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NeoGeo 4 Slot Error


schmake

Question

Hi Guys, looking for some guidance here.

 

After updating my 4 slotter NeoGeo to Uni-Bios 2.3, the board has not been happy (must've liked the dust layer on it).

 

After a cold start you can usually play for around 15mins before getting an exeption error. Then it's all over, the machine will usually just boot up into an exception error pretty much straight up. That is either from a soft reset on the uni-bios or powercycling. The bios is not the problem as if I put the original bios back in it begins a continuous reboot cycle.

 

If I remove the top board, and start it cold it will boot to the test pattern and can easily navigate all options. I left it sitting like so for hours and didn't get any exception errors.

 

I've attached some pics of some of the errors that I've been getting. I don't have a logic probe on hand, but could get access to one for a check of chips... but I'm not sure what to check :unsure

 

Any help would be much appreciated

neo1.jpg

neo2.jpg

neo3.jpg

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I have thoroughly cleaned the top board, no sign of ICs with corroded pins etc, or any broken traces.

 

Cart connectors are completely clean, plus carts work fine in another board, so no problems there.

 

Once again after working for a while it will then go into watchdog reset if using original bios, or exception error if using uni-bios.

 

I was hoping that someone could decipher the uni-bios error messages and give me some direction of which IC's to check :(

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With the top board off the board isnt really doing much so its not really a valid assumption that the error is wholey on the top board.

 

Try putting the old BIOS chip back in, if the board is suddenly rock solid again then perhaps its some incompatibility with the new BIOS thats causing the problems.

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Once again after working for a while it will then go into watchdog reset if using original bios, or exception error if using uni-bios.

 

hes already tried that. If any of the program buffer IC's on the top board are faulty then you could get this error.

A second board would be helpful at this point.

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So top board off its fine, top board off without cart?

have you tried getting into the uni bios start up menu and enabling startup hardware test? its turned off by default.

 

I just enabled startup hardware tests in uni-bios, but I can't notice any difference :unsure There's no on screen reporting of any description

 

Something else strange is that after its 'crash'/reboot after 5 mins running, if I take off the top board, it boots to the cross hatch /mem viewer screen then pretty much straight away goes into the watchdog reset :( I'm really confused now

 

I will have to give the bottom board a good look over too

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Seriously you should put the old BIOS back in and test the board in its original state. You could spend hours and hours looking for a hardware fault when none exists. Your board should be compatible with the new BIOS but there is no real guarantee. If the problem remains with the old BIOS then you are dealing with a hardware problem.

 

Afterall you know you have made a change and that it worked before, therefore main suspect at this stage has to be the change you made, which if its just a new BIOS eprom then its very easy to roll it back and rule out the BIOS code, you also need to rule out the chip itself I guess.

 

Its basic troubleshooting process, so apologies if you have already done the above.

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Thankyou for everyones replies

 

The old BIOS was uni-bios 2.2, I removed the IC and relfashed to uni-bios 2.3. After these errors started occuring I decided to put the stock bios back in again. Unfortunately the same errors are occuring :(

 

Hopefully I will get some time this weekend to give the board a good look over. The fact that everything runs fine for while until 'heating up' makes me unsure what the problem could be.

 

I thought I had isolated the issue to the top board, however last night I knocked that idea on the head.

 

I'm beginning to wonder if it is the Z80 CPU not wanting to work after heating up :unsure

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It could be heat related but I dont see why noone has questioned the PSU or the condition of the power.

Measure +5v before and after the edge connector and measure at the far end, voltage drops could be a cause of the problem.

Clean the edge connector with a rubber and make sure +5 is no less than 4.85 at the top board....

It could also be dry joints on the custom chips a common problem for the type of IC, investigate with a magnifying glass...

If a IC is getting hot and failing running your finger on each IC will help find it, generally no should be to hot, if you find one thats hot you can use freeze spray and see if the effect are immediately reversed... I consider this a long shot though.

Its possible you have some main program memory thats faulty, that memory when it goes bad causes watchdog tripping with the original BIOS as well as the customs, after that the board will not watchdog but will tell you what IC is bad...

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Well last night I finally got a chance to look at this again.

 

I checked the voltages last night, and there is no problem there at all.

 

It appears though whatever the issue is, it is progressively deteriating. The board no longer works for around 5+ minutes, it's down to around 30sec to 1 minute now. Once it crashes, it won't work again until cool :(

 

I couldn't detect any IC's that appeared to be running super hot, but I didn't spend much time last night.

 

I think that I will need to dedicate a fair whack of time this weekend to go over the board with a fine tooth comb

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