Vintage Synth Repair

Hi everybody,

I'm looking for a UPD8021 microcontroller chip for a Sequential Circuit Pro One synthesizer. 
Does anybody knows a source or a replacement for this chip?
Thank you!

Nicolas

http://cpluselectronics.com/u__UPD8021C048.html

Unsure if this *really* means that they can source though
________________________________

From: Nicolas<mailto:nico678@...>
Sent: ‎15/‎08/‎2013 18:31
To: vintagesynthrepair@yahoogroups.com<mailto:vintagesynthrepair@yahoogroups.com>
Subject: [vintagesynthrepair] Sequential Circuit Pro One  UPD8021 chip

Hi everybody,

I'm looking for a UPD8021 microcontroller chip for a Sequential Circuit Pro One synthesizer.
Does anybody knows a source or a replacement for this chip?
Thank you!

Nicolas

There's an eBay seller (based in California I think) that has two different 8021 replacements specifically for the Pro-One. One replaces the original functions and the other adds MIDI capability as well as the original functions.  Also, if I remember correctly, these replacements expand the number of sequencer steps available by quite a bit.  There are none currently listed but they pop up every few weeks.  They're little PCB assemblies using modern components that plug into the original 8021 socket.  The MIDI version also comes with a midi interface PCB assembly and requires some modification to the Pro-One housing to accommodate the MIDI connector and to mount the interface PCB.  Working from memory, I think the costs are about US $129 and $189 respectively but don't quote me.  I've been thinking about getting the MIDI version as I have a Pro-One main board without keyboard or housing but populated with all of the custom VCO-VCF-VCA chips but Ive
 had other priorities.  I have a saved eBay search that these guys show up in every now and then so I'll post the link the next time this guy lists either one.
 
There may be an problem if you get an original 8021. I have been told (but have not confirmed) that you need the program mask in order to instruct the 8021 what to do in order to make it work with the Pro-One.  Without that, it's just a black rectangle with silver legs.  I read someplace, years ago, that this same IC was used in a number of original Apple MacIntosh keyboards. 
 
Perhaps someone with more knowledge can either confirm or refute my program mask statement.
 
            James

From: Nicolas <nico678@...>
To: vintagesynthrepair@yahoogroups.com 
Sent: Thursday, August 15, 2013 10:31 AM
Subject: [vintagesynthrepair] Sequential Circuit Pro One UPD8021 chip

  
Hi everybody,

I'm looking for a UPD8021 microcontroller chip for a Sequential Circuit Pro One synthesizer. 
Does anybody knows a source or a replacement for this chip?
Thank you!

Nicolas

The seller is on vacation, but more info here: www.musictechnologiesgroup.com 

GB

Hi,

I sent him a message and I think it's the same guy. He's on vacation too. 
The price is 120$ + shipping which seems a little bit high to me.

I'd like to find the original chip if it's still possible.
The number written on the chip is D8021C and it was made by NEC.

Thank you!

Nicolas



--- In vintagesynthrepair@yahoogroups.com, "grantpbt" <grantbt@...> wrote:

>
> The seller is on vacation, but more info here: www.musictechnologiesgroup.com 
> 
> GB
>

I received the P8021 chip that I ordered from www.musictechnologiesgroup.com  for the Sequential Pro One synthesizer and that seems to work. 
The only small problem that I have is that the arpegiator stays ON most of the time. Sometime, when I turn OFF and ON the power, the arpegiator turns OFF and the synth behave normally.
I cleaned and checked the arpegiator switch but that's seems to be fine.
Anybody has seen this problem before?
Thank you!

Nicolas

--- In vintagesynthrepair@yahoogroups.com, Philip <eggwheatis@...> wrote:

>
> The original chip is custom programmed during manufacture. You'd have to find one that had actually been pulled working from a Pro-One..
> 
> Basically impossible to find..that's why this guy developed a replacement and whilst doing it added new features.
> 
> 
> ________________________________
>  From: Nicolas <nico678@...>
> To: vintagesynthrepair@yahoogroups.com 
> Sent: Friday, 16 August 2013, 21:20
> Subject: [vintagesynthrepair] Re: Sequential Circuit Pro One  UPD8021 chip
>  
> 
> 
> Â  
> 
> 
> Hi,
> 
> I sent him a message and I think it's the same guy. He's on vacation too. 
> The price is 120$ + shipping which seems a little bit high to me.
> 
> I'd like to find the original chip if it's still possible.
> The number written on the chip is D8021C and it was made by NEC.
> 
> Thank you!
> 
> Nicolas
> 
> --- In vintagesynthrepair@yahoogroups.com, "grantpbt" <grantbt@> wrote:
> >
> > The seller is on vacation, but more info here: www.musictechnologiesgroup.com 
> > 
> > GB
> >
>

Typically sounds like the capacitor used to init the chip has drifted. My guess is the INIT pin is not maintained at low-level long enough.

Hi,

Thank you for replying.
I think I found the problem. There was some key contacts that were touching the casing and it was triggering the arpegiator for some reason.
I fixed that and now the Pro One is back to normal again.

Nicolas

Hi,

Thank you for replying.
I think I found the problem. There was some key contacts that were touching the casing and it was triggering the arpegiator for some reason.
I fixed that and now the Pro One is back to normal again.

Nicolas

Hi,

Thank you for replying.
I think I found the problem. There was some key contacts that were touching the casing and it was triggering the arpegiator for some reason.
I fixed that and now the Pro One is back to normal again.

Nicolas