Oberheim OB-8 restoration

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Iain McNeill

Iain McNeill

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Joined 2007
impaudio.biz
#1
Hi,
I'm restoring an OB-8 and was lucky enough to actually meet Tom Oberheim yesterday at the AES convention. He graciously spent some time helping me with debugging a bad voice and his 1st recommendation was to replace the EPROMs.

I've done some searches but can't find any programed parts. Does anyone know of anyone selling replacement programmed EPROMS for OB-8 synths?

Alternatively, is there anyone out there with a working OB-8 who would allow me to clone the EPROMS? In return I'll give you a back up set!😎

Any links would also be gratefully accepted!
 
#4
Well, I'm still trying to find a source for rev B5 EPROMS for this OB-8. Drawing a blank on all fronts.

Does anyone know if I could substitute a previous rev EPROM? Or would that mean giving up the add-on MIDI board?

Neither Archive Sound or Synth Fool were able to help.
Thanks in advance.
 
#5
I would try cleaning the sockets and pins on everything before replacing UV or EE or Flash Proms of any variety. Unless they have been subjected to massive ESD or EMP they almost never go bad.

Also If you have Eproms and a programer and they are just flaky you could try copying them yourself and if you lack the tools let me know I have them.




Iain McNeill said:
Hi,
I'm restoring an OB-8 and was lucky enough to actually meet Tom Oberheim yesterday at the AES convention. He graciously spent some time helping me with debugging a bad voice and his 1st recommendation was to replace the EPROMs.

I've done some searches but can't find any programed parts. Does anyone know of anyone selling replacement programmed EPROMS for OB-8 synths?

Alternatively, is there anyone out there with a working OB-8 who would allow me to clone the EPROMS? In return I'll give you a back up set!😎

Any links would also be gratefully accepted!
Click to expand...
 
#6
Hi Iain,
I sometimes look over different recent posts on diyaudio and once in a while, there's one that catches my attention. I am not a synth player, but having listened to many Van Halen songs and read his interviews, I can guarantee you that he must still have his lying around! I have no idea how to contact him though..

OK SERIOUSLY, I might have a link for you. I decided to check on ebay, I know I know, you must have tried this. In the case that you have not, or possibly overlooked this, check out: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=170290424178
The guy is selling the OB8 without Eproms and curtis chips (I have no idea what those are) but he also is keeping them. So, in other words he has them! Maybe you should ask him a question, if he could copy the Eprom chips for you.

Just my two cents.
 
#7
If the seller had the capability to reproduce those eproms he would be selling the ob8 with them. It could also be that some technician in the late 80s early 90s robbed them out of the device becuase eprom programmer were not very cheap 20 yrs ago.

Either way if someone can find the files and the eprom type I assume most like its is a 2 4 or 8kb hex,Srecord,binary file I can load those up on the some eproms for a few $$$ to cover the costs of the chips+shipping. I sell a number of chips to friends for $5-10 each depends on the chip.

Still i would try cleaning the sockets.


gain-wire said:
Hi Iain,
I sometimes look over different recent posts on diyaudio and once in a while, there's one that catches my attention. I am not a synth player, but having listened to many Van Halen songs and read his interviews, I can guarantee you that he must still have his lying around! I have no idea how to contact him though..

OK SERIOUSLY, I might have a link for you. I decided to check on ebay, I know I know, you must have tried this. In the case that you have not, or possibly overlooked this, check out: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=170290424178
The guy is selling the OB8 without Eproms and curtis chips (I have no idea what those are) but he also is keeping them. So, in other words he has them! Maybe you should ask him a question, if he could copy the Eprom chips for you.

Just my two cents.
Click to expand...
 
#9
gain-wire said:
But how do you clean sockets?
Click to expand...

I think it's more cleaning the pins of the chip (a pencil eraser is good). If the socket has oxidized and re-seating the chip doesn't cut through then its new socket time.

You're right, they're good old D2732A's but I think the problem is getting the musician with the OB8 together with the computer guy with the EPROM reader. Still working on that.

Does anyone have experience working with 25yr old EPROMS and how they keep their data? I've heard rumours that background radiation can flip bits and so over time the image gets more and more corrupt. How many Linn drums are there still out there working??

Thanks for you help, I haven't given up yet.
 
#10
I reprogram Automotive engine control modules as an occupation. Somtimes I refer to it as insanity for money but nontheless it keep clothes on my back and a roof over my head.

d2732a eproms are easy to come by. How many do you need ? I have hundreds of New ones I got at a Ford Engineering auction some years ago.

as for stability pretty much you would have to seriously ESD those devices I am talking enough milliamps/volts to knock you unconcious and or a nuclear explosion sized EMP event.

I would try some CRC contact cleaner and make sure the Eproms fit snugly in the sockets. You can do this by bending the legs out just a touch so that you have to nest the chips in one side at a time.

If you have Eproms you want copied ship them to me $10 a chip and I send back your originals.

I would be highly dubious of a EPROM failure unless it was left out in direct sunlight for weeks with no UV window block.

Iain McNeill said:


I think it's more cleaning the pins of the chip (a pencil eraser is good). If the socket has oxidized and re-seating the chip doesn't cut through then its new socket time.

You're right, they're good old D2732A's but I think the problem is getting the musician with the OB8 together with the computer guy with the EPROM reader. Still working on that.

