Q&A Thread

[porchy]

Thanks for the info.
I did eventually end up reading one as a 27c301 after your original advice. I read then as a 512 before i knew what i was dealing with, but now its all becoming clear.

Thanks again, youve been a real big help to me
Jon

[dlfrsilver]

Hello Raymond,

I'm back with a problem with a pipi & bibi Toaplan game board.

1) The custom gfx chip had some legs desoldered, with my very thin ironsolder tip i solder them back, the graphic corruption is out.

2) The sound was missing, due a deep cut on a part of the audio circuit part.

I can almost get the sound correctly now, but get Crrrrsshhhhh and the sound is not clear, but i have the music and fx.

My question is : By replacing the capacitors, will the problem be resolved, and is it due to bad capas ?

thanks !

[channelmaniac]

Could be related to missing sound samples on the sound section. The best bet is to check the outputs of the sound section with an oscilloscope before it goes into the amplifier section. If you don't have an oscilloscope then recap it and see if that fixes it since that will be the easiest thing you can do without the scope.

[dlfrsilver]

Could be related to missing sound samples on the sound section. The best bet is to check the outputs of the sound section with an oscilloscope before it goes into the amplifier section. If you don't have an oscilloscope then recap it and see if that fixes it since that will be the easiest thing you can do without the scope.

Thank you for this quick'n'fast reply it makes like a parasite noise in the sound. I have an electronic multimeter, could it be enough ?

There is also something else that annoy me seriously, my board has radial caps, but i saw another board of the exact same type, but this one use axial ones.

Could it be also a source of troubles ?

[channelmaniac]

Possible, but unlikely those caps would cause that kind of problem.

You can't really test that audio stuff with a multimeter. Maybe you could build an audio probe? Check Google for schematics.

[Macro]

Have you seen this before - Neo Geo 4 slot, (SLOT4F) - sorted out the main problems, and it works fine with most carts, however, on the odd one, such as metal slug 2, if gives me an error telling me I'm using a bootleg board. (screen image attached)

Any ideas on what could cause this and where I should be looking. (which part of the circuit)

Thanks

[channelmaniac]

Common issue.

Open the cart and take the boards out. Scrub the edge connectors top & bottom with a pink pencil eraser.

If that doesn't take care of it then clean the slots on the board. Instructions are out on http://www.hardmvs.com

Raymond

[Macro]

Actually turned out a bit easier than that!

I looked at the Mame source for inspiration, and it mentions that some carts use the watchdog as part of a security check, that wasn't happening on this PCB - sorted it out and MS2 now plays along with everything else.

[Peri]

Hi!,
    What if the SMD GALS go bad on Tekken 3/Tag?  I mean how to reprogram them as there is no data available...if you have please share

[channelmaniac]

I don't have those GALs dumped.

GAL/PAL/PALCE and PEEL chips are the achilles heel for arcade games. Most are not dumped so if a board has a bad chip you are stuck with trying to find a parts board to pull one from.

They are difficult to dump too. You may have to desolder them to be able to put them in a reader... and some have security fuses blown so you can't read how they were programmed. If this is the case the only thing you can do is try different combinations of inputs on the chip to try to reverse engineer the programming based on the outputs you get. I've never tried this so I can't offer any steps on how to do this.

[Macro]

If you have access to an ABI Boardmaster, then I did a script that will dump all of the IO conditions for the PAL / GAL, and a guy called Charles Macdonald did some code that will convert that back to compatible code to re-create the PAL. He also did some hardware to dump PAL's.

It works on combination PAL's, (hopefully) gives enough info to allow you to manually reverse engineer registered ones.

My page is http://www.arcades.plus.com/paldump.htm

[channelmaniac]

Thanks!

Those boxes look $$$$. I didn't see any on Craigslist or eBay but will look around to see how much I can pick one up for.

RJ

[porchy]

Hi,
Ive got a Neo Geo MV1A board thats giving me a Color Ram Bank0 fault.
Write 5555    Read 55FF

Have you any ideas where to start looking? Ive tested RAM 7 and RAM 8 and they test ok. Is bank 0 somewhere else?

Thanks in advance

[channelmaniac]

If it's not in the 64k SRAM chips (CXK-5864) or the chips that interface them then it'll be a chipset issue.

