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Long story short, shitty monitor fried my 2 slots sync. Just a rolling image now. It fried several resistors and all have been replaced, but didnt fix the problem. Any ideas?
Thanks
Thanks
Busted Sync on 2 Slot
- Thread starter NeoTurfMasta
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On early boards (not sure about yours but the basic facts will be the same) the sync is generated by the graphic chip LSPC A0 (pin 126) and from there it goes to gate 4 of a 74LS86 and then it's sent to the jamma connector through a 100 ohm resistor. So the complete path is:
LSPC A0 (pin 126)
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74LS86 (pin 12)
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74LS86 (pin 11)
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100 ohm resistor----470 ohm---VCC
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Jamma pin P
If the resistors were burned and replacing them didn't change anything, then the LS86 is also burned and you need to replace that too. If it reached the LSPC you're totally screwed.
LSPC A0 (pin 126)
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74LS86 (pin 12)
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74LS86 (pin 11)
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100 ohm resistor----470 ohm---VCC
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Jamma pin P
If the resistors were burned and replacing them didn't change anything, then the LS86 is also burned and you need to replace that too. If it reached the LSPC you're totally screwed.
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stuffmonger
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a trace might also have been burned up, and is no longer connecting components...
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Thanks guys.
I went through all the traces and they seemed fine.
MKL, I cant seem to find the 74LS86 chips you mention, but I do have 2 74LS273 chips in that general area. They dont seem to have any signs of damage. Would they if they were fried?
I went through all the traces and they seemed fine.
MKL, I cant seem to find the 74LS86 chips you mention, but I do have 2 74LS273 chips in that general area. They dont seem to have any signs of damage. Would they if they were fried?
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NeoTurfMasta said:
The LS273's have nothing to do with sync.
Just follow the sync trace until it arrives at some component: it must go somewhere and most likely it will be some OR/XOR gate. I've just checked a MV-1FZ and it's basically the same as what I said before: sync output is on pin 150 of the LSPC2 A2 (a later version of the graphic chip), from there it goes to pin 1 and 2 of a 74LS32 and from pin 3 of the same IC it goes out to the Jamma connector (with 100 and 470 ohm resistors in between). Now I don't have a 2-slot to check (sold it last week) and perhaps it will not be a 74LS86 but no doubt something similar...
Look at the LSPC, it's one of those large square chips. If it's a LSPC A0, then follow the trace that goes out from pin 126, it'll lead somewhere...
And if you can't seem to find anything post some hires closeups.
BTW, where is the DIP switch bank located on your 2-slot, near the controller port? (this would tell whether you have an older or newer board)
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The dips are located by the battery and not the controller ports.
Looks like it goes from the 100 ohm resistor to pin 24 of NEO-IO. I can trace the LSPC chip tomorrow. I hope its not the NEO-IO.
Thanks again!
Looks like it goes from the 100 ohm resistor to pin 24 of NEO-IO. I can trace the LSPC chip tomorrow. I hope its not the NEO-IO.
Thanks again!
MKL said:
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That board has an alarmingly low number of standard TTL chips and many custom ICs 
Perhaps the logic gate that on other MVS boards is in a self-standing TTL chip here is contained in a custom chip (obviously serving also other functions). If the problem is indeed this custom chip, then the only thing to do is bypass it and create a direct connection between the LSPC and the sync pin on the jamma connector. It's worth noting that on AES boards there is a direct connection for sync between the graphic chip and the RGB encoder.
Perhaps the logic gate that on other MVS boards is in a self-standing TTL chip here is contained in a custom chip (obviously serving also other functions). If the problem is indeed this custom chip, then the only thing to do is bypass it and create a direct connection between the LSPC and the sync pin on the jamma connector. It's worth noting that on AES boards there is a direct connection for sync between the graphic chip and the RGB encoder.
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