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Thread: Typical Video Ram error but also grounding questions

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    . DoomyDoomer's Avatar
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    Typical Video Ram error but also grounding questions

    Hi All. I recently bought an MV1C from eBay. I had it up and running with a jamma harness and video out through Helder's RGB to Component board (based on Ace's design). While playing KOF98 (actual cart), the screen started showing artifacts and then finally failed to the typical Video Ram Error:
    IMG_20190814_235427.jpg

    After doing some research, it sounds like this is my slow ram (5 or 6) so I ordered the ram and hopefully this fixes the problem. The real confusion I'm having now though is while testing the board for continuity, I noticed the GND and +5v shows continuity. Is this normal for this board? Note, nothing is connected while I tested this. The board itself doesn't show any signs of bad/bridged traces from what I've inspected. Another odd thing about this board is the sync line doesn't work properly with the RGB to Component circuit through the sync separate LM1881 chip like it should. The picture was b/w and jumpy until I moved the sync to the green line out prior to the 220 uF cap and 75k resistor. I'm really just trying to make sure that if the new ram fixes the problem that I don't end up frying it again if indeed it was a grounding or voltage issue. Anyway, thanks in advance for the help.

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    Cham Cham's Banana
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    So does your multimeter have a long continuous beep or just a short beep when testing ground to 5v? Short beep is fine and it's usually just a sign of dying batteries in the meter pr a small amount of residual charge left in the circuit. My MV1FZS won't work with a sync stripper, it's kind of hit and miss. I've discussed it a bit with Xian Xi and it's usually something that's TV dependent. For example on my TV I can't use it, but at my grandmas house it works with or without it. The new ram should work fine, just test the pads before you put the new ram on to make sure there isn't a bridge.

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    So I probably need to invest in a better multimeter at this point. It doesn't have the beeps but shows anywhere from 000 to 003 on the display when I last checked. That's interesting about the sync stripper. I only have one newer TV that will play nice with the MVS' clock.

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    If no sound, it should have a symbol like a minus sign next to the number to indicate continuity.

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    Interesting. I'm not sure I've ever noticed a minus sign on my multimeter for continuity. Usually it reads 1 for no continuity and then 000 for continuity. It's a Commercial Electric MAS830B, very inexpensive meter. I just ordered a nicer one that apparently does ttl logic as well as has the audible sound for continuity. I installed my unibios last night and was able to get past the watchdog error and boot up KOF98. The new RAM comes today so hopefully it fixes the issue:
    IMG_20190818_223759.jpg

    Another question I have is about voltage. I bought a PSU that does 5v/5A to work with both my NEO-POW (I created a reverse polarity adapter for this) and MV1C. Without getting into 5A being overkill 99% of the time, I'm reading 5.33v at the tip and 5.22v at the jamma edge, nothing attached (cart, controller, speakers etc). Is this too much voltage?

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    Cham Cham's Banana
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    I have a 2016 4k UHD TV so it's definitely newer and plays well with the weird sync as well. 5.22v should be fine as I've seen people crank it up higher than that to get their cabs working, but I wouldn't raise yours more since it's not in a cab. However you should test with a cart since some power is diverted into the cart, however with 5A you'll most likely see little to no change. Have you checked that you wired the sync stripper in properly? I have mine on a toggle so if I get a different TV I don't have to install it again.

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    The sync stripper isn't the cause of all the artifacts on screen, that's bad ram. The sync stripper is wired "correctly" according to the board (you really can't screw it up). I can't say if Helder's PCB is or isn't wired correctly but it appears to be based on the LM1881 datasheet. Here's the PCB I'm referring to:helder_rgb2comp.jpg

    So your sync is on a toggle to toggle between running to the LM1881 or directly to cap/resistor or direct to green (Y) out? At 2.2 gamma, mine looks dark at the last cap/resistor before the green out but it also looks too bright on the opposite side of that cap, directly on the resistor. I probably need to adjust the cap on the sync and then feed it directly to the resister before the green out. It really does seem like trial and error with this circuit.
    Last edited by DoomyDoomer; 08-19-2019 at 01:07 PM.

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    Cham Cham's Banana
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    I didn't use Helders PCB, I used a JROK component encoder and a separate sync stripper. I wired it according to jammanation-x "Middle pin to output, top pin you splice Jamma sync and sync in to the sync cleaner then sync out from the cleaner to the bottom pin."

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    I'll have to take a look at that tutorial at JNX. It sounds like the 8 pin din connector as where I'm going straight YPbPr component. I'm fairly new to video encoders, if it wasn't obvious, but I understand the concept. I might reach out to Helder directly about the board but I hate bugging him.

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    Cham Cham's Banana
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    I'm not sure how you would wire in the toggle for that PCB but hit up JNX on messenger. I feel bad about how much I bug them but hey they're the most accessible and knowledgeable people in the community for this type of thing

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    Just a quick update on this. I was able to replace the ram easily enough so no more artifacts/video ram errors. My component signal looks as good as it's going to get at this point with this circuit. It actually looks really good and what I did was pull the 680ohm resistor after the LM1881 and then took the output to the last cap on the green line. The LM1881 was actually going back into the encoder IC in this circuit which is odd at least for the MVS/AES. I took a stab at creating my own composite / S-video encoder and followed the CXA1645 datasheet's schematics but I think my CXA1645M (SMD version) is toast from an old PS1. I might give the AD IC a shot since those are readily available. I'm still concerned about the amount of voltage coming in. These PSUs should have a tighter range on 5v... I might look to replace it but most show a similar range.

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    Cham Cham's Banana
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    Do you use a computer power supply or is your board modded for 5v only? I can link you to some good 5v power supplies

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    Quote Originally Posted by DoomyDoomer View Post
    The sync stripper isn't the cause of all the artifacts on screen, that's bad ram. The sync stripper is wired "correctly" according to the board (you really can't screw it up). I can't say if Helder's PCB is or isn't wired correctly but it appears to be based on the LM1881 datasheet. Here's the PCB I'm referring to:helder_rgb2comp.jpg

    So your sync is on a toggle to toggle between running to the LM1881 or directly to cap/resistor or direct to green (Y) out? At 2.2 gamma, mine looks dark at the last cap/resistor before the green out but it also looks too bright on the opposite side of that cap, directly on the resistor. I probably need to adjust the cap on the sync and then feed it directly to the resister before the green out. It really does seem like trial and error with this circuit.
    I have made a few of those boards. I have recieved mixed results.

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    I use a "brick" style 5v/5a power supply that resembles something you'd see on a laptop. Thanks, links would be great.

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    Quote Originally Posted by NexusX View Post
    I have made a few of those boards. I have recieved mixed results.
    I talked to the designer of the board and he said this version of the circuit wasn't his favorite. Apparently there's a vers 3 that has better output. I did eventually get a good picture out of it but if I were to do it again, I'd follow ver 3 of the circuit and just perf board it.

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