[Coco] OT: TRS-80 Model I repair info

[Christian Lesage]

Rogelio:

Yes, I will post to the comp.tandy.sys group. Thanks for the info.

Malcom, Dean:

I found the following books/manuals :

/TRS-80 Technical Manual/, by Radio Shack
/The Custom TRS-80/, by Dennis Báthory Kitsz (host of the CoCoList!)

The latter describes some common mods.

I almost repaired the first computer; I still need to replace a 
defective 74c04 inverter in the video circuit.

However, the second computer is heavily modified. I thought they had the 
same mods, but I was wrong. It has two additional switches, a larger 
extra daughter board (with erased out chip numbers), much more wires, a 
Z80B (which is a 6MHz part), an adapter with an EPROM in place of the 
character generator ROM, and a few piggybacked chips. I will have to 
examine it further in order to better describe the mods.

Let me ask a question about the original TRS-80 video monitor: is it 
normal that displaying a stable image requires a lot of tweaking? I have 
only one such monitor, and it seems to be picky about the video signal. 
Last month, I repaired a home-brewed computer made from an LNW-80 
(TRS-80 clone) logic board, and in order to display a stable image, it 
is often necessary to tweak the controls on the back of the monitor 
and/or reset the computer a few times. I thought the LNW-80 had a 
marginal video generation circuit, but then I encountered a similar 
problem with a real TRS-80. Well,I think the latter has a defective 
component in the video circuit, but still...

Christian