MVS with ticking noise/garbled screen, no boot

got a mv-1A for cheap off an auction site.. following sympthoms:

Garbled screen, constant resets, ticking noise.. screen has random patterns, sometimes letters etc in the squares too. bios is NOT at fault, all pin connections checked out fine, unibios won't boot either. verified on another mv-1a, no bios/bad bios causes greenish ticking screen, not totally random colors.



no visible damage, board looks actually very clean.

any ideas?

up

This does look like a BIOS problem to me (you get the exact same simptoms turning on a system with no bios in). If you are sure the bios is good and the socket is good then I would say either some address/data lines to the 68k are bad or the actual 68k cpu is dead.

From what you are getting at the moment I feel there is no 68k code executing at all.

Raz

Looks like the problem I have... check your ram chips
-BB

***edit***

Just read its not a bios problem...nevermind.

There must be something else missing from the board then?

I have the mv-1f and have the same problem except my screen goes all garbled with a green screen and the ticking noise.

@rudekid: that does sound like a bad bios or bad trace to it.. greenish screen is what I get on my other 1-slots when I unplug the bios.

@raz: is there any way to check the 68k? i.e. some lines that should be high when it's functional? the bios chip itself is fine (tried several), the pins also all check out fine (no bad traces). it also does the same when I leave the bios completely out.

I noticed that when I touch pins on the connector of the cart slot, some of the square boxes will have changing pixels running through them, if that's any help.

Arakon said:

[B@raz: is there any way to check the 68k? i.e. some lines that should be high when it's functional? the bios chip itself is fine (tried several), the pins also all check out fine (no bad traces). it also does the same when I leave the bios completely out.
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Im not sure, what I can say is that the 68k isnt getting far enough to start the RAM tests. I had a quick look through the bios code and it is possible that dead RAM (like big bear said) is causing this problem. Basically if the 68k's stack is becomming currupted (goes from 0x10f300 backwards) due to bad work ram then the 68k would fail probably with and address error exception as soon as it tires to return from either a BSR or JSR as the stored pc would be bad.

You could try to move the stack to a differnet section of ram to test this. If you have a EPROM programmer try the following;

Change 0x000000 in the bios from 0x1000 0x00F3 to 0x1000 0x0003. This will place the stack at 0x100300 in work ram instead.

If that dosent work;

Change 0x000000 in the bios from 0x1000 0x00F3 to 0x4000 0x0003. This will place the stack at 0x400300 in palette ram.

Either of these changes should be enough for the system to do a full work ram test I think as long as the new ram position of the stack is good. Of course if the cpu is dead or a different problem then it will simply do the same.

Raz

no change at all with either.. only thing I noticed is that with any bios in, most of the fields flash yellow/light green, while without bios, they flash purple/yellow or purple/light green.

I even removed the 68k completely, but then the screen stayed completely in one (random) color, so I think the 68k is ok, otherwise it'd give me that single colored screen with the 68k in too.

any other ideas?

Im not sure what else to suggest now sorry.

Raz

here's a better pic of what it looks like..