TED based motherboard

From: Anders Carlsson (anders.carlsson_at_sfks.se)
Date: 2007-03-27 10:08:03


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
U2 = P8214A DM7406N
U3 = U4LS139N 8137 SA
U4 = empty
U5 = INMOS 8329-A IMS 2629P-15 C1059A KOREA
U6 = INMOS 8329-A IMS 2629P-15 C1065A KOREA
U7 = 74LS257AN 8216 SA
U8 = ?? (unnamed logic chip, perhaps CPU?)
U9 = empty
U10 = 27128 EPROM marked "TED LO"
U11 = 2764 EPROM marked "TED HI LO-V1.0"
U12 = 2764 EPROM marked "TED HI HI"
U13 = 74LS257AN 8216 SA
U14 = MOS 7360R4A 4183 (TED)

Low resolution image at: http://www.cbm.sfks.se/pics/tedmb.jpg
I can upload a higher resolution image at a later time.

Where is the 7501/8501 CPU, is that the unnamed one in U8? As you can see, there are two diodes running between some pins on the TED chip, and some extra (cut?) wire near the cartridge port. Later I can look up exactly which pins the diodes go between.

On the under side of this motherboard, it is stamped "Q.C INSP'D AUG 3 1983". Is this normal for an early TED line motherboard, given that they started to sell sometime during 1984 if I recall correctly? I was thinking maybe this is some prototype.

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?

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.


Anders Carlsson

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