MV6 Slot crosshair from hell (0x000100 0x4E45 0x4F2D 0x0A60 0x4F01)

[bytestorm]

Good evening all!

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

I have also cleaned the slots, double checked voltages, resoldered all connector and cart.

Thanks in advance!

 

[ack]

I would do a larger comparison from the memory viewer. Goto 0x000100 like you did and a take a picture on both boards. From that identify the differences and try to deduce if its a data or address lines issue.

 

[bytestorm]

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

 

[ack]

I was expecting some level of repeating corruption. Perhaps all the 0x00's in that range are masking it, you might try comparing the memory a little father down. You can get the same memory viewer on your working board by going to the hardware test page. It will make it easier to compare.

The z80 D0-D7 are related to sound so I they shouldn't play a role in being able to boot the game.

 

[bytestorm]

slot 1 aint giving me any love either

https://youtu.be/iP-Cu-tJ-Mo

 

[ack]

If you go to 0x8100 memory location it matches up with with the bad data from the video and your original pic. This would imply something is up with A16 of the 68k address lines as its randomly switching on/off.

 

[bytestorm]

ooohhhh!! I will kick myself in the nuts for ever trusting another techs work on a non working board... Jesus. There was a big blob of hot glue with the text "OK" on the solder side.. patching of 8 lines whereas 2 went to the wrong chip, they were mixed up.

Grrrrrrr!! Now slot 6,4 works, 5,3,2,1 has jailbars in the S and C areas. But from here I hope it will be easier to find the rest

I spent 2 full days with this bastard.... patching many many traces and at least 5 good hours trying to figure out what else could be wrong.. before i decided to remove all the hot glue...

I invested way to much time into it but I didn't want to give up..

Pics coming tomorrow just some jailbars left!

 

[bytestorm]

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