What would stop an MVS 4-slot from booting up? BREAKTHROUGH: VIDEO RAM ERROR

So I bought a Neo, should get here on wednesday. But the mobo appears to be dead. When you power on the machine, the monitor and everything else comes on, but no picture/sound/credit LEDs. Now I thought it could be the voltage, but the guy I'm buying it from says he put the motherboard on a test rig and it didn't boot there either. So lets assume power is not an issue, what would cause the MVS to not start up?

Hmm...Dead board huh..

I'd not know the first place to look but I'd look for something burnt,broken traces,cracks..

.. the bad boards I had always went into cross hatch screen..or some error.

Nonetheless before putting another board in the cab I'd check the power supply making sure the voltages and connections are right otherwise it could just keep popping board after board..A Multimeter is a must when owning one of these cabs.

Unless the seller knows what he is doing and has tested the power supply..

I've see way too many hack jobs via Operators trying to get a cab going again that I have to go over anything I buy used..

There is a Fuse near the Power on switch..I'm not sure exactly what that fuse protects..If bad it may just keep the whole machine from coming on...I've also noticed a fuse in some MVS cabs running up the inner right side of them in a fuse holder.
Just things I'd check..


channelmaniac for board repair

I do want to note that the only other thing that doesn't come on is the marquee lights. It slipped my mind to mention it before. I really can't see all 4 bulbs being dead...

sounds like a ps to me but the lights can all go bad pretty easy there not bulbs but lighted pcb's

Pause Dip?

If the board tries to boot - goes through the normal gyrations with the green screen then goes to black then check the dips. They should all be up.

If the board clicks through the speakers and has colored blocks on the screen then it is stuck in watchdog and needs repairing.

If the board has junk on the screen and is frozen - no clicking - then it needs repairing as well.

RJ

channelmaniac said:

If the board tries to boot - goes through the normal gyrations with the green screen then goes to black then check the dips. They should all be up.

If the board clicks through the speakers and has colored blocks on the screen then it is stuck in watchdog and needs repairing.

If the board has junk on the screen and is frozen - no clicking - then it needs repairing as well.

RJ

Click to expand...

What if the board doesn't display anything... at all? It might have displayed garbage when I first turned it on and I missed it because the monitor was warming up, but I don't think it did. I think it was just a black screen from the second I turned it on.

If you get absolutely nothing then replace the 74LS368 chip that is next to the main crystal. Either it's bad or the crystal is bad.

DO NOT substitute a 74HC368 for an LS if you can't find the LS. A 74HCT series will work but not an HC.

RJ

OK I dont know if I can get the actual cabinet home today (pray for me) but I'm going to get the motherboard now. A few questions

1.) Am I correct in assuming that if the motherboard is working, with no carts it should display a cross hatch?

and

2.) The test rig I have setup is JAMMA. I know JAMMA and MVS are different, but not by much. Am I also correct in assuming that as long as I disconnect the speaker of the test rig, it will be safe for me to connect the MVS? Edit - I am incorrect, as it would seem the JAMMA harness would destroy the audio AMP.

OK. I went there today and took pics of what it does. I thought it did nothing, but it does show junk. And the speakers tick like you mentioned, so from what you said it most likely is the watchdog. Here are the pics:







CM, how can I repair this? I'm literally ready to work on it the second I get your reply. I'm a newb as far as knowing what lines are what on the MVS, I read a similar post you made about a 6-slot having "bad enable lines on the backup ram" which caused the COD, but I don't know where the ram is. I havent opened it yet, but if the only thing I have to do to fix this board is fix a broken trace, I'll be a very very happy camper. The only thing that sucks is that I'm very short on time too.

Edit- CM, what do you mean when you say things are "stuck high"? I have a multimeter here but I'm not sure what to set it to.

Edit again - added one more pic from my test rig. I opened up the board and took a look at it... honestly, it looks minty fresh. It's dusty, but other than that the board is clean. There was one cause of concern when I saw what appeared to be flux grease (thats the only way I can describe it, it's not flux but that yellowy grease that comes from it) on the underside of the top board (if youre looking at the top board with the arrows facing up) the connector on the left, and on the third F253 chip in the top left corner of the same board (third from the top down left most row). I'm charging my camera to take better pics of it.

ShmengeTravel said:

CM, how can I repair this? I'm literally ready to work on it the second I get your reply. I'm a newb as far as knowing what lines are what on the MVS, I read a similar post you made about a 6-slot having "bad enable lines on the backup ram" which caused the COD, but I don't know where the ram is. I havent opened it yet, but if the only thing I have to do to fix this board is fix a broken trace, I'll be a very very happy camper. The only thing that sucks is that I'm very short on time too.

Edit- CM, what do you mean when you say things are "stuck high"? I have a multimeter here but I'm not sure what to set it to.

Click to expand...

You need a logic probe to check what I'm talking about in those posts, preferably a logic probe with audio functions.

RJ

Well even if something is stuck high, the only way to fix the issue would be to replace the chip provided there are no broken traces, which I haven't seen any. Am I right? If this is the case I think I'm just going to order a replacement board. I think I might order the replacement board anyway and just sell this one back to the guy I bought it from. He can fix it, just not in time for Christmas.

Edit- I'm trying this board repair one last time. Out of curiosity, what would happen to an MVS board if you booted it *without* the top board attached? Would it produce the same garbage screen? Because mine did, only the system did not reset like it did with the top board attached.

Edit again - added pics. I also checked each chip to make sure they were getting power and everyone of them came back at 5.03v.






Edit a third time - breakthrough! after doing what appears to be absolutely nothing, having the top board disconnected and testing the bottom boards chips for their voltage, the board started the test cycle! I finally got a visible error message, and it was as follows:

VIDEO RAM ERROR

ADDRESS WRITE READ
00008000 5555 5500

Now if only I knew where that was, and how to fix it I might have a great sluggers PCB that I can use for spare parts... maybe thatll have the IC I need? Also, once I put the top board back on, it started the watchdog thing again. HOWEVER, sometimes it doesn't. Sometimes it will do the watchdog thing, other times there will be random garbage on the screen, then a black screen, but no attempted reset - it just sits there. I know this particular post is 9000 words long but heres the basic summary: With just the main board attached, the board goes through watchdog quite rapidly 5 or 6 times, then begins the hardware test before showing the video ram error. Once the other board is attached (with the cart), it just repeats the watchdog every 7 seconds or so.

You might have a bad Video RAM chip(s), though if the sound is also not working then it might be a global problem effecting the entire board. I would go across all the chips on the two boards and check to make sure there are no broken traces. I don't know where the Video RAM is located on a 4-slot but I'm just assuming that it would say on the PCB what the chips are.

I know I'm not being much of a help but I thought I'd chime in and speak my opinion.

Actually, looking over those boards again, they look pretty good. I don't think it would be traces on the board that would be causing the problems you're having, perhaps it's the Video RAM chip(s) themselves that are bad.

Oh yeah, I have a question. Why is there Electrical tape on the JAMMA edge connector?

Koopa64 said:

You might have a bad Video RAM chip(s), though if the sound is also not working then it might be a global problem effecting the entire board. I would go across all the chips on the two boards and check to make sure there are no broken traces. I don't know where the Video RAM is located on a 4-slot but I'm just assuming that it would say on the PCB what the chips are.

I know I'm not being much of a help but I thought I'd chime in and speak my opinion.

Click to expand...

It's always welcome Koopa I'll keep you posted!

That particular video RAM chip will not keep the system from booting.