Vintage Synth Repair

Hi again all,

You may remember I asked about a Korg Poly 800 with damage from
a leaking battery a few weeks ago. Well, the bicarb and toothbrush
technique has cleaned it up reasonably well, but there are other
problems now.

The first is that the CPU seems to be faulty - on reset the address
and data lines, ALE and ~RD all pulse madly, but the ~WR line doesn't
do anything. After a short while, the lines go into a regular
pattern as if the CPU is in a fairly tight loop doing nothing.

The CPU is an 80C85. Is this chip still in production or does
anyone know of a surplus outlet who'll sell a one-off at reasonable
cost?

Cheers

mark-r

You can find 8085 CPUs, but some are a little bit different so try to 
stay with the same brand and model number.

Jameco has a 80C85. You can try it if you want.


mark_r_abcd a \ufffdcrit :

>
> Hi again all,
>
> You may remember I asked about a Korg Poly 800 with damage from
> a leaking battery a few weeks ago. Well, the bicarb and toothbrush
> technique has cleaned it up reasonably well, but there are other
> problems now.
>
> The first is that the CPU seems to be faulty - on reset the address
> and data lines, ALE and ~RD all pulse madly, but the ~WR line doesn't
> do anything. After a short while, the lines go into a regular
> pattern as if the CPU is in a fairly tight loop doing nothing.
>
> The CPU is an 80C85. Is this chip still in production or does
> anyone know of a surplus outlet who'll sell a one-off at reasonable
> cost?
>
> Cheers
>
> mark-r
>
>
>

> You may remember I asked about a Korg Poly 800 with damage from
> a leaking battery a few weeks ago. Well, the bicarb and toothbrush
> technique has cleaned it up reasonably well, but there are other
> problems now.

You might want to test to the continuity between the CPU and the memory
chips for all the data/address/control lines and at the same time make sure
there are no shorts to other data/address/control lines.
 
> The CPU is an 80C85. Is this chip still in production or does
> anyone know of a surplus outlet who'll sell a one-off at reasonable
> cost?

Is it in a socket?  If it's not, put it in one (well, the replacement IC).
What's the whole part number on it?  Do you have schematics? I'd
like to see them.  You might be able to find one on ebay, although
you might also have to buy something that has one on/in it.  I don't
know of anyone that has them off-the-shelf.

GB

Is the 80c85 the cmos version of the 8085? if so they should still be
around. Just a thought, if the address and data lines are changing, the CPU
could be ok and it is an outside issue.
John.

----- Original Message -----

From: "mark_r_abcd" <mark@...>
To: <vintagesynthrepair@yahoogroups.com>
Sent: Sunday, March 26, 2006 10:48 PM
Subject: [vintagesynthrepair] 80C85 CPU - still current?


>
> Hi again all,
>
> You may remember I asked about a Korg Poly 800 with damage from
> a leaking battery a few weeks ago. Well, the bicarb and toothbrush
> technique has cleaned it up reasonably well, but there are other
> problems now.
>
> The first is that the CPU seems to be faulty - on reset the address
> and data lines, ALE and ~RD all pulse madly, but the ~WR line doesn't
> do anything. After a short while, the lines go into a regular
> pattern as if the CPU is in a fairly tight loop doing nothing.
>
> The CPU is an 80C85. Is this chip still in production or does
> anyone know of a surplus outlet who'll sell a one-off at reasonable
> cost?
>
> Cheers
>
> mark-r
>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.1.385 / Virus Database: 268.3.1/292 - Release Date: 24/03/06
>
>

I think there is a great chnace you can still get it (I know these 
type of parts are still in use on some student projects etc.)