Does anyone have experience working with 25yr old EPROMS and how they keep their data? I've heard rumours that background radiation can flip bits and so over time the image gets more and more corrupt. How many Linn drums are there still out there working??

Thanks for you help, I haven't given up yet.
Click to expand...
 
#13
Thanks for your kind offer Kramerguy. Actually, programming the EPROMs is not my problem, been doing that myslef for decades since the old D8051 EPROMs😉

No, as I mentioned, I'm following Tom Oberheims advice. He said the first thing I should do is replace the EPROMs which led me to believe that the data image was corrupt and therefore copying to a new part wouldn't help.

Actually, I think I agree with you. This OB8 has been lovingly stored in a constant temp/humidity home. The EPROMs all have labels and were inside the metal case. As you say it would need a nuclear detonation in the neighborhood to irradiate these bad boys.

Personally, I think I have a demux problem. I have 6 good voices that work fine and two that won't calibrate. If I move the VCO and VCA chips (the curtis chips) the problem stays with the voice. Replacing all the CMOS didn't help. I need to spend more time debugging.

Sonus3, my DAC's fine but thanks for the link. That wouldn't be you selling the HS3140 would it? I notice the seller is in Sussex and as I grew up in Brighton I know where Sussex is😀
BTW, my DAC is a MP7614. Probably pin compatible but I'd have to break out my old databooks.

Thanks all and glad to see that there is some interest in this classic synth. I'll let y'all know how I get on.
😎
 
#14
Got the schematics ?


Iain McNeill said:
Thanks for your kind offer Kramerguy. Actually, programming the EPROMs is not my problem, been doing that myslef for decades since the old D8051 EPROMs😉

No, as I mentioned, I'm following Tom Oberheims advice. He said the first thing I should do is replace the EPROMs which led me to believe that the data image was corrupt and therefore copying to a new part wouldn't help.

Actually, I think I agree with you. This OB8 has been lovingly stored in a constant temp/humidity home. The EPROMs all have labels and were inside the metal case. As you say it would need a nuclear detonation in the neighborhood to irradiate these bad boys.

Personally, I think I have a demux problem. I have 6 good voices that work fine and two that won't calibrate. If I move the VCO and VCA chips (the curtis chips) the problem stays with the voice. Replacing all the CMOS didn't help. I need to spend more time debugging.

Sonus3, my DAC's fine but thanks for the link. That wouldn't be you selling the HS3140 would it? I notice the seller is in Sussex and as I grew up in Brighton I know where Sussex is😀
BTW, my DAC is a MP7614. Probably pin compatible but I'd have to break out my old databooks.

Thanks all and glad to see that there is some interest in this classic synth. I'll let y'all know how I get on.
😎
Click to expand...
 
#15
Iain McNeill said:

Sonus3, my DAC's fine but thanks for the link. That wouldn't be you selling the HS3140 would it? I notice the seller is in Sussex and as I grew up in Brighton I know where Sussex is😀
BTW, my DAC is a MP7614. Probably pin compatible but I'd have to break out my old databooks.
Click to expand...

Yep, looks like the seller is near me but I have no affilliation with them. I just included it as an interesting link for the only thread on this forum relating to the Oberheim.

Apart form the price :bigeyes:, I found this statemant hard to believe: 'APPARENTLY THIS IS THE ONLY ONE AVAILABLE ON THE PLANET !!! YES !!!!'

That's all. 🙂
 
#17
this should help you:

There are 6 polystyrene capacitors (ITW brand 223k/.022 uf) on the left side of the voice board that are responsible for grounding each voice. Caps #10 and 11 will be responsible for all voices filter cv(which if faulty will cause the entire voice board to sound messed up), and caps 12, 13, 14, 15 (off the top of my head) are responsible for each seperate voice's cv. If you want to check if they are causing the problem (which is most likely) then unsolder two of them and swap their spots and see if the problem voice goes to another voice.

After much experimentation i've narrowed down this voice issue on the OB8 to be these polystyrene caps. The problem with the OB8 is that it is very picky what caps go in there, so make sure they are polystyrene. Polyester will work but will need about half hour of warming up before the OB8 will sound as it should.

Be careful soldering polystyrene caps because they are very sensitive to heat.

Try getting them here:
http://www.electronicsurplus.com/commerce/catalog/product.jsp?product_id=90691&czuid=1254445194525
 
#19
Help! I'm also restoring an Oberheim OB-8 I came across. It's a late one, B5 with MIDI. I replaced the supply lytics and battery, trying to get through the cal procedure.

In calibrating the DAC, I can set the zero volt setting, but the 10V setting won't go above about 9.6. Looking at the DAC, when attempting the 10V setting, the 4 most significant bit inputs are high, the rest low. Anybody know if that's normal? Is that why I can't get to 10?

Also, when first turned on, it makes some nasty noises, and quiets down after a while. I was hoping it was the supply lytics, but that didn't help. I haven't tried scoping around yet, figured I'd calibrate it first.

Thanks in advance!

Marty
 
#20
Ian,
I hope you have restored your Oberheim. I am trying to help my son with his 2 Voice. I was wondering if you by any chance have schematic? Even for 8 voice might work to the some point. I tried link you posted but they do not have any more OB schematics posted.

Thanks

AR2
 
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