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 Forum index » Instruments and Equipment » General Discussion
OSCar synth - schematics + service manual + prom?
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elektro80
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PostPosted: Sat Nov 03, 2007 7:06 pm    Post subject: OSCar synth - schematics + service manual + prom? Reply with quote  Mark this post and the followings unread

Seems like I have an old OSCar synth incoming. The prom is supposedly dead and the whole thing needs some work. The synth has most likely been in storage for at least some 20 years.

Anyone? Tips, schematics and docs? Are there some out there who can shoot a prom with the right code for the OSCar?

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elektro80
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PostPosted: Sat Nov 03, 2007 7:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.
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Nosferatu



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PostPosted: Sat Nov 03, 2007 8:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ddepends on which version of the Oscar you have.
Supposedly dead! Well is it dead or not? It cant be half dead Laughing
If the board gets quite warm its not dead, reseat every chip in their sockets
to start with, check all clocks, its just Z80 the whole hoopla, very easy.
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elektro80
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PostPosted: Sun Nov 04, 2007 6:28 am    Post subject: Reply with quote  Mark this post and the followings unread

I don´t have it yet. We´ll see.
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mono-poly



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PostPosted: Sun Nov 04, 2007 8:49 am    Post subject: Reply with quote  Mark this post and the followings unread

The build quality of the oscar is very very poor.
Main problems are the bad connectors and sockets.
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Peake



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PostPosted: Sun Nov 04, 2007 3:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Check the AH archives at retrosynth.com. I'm pretty sure that it was there or Keyboard Mag US that a hint about easily fixing some OSCar problems came up. Let me rack my memory...Something about the battery or MIDI upgrade? I may be off on this one, but still send my regards for a great synth. Have fun!
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Synthtech



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PostPosted: Fri Nov 23, 2007 9:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Oscars weren't so well built, I used to do warranty repairs on them when they were new. Main issues are:

MIDI piggyback board sits too high above the mother board, making the top of the case bulge up on the RHS of the machine. This leads to cracking of the solder joints and tracks around the chip sockets connecting the 2 boards together. I usually replace the sockets and solder strips of new gold plated posts to the underside of the MIDI board at the correct length.

Interconnect pins between the pot board and the mother board corrode and crack.

Machine needs to be turned on each month to re-charge the battery. If the battery goes flat then much like a PPG the wavetables are lost and must be re-loaded, otherwise no amount of knob twiddling will give you a sound.

Tape loading of data is very level dependent, and the load procedure is not intuitive.

Useful trick: after re-assembling the unit with a good battery in place, the machine usually needs to be turned on and off several times to get it to boot OK, you can tell that it has properly booted because one (usually the center) of the row of LED's on the left of the machine will blink slowly.

I never saw a proper service manual for the Oscar, the only service data I ever had supplied to me was is a large sheet with a hand drawn schematic on it.
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EdisonRex
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PostPosted: Fri Nov 23, 2007 12:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

hey, welcome to the forums, Synthtech!
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Synthtech



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PostPosted: Fri Nov 23, 2007 3:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

EdisonRex wrote:
hey, welcome to the forums, Synthtech!


Thank you, I found the forum by chance, it has been very interesting to read some of the topics here. I mostly work only on vintage gear, I still see quite a few Oscars. Once the common problems are fixed they actually are pretty reliable as long as the batteries are changed every few years to prevent leaks. I had a Prophet 10 in this week and the battery had made a real mess of the processor board.
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elektro80
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PostPosted: Fri Nov 23, 2007 4:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey, thx for the advice. Most excellent! Very Happy [/i]
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Synthtech



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PostPosted: Fri Nov 23, 2007 5:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

once you get the machine let me know and I will help out if you need it.
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elektro80
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PostPosted: Sat Nov 24, 2007 8:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

I will! THX for the help so far! I think I´ll have it in next week or so. Right now I´m a bit rattled re an MCI JH-600.
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PostPosted: Sun Nov 25, 2007 12:44 am    Post subject: Reply with quote  Mark this post and the followings unread

elektro80 wrote:
I´m a bit rattled re an MCI JH-600.

it could nicely sit next to the Petrof Cool

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PostPosted: Sun Nov 25, 2007 7:17 am    Post subject: Reply with quote  Mark this post and the followings unread

mono-poly wrote:
The build quality of the oscar is very very poor.
Main problems are the bad connectors and sockets.

That's why I have the ImpOscar! All the sound without the hassle. Laughing
Seriously though.....congrats on securing one even in it's present state. I don't know much about the repair but I'm sure we'll all knock out heads together and figure it out. Wink

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Synthtech



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PostPosted: Wed Nov 28, 2007 2:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't generally supply copies of schematics except to other service techs that I know well, but if you have problems with your OscAR I will be happy to direct you around the circuit until you find any faults. The OscAR schematics are too big for my scanner anyway.
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Regebro



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PostPosted: Thu Mar 30, 2017 12:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Machine needs to be turned on each month to re-charge the battery. If the battery goes flat then much like a PPG the wavetables are lost and must be re-loaded, otherwise no amount of knob twiddling will give you a sound.


I have one incoming soonish, and this has definitely happened (there may be more things wrong, the lights behave strangely).

How to I reload the wavetables? It seems I can dump them with sysex? Where can I find a sysex dump, in that case?
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Regebro



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PostPosted: Sat Apr 22, 2017 5:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Found sysex dumps, will try, but the machine is not booting, at the minimum this is because of a bad battery. Will attempt repair but not this month.
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