Commodore 128 - Very hard to repair!

[demonlg]

This is with epyx fastload chart inserted and any resets.. in one case its boot in 128 mode during resets!!! The cursors blinking...

 

[demonlg]

Working......oooo my goood.... replaced 74ls373 on U12 with another old one....the new are defect!

Now start correctly every time i turn on and the diag in 128 mode working perfect! The 373 replaced is working on a c64 board....i don't know why not on this!

Attached the results of c128 test and c128 boot.

 

[demonlg]

The replaced 373 is a 74SC373......probably is the problem the SC type....i don't have see this SC when replaced 2 year ago!!

 

[demonlg]

With all Diagnostic harness connected the board as passed 15 test without problem.

 

[dabone]

Congrats! You've learned an important lesson with this repair, that not all chip types are created equal.

 

[demonlg]

Yes, for notification the 74SC373 do not working on U12, instable boot, wrong boot, garbage screen, but its working on U17, also the 74LS32 now working on U9, probably i have repaired the 2-3 holes bottom of the logic chips but the board won't boot correctly with this 74SC373 installed on U12.

At the end, the 74LS245 working on U55 (originally 74F245), and 74LS07 working on U60 (originally 7407.

Thanks at all for support and psyco support.
Now other threads for 1084 monitor.

Emanuel