Help 4 slot graphic problem

[mainman]

Ok guys I have a 4 slot with a failure I can not solve. The board only boots up 50% of the time and when it does it boots to a black screen with white blocks. This is of course with no cart inserted because even without a cart it should boot to the cross hatch. I have change the bios and resocketed the chips and still it persist. I have fiqured the problem was with a bad 68000 processor so I changed it but no success. I have checked around the board for broken traces but can not find any. I still suspect there a broken trace but if its on the processor I don't even know where to start to look.

here is a pic

 

[Razoola]

Have you checked the voltages etc, maybe something on the PCB is causing power to drain. You could also try booting with the top PCB removed. I think it should still get to the crosshatch like that.

Raz

 

[mainman]

Have you checked the voltages etc, maybe something on the PCB is causing power to drain. You could also try booting with the top PCB removed. I think it should still get to the crosshatch like that.

Raz

Yes I checked the voltage and the 4 and 6 slot board can both boot to the cross hatch without the top pcb by the way. I suspect a trace on the 68000 but since each pin on that damn thing spreads out 3 ways it would take forever to to check it without knowing where to start

 

[Razoola]

If the 4slot can get to the cross hatch without the top board attached that tell you that there is nothing wrong with the 68k or Bios traces. The problem is going to be something on the top board shorting or the conectors between top and bottom board. Maybe some bent pins inside the cart sockets touching each other?

Raz

 

[mainman]

If the 4slot can get to the cross hatch without the top board attached that tell you that there is nothing wrong with the 68k or Bios traces. The problem is going to be something on the top board shorting or the conectors between top and bottom board. Maybe some bent pins inside the cart sockets touching each other?

Raz

No raz its not getting to the cross hatch at all, its dead weight. What you see in the picture is what is going on. The pic you see is the 4 slot powered up without the top board on as I do not need it.


I was just trying to say for the record that the 4 and 6 slots in general can go to the cross hatch without the top board.

 

[Razoola]

Ahh ok. Another thing to try.... Check that both Work RAM chips are Ok, I say this because if there is no workRAM the system will not boot in any way because it cannot save the 68000 stack. In short when the CPU executes a branch it uses the stack to remember where it came from, if the memory is bad that can cause an address error or endless other problems. Looking at the Bios code this will happen almost instantly on boot, well before it starts putting anything on screen.

I quick test would be to maybe change the stack to a different section of memory (say palette RAM) To do this get your Bios and edit the stack default offset, this is location 0x000000 to 0x000004 in the Bios. Change the 0x1000 0x00F3 thats there to 0x4000 0x0020. This will move the stack into the palette RAM which I think is in different memory chips. If this fails though it does not mean the RAMs are still not the problem as the palette RAM could be just as faulty.

Raz

 

[juanmiglesias]

im having almost the same problem.. my board a mv2f doesnt boot samurai shodown 3 or sengoku 3, but it boots perfectly neo geo cup 98, in both slots.... i got a green screen with the other two games.. with weird graphics all around like yours.. i boot one time only SS3, already clean the contacts and adjusted them...

these two games use a lot more data or roms that neo geo cup.. maybe try a game that doesnt have much data on it... neo geo cup only got C1,C2,M1,S1,V1,V2,P1 chips. ans ss3 C1 to C8 chips, M1, S1, V1, V2, P1 SP2 chips.
try a game like neo geo cup.
the difference with my board is that i get the bios to boot with or without games, and always show the three games in any order in soft dip, i tried to post a topic about it but i dont know why it hasnt been publish....
to raz:
do you know what chips does read (any ram, cpu etc, that i can check), roms SP2, and C3 to C8?.. how it works... maybe the answer to both of us is in a broken ram or component.
thanks.

 

[Razoola]

im having almost the same problem.. my board a mv2f doesnt boot samurai shodown 3 or sengoku 3, but it boots perfectly neo geo cup 98, in both slots.... i got a green screen with the other two games.. with weird graphics all around like yours.. i boot one time only SS3, already clean the contacts and adjusted them...

these two games use a lot more data or roms that neo geo cup.. maybe try a game that doesnt have much data on it... neo geo cup only got C1,C2,M1,S1,V1,V2,P1 chips. ans ss3 C1 to C8 chips, M1, S1, V1, V2, P1 SP2 chips.
try a game like neo geo cup.
the difference with my board is that i get the bios to boot with or without games, and always show the three games in any order in soft dip, i tried to post a topic about it but i dont know why it hasnt been publish....
to raz:
do you know what chips does read (any ram, cpu etc, that i can check), roms SP2, and C3 to C8?.. how it works... maybe the answer to both of us is in a broken ram or component.
thanks.

Your problem is totally different. I would have to go with some traces shorting in your case when games use higher gfx sizes. You should check those games on a different MVS also to confirm they are good.

Raz

 

[juanmiglesias]

sorry i forgot to say i tried them in an one slot machine.. first try they were all good... ill try to post mine apart dont know why the system kept rejecting my topic...