[porchy]

ive check those two so ill put it down to option number 3 of a chipset issue. Beyond my capabilities but thanks very much for your reply once again.

[kdubs2308]

Hi ChannelManiac, first off I want to say thanks for all of the great information you provide here, I wish I had just a subset of your troubleshooting skill.  I see on your incredible technologies page that you've repaired a few older Golden Tees in the past with some pretty bad damage.  I have a Golden Tee Fore! Complete green board that doesn't want to boot.  When trying to enter the test mode (holding start on boot up) I get 6 flashes on the status 1 light which apparently indicates an issue with the ram and possible open trace.  Have you ever come across anything like this before and is it something you might be able to fix?  I've been checking the continuity of the traces on the ram and currently everything is checking out.  I've also looked for any scratches on the pcb but I don't see any that are causing an open trace.  The game was working and just recently stopped and was housed in the dedicated cabinet the whole time so it shouldn't have any crazy physical damage.  The power supply is still providing the necessary 5V at the boot rom and the hard drive is also operational.  I feel as though I've reached my knowledge limit based on the tools that I have available.  Is there something obvious that I could try?  I'm also curious if you knew how long those other Golden Tee boards took for you to fix for cost purposes.  Thanks in advance for any help that you can provide!!

[channelmaniac]

Hi!

Thanks for the kind words!

Those pesky IT boards are difficult to work on. The last 2 I did took a couple hours each and I charged far less than I should've for the time I had invested, but the boards weren't worth a whole lot more than what the charges were.

I haven't worked on that particular type of board you have so I'll tackle this from a generic standpoint. For boards that come up with RAM errors the things to look for are the obvious physical damage from scratches, popped solder from physical hits to the board, or corroded pins/traces from foreign substances such as soda pop, beer/wine, rodent urine/feces, and other gunk that gets on boards. Next check for missing signals on the RAM chips and look for the reasons they are missing. Once that is exhausted then RAM chips have to be replaced one by one.

Sometimes you can get lucky and find the bad RAM with a logic probe or an oscilloscope. As an example, the Neo Geo systems still hold the CPU bus at 0 or 1 levels when the CPU or Backup RAM tests fail. This helps with finding some issues when there is no display telling what RAM is bad.

Raymond

[kdubs2308]

Raymond,

Thanks so much for the reply, unfortunately that's precisely the news that I was dreading.  I'm going to give it another once over to see if I can find anything amiss, but it's looking more and more like I may have to send it out to get fixed.  Is this something you would be willing/have the capacity to take on?  Just reading all of your forum information and seeing some of your past board fixes (all of which I find very interesting, just way over my head), you seem like you do great work.  I was hoping to find someone in the Cleveland, Ohio area but haven't been able to find anyone that does repairs.  My other option would be to send it directly to the maker, IT, to see what they can do.  Have you heard anything about the quality of their repair services?  They would obviously know the most since it's their board, but their rate is pretty pricy, and I'm trying to minimize the damage since I've already got a lot invested in the game.  Thanks again for your time and help.

Kurt

[channelmaniac]

Right now our repair services are shut down as we're moving and I have to get a new workshop built.

[kdubs2308]

Oh, Okay, then I will wish you good luck with your move.  Hope all goes well!!

[kn2000]

Hello!!  I'm new to the forum and have been a old school game collector for a few years now.  I'm having trouble finding repair or trouble shooting solutions for the Commodore VIC-20.  I came across one at the swap meet and didn't pay to much for it.  Seller didn't know if it worked.  Came with all the connection cables, tape deck, games and manuals.  All for $15!.  However when I plugged it all up it didn't work.  The red light comes on but the screen is all black.  I've check the RF adaptor and it works.  I check the power adaptor (first gen. 2 prong type) and it works. I opened her up and all looks visually 'ok'  the big capacitor is in good shape and nothing look damaged.  I tried leaving it one for about 1/2 hour to see if she 'warmed' up some of the old connection points and nothing.  Removed and reinstalled all the removable IC chips and nada.  I also tried to see if the tape deck would power up and fast forward and/or rewind and zilch.  Any one know where I could get some troubleshooting info or know what could be the problem.  I knew purchasing it that it might not work but I enjoy trying to bring 'new life' back to old machines.

