1 Sep
2023
1 Sep
'23
4:42 p.m.
On Fri, Sep 1, 2023 at 4:31 PM dwight via cctalk <cctalk(a)classiccmp.org> wrote:
I do understand the warranty sticker. Say we have the average computer buyer. He has a
screw driver and mostly knows how to use it. He also went to Radio Shack ( long gone 🙁 )
and bought a cheap soldering iron. He is now fully equipped to repair what ever is wrong
with his box. ( obviously not at Tony's level of competence ) He takes the cover off
and has no idea what he is looking at or what he is looking for. ( I think we have all
been there at one time ) He sees something with a screw driver slot. He has a screw
driver. Perhaps all it needs is a minor adjustment. He turns the screw one way, and
nothing changes. He turns it the other way and, pop, some smoke comes out of the other
side of the chassis.
You clearly know the TRS-80 Model 1 (or are a good guesser).
There are 4 presets ('things wth a screwdriver slot) on the Model 1
logic board. Two of them are associated with delays on the horizontal
and vertical sync signals. Adusting those can cure a
video-going-off-screen issue.
The other 2? They set the output voltage of the +12V and +5V
regulators. There is no overvoltage protection on the former, turn
that too hgh and you may wipe out all the DRAMs. The latter has a fat
zener across the output, but I am not sure I trust it. And if you turn
the +5V line up you could be looking to replace a lot of ICs...
-tony