TRS80 mod 4 ver1 video/memory problems

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri May 30 17:37:43 2003

> Hi,
> I recently picked up a model 4 ver 1 with a problem. The system originally
> worked and booted, after moving the system it started to display random
> characters
> on power up and failed to boot.. I removed socketed ICs and cleaned
> the connectors.
> The system now displays a blank screen on power up ( although the drives
> spin, and
> it could be booting ). If I disconnect the FD controller from the main
> board, the
> system jumps into basic ( with video ) and seems to operate. Print
> fre(0) returns
> somthing over 48K with the fd disconnected. Any hints?

It sounds like the CPU board is basically (!) OK -- the ROM BASIC only
uses 48K of the RAM (no matter how much you actually have fitted).

When you reseated socketed chips, did you also do the ones on the FDC
board? Have you checked -- carefully -- the ribbon cable between the CPU
and FDC boards? I've had a lot of problems with those cables in M3s and M4s.

-tony
Received on Fri May 30 2003 - 17:37:43 BST