Ensoniq EPS system disk needed.

Discussions about anything related to samplers and sampling techniques.
Post Reply
gkmaia
Newbie
Newbie
Posts: 42
Joined: Wed Dec 05, 2018 9:02 am

Ensoniq EPS system disk needed.

Post by gkmaia » Tue Feb 04, 2020 9:24 am

I just finally managed to fix my EPS after months onto it. Ended up replacing some faulty RAM ICs and a faulty disk drive.

I managed to get it going with a Gotek-HxC but still curious to see if there is a way to save the original drive.

To do that I will need a 100% proven working OS disk.

Any good soul out there keen to save and sell a system 2.49 disk and ship it over to oregon?

cascadian
Newbie
Newbie
Posts: 3
Joined: Sun Feb 16, 2020 3:55 am

Re: Ensoniq EPS system disk needed.

Post by cascadian » Sun Feb 16, 2020 4:05 am

Hey, based in the EU and currently rehabilitating an EPS from an estate sale that lay in storage for some time here. I've got an extra disk, but due to location might that not be so convenient. There is an eBay seller based in the UK whose disks work for me, if that's of any help.

Also curious to ask, this EPS has an issue where the samples randomly drop out of RAM after a short time. Suspecting the ICs are going, and curious where you found working replacements?

Rasputin
Senior Member
Senior Member
Posts: 791
Joined: Thu Jul 21, 2016 4:52 am

Re: Ensoniq EPS system disk needed.

Post by Rasputin » Wed Feb 19, 2020 8:30 pm

cascadian wrote:
Sun Feb 16, 2020 4:05 am
Also curious to ask, this EPS has an issue where the samples randomly drop out of RAM after a short time. Suspecting the ICs are going, and curious where you found working replacements?
All of the sample data drops out of RAM at once? Or just parts of samples? Do you have a memory expander or just the stock amount of RAM?

gkmaia
Newbie
Newbie
Posts: 42
Joined: Wed Dec 05, 2018 9:02 am

Re: Ensoniq EPS system disk needed.

Post by gkmaia » Wed Feb 19, 2020 9:32 pm

cascadian wrote:
Sun Feb 16, 2020 4:05 am
Hey, based in the EU and currently rehabilitating an EPS from an estate sale that lay in storage for some time here. I've got an extra disk, but due to location might that not be so convenient. There is an eBay seller based in the UK whose disks work for me, if that's of any help.

Also curious to ask, this EPS has an issue where the samples randomly drop out of RAM after a short time. Suspecting the ICs are going, and curious where you found working replacements?
I got them all from Aliexpress. If you do get some select Ali express standard shipping. Arrive in a couple weeks. If you select those cheap ones it will take months.

cascadian
Newbie
Newbie
Posts: 3
Joined: Sun Feb 16, 2020 3:55 am

Re: Ensoniq EPS system disk needed.

Post by cascadian » Fri Feb 21, 2020 5:36 pm

Rasputin wrote:
Wed Feb 19, 2020 8:30 pm
All of the sample data drops out of RAM at once? Or just parts of samples? Do you have a memory expander or just the stock amount of RAM?
It's as if the sample RAM is reset, all sounds reduced at once to a faint click, eventually followed by total silence. I do have a PS Systems 4X Memory Expander, unfortunately uninstalling it did not resolve the issue.

edit Also considering that the PSU output to the main board could be the culprit, although there are no other issues there. Tried resetting ribbon cables to no avail, will investigate further with a multimeter. Can you think of any other possibilities that I might have missed?
Last edited by cascadian on Fri Feb 21, 2020 7:33 pm, edited 1 time in total.

cascadian
Newbie
Newbie
Posts: 3
Joined: Sun Feb 16, 2020 3:55 am

Re: Ensoniq EPS system disk needed.

