Re: TED based motherboard

From: Ethan Dicks (
Date: 2007-03-27 14:30:30

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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