MV1AX repair

Rom1

n00b
Joined
Feb 9, 2017
Posts
11
Hi,

I got a MV1AX MVS stuck on a click of death.

What I already done (or at least what I remember) is:
  • checking for bad traces - both looking at them and using a multimeter
  • removing the battery (had no leak)
  • changed work ram
  • changed backup ram
  • tried with a MV1FZ bios
  • checked 5v and 12v
  • CPU clock is ok (checked with oscilloscope)

I checked OE/CS/WE of the work and backup RAM chip.
On work RAM I get some pulse on the OE and WE but CS always stay high.

I suspect CS is not ok. I checked trace, it goes to the SNK1A on the upper left of the board.


Is there anything I can do to narrow the origin of the problem ?

Maybe an unibios can help me to find what's wrong ?

Thanks a lot
 
Last edited:

pulstar

Mickey's Coach
10 Year Member
Joined
Jun 6, 2011
Posts
578
Have you tried the diagnostics bios from smkdan? Might narrow it down a bit for you or suggest which particular piece of ram you need to be looking at.

Also did you replace the battery at all or just remove it?
 

Rom1

n00b
Joined
Feb 9, 2017
Posts
11
No I have no eeprom programmer so I didn't tried diagnostic BIOS (nor unibios). I'll try to get them but might take some time...

I just removed the battery without replacing it.
Edit: I tried adding a coin cell (3v) and it doesn't change anything.
 
Last edited:

Rom1

n00b
Joined
Feb 9, 2017
Posts
11
I tested the diagnostic BIOS and... no change :crying:
I think there is something wrong next to the GRC/MGA/PAL chips. I will test logic gates around and keep this thread updated.

If anyone got an idea of what to test please tell me :)
 

HeavyMachineGoob

My poontang misses Lenn Yang's wang
10 Year Member
Joined
Apr 3, 2011
Posts
5,816
Just so we're on the right page on this repair, the click of death happens when the 68k CPU crashes right shortly after the MVS is turned on, one of the SNK custom chips will automatically reset the 68k CPU if it does crash. As the CPU resets and crashes in a loop, the speakers emit a clicking sound with each reset.

The problem area is between the 68k, the BIOS and the CPU's "Work" RAM. The Backup RAM near the battery can also cause problems, because they are connected in line with the Work RAM. A broken trace, floating enable line or failed component can all cause the click of death. Especially check the board for gouged traces or corroded via holes (places where a trace switches sides of the board).
 

Rom1

n00b
Joined
Feb 9, 2017
Posts
11
Hi,

Just put my hands on this board again, with the Smkdan diag bios i got "BIOS ADDRESS (A13-A15)" with most of the time "expected 04 / actual 00" and sometimes "expected 06 / actual 02".
I do not find many hints about the meaning. Does this error mean the 3rd bit stays low and so there is a problem on the A15 line ?

Any hint ?
Thx.


Edit:
Also, the screen background is green and hatched and text written in yellow.
When I press ABCD it go in a reboot loop.
 
Last edited:

Rom1

n00b
Joined
Feb 9, 2017
Posts
11
I had some time to work on this board again. It's now far more stable (fixed some buffer).
I figured than there is only 100ohms between A14 and A15 when board is powered. This explain what it gets 6 instead of 2.

I will try to disconnect everything one by one on this line to find what's causing this "almost short".

If someone got an idea, feel free to reply :)
 

Rom1

n00b
Joined
Feb 9, 2017
Posts
11
Disconnected A14 & A15 from work and backup RAM => still the same (error and resistance)
Disconnecting A14 from MGA cause click of death.
Disconnecting A15 from MGA, same kind of error and still 100ohm between A14 and A15.

Does this mean the 68k is dead ?
 
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