Quick question. I'm currently dealing with trying to fix my bootleg Mortal Kombat board but I tested the voltage of the board while it was powered on just to see. The +5v was at something about 4.4v. I tried just turning on my power supply (it's a PC ATX PSU) and it did seem to have 5.0v then if I recall. Or atleast it was higher. I didn't have time to measure any other boards of mine yet, but is this normal? The voltage was the same at the edge and on the other side of the board, the daughter board as well. Should the +5v rail be at +5.0v while under load? Do I need to replace the ATX PSU with a real arcade PSU like this? http://na.suzohapp.com/powersupplies/80006400.htm I believe -5v and the +12v were spot on, +12v may have been slightly over but I forget if that was on load or just the PSU on by itself. To be clear though, the same PSU ran Mortal Kombat II, NeoGeo MV-1, CPS1 SF2CE, and CPS2 MshVsSF with no problems. But I guess some boards could be more sensitive to lower voltage. Update: Had the chance to test some more. No load the PSU was something like 5.3v. I tested it under load with my NeoGeo MV-1, 4.9v steady. I'll retest the MK1 board but 4.4v is a big difference.
I realize your board is a boot but the actual Midway boards from this era require around +5.2v to run correctly.
Should it measure that under load, or with no load? Is my only option to replace my PSU with an adjustable one that can raise the 5v output?
With load. If you're running PCBs, always best to have an adjustable PSU as there are some very picky ones out there!
Sounds like I may need to replace my PSU, though none of my other boards seemed to have issues. I recall running MK2 on it ok before. Also I retested the voltage on the MK1 pcb (after cleaning the edge connector some) and it measure 4.6v with some dips to 4.5v. Still could clean the connector up a bit. The board has something like 100+ chips on it, many are 74LS series. I wonder if replacing them with compatible HCT chips would reduce the current draw and help.
No one anywhere seemed to suggest that the ATX style PSU's would have such an issue. And to be fair my Capcom and SNK boards all function fine with it.
Well my point was unlike the infamous issue with Midway games running at an odd 53hz or 54hz refresh rate, this voltage issue with Midway boards I hadn't heard about. I certainly hadn't heard anything negative about using ATX PSUs until now, other than more recently that newer ATX supplies lack the -5v line.
A PC supply should easily handle 2-3 A drawn by the bootleg. Since this board is damaged perhaps there's a short (damaged chip), too much current is drawn and the current-limited output kicks in at whatever 4.4V happens to be. I really don't understand why people insist any arcade games need >5.0 V. Exactly which components recommend that?
Which Midway games run at that rate? Seibu games do that but not aware of any Midway games and I have almost all of their boards from their JAMMA/non-PC hardware era.
Mortak Kombat and I imagine all Y-Unit, T-Unit, and Wolf Unit games run at that rate. Calpis, the board is functional though. I don't see any obvious cause of something drawing too much current. When I have a better PSU I guess we'll see. Unfortunately the JammaBoards website posted saying something about a medical emergency and it seems like my order may be delayed.
You need a decent ATX PSU as well. Cheap yum-cha brand PSUs will give voltage drop on relatively small loads, despite what their badge wattage rating might suggest.
Agree with RetroSwim - I just had to replace my "750w" PSU, as under full load with my new graphics card the 12v line was down to 11.16! New (branded!) PSU and all is well.
I was worried to go with another ATX PSU because who knows what a good one really is and ATX no longer supports -5v which is a big no-no. Atleast I noticed that with newer PSUs. -5v is part of the JAMMA standard and required for games that I own. Anyway, when I get my Arcade PSU possibly today or tomorrow I'll just have to install it into my SuperGun. It'll take a bit of reworking things but hopefully I can fit it in there in the space allocated for the PSU. But I'm hoping it solves the issue with that particular board.
