RE: TED based motherboard

From: J Ellsworth (
Date: 2007-03-28 00:16:22

More from bil,

"Well there ya go.. Clearly a TED, the unnamed 40pin chip is something like
a 7501 cpu which is a processor with a gated r/w line to hold the line valid
through the DRAM cycle.  I added U1 myself as the design when I got to CBM
tried to use the 7406 as a level detecting reset circuit.  


The design also called for the data lines to go directly out the keyboard
port (hence diodes, Germanium no less, to keep the data lines from shorting
out when you pressed multiple keys) which was also the joystick port. the
problem was the noise the joystick port would pick up would create sparkles
in the picture due to blown data.  I added an 8 bit latch (nmos MOS 8529 or
something like that) to isolate the data lines form the keyboard/joystick.
When my boss walked in after he had given me a "just fix it attitude" when I
was explaining the original TED design (remember I inherited TED),  I was
playing a video game.  When he gave me a hard time about why I wasn't
working on the problem I pointed the monitor, which he totally failed to
grasp the significance of.  Finally he realized I had taken the case off the
monitor and wrapped 6 foot of joystick cable around the yoke of the picture
tube and there were still no sparkles. Since he had been short with me, I
was short with him, the only thing I would say was "it's fixed", since he
obviously didn't want to know what was wrong I assumed that he didn't want
to know what fixed it.  I made that guy a lot of money over the next 2


-----Original Message-----
From: [] On
Behalf Of Ethan Dicks
Sent: Tuesday, March 27, 2007 4:31 AM
Subject: Re: TED based motherboard

On 3/27/07, Anders Carlsson <> wrote:
> Hello,
> I have come across an unknown, TED based motherboard which I would
appreciate pointers about. It only has 14 chips, named as following:
> U1 = NE555N 8144

8-pin timer chip (date code 44th week of 1981)

> U2 = P8214A DM7406N

7406 open collector inverter (early 1982)

> U3 = U4LS139N 8137 SA

dual 1-of-4 decoder (mid 1981)

> U5 = INMOS 8329-A IMS 2629P-15 C1059A KOREA
> U6 = INMOS 8329-A IMS 2629P-15 C1065A KOREA

Given the "-15" and that there are two of them, I'd say these are
DRAM, perhaps 16Kx4 each.

> U7 = 74LS257AN 8216 SA
> U13 = 74LS257AN 8216 SA

tri-state quad 1-of-2 selectors

> I tried to power it up, despite lacking some chips. It makes a faint
buzzing noise. Using a video cable, the monitor detects power on, but no
picture. Using RF, there is no signal at all, at least not at UHF 36. I
noticed the RF modulator has a small switch, which suggests it may be a NTSC
unit rather than PAL?

US RF modulators typically have a switch between stations 3 and 4 (We
have a broadcast channel 4 in my area, and others have a channel 3).

> I see that Zimmers have some schematics for different Plus/4, Commodore 16
and 116. Which one would best match this board, and how can I find out which
chips should go into U4 (logic gate?) and U8 ? Probably it'd be tricky to
get working anyway, given that fully equipped Plus/4 tend to break in CPU
and TED chips, much less a loose board that for some reason has been sitting
on a shelf for 15-20 years.

I would start with the EPROMs and the TED, since those are known
chips.  U4 is probably some flavor of 82S100, but that won't help
define any signals by itself.  You can probably verify the data and
address busses and check the DRAMs.  Without knowing what memory map
the board is supposed to have, fabricating a new 82S100 map is going
to be a bit tricky.

Interesting specimen.  It seems to have been made early in the C-64 days.


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