Thanks in advance!!!

[channelmaniac]

Unfortunately on the VIC-20 it could be a number of issues... bad RAM, back CPU, bad ROMs, etc. Something is causing the computer to just not boot and there will be no video on the display until the computer gets into its startup routine.

[Sprout]

Greetings!  New to the forum, and hoping somebody has some insight.

Been digging around online, and not having any luck determining whether I can use an adapter to allow replacing 82S123/82S126 PROM's in a Ms. Pac.

I find some folks who've figured out how to sub a GAL for these, and at least one site is selling 82S123 to 2716 adapters (for older Bally pinball sound boards) - so I'm assuming this *should* work.

My project - I've got a Ms. Pac cabinet, and am configuring it so I can stuff various boards into it - MultiPac, Jr. Pac, etc.  I'm currently working on an extra Ms. Pac board, and attempting to convert it to a Crush Roller (aka Make Trax) board.

Game plays fine; colors are off.  Built two adapters today, for the color PROM's at 4A & 7F.  Adapter at 7F seems to function; regardless of whether I have my adapter in, or the original PROM, the screen looks the same.

However, for the 82S126 at 4A, I'm seeing *different* colors, but not the *correct* colors. 

Any reason why this wouldn't work for my purposes?  Also, the 82S126 has two CE's - do I need to have them both tied to the 2716's CE, or a specific one, or will either suffice?  I've tried tying the first CE, and both, but not seeing a difference.

The PROM code in this case goes from 00 to FF, and I've tried mirroring it all through the 2716 to be safe (00 to FF, 100 to 1FF, ...700 to 7FF).

I've tried burning the PacMan code for this PROM to a 2716 and dropping it in, and the graphics are NOT the same as they are as when I have the actual PacMan PROM installed.  I'm going to double-check all my wiring, but everything checked out immediately after I assembled the PROM.  Could this be related to the 2716 being too slow for this particular use?

My goal is to be able to burn 2716's for various games that are compatible with this boardset, and then swap them in when I swap out the other ROM's.  Those older PROMS are harder to find, can't be erased, and my various burners won't tackle them as well.

Thanks in advance for any ideas/suggestions!

Brent

[channelmaniac]

The 2716 is WAAAAAAAY slower than a PROM.  We're talking 50-70ns vs 300-600ns in speed.

However, the circuit you are using it on is pretty slow. To be sure you'd want to check it with a calibrated oscilloscope or logic analyzer.

Now... The 82S23/123 chips have a single /CE line (the / means active when at logic low) and the 82S126/129 chips have TWO /CE lines. The chip goes active when both are low.

On the 2716 you have 2 enable lines, a /CE and a /OE (chip enable and output enable) and both must be low for the chip to go active. Some data sheets call the /CE line (pin 18) "PD" and the /OE line (pin 20) "/CS" so read the data sheets carefully. In reading the Hitachi 2716 data sheet it appears that if you tie /CE low and use /OE to toggle the chip for activity that the cycle time is far less.

Now each of those chips have varying numbers of address and data lines...
2716: 11 Address lines and 8 Data lines
82S23/123: 5 Address lines and 8 Data lines
82S126/129: 8 Address lines and 4 Data lines

Extra upper Address lines must be grounded. You could use the upper address lines and connect them to switches to switch between banks for different games.

For example: 82S23 uses 5 address lines - A0 through A4. On the 2716 you could use A6 and A5 to toggle through different "banks" or versions of code.
00 - first bank
01 - second bank
10 - third bank
11 - 4th bank

Where the first digit is A6, the 2nd is A5, and 0=ground, and 1 = 5v.

If you leave the address lines floating you are asking for trouble. Same thing if you leave the chip select or chip enable lines floating. Some chips will internally have them tied high or low, but you can't trust all manufacturers to do that or to do it the same way (high or low)

Now... Looking at the schematics for Pac Man - 4A has both /CS lines grounded. The chip is always active. The chip at 7F is used the same way. It's select line is grounded too.

Enjoy!

[gamehits231]

I have just purchased a Neo Geo Arcade and Bust A Move.  I was curious on how one may reset the high scores.