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 Forum index » Instruments and Equipment » General Discussion
OSC OSCar synth not starting
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wahee



Joined: Jan 27, 2019
Posts: 6
Location: Belfast

PostPosted: Sun Jan 27, 2019 2:58 pm    Post subject: OSC OSCar synth not starting Reply with quote  Mark this post and the followings unread

My rather nice OSCar synth started to make some strange noises whilst on and then died.

I just get all the octave LED's lit up but most times nothing.

If I use the keyboard every 8 note makes an octave LED light up and the space button will light a LED also.
No sound

So I have:
checked the +5/-5v power rails. All good
checked battery voltage OK at 3.4v
checked the keyboard and power ribbon cables for continuity, all OK
Rewired the control board and voice board interconnects with new quality connectors
checked the continuity of sockets with the piggy back MIDI board, all OK
checked practically all the 40 and 74 logic IC's with a tester.
Swapped out the 6116 RAM x2 for known good, no change.
checked the clock on the ADC and there is a square wave present on the scope, so seems OK

but I still have no luck


I have checked the Z80 with a scope and it seems lifeless,so swapped it for a known good. But again no luck.

I suspect the reset circuit. Should I see something on the output of this circuit when the synth is first powered up?

is there anything else I can try as this synth seems relatively simple but has thrown me.

Embarassed
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Regebro



Joined: Sep 12, 2004
Posts: 61

PostPosted: Thu Jan 16, 2020 4:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Late answer, but that's exactly how they behave when the battery is dead.
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Regebro



Joined: Sep 12, 2004
Posts: 61

PostPosted: Fri Jan 24, 2020 5:39 am    Post subject: Reply with quote  Mark this post and the followings unread

To be clear, they behave like this even AFTER the battery has been recharged/reset. Booting multiple times usually gets by pure luck, to a place where LEDs blink. The fastest thing to do then is to load a memory dump over MIDI.

You can also press the "Panel" button, and then twist every single knob. This usually gets things into a more reasonable mode. Then save the current settings to every single memory.

Reboot, and you should be in business. Smile

However, I read a few days ago, that if it continues to not boot properly, then yes i can be the reset circuit, and the solution is apparently to pull extra power lines directly, which seems like a hack...
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citygas



Joined: Feb 10, 2020
Posts: 3
Location: irland du nord noir

PostPosted: Sat Apr 04, 2020 4:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

Long time gone..
Any joy?

I just fixed my deloren synth..hope your one is going again, so bad yet so good design
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Regebro



Joined: Sep 12, 2004
Posts: 61

PostPosted: Mon Oct 05, 2020 4:04 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm just gonna spam for a new email list that was started for OSCar owners.

https://www.freelists.org/list/oscar-synth-owners

Come and help look for button replacements and other issues. Smile
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Regebro



Joined: Sep 12, 2004
Posts: 61

PostPosted: Mon Oct 12, 2020 5:28 am    Post subject: Re: OSC OSCar synth not starting Reply with quote  Mark this post and the followings unread

wahee wrote:
I suspect the reset circuit. Should I see something on the output of this circuit when the synth is first powered up?


As a headsup, Bob Grieb has made a new daughterboard for the OSCar, so that he could put in larger ROM's, to add features like CC control etc. I got a copy to beta test recently, and realized that he has incorporated a little IC called MCP100-460DI/TO or MCP100-475DI/TO

https://www.digikey.com/en/products/detail/MCP100-475DI%2fTO/MCP100-475DI%2fTO-ND/275213?itemSeq=341347278

That's simply a little IC that holds the reset low until the power has stabilized. I don't know how to integrate it in the standard OSCar circuit boards, but in the new one, as far as I can tell, you can bypass the normal reset circuitry and use this one instead.

This could solve your startup problems.
His software changes also include detection of memory loss, so that you no longer have to switch on and off the OSCar after memory loss hoping that it randomly will boot.

More info here: http://tauntek.com/OSCar.htm

Also, we are discussing this on the mailing list above.
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