19 Feb
2003
19 Feb
'03
9:42 a.m.
You say
it's an L2 machine. Does it have the ROM in 2 off 24 pin chips on
the mainboard (one is 8K, the other 4K, and there are some cut-n-jumper
mods), or is it old enough to have the extra PCB with 3 24 pin chips
(eack 4K) and the address decoder?
It's the former - 2 ROMs and 2 DIP shunts. Indeed. The
introduction is rather amusing... (As you may have guessed, I
have this manual...)
The whole thing is amusing IMO, I loved the 'real world' section where he's
done a schematic to allow your TRS80 to control the power on your coffee
machine :) Be warned that much of the tech manual is written
assuming you have a L1
machine. I don't know what L2 does if it can't find any RAM, for
example...
It does predictable things along the lines of no ROM; I can't remember the
resulting screen though. The couple of replies I got on comp.sys.tandy also suggest ROM failure and/or address lines and/or data
lines.
The -ve side of the largest capacitor in the PSU section is ground IIRC.
With the ROMs pulled, all the address lines
should be toggling (as the
CPU tries to continually push 39 00 onto the stack). You can check this.
Yep, I'm being dense again and struggling to find a good link to ground I Yes, the M1
uses DRAMs for the main memory. Either 4K or 16K parts.
The schematic also mentions 8K parts, but since that's from the tech ref it might only apply to L1 machines? I suppose I can
always steal memory from
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).
-tony