TRS80 mod 4 ver1 video/memory problems

From: Jim Davis <jpdavis_at_gorge.net>
Date: Fri May 30 19:16:01 2003

Tony Duell wrote:

>>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
>
>
>
The floppy cable is indeed fragile, Having been forced to use the same type
on a project 20 some years ago. When I had it disassembled, I pulled the fdc
controller, burnished the leads, cleaned the socket and the fdc I/F
connector
on the cpu board with 90% isoprop. I'll check cable continuity and fdc lead
to controller trace.
Thanks,
Jim.
Received on Fri May 30 2003 - 19:16:01 BST