Dead MVS 1FZ - Where do I start?

X

X5900

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Recently, I've got a MVS 1FZ board as a gift. The board boots up with only garbage on screen, but no watchdog kicking in, no click, just a static image of pixel soup. The clock on the 68k is there, clean 5 Volts around the board and no previous repair attempts visible. I've checked for broken traces, but the board is in overall good shape, no battery leakage either.

There is however, little to no activity on the address and data lines, the reset line on the 68k is low and so is the halt line.

Where do I go frome here? I've already swapped out the SP1 rom and checked continuity on the address and data bus, seems to be all there.
 
HeavyMachineGoob

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Sounds like the 68k is inactive or dead. Make sure it's getting a working clock signal.
 
HeavyMachineGoob

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Check the 68k for bus activity with your logic probe, or an oscilloscope if you're lucky. It sounds like the 68k is just plain dead and would need a replacement. The 68k can't get reset by the watchdog timer if it's dead.
 
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X5900

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I already did, see first post, there's not much going on. I just replaced the 68k with a known good one and no changes. The watchdog isn't even going off, the cpu just sits there /reset and /halt low, doing nothing.
 
Xian Xi

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If it's the green screen then it's a calendar problem. Either the crystal(32k) is bad or the D4990 is bad, or just a trace from either is bad.
 
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X5900

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This is what I get, colors change sometimes after powering up again, but it's pretty much like the click of death symptom, except the clicking and resetting is missing.

IMG_20170215_242025905.jpg
 
GadgetUK

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The clue is going to be related to the lack of watchdog. I've not got time to look at the schematics at the moment, but I would focus on trying to understand why the watchdog isn't kicking in when its clearly in need of one. You could try the SMK Dan diag bios to see if that shows anything but it might be that the 68K is not booting at all or never coming out of reset?
 
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X5900

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Swapped out the Neo-C1, still the same fault like before. From what I've found, the watchdog sits inside the Neo-B1, which in part controls the reset line on the 68k. But if it doesn't pull the reset line high after the watchdog timer runs out, what should be happening in any case, it could be the B1 is faulty. Bummer. There's another reset going from the 68k to pin 15 of the 74hc259, some address decoding stuff going on there, but I can't figure out what for.
 
HeavyMachineGoob

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Just to clarify, the watchdog timer just resets the 68000 when it crashes. Your MVS isn't resetting, that usually means the 68000 isn't executing code for whatever reason.

Maybe replacing the 68000 is a bit drastic (not as much as replacing the NEO-C1 though). Have you by any chance replaced the SRAM chips for the 68000? It's called Work RAM. Going by this older thread, bad Work RAM can cause the 68000 to screw up in strange ways.

http://www.neo-geo.com/forums/showthread.php?264286-1ST-gen-AES-dead-68K
 
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X5900

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Oh, I was going by the description given on the Neo Geo Wiki and thought it was the other way around, as in the counter always runs and resets the 68k if it isn't told otherwise before the counter runs down?

The watchdog is integrated into NEO-B1. Sig_HALT and Sig_RESET are generated by this chip on power-on and whenever the 68k fails to kick the watchdog in time. It consists of an internal resettable counter in NEO-B1 which resets the whole system if it goes over a certain value. To avoid this, the software needs to regularly reset the counter by writing any value to REG_DIPSW ("kick" the watchdog).
Click to expand...

I haven't replaced or tested the work ram or backup ram yet because I've thought that those would either show up on boot or result in click of death ... but this should be easy enough to pull out and test it.
 
HeavyMachineGoob

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In the neogeodev wiki description, that only really applies if the 68000 is executing code and then crashes. With your MVS, the system is at a total standstill, the 68000 isn't doing anything and therefore the watchdog timer isn't doing anything.
 
Xian Xi

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I'd check to make sure the /CE and /OE lines on RAM, CPU and BRAM are all good. If any are high then we have a problem.
 
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X5900

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To quickly summarize, changed NEO-C1, 68K and System ROM, no change in behaviour (Clock is there). The logic probe says:

#2 WRAM: 27(WE): H, 22(OE): H, 20(CE): L
#1 WRAM: 27(WE): H, 22(OE): H, 20(CE): L
#3 BRAM: 27(WE): L, 22(OE): H, 20(CE): L
#4 BRAM: 27(WE): L, 22(OE): H, 20(CE): L
74HC259: P15 (RESET) : L
68K: RESET: L, HALT: L
 
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Jarryson

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X5900 said:
To quickly summarize, changed NEO-C1, 68K and System ROM, no change in behaviour (Clock is there). The logic probe says:

#2 WRAM: 27(WE): H, 22(OE): H, 20(CE): L
#1 WRAM: 27(WE): H, 22(OE): H, 20(CE): L
#3 BRAM: 27(WE): L, 22(OE): H, 20(CE): L
#4 BRAM: 27(WE): L, 22(OE): H, 20(CE): L
74HC259: P15 (RESET) : L
68K: RESET: L, HALT: L
Click to expand...


I have some MV1FZ with the same issue and never have booting replacig all chips :(
 
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X5900

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Pulled the Wrams and Brams out, tested them -> OK. Continuity:

D0-D15 Cpu->Wrams OK
A0-A14 Cpu->Wrams OK
D0-D15 Cpu->SRom OK
A0-A15 Cpu->SRom OK

Replaced 74HC259.

No changes :(
 
Xian Xi

Xian Xi

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Check if the HALT and RESET are low on power up or if it's goes high first then low.
 
Xian Xi

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One thing to check to is, the CPU is the thing that should generate the HALT. If you lift the halt pin, check if the signal from the B1 is pulling the HALT low. If that's the case, then I think it's a bad B1.
 
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X5900

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How long should it stay high? I've just tried it, the probe starts with pulse and goes straight to low, if I use MEM, I can see a faint glow on red/high+pulse+bright green/low. On both lines.
 
Xian Xi

Xian Xi

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X5900 said:
How long should it stay high? I've just tried it, the probe starts with pulse and goes straight to low, if I use MEM, I can see a faint glow on red/high+pulse+bright green/low. On both lines.
Click to expand...

What happens if you lift the HALT pin?
 
X

X5900

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Well, I've lifted the Pin on the B1 and probed that Pin (128), that one is outputting a LOW. The HALT Pin on the 68k is still soldered on and now it's HIGH. Different approach, same result :) ... But yes, it looks like a bad B1. Man, that thing is gonna be a pain to get off and put another one in.
 
X

X5900

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Swapped the B1 out, wasn't fun, didn't work ... The only thing left ist the Neo E0, that one I haven't tried yet. Any suggestions? :(
 
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