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Sega Model 3 (Rally 2) Voltage Issue

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Orphanzombie View Drop Down
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    Posted: 09 May 2019 at 6:08am
Hi

So im in the middle of restoring/fixing a model 3 sega rally 2 championship and am having issues with the left side psu and board.

I keep needing to change the voltage of the 5v on the psu to avoid the texture glitches and the rule of 5.07 that ive seen online for me is completely wrong as for the most part 5.04 has worked the best on my right side machine with no issuse due to stack rebuild with new video and cpu boards.

Could it be that my psu just is not reliable and just puts out whatever voltage is wants to that day with it being quite random and as i said before often requires i turn the pot to change it slightly every time it comes on.

Also it just slowly gets worse when i start it up at first its perfect no image sistortion and flashing but by race 2 or 3 some things look garbled such as car select screen car images and the manual and auto select buttons but technically still readable and in game the only noticable issue is the occasional white square in front which flashes occasionally usually once ever 20 to 30 seconds so when playing its not too noticable.

Sorry for rambling im sh*t at writing these and formatting but props to anyone who can decipher that wall of text.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote smc Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2019 at 11:18am
hi orhanzombie have you tried a new psu? try putting machines in stand alone and swapping psu;s over.
is this happening on both screens when units are synced? or just one side ?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Outrun2 Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2019 at 12:16pm
Original Model 3 PSUs are well known for being troublesome. Get a known good replacement Model 3 PSU, or better still, the newer Sun PSU found in Naomi cabs and more modern drivers (initial D, OutRun2 etc.) and use a converter loom.

This is an official 'upgrade' as Sega themselves even sell the converter looms.

If your setup is that sensitive though, you probably have a glitchy board in the stack.. probably video board or ROM board. Sometimes you get improvement when the components warm up, sometimes the opposite.

One easy thing to try is making sure all socketed chips are pressed down fully on the ROM board as this board is prone to flexing when removed from the stack.
Would like:
No more cabs.. please!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orphanzombie Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2019 at 5:57pm
Soy right side cab has a psu from houee of the dead 3 it had the same connectors as the naomi and seemed to work well but both sides wont work with the full 5.07 voltage with the right side perfering 5.04

The left side uses a giz10p maybe naomi psu its the same connectors and loom.

Also if the board has flexed does that mean permant damage because i have had an audio issue where no sfx play but music is perfect i jave also tried reseating ic37 and it hasnt done anything so could it mean i need a whole new rom board?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Outrun2 Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2019 at 7:28pm
Are you measuring at the board or at the PSU? If you're measuring at the PSU then some differing resistance in the wiring might explain the small difference.

In any case I don't think a board should be that picky about voltage if it's 100%.

Like I say, try the PSU that remains stable with the boardset that is glitchy.. that way you can rule out the PSU.

A flexed ROM board won't necessarily be damaged as such, just that one or two socketed chips might have been pushed/pulled out very slightly making for poor connection and maybe the slight errors you explain. Worth removing the ROM board and ensuring all chips are nice and snug.. without flexing it further.. just hold the back of the board with one hand and press down each chip with your other hand/thumb.
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No more cabs.. please!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orphanzombie Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2019 at 7:48pm
Im measuring the voltage from the 74 series chips on the rom board and il il try reseating all of the roms to make sure they have a good connection thanks for the suggestion
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Post Options Post Options   Thanks (0) Thanks(0)   Quote devtty0 Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2019 at 8:07pm
I had a bunch of board issues with my Sega rally 2 that were fixed by swooping out the original psu for a Naiomi one
wanted :
sega model 3 racing games
namco system 22 racing games
model 3 to naomi psu adapter
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orphanzombie Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2019 at 3:24am
i put a psu from sega chiriro virtua cop 3 into a daytona usa 2 machine and the loom matched up perfectly i also have another house of the dead 3 psu which is also another of the same psu with same connectors im guessing that will work
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