I do have a logic probe. What do I probe on the 68k?
- Thread starter Mitsurugi-w
- Start date
Assuming the worst possible case (data or address pin stuck or shorted), you might want to ensure:
- RESET pulses low at boot, then gets stuck high
- HALT is high
- BR is not stuck low
- Address, R/W and data bits are all changing state
- What is the state of the FCx bits
One important thing to check is to see if you get activity at boot just to stop moments later.
AFAIR, part of the addressing logic for the 68k is in the custom, so you can check that the BIOS actually does get read (data, address, CS, OE are moving at the BIOS).
By the way, as somebody already pointed out, you could check if you see the sync pin at the jamma changing state.
EDIT: Also, replacing the xtal / oscillator does not guarantee that all parts of the board get the required clocking signals, including the CPU.
- RESET pulses low at boot, then gets stuck high
- HALT is high
- BR is not stuck low
- Address, R/W and data bits are all changing state
- What is the state of the FCx bits
One important thing to check is to see if you get activity at boot just to stop moments later.
AFAIR, part of the addressing logic for the 68k is in the custom, so you can check that the BIOS actually does get read (data, address, CS, OE are moving at the BIOS).
By the way, as somebody already pointed out, you could check if you see the sync pin at the jamma changing state.
EDIT: Also, replacing the xtal / oscillator does not guarantee that all parts of the board get the required clocking signals, including the CPU.
xodaraP
Legendary
Here's a pinout for the 68k so you know which pin does what
https://console5.com/techwiki/images/1/1c/MC68000-MC68010-MC68HC000-64-DIL-Pinout.png
For your purposes you're looking to probe
BR - Pin 13
HALT - Pin 17
Reset - Pin 18
Clock - Pin 15
And if these are all good, chances are the issue is with something else.
https://console5.com/techwiki/images/1/1c/MC68000-MC68010-MC68HC000-64-DIL-Pinout.png
For your purposes you're looking to probe
BR - Pin 13
HALT - Pin 17
Reset - Pin 18
Clock - Pin 15
And if these are all good, chances are the issue is with something else.
friedpotatoz
Enthusiast
Great thread, but asayuki lost me lol, I need to learn this stuff!
Any progress Mitsu?
I believe the custom is dead so it's in the scrap bin.
l_oliveira
Professional
Just for you guys to note:
Neo Geo boards use a complex video system hardware which generates video from a 24Mhz quartz oscillator.
The video generator spans through three chips on the original PRO chipset (PRO-A, B and C) and on second generation it's two (LSPC-A2 and NEO-B1).
LSPC-A2 (PRO-A on older chipsets) generate video timing and synchronization so if it's toast you won't get any sync on your monitor. NEO-B1 (PRO-B and C on older chipsets) deal with palette hardware and image generation (R,G and B signals control and generation) so a fault on that could cause the system to not boot, as well. The CPU Watchdog is on the B chip.
Usually a board that measures up with the 24Mhz clock being fine but has no sync output has enormous chances of having a dead/fried LSPC so stay away if you can.
Neo Geo boards use a complex video system hardware which generates video from a 24Mhz quartz oscillator.
The video generator spans through three chips on the original PRO chipset (PRO-A, B and C) and on second generation it's two (LSPC-A2 and NEO-B1).
LSPC-A2 (PRO-A on older chipsets) generate video timing and synchronization so if it's toast you won't get any sync on your monitor. NEO-B1 (PRO-B and C on older chipsets) deal with palette hardware and image generation (R,G and B signals control and generation) so a fault on that could cause the system to not boot, as well. The CPU Watchdog is on the B chip.
Usually a board that measures up with the 24Mhz clock being fine but has no sync output has enormous chances of having a dead/fried LSPC so stay away if you can.
