CPC 6128 acting as a 464

[deepfb]

I have finally fixed a CPC 6128 with a problem that was a pain to diagnose: when trying to catalogue a disc, it acted as it was a CPC 464:





I traced the (supposedly) usual responsible ICs, but none of them was the cause of the failure. Since it is not an obvious problem I have decided to write this post in order to help other people with a similar issue.


Looking at the schematics of the 6128 -and taking into account that I have at hand lots of tools to solder & unsolder easily-, I first replaced all the ICs that are socketed in this picture:





...But the problem remained. I connected a M4 board and I found that I could load programs from it. I checked the RAM with a test program and loaded successfully some games.


I then realized that the disk flat cable connector on the PCB had some marks, as if somebody tried to take it apart using a screwdriver. A very small crack was visible on D201 when looking at it with a magnifying glass: I pushed it slightly with the tip of the tweezers, and it broke:





Replacing the diode didn't solve the problem, so I unsoldered the flat cable connector just to find this:





Once I fixed the tracks, I could load programs from the disk drive again:








What is the lesson of this repair? CPCs with Centronics connectors (Schneider & Solavox) are quite protected against human action and moisture from outside; but those with 'open' connectors may have rusted diodes, tracks and/or resistors close to the edge connector. And if D201 is open, or the track to the resistor array NR201 is cut, or if NR201 is blown, the disc ROM will not be present and you may go crazy trying to find the cause.


Again, hope this helps somebody -and sorry but I forgot my English and you may find some stupid expressions on this post! :-/


PD: the original version of this message is written in castellano, is more detailed & has more pictures, and is to be found here.

[00WReX]

Nice work on the fix.

As you said, it appears somebody did not realise the floppy disk connector is soldered to the board (and not in an IDC type socket) and thought they could lever it off with a screwdriver.

(Your English is better than mine). 

Cheers,
Shane

[DanyPPC]

Well done !

[Querubin]

Brilliant!