 

[mainman]

Well raz I replaced the work ram and the problem is still there. Its something I can not put my finger on. I have compared the screen that this screwed up MVS unit freezes on with the screen of a working 1 slot and noticed that those black and white pattern are part of the boot up screen as they are the first images you see when you power on. My problem is it will not go past that black and white screen to the green screen and lastly the cross hatch. Anymore ideals raz?

 

[Razoola]

Is the screen static or is there a clicking sound with it? The Bios does this from boot...

1) Set a few HW registers to reset LED,s and coin lockouts etc
2) Check workRAM
3) Check backupRAM
4) Check pallatteRAM 0
4) Check pallatteRAM 1
5) Check videoRAM

blah blah bhah

So this can narrow down the problem if we assume the 68k is running. From the picture we know that the videoRAMs are not being tested and possibily some of the paletteRAM also. That said however, maybe its all running fine but there is a problem with the HW fetching data from the RAM to display on screen. Have you tried running a game with the original bios to see if game sound is being outputted?

Raz

 

[mainman]

Is the screen static or is there a clicking sound with it? The Bios does this from boot...

1) Set a few HW registers to reset LED,s and coin lockouts etc
2) Check workRAM
3) Check backupRAM
4) Check pallatteRAM 0
4) Check pallatteRAM 1
5) Check videoRAM

blah blah bhah

So this can narrow down the problem if we assume the 68k is running. From the picture we know that the videoRAMs are not being tested and possibily some of the paletteRAM also. That said however, maybe its all running fine but there is a problem with the HW fetching data from the RAM to display on screen. Have you tried running a game with the original bios to see if game sound is being outputted?

Raz

Its running with a original factory bios not a unibios, no sound is outputed. No clicking and the picture is not flickering. It has the black and white graphics as you see in the pics and it remains like that. Tried to run a game and the system gives me the finger and will not run graphics or sound.

 

[Razoola]

Something very strange is going to there then and I'm really lost for other suggestions. Its very hard to say weather the 68k is really running or not. What is strange is there there is no clicking sound as that sound is basically the reset watchdog kicking in. From what you say, either the entire mobo is locking up or the 68k is running fine and an error message is getting to screen that is not being displayed for some reason. I say this because that would put the 68k into a loop that would stop on the error and keep the watchdog alive (to stop the system from resetting.

If you put no bios in do you get the normal checqered screen with clicking sound?

Raz

 

[channelmaniac]

I'm wondering if there's a buggered reset* line on the CPU.

Take a logic probe and check pin 18 on the CPU. When you power it up it should drop low then raise back to a high logic level.

If it's stuck low the CPU will be stuck in reset and not doing anything.

I haven't traced the reset line on the Neo Geo back yet but on many other computers it's tied to a cap & resistor somewhere to give it a bounce on startup. If one of those devices are broken then you'll get all kinds of problems.

RJ

 

[mainman]

Something very strange is going to there then and I'm really lost for other suggestions. Its very hard to say weather the 68k is really running or not. What is strange is there there is no clicking sound as that sound is basically the reset watchdog kicking in. From what you say, either the entire mobo is locking up or the 68k is running fine and an error message is getting to screen that is not being displayed for some reason. I say this because that would put the 68k into a loop that would stop on the error and keep the watchdog alive (to stop the system from resetting.

If you put no bios in do you get the normal checqered screen with clicking sound?

Raz

There is no clicky sound and no audio what so ever raz, with the bios not installed I get the same screen. Howver I think I getting a ideal why. I checked pin 18 of the 68000 which is the reset line and noticed it keeps getting reset which would explain why its not getting past this screen, but I still don't know why its getting reset.

I'm wondering if there's a buggered reset* line on the CPU.

Take a logic probe and check pin 18 on the CPU. When you power it up it should drop low then raise back to a high logic level.

If it's stuck low the CPU will be stuck in reset and not doing anything.

I haven't traced the reset line on the Neo Geo back yet but on many other computers it's tied to a cap & resistor somewhere to give it a bounce on startup. If one of those devices are broken then you'll get all kinds of problems.

RJ

You were right it keeps getting reset but I have not fiqured out why

 

[channelmaniac]

That's what's known as a watchdog... if the CPU doesn't do something in a certain time interval then the circuit resets it... Razoola can comment more on it. I'm not sure how often it whacks the CPU on a Neo system...

RJ

 

[Razoola]

Ok, the fact your getting the same screen even with no Bios is tells us allot. More and more by the sounds of it the GFX is not being pulled from the GFX RAM and being pisplayed on screen. One thing that can help confirm this is the following.

Check that pin 18 of the CPU with and without the Bios. Does it only keep getting polled if the bios is not present or both with and without the Bios? What you should really be seeing with no Bios in is the random checkured colored screen with the clicking sound. The fact your seeing the same info each time with the same colors from a cold start goes beyond logic because the RAM (both VRAM and PALLETTE) should have garbage/ no info. This is what leads be to believe that the GFX drawing chip has become frozen with whatever data is inside its internal buffer which explains the same details always being drawn. I personally feel that its posible its this part of the HW where the problem lies.

btw its totally normal for that line to keep being triggered if no Bios is in, thats what causes the click and reset with no bios. It triggers very often but I have never totally timed it but I think the port in the HW needs writing to once every couple of vblanks to stop the system from resetting. This reset line probably triggers various chips so its possible if its broken somewhere that some HW is not getting initilised correctly.