--- In vintagesynthrepair@yahoogroups.com, "John Brewer" <john@...> 
wrote:
>
> Is the 80c85 the cmos version of the 8085? if so they should still 
be
> around. Just a thought, if the address and data lines are changing, 
the CPU
> could be ok and it is an outside issue.
> John.
> 
> ----- Original Message -----
> From: "mark_r_abcd" <mark@...>
> To: <vintagesynthrepair@yahoogroups.com>
> Sent: Sunday, March 26, 2006 10:48 PM
> Subject: [vintagesynthrepair] 80C85 CPU - still current?
> 
> 
> >
> > Hi again all,
> >
> > You may remember I asked about a Korg Poly 800 with damage from
> > a leaking battery a few weeks ago. Well, the bicarb and toothbrush
> > technique has cleaned it up reasonably well, but there are other
> > problems now.
> >
> > The first is that the CPU seems to be faulty - on reset the 
address
> > and data lines, ALE and ~RD all pulse madly, but the ~WR line 
doesn't
> > do anything. After a short while, the lines go into a regular
> > pattern as if the CPU is in a fairly tight loop doing nothing.
> >
> > The CPU is an 80C85. Is this chip still in production or does
> > anyone know of a surplus outlet who'll sell a one-off at 
reasonable
> > cost?
> >
> > Cheers
> >
> > mark-r
> >
> >
> >
> >
> >
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > --
> > No virus found in this incoming message.
> > Checked by AVG Free Edition.
> > Version: 7.1.385 / Virus Database: 268.3.1/292 - Release Date: 
24/03/06

> >
> >
>

Do a search on E-Bay.  There is a mother board with a working one for 
about $15.00 plus S&H.

Also, do a google search.


Regards;

Peter

--- In vintagesynthrepair@yahoogroups.com, "GB" <grantbt@...> wrote:
>
> You might want to test to the continuity between the CPU and the 
memory
> chips for all the data/address/control lines and at the same time 
make sure
> there are no shorts to other data/address/control lines.

Hmm, good thought. There are some pull-up resistors in a SIL
package that got a fairly good covering of battery gunk. I'll
do some more prodding before condemning the CPU.

> Is it in a socket?  If it's not, put it in one (well, the 
replacement IC).

No, unfortunately. All chips except the EPROM are soldered in.

> What's the whole part number on it?  Do you have schematics? I'd
> like to see them.  You might be able to find one on ebay, although
> you might also have to buy something that has one on/in it.

I'm afraid the full part number has rubbed off with the cleaning
up operation. Schematics I downloaded from here:

http://www.oldcrows.net/~patchell/poly800/poly800.html

but the quality is very poor. If I can establish that it's worth
spending the money on, then I'll get a proper manual from
wdgreenhill.com, but these synths are 10-a-penny on ebay so I'm
not going to go overboard on it. It is a rarer reverse-keys model
though, so I may see if I can find a bargain normal one to use
as a parts donor.

> You might be able to find one on ebay, although
> you might also have to buy something that has one on/in it.

According to:

http://www.solarviews.com/eng/rover.htm

it was used in the Mars Sojourner rover, but shipping costs might
be a bit excessive :-)

Cheers

mark-r

The safest way to get a dud CPU out is to cut all the pins as close to the
CUP as possible then take the pins out one at a time by heating the pin from
the component side of the board and easing it out with the iron.  Apologies
if you already knew this. Battery residue would make a great conductor :-)
try getting at it with an old tooth brush.
John.
----- Original Message -----

From: "mark_r_abcd" <mark@...>
To: <vintagesynthrepair@yahoogroups.com>
Sent: Tuesday, March 28, 2006 4:07 PM
Subject: [vintagesynthrepair] Re: 80C85 CPU - still current?


> --- In vintagesynthrepair@yahoogroups.com, "GB" <grantbt@...> wrote:
> >
> > You might want to test to the continuity between the CPU and the
> memory
> > chips for all the data/address/control lines and at the same time
> make sure
> > there are no shorts to other data/address/control lines.
>

> According to:
> 
> http://www.solarviews.com/eng/rover.htm
> 
> it was used in the Mars Sojourner rover, but shipping costs might
> be a bit excessive :-)
> 
> Cheers
> mark-r

That's the radiation hardened version and is probably different
in other ways too.

GB

Jameco has 80C85s for sale.

GB a \ufffdcrit :

> > According to:
> >
> > http://www.solarviews.com/eng/rover.htm
> >
> > it was used in the Mars Sojourner rover, but shipping costs might
> > be a bit excessive :-)
> >
> > Cheers
> > mark-r
>
> That's the radiation hardened version and is probably different
> in other ways too.