Post by cascadian » Fri Feb 21, 2020 5:45 pm

gkmaia wrote:
Wed Feb 19, 2020 9:32 pm
I got them all from Aliexpress. If you do get some select Ali express standard shipping. Arrive in a couple weeks. If you select those cheap ones it will take months.
The recommendation is appreciated :mrgreen:
Any luck finding a system disk?

edit Is there a chance you have the part ID number for the RAM ICs, by the way? For whatever reason the readily circulated version of the EPS service manual in my possession is lacking in schematics and a comprehensive parts list.

gkmaia
Newbie
Newbie
Posts: 42
Joined: Wed Dec 05, 2018 9:02 am

Re: Ensoniq EPS system disk needed.

Post by gkmaia » Fri Feb 21, 2020 7:39 pm

I would not blame the PSU. Basically because if the voltage changes to a point where it affects the RAM threshold it would affect all other TTL devices, such as CPU and CPU rom, you would experience a system crash.

one good thing you could do is to recap the PSU. That is always a good thing.

Just a note when removing the IC from the main board. The solder they use there is pretty hard to remove. I needed a good amount of low temp solder, suction station and rework station to remove those without damaging the traces.

I could find a guy selling original Floppy drives for 20$ on ebay. I got one, and then will try to make a disk with ominidisk first.

Rasputin
Senior Member
Senior Member
Posts: 791
Joined: Thu Jul 21, 2016 4:52 am

Re: Ensoniq EPS system disk needed.

Post by Rasputin » Tue Feb 25, 2020 7:19 pm

cascadian wrote:
Fri Feb 21, 2020 5:36 pm
It's as if the sample RAM is reset, all sounds reduced at once to a faint click, eventually followed by total silence. I do have a PS Systems 4X Memory Expander, unfortunately uninstalling it did not resolve the issue.
About part number:

Ensoniq service manuals do not have schematics or part numbers, so that's to be expected. In the case of the EPS, the schematics do happen to exist though. The RAM in question is 41256-type 256K dynamic RAM (DRAM), but I do not believe it is going to be worthwhile for you to acquire or replace any of the DRAM.

About EPS sample memory:

When using the 4X expander (such as you have) the EPS internal DRAM memory is allocated to the sequencer exclusively. The DRAMs within the 4X expander then become the only place where samples are stored into memory.

With the 4X expander removed, the EPS internal DRAMs are shared between sample and sequencer use.

Therefore, the fault should not persist with the expander installed and removed, if we're going with the bad DRAM hypothesis. Besides, if it was a bad DRAM or two then it would very likely manifest as pops and clicks within certain sample memory ranges rather than all sample memory being empty.

The normal EPS system RAM is static RAM, so it does not need to be updated constantly -- there is no refresh cycle. The sample/sequencer RAM is dynamic, so it has to be periodically refreshed or else the contents will be lost.

Since all the dynamic RAM contents seem to be disappearing, that points toward something like column or address strobe timing being too slow to properly keep the RAM refreshed.

I disagree on the point that it cannot be PSU related. If the PSU is performing marginally, some sub-systems could be affected even though most or all of the logic chips appear to work.

EDIT: gkmaia makes a good point though. On one hand, it seems like the +5M power supply line to the DRAMs might be an obvious culprit, yet that line is also shared by the 27256 program ROMs, so how can the EPS still function with unreliable power for the critical EPROMs?

On the other hand, the EPROMs and 74LS logic which share the +5M line with the DRAM could be more fault tolerant than the DRAM, and that the DRAM is just slightly more sensitive. The +5M line could be close enough to spec that mostly everything works, but also out-of-spec just enough that the DRAM occasionally fails and loses all its contents.

Totally guesswork, but I think it's worth measuring PSU J4 pins 7+8 for ripple and VDC*

*Represented in the EPS service manual as terminals "13" and "16", if you're following along with that.
Last edited by Rasputin on Tue Feb 25, 2020 10:21 pm, edited 2 times in total.

gkmaia
Newbie
Newbie
Posts: 42
Joined: Wed Dec 05, 2018 9:02 am

Re: Ensoniq EPS system disk needed.

Post by gkmaia » Tue Feb 25, 2020 8:33 pm

I agree with Raputin. His approach makes more sense.

Post Reply