Raz

 

[mainman]

Ok, the fact your getting the same screen even with no Bios is tells us allot. More and more by the sounds of it the GFX is not being pulled from the GFX RAM and being pisplayed on screen. One thing that can help confirm this is the following.

Check that pin 18 of the CPU with and without the Bios. Does it only keep getting polled if the bios is not present or both with and without the Bios? What you should really be seeing with no Bios in is the random checkured colored screen with the clicking sound. The fact your seeing the same info each time with the same colors from a cold start goes beyond logic because the RAM (both VRAM and PALLETTE) should have garbage/ no info. This is what leads be to believe that the GFX drawing chip has become frozen with whatever data is inside its internal buffer which explains the same details always being drawn. I personally feel that its posible its this part of the HW where the problem lies.

btw its totally normal for that line to keep being triggered if no Bios is in, thats what causes the click and reset with no bios. It triggers very often but I have never totally timed it but I think the port in the HW needs writing to once every couple of vblanks to stop the system from resetting. This reset line probably triggers various chips so its possible if its broken somewhere that some HW is not getting initilised correctly.

Raz

pin 18 is constantly getting pulled high and low with or without the bios installed. Ok which of the custom chips controls the graphics, is it the LSPC. Can you also clarify what the pro-co and the pro-bo do.

 

[Razoola]

I do not know the answer to that question sorry. The fact the line is getting pulled all the time though with and without the bios is probably not a good sign though. Maybe you should confirm behavior of that line on a working MVS with and without Bios and compare just to be sure we are not assuming how that line is being used.

Raz

 

[mainman]

I do not know the answer to that question sorry. The fact the line is getting pulled all the time though with and without the bios is probably not a good sign though. Maybe you should confirm behavior of that line on a working MVS with and without Bios and compare just to be sure we are not assuming how that line is being used.

Raz

On a confirmed fully working multislot mvs system I have found that when I pull the bios and power up the reset lline keeps reseting just like on the problem MVS unit and the screen shows the same screwed up graphic. However with the bios removed from the good MVS unit you hear the clicking that you are suppose to hear. The problem MVS unit does not have this sound. Additionally the problem MVS screen does not always come on when I power up, it usally take 6 tries.

 

[Razoola]

I have never had a MVS show that graphic in your screenshot without the Bios, even if its fully working. Its always been a random colored flashing checkered screen with the clicking sound. How did the test go with the reset line on a working MVS with bios in?

I'm at a loss at others things to look at now.

Raz

 

[mainman]

Just wanted to say thanks for the help raz and guys. I think this one will become a parts board

 

[channelmaniac]

Before you give up...

Check the OE* line on the BIOS... Pin 20 on the BIOS goes to Pin 59 on the NEO-GO chip. If it's not pulsing then the BIOS isn't being read.

On the BIOS, pin 2 is CE* (Chip Enable, the * means it's active when low) and is kept low by being grounded. Pin 20 is the Output Enable line and it's driven by the NEO-GO chip.

If it's stuck or floating then check the pin on the NEO-GO chip. maybe the trace is buggered or the chip is bad.

If it's looking OK then check continuity between the CPU and the BIOS for the address & data lines as maybe you have a bad connection there.

Pinout for the ROM: http://www.datasheetarchive.com/datasheet.php?article=200387

Pinout for the 68000 CPU: http://www.datasheetarchive.com/datasheet.php?article=572166

RJ

 

[mainman]

Before you give up...

Check the OE* line on the BIOS... Pin 20 on the BIOS goes to Pin 59 on the NEO-GO chip. If it's not pulsing then the BIOS isn't being read.

On the BIOS, pin 2 is CE* (Chip Enable, the * means it's active when low) and is kept low by being grounded. Pin 20 is the Output Enable line and it's driven by the NEO-GO chip.

If it's stuck or floating then check the pin on the NEO-GO chip. maybe the trace is buggered or the chip is bad.

If it's looking OK then check continuity between the CPU and the BIOS for the address & data lines as maybe you have a bad connection there.

Pinout for the ROM: http://www.datasheetarchive.com/datasheet.php?article=200387

Pinout for the 68000 CPU: http://www.datasheetarchive.com/datasheet.php?article=572166

RJ

Thanks for giving me new hope although I did use two different bios to test even changed the 68000 and I think I performed a continuity check between the processor and bios but will do it again along with probing those area you suggested and get back with you on it

 

[channelmaniac]

Hey mainman

In the course of fixing a few boards I've found that this set of symptoms can show up if you have boogered control signals to the Backup RAM. There are three controls: WE*, CE*, and OE*

( * means active when the signal is at logic low)

If the Write Enable, Chip Enable, and Output Enable lines aren't working right then the board may end up where it won't boot. I had a couple of boards I've fixed over the summer with that issue.

Raymond