[Coco] (Marginally Topical) TRS-80 Model I Troubleshooting

[Chris Dent]

> But if I power it up with the expansion unit switched on I get garbage on the screen



When a Model I is connect to an expansion interface the first thing it tries to do is load and

execute the boot sector from the floppy.  If it fails to boot, it doesn't fall back to the BASIC

Interpreter, it just hangs.

Hold the BREAK key down when powering up and that should get you into BASIC



 _____ _          _     | Chris Dent

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If you mod me down, I will become more insightful than you can possibly imagine



-----Original Message-----
From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] On Behalf Of Joel Ewy
Sent: Monday, 5 August 2013 1:09 PM
To: CoCo-MaltedList
Subject: [Coco] (Marginally Topical) TRS-80 Model I Troubleshooting



So I was given a TRS-80 Model I system on Friday.  It includes the TRS-80, an Expansion unit, a monitor, a very, very strange "screen printer", a pair of floppy drives, a broken but physically very nice CTR-80, a bunch of of programs on cassette (including a boxed Avalon Hill Planet Miners game), and a box labeled "TRS-80 floppy disks" that appear from the labels on the individual disks themselves to actually be Apple 2 disks, though I don't yet know what is on them.



The computer powers on.  The monitor works but has an extremely touchy vertical hold.  But if I power it up with the expansion unit switched on I get garbage on the screen.



Next time I have the time to clear the space to set it up and play with it, I'll try cleaning the card edge contacts between the TRS-80 and the expansion unit, as I gather this is a common failure.  But if that doesn't work, is there any other wisdom about likely problems with the Expansion unit?  Reseat socketed chips?  Check for bad caps?



What about the vertical hold on the monitor?  I'm not afraid of a soldering iron, can read a schematic, know what not to touch inside a TV, and where to keep my other hand, but don't have a good enough grasp of CRT circuits to really know where to find the V. hold parts or know what to suspect.  (I do have an ancient copy of TAB's "101 TV Troubles and How to Fix Them" or some such.  But it predates even the TRS-80 monitor by a few years.)



Thoughts?  Suggestions?



JCE





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