vintage digital necromancy

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vintage digital necromancy

Postby no-fi » Sun May 11, 2008 3:06 pm

so.. I have this habit of acquiring "stray" gear that needs work, and slowly working on it, as a way of getting fun gear I couldn't normally afford.

In this case, I got an SP-12 turbo that wasn't powering up.... but on inspection, the main logic regulator had lost its feedback reference and been dumping 10-12V across the whole digital section minus the RAM chips. (as a side note, wiring a 3-terminal regulator off-board and just soldering stripped wire into the PCB has to be the most thoughtless and stupid power supply design I have ever seen in a piece of electronics - worse even than dave smith's 5V linear regulator brainfart he had with the prophet 5)

so - looks like I got me a nice longterm project.

Right now, I have the service manual from emulatorarchive, and i have all the EEPROM and PAL images.

what would be really handy right now, would be the SP-12 diagnostic EEPROM image... I really like the idea of just going in and replacing the core digital section of the unit, then having it tell me what else is wrong.

So, does anyone know where I might get a diagnostic EEPROM image (or even a diagnostic EEPROM?) free is always nice, but happy to pay someone money for their troubles if it's any hassle for them, too...


pretty please?
:wink:
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Postby Thirteen » Sun May 11, 2008 10:46 pm

I was one of the 2 E-mu warranty techs in Oz back then, and we never saw any diagnostic PROMS for any of their gear. Come to think of it I was also a Warranty guy for Sequential, and they never supplied any either. I have started to think that diagnostic PROMS were a cruel American joke designed to make tech's feel a sense of longing. If there are any 4000 series chips in that circuit they may have survived, but any 74xx chips will be brown bread. If you need any parts let me know and I will see what I can dig up.
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Postby no-fi » Tue May 13, 2008 1:14 am

damn... so the diagnostic eeprom is only a fairy tale??
:-(

well in that case, I guess I'm up for replacing everything in one go.
At least all the ICs are socketed....

no 4000 series stuff. 74HCT mostly, and a few other 74 types (74C, 74HC, 74S, 74LS) for good measure... all of them apart from the C, from what I can tell, aren't specified as tolerant of more than 7V on VCC...

the only parts that seem particularly hard to find are the PALs (it has a 12L6 and a 12H6) and maybe the Z80A SIO/2 is going to be a special order somewhere... I haven't looked into how to program PALs yet, either. should probably sort that out before I go any further.
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Postby Thirteen » Tue May 13, 2008 1:32 am

Try Wes/Wagner at Ashfield, they are cheaper than Farnell and RS. If you get really stuck let me know.
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Postby no-fi » Tue May 13, 2008 10:11 am

thankyou!
:-)

I think I can get almost everything from futurlec, bar a few of the rarer HCT parts, the z80 SIO/2, and the PALs.
http://futurlec.com.au/
they ship out of thailand, but it only takes about a week. And much better prices than farnell/rs.

I've never tried WES before, because I never found prices on their website.... but I'll give them a go for some of the tricky bits, and see what they can do.

I read somewhere else last night that the Forat guy in the USA can supply the PALs already programmed up, so maybe that's the way to go for them? just emailed him. That would save me having to find a way of programming them, too.
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Postby no-fi » Fri May 16, 2008 11:42 am

woooo!!!
it lives!!!

I'd already replaced the regulator, and a chip that I noticed had burned, but still had no love...

well, ed and I were looking at it last night, and ed noticed another obviously burned IC I hadn't.... I had some HCT logic here that I'd bought for it "just in case" when I ordered the new regulator and the first burned IC, and luckily enough, the part that needed replacing was in that pile....

so, I replaced the chip, powered up the drum machine, and it lived! but with really funnyl glitchy digital noise for drum sounds, and sequences that crashed the machine. I went and found the RAM init function in the manual, and boom - one working SP-12 turbo!

actually, I kinda wish I'd sampled some of the glitchy noises before I initialised the machine.

I guess the dead chips (one was getting really hot when I first got it and powered it up to see what was wrong) were pulling enough current to drop the voltage down enough that the other chips were protected???
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Postby Thirteen » Fri May 16, 2008 11:55 am

Well done, it's great when you manage to pull something like that off. You may be right, one chip may have gone short circuit fast enough to pull the PSU down before it trashed everything. If all the IC's are socketed it may be a good idea to replace any that are cheap and easy to get anyway, in case they were damaged slightly so that the machine will stay reliable. Nothing worse than some chip having a thrombo in the middle of a session.

