TRS80 Model 1 Level II

From: Witchy <>
Date: Thu Feb 20 22:33:04 2003

> -----Original Message-----
> From: []On
> Behalf Of Tony Duell
> Sent: 19 February 2003 22:52
> To:
> Subject: Re: TRS80 Model 1 Level II
> So it's a fairly late one. The older version still has the 2 DIP sockets
> (filled with 2K chips for the L1 BASIC!) but the L2 upgrade was a PCB
> that was stuck to the solder side of the main PCB. It had a ribbon cable
> that plugged into one of the ROM sockets (now empty) to pick up power,
> data lines, and most of the address lines, and a 4-wire (I think) cable
> that was soldered topins of the chips on the mainboard for the extra
> address lines.

I love upgrades like that, wringing extra functionality out of the kit. Had
an Atari 520STfm in bits yesterday and it had been upgraded with a later
version of TOS and a memory module that plugged into (well, ONTO actually)
both the video shifter and the MMU, then ribbon cables took the lines out to
the module itself that sat on top of the shielding between the floppy drive
and PSU and allowed you to use standard SIMMs. Excellent :)

> L1 machines give a 32*16 mode display of colons if there's no RAM (or if
> the RAM DIP shunt is pulled). I don't know if L2 machines do the same.

With Z3 pulled I got _at_9 again (after double checking the ROMs were in
place!). I pulled Z71 as well and got _at_S. Remember, styrofoam eats MOS
devices like candy :o) (from the RAM testing section of the tech ref)

> The -ve side of the largest capacitor in the PSU section is ground IIRC.

Yep, I've just found that bit - 'ground yourself by momentarily touching the
right side of C9'. Earlier on there's a voltage test that tests for +5V on
the top link of R18 so I can run my probe from that.

> > the model III that's still in bits? (mail in your inbox about that)
> Yes, both machines use the same 16K DRAM chips (4116s or equivalent).

I'll have to pull them from the III then, of course I haven't powered that
one up yet (aside from momentarily) so I don't know if IT has any problems!
At least I got fully working life (hardware wise that is) out of my early
PAL Amiga 1000 last night so that's one down, 2 to go :)


adrian/witchy - the online computer museum - monthly gothic shenanigans
Received on Thu Feb 20 2003 - 22:33:04 GMT

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