Got 2 mv6 slots for repair from a friend and have fixed all boards but 1 of the top pcbs..
it had massive corrosion damage and I have patched it extensively, checked all busses for continuity to the connectors.
it will not boot from any slot, and slot 3 wont even show the memory viewer.. and if I check the memory viewer from slot 6 it reads:
0x000100 0x4e45 0x4f2d 0x0a60 0x4f01
the working top pcb gives me:
0x000100 0x4e45 0x4f2d 0x4745 0x4f01
I have been using my logic probe to compare the areas for slot 6 on both boards and the nonworking board seems to have trouble with the signals to/from chip 15 (SDD0-SDD7 according to:
https://wiki.neogeodev.org/index.php?title=SLOT6_board
the working pcb is pulsing nice on all i/o and the non working is just a combination of steady high or low signals.
the 1x 138, 1x 178 controlling the slot selection behaves same on both the non-working and working board, same goes for the 4x 151.
both selects are low on the 244 (chip 15 on wiki).
I am running out of ideas now and getting a bit blind after sitting with the same board for a long time
(I have also cleaned the slots, double checked voltages, resoldered all connector and cart.)
Here is a comparison shot from the non-working (left) and the working board.
01000111 01000101 - 4745 (working)
00001010 01100000 - 0A60 (non-working)
I am not sure how to interpret this, I mean all other data is read correctly (at least for this range in the pic). That tell me that the 68k adress bus is OK?
The buffer chip 15 mentioned in the first post thats not pulsing ok, thats the Z80 bus D0-D7
Thanks in advance!
it had massive corrosion damage and I have patched it extensively, checked all busses for continuity to the connectors.
it will not boot from any slot, and slot 3 wont even show the memory viewer.. and if I check the memory viewer from slot 6 it reads:
0x000100 0x4e45 0x4f2d 0x0a60 0x4f01
the working top pcb gives me:
0x000100 0x4e45 0x4f2d 0x4745 0x4f01
I have been using my logic probe to compare the areas for slot 6 on both boards and the nonworking board seems to have trouble with the signals to/from chip 15 (SDD0-SDD7 according to:
https://wiki.neogeodev.org/index.php?title=SLOT6_board
the working pcb is pulsing nice on all i/o and the non working is just a combination of steady high or low signals.
the 1x 138, 1x 178 controlling the slot selection behaves same on both the non-working and working board, same goes for the 4x 151.
both selects are low on the 244 (chip 15 on wiki).
I am running out of ideas now and getting a bit blind after sitting with the same board for a long time
(I have also cleaned the slots, double checked voltages, resoldered all connector and cart.)
Here is a comparison shot from the non-working (left) and the working board.
01000111 01000101 - 4745 (working)
00001010 01100000 - 0A60 (non-working)
I am not sure how to interpret this, I mean all other data is read correctly (at least for this range in the pic). That tell me that the 68k adress bus is OK?
The buffer chip 15 mentioned in the first post thats not pulsing ok, thats the Z80 bus D0-D7
Thanks in advance!