Ensoniq EPS distorted sound

I recently picked up a near mint Ensoniq EPS classic, yet it has one issue. It outputs a varying level of distorted sound. Sometimes not that bad, but sometimes it just kicks in and sounds like raw voltage ran through an amp! I bought the service manual, checked the fuses, power supply reseated all connections and ribbon cables, removed the memory expander trying to narrow everything down as the service manual states, yet I can not find anything wrong. Every thing I checked had the correct voltage. The EPS works flawlessly, I can play any sound, sample anything, sequence, load any sound, etc., it’s just the output that is killing me! Even sampling in, it still outputs distorted sound. Even at it’s best, its almost useable, yet you can clearly hear what almost sounds like faint interference distorting every note.
If anyone has had this and has any advice I’d love to hear it! I’m pulling my hair out over here with this, as I can not for the life of me find anything wrong.

If the distortion comes and goes randomly, that is very odd. Surely it happens in a consistent way - and whatever you can do to narrow down the circumstances under which it occurs will be helpful.

Does it happen with only sounds that you are sampling, or do the factory disks that you know are clean samples distort also?

Do both outputs (Left and Right) distort and sound the same? Same in headphones as speakers?

Does the distortion occur even when the EPS Volume slider is low?

Yes it comes and goes, yet it is always present in the sound even in the slightest. I’ve tried everything the service manual mentioned, checked all voltages with a multi meter, removed the memory expander, tried to narrow it down with no results.

It happens when I use factory disks and when I sample. essentially all sound the unit outputs is oddly distorted. I checked both outputs, headphones and speaker and both are the same distorted sound. When the distortion is occurring badly, yes moving the volume fader makes no difference, but sometimes it is quiet and only distorts the sound when i play the keys, it’s very odd. The frustrating thing is other than the distorted sound, the EPS works flawlessly, and I can do anything on it, it’s maddening. I’m recording a video with my phone, I will try to upload that in a minute

Here is a video I quickly took (turn your speaker down…sorry the noise is loud)

You can see the sound comes and goes to varying degrees.

Here’s one more video, this one shows the oddness of the entire thing, as the distortion starts after a while then quiets down, yet you can hear what I was talking about on each note played, listen for the clicks and static distortion sound in each sound played

This is going to be a very difficult thing to track down. The fact that it makes the noise when a key is not being played says that it is a processor chip failing or something like that. Could be a weak solder joint somewhere also. I think you would spend a LOT of time to pinpoint the cause of this, and if you were paying a tech to do it, the cost would easily exceed the value of the EPS.

Replacing the main board should fix the problem; we don’t have that board available right now, and never know when we will get another. You might just consider buying another EPS and selling that one for parts, or even upgrading to an EPS-16 Plus (which will load all of your EPS sounds and sequences).

Thanks for the input! I was afraid of that…I’ll probably just check here and there for a main board periodically, and most likely invest in an EPS 16+. This EPS was very cheap, under $100, so if I can ever find a main board it would be worth fixing. Thanks again!

Ok, so I figured I would ask here as this thing is driving me nuts! I came across a main board that was guaranteed to be working. I swapped it out, and now the screen just says “disk not formatted”. Just by chance I switched back to the old board (that made the strange noise) and the os disk boots right up and loads sounds (albeit still with the strange noise). I put the “new” board back in and instantly “disk not formatted” stays on the screen and all the lights are light up. Any clue on what it might be? It has to be something on the new board, as swapping the old board in everything works great. I even unplugged the disk drive ribbon cable and it started it up and it still reads “disk not formatted”. It’s like it is stuck in that mode, the disk drive doesn’t even make a sound upon starting, the screen just displays that error message. Im about ready to use this thing as an anchor…

Hello Ferenc723:

Sounds like it could be a bad floppy controller chip. If the chip is socketed on both main boards i would try swappng the chips and see if you can get the new main board working. The chip is numbered WD1772.
On my EPS it is labeled U22 on the board near the MIDI out jack.
Hope this helps.

Hi Pat,

Thanks for the reply and help! Well, I did swap the chip out and it somewhat worked, it changed to “Drive not responding”. It made a slight difference, but something is still off…

Glad to hear you’ve made some progress.
There are some 14 pin chips near the floppy controller chip that interface directly with the floppy drive.
Most likely one or more of these chips have failed. On my EPS they are U16 - 7406, U17 - 7407 and U19 - 74LS04. If you’re comfortable with soldering i would start with the U17-7407 chip first.