least do some basic path testing to narrow down where the signal goes wonky.

[Jazz P Bass]

At the very least you or a tech should perform the following tests. (Item I is specifically for Feedback & Hold)

[The Dude]

...... unfortunately the service manual isn't very descriptive as to what each component does what in the schematic......

It's often helpful to look up the data sheets for the chips if you want to know what they do.

[Enzo]

The analog circuits are on two pages, and as far as I can see they are plain old common audio circuits. The only odd item is the 570 compander chip, and you can look up its data sheet as Dude said. The next pages are the digital circuits. This unit is from 1983, so the technology is just basic TTL. If you don't know logic and TTL/CMOS type circuits, there is little I can do for you here. I'd have to plead being rusty, but there was a time that was my main area, but it is like riding a bicycle. But hard to teach from scratch in a few posts. Any of the larger ICs are identified and are easy to look up. The row of rectangles across the top on the right half are your 4164 RAM.

[doctor]

If the device works, I do not think there is a major problem.
Either the HOLD button is faulty, or HOLD jack, as the HOLD function control signal passes through HOLD jack.

[tylerpenn]

I'll record a video sample of what the issue is so it's a bit clearer for you all to determine where the possible issue may be.

The unit is generally noisy but I'm guessing some dexoit in the jacks and pots would probably clean some of that up.

The HOLD feature does work just fine sometimes but you can immediately tell when it goes wonky as the audio begins to really break up and starts decaying. I've tried using both the front panel HOLD button as well as the footswitch engaged HOLD, both with the same results. One interesting thing is that the front panel buttons generally take 5-10 pushes before they respond (MOD, HOLD and BYPASS are all impacted by this). I'm guessing that's just crud around the contacts

[The Dude]

So, a good start would be cleaning all the switches. If you think the switches are making poor contact, check them with a meter for continuity while pressing the switches.

[Enzo]

Resistance, rather than continuity. Or watch them on a scope while it runs.

[The Dude]

I guess so. By continuity, I meant that there shouldn't be resistance if the switch is working properly- it should be a dead short. So yes, there might be some resistance there, if not. Point taken.

[Enzo]

Not quibbling about the idea, but lately I see more and more guys using the "continuity" test on their meter instead of resistance.