Chromedome45
Veteran Member
You can try to run just with bank 0 of the memory. Will be limited to the base 64k. Remove the 8 ram chips on the right hand side U85-U92. Normally those chips are not accessed unless you run a Memory disk or a program called Double Duty a task switcher. See if that helps. Also make sure that all the pins are in the holes of the socketed chips. Especially the 40 pin chips like the Z80a and the Video controller chip. I have had one or 2 pins not go into the holes cause they were bent inward and caused me a lot of headaches. Till I pulled them again and found the pins bent. So something to double check. Lot's of luck Whizzi!
And just FYI I had the exact same problem on a Gate Array model 4 with that same bad display. Had a floating ground on a 74LS02 chip which I corrected and 2 Gate chips went bad. The PLL (Phase Lock Loop) controller gate chip and the address decoder gate chip. Replaced those and all worked like a charm.
Also if you need the service manual/Technical manual look here. It is in alphabetical order. Look for Model 4 Technical Reference Manual and be sure it is the 1983 version. You may need 7-zip to open the archive. Hope this helps.
http://www.classiccmp.org/cpmarchives/trs80/Library/Manuals/Hardware/
And just FYI I had the exact same problem on a Gate Array model 4 with that same bad display. Had a floating ground on a 74LS02 chip which I corrected and 2 Gate chips went bad. The PLL (Phase Lock Loop) controller gate chip and the address decoder gate chip. Replaced those and all worked like a charm.
Also if you need the service manual/Technical manual look here. It is in alphabetical order. Look for Model 4 Technical Reference Manual and be sure it is the 1983 version. You may need 7-zip to open the archive. Hope this helps.
http://www.classiccmp.org/cpmarchives/trs80/Library/Manuals/Hardware/
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