Maybe I should get to my "digital stuff that I own that isn't working that I just couldn't be bothered fixing" shelf. I spend so much time fixing everyone else's gear that I kind of leave my own stuff to fade away sometimes... 2 Emulator II's, Lexicon Prime Time, Sony DRE2000, AMS delay. Every year I think that I will get around to them, but it never seems to happen, can I send them over to you? ;-).
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Postby no-fi » Fri May 16, 2008 12:27 pm

I know what you mean about working on your own stuff. I'm an engineer, and I design electronics for a living (mostly boring data logging & telemetry, but I did work for lake for a while) the last thing I usually want to do when I get home, is more electrionics. With my time, I'd much rather be bashing pads on my SP-12 than poking about in it.

BUT JUST THINK HOW AWESOME WOULD IT BE TO HAVE TWO EII'S TO PLAY WITH?!??!?!?!

"Physician, Heal thyself"!!!
:-P


I think that "maximum stress" rating is a design issue thing - they put it in the datasheet saying they guarantee 100% of chips exposed to it will survive... but maybe 99% of chips are good to 10V, and some survive even more? But yeah you're right. I am a bit worried of damaged gates and future IC death here. Also, I still really have no idea about the PALS (it turns out I don't have both PAL files) and I wonder if it's worth me doing something with the ones I have, while I have them? no email back from mr forat yet.

I've done a bit of reading up on PALS, and they seem pretty simple, just mostly unavailable, and not easy to get programmers for. I have experience with PLDs, and these 2 are just logic - they have no registers, and so I could conceivably just make a microcontroller program to tickle them with all 2^12 (4096) input combinations and read the 6 bit output for each and send it to a PC. from there, new PAL code could be reverse engineered for a small PLD on a daughterboard (aaaaargh - the logic terms would be hell, though! would have to write a custom program to do it, i reckon...) or maybe just replaced with an EEPROM on a daughterboard? what do you think?? worth taking the effort to do now? or is there an easier way to copy PALs??
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Postby Thirteen » Fri May 16, 2008 12:51 pm

I have never programmed a PAL, but I would like to be able to copy them, as so many machines that I work on have lots of them, such as E-mu, PPG and Synclaviers. Rohan Mansell would probably know a lot about these, he is the Publison guru among other things, I will give him a call.
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Postby no-fi » Fri May 16, 2008 1:22 pm

Yeah - if you could find out what someone who knows about PALs thinks, that would be really cool.

This drama has got me really thinking about the future of old digital machines I love - analogue gear seems pretty well covered for replaceability (well, until there are no more CEMs and SEMs anywhere) but obscure special-purpose digital parts could very well be the Achilles heel for a bunch of things if there's no way to remake them in the future. I don't even know if things like PALs even have a working lifetime?
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Postby Futureman » Sat May 17, 2008 10:13 pm

Hey Julian.. I was working on getting my Drumulator 100% and remembered how much the trigger buttons (The big black ones) bounce & double trigger.

Has anyone out there cleaned these / opened them up / flushed em out etc..

(I'm assuming these are the same as the SP-12.. or is the SP-12 velocity sensitive etc? / Rubber etc)

These are pretty much the same buttons in my Linndrum, Oberheim DMX , Drumtraks etc..

Cheers

Mike
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Postby no-fi » Sun May 18, 2008 3:55 pm

all buttons on mine seem mostly OK. there's a need to press some one the number and module buttons a bit solidly, but no weirdness or double triggering, so I have left the whole front panel alone..

I believe the drum buttons on the SP-12 are the same as your drumulator, but the SP12 has an additional piezo element underneath all the drum buttons, that senses how hard you hit them.

I guess I could open it up and have a look for you?

It turns out I need to replace the backup battery - SRAM, is dumping its contents and the drum machine is coming up in glitch mode when I turn it on after leaving it off for a while.....
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Postby no-fi » Tue May 20, 2008 10:10 am

Well, it seems that PALs for the SP-12 are at least available from forat, should I ever need them..... which is good to know.

It would still be nice to copy/read them into my PC for safe keeping, if it was easy to do. probably not worth doing a whole reverse engineering process on them any more, though.

did you find out anything more about PALs from your friend?
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