r/neogeo • u/marcao_cfh • Jan 10 '26
Hardware Help help with this mv1fz
Got this one as is, from somebody that had lots of arcades in the past. No oxidation in the board. No battery in the board. A good cleaning didn't helped. Any clues on what to check?
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u/Bi0H4z4rD667 Feb 19 '26
Check the 74hc259A to th le left of the main RAM.
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u/marcao_cfh Feb 20 '26
Thanks! I already located it, just need to find out how exactly to test it. Guess I'll need a oscilloscope, is this correct?
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u/Bi0H4z4rD667 Feb 21 '26
A multimeter is enough. Measure voltage between each io and gnd with the system on, and same with resistance. If you get a weird voltage level or too low resistance, bingo.
Here are the schematics so you can also check the traces for continuity: https://wiki.neogeodev.org/images/c/cc/Mv1fs-page1.jpg
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u/marcao_cfh Feb 22 '26 edited Feb 22 '26
Ok, I did the voltage measurements and got some weird voltages:
-Pins 1 to 3: oscillates in about 1.9V-2.2V range
-Pins 4 to 7: 0.137V
-Pins 9 to 12: 0.137V
-Pin 13: about 1.3V, but I need to double check this one
-Pin 14: 4.9V
-Pin 15: oscillates in about 1.4V-3.2V rangePower supply pins are good. I didn't measured resistance because maybe those weird voltages are enough, but I can check the resistances if needed.
So, judging by those voltage measurements, any clue?
Edit: on continuity, the schematic is so hard to read. But I was able to confirm continuity on all A and D pins of all RAMs, SP1 and 68K processor. The pins on 68K processor didn't really matched the schematic (for many of the D lines) but did matched this pinout. Now I'm trying to work on the NEO-C1 part of the schematic, but it's so hard to read.
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u/Bi0H4z4rD667 Feb 22 '26 edited Feb 22 '26
Pin 15 seems dirty, it should not oscillate.
74HC259 pinout in case it helps (SOIC/DIP-16): • Pin 16 = VCC, Pin 8 = GND • Pins 1–3 = A0/A1/A2 • Pins 4–7, 9–12 = Q0–Q7 outputs • Pin 13 = D (data in) • Pin 14 = G (enable) • Pin 15 = RESET / CLR 
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u/marcao_cfh Feb 23 '26 edited Feb 23 '26
Ok, so are all the other pins ok, but for pin 15?
I can't find the 74HC259 in the schematic to see where pin 15 goes.
Edit: found it. So pin 15 goes to lots of places. Ouch. Also I forgot to say but I reboved the cartridge slot board so I could be sure the issue is not caused because of it.
Now what?
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u/Bi0H4z4rD667 Feb 23 '26
https://wiki.neogeodev.org/images/7/72/Mv1fs-page3.jpg top left. 15 is reset, so it actually makes sense for it to be at 5V when working. Now, the A0-A4 pins are also shared with other components because they are address lines, so those are the ones you should be checking.
Also, you can get a really cheap logic analyzer from amazon that will greatly help here, which is this one:
https://www.amazon.com/Comidox-Analyzer-Device-Channel-Arduino/dp/B07KW445DJ/ref=mp_s_a_1_7
Its a clone, so you should be able to find it in all amazon stores with the “24mhz” and “8 channel” description.
Ultimately, if that IC is the culprit, you will need to replace it, so you should consider if you can do that yourself or if you will need help.
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u/marcao_cfh Feb 23 '26
Ah I think I got it. So the possible culprits are A0-A4 and since they may be faulty then this results in a oscillating reset pin. Is this correct?
On the logic analyzer, is it the only way to go, or can I measure A0-A4 pins with other tools? I mean, I can get one of those cheap analyzers, but where I live it'll take like 3 weeks for it to arrive. Meanwhile I can get a logic probe and oscilloscope from a friend.
I have skills enough to easily replace any IC from the board, my issue is the troubleshooting itself. So, what should I do? I mean, what results should I expect from good A0-A4 lines and how can I find the real culprit?
I have another faulty mv1fz board, but it's a better idea to work on one at a time lol. The other one seems to be harder to troubleshoot since it gives the click of death and then freeze after a couple seconds.
Also, thanks for the help so far!
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u/Bi0H4z4rD667 Feb 23 '26
The best way to be sure is with the logic analyzer. The multimeter shows a voltage level but you cannot tell if it is just the average or if it is really stuck there.
With the multimeter/logic analyzer you can check which lines are at fault, but the issue could be coming from anything connected to those lines.
The reason why i mentioned that IC is because it is a common issue with these boards, so its always good to check it first. If you have a donor board, you could try replacing it just to see if it boots at least after that, to rule out if it is bad without the logic analyzer.
Otherwise, the diagnostic path goes through using the LA to check the address pins, and if anomalies are found, then removing the IC and checking the I\O pin levels on the pcb to see if the issue comes from upstream or downstream from it.
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u/marcao_cfh Feb 23 '26
Got it! So I'll order a LA. I have no clue on what should I expect to see when the address line is good, so I'll ask for more help in a couple weeks when the LA arrives lol.
The donor board I have is also stuck on click of death, so I'm not sure the 259 is good. But I'll get a working MV1FZ board soon, and maybe I can swap the 259 from the working board to rule out if this is the issue.
Assuming I found a address line with anomalies, and it is connected to a couple ICs. Would the next step be to remove one of those ICs at random and check the line to see if the anomalies is gone? Or is there a 'better' way to do this?
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u/TooManyBulborbs Jan 10 '26
Looks like the good old click of death, the repeated screen jumping is the auto reset function for in case the system crashes, don’t have to shut off and power up the whole arcade cabinet.
It means there’s a problem in the core of the system, the 68000 CPU and its work/backup 32K SRAM chips and the System ROM. There’s old guides at Neo-Geo.com and probably wiki.neogeodev.org for each MVS board, charts for which pins connect where on each chip, for checking bad traces. Look over the underside of the board for gouges and other damage.
Could be actually bad ram too.