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TobyRieper

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Heyy folks, I'm new here and would just like to greet everybody on these forums. I am helping out a firend who runs an arcade and needed some help with the model 3 videoboard. According to this help document over at aussie arcade forums (https://www.aussiearcade.com/forum/...logs/94380-sega-model-3-step-2-0-repair-guide) I have a faulty IC12.

The 'Polygon Memory, IC70 and IC71 fail the test and according to this guide the step 2 boards use a single IC (IC12) instead of the two afformentioned chips. I cannot find these chips NEC D4811650GF-A12 anywhere online apart from obscure Chinese sites. I read an article that said these chips can be found on an old Compaq laptop motherboard (https://www.techrepublic.com/blog/c...n-ultrabook-from-1999-the-compaq-armada-m300/).

The Mobo arrived today, alas the SGRAM chips are different! Instead they are Siemens HYB39S16320TQ. They are the same dimensions with a near identical pinout. Could I use these slightly different chips instead? If anyone could have a look for me and see if these are a compatible replacement that would be great as I'm not too clued up on the ins and outs of RAM chips. Replacing them is not a problem but finding the part is!


Here are the links to the datasheets:
https://www.usbid.com/assets/datasheets/8C/upd4811650.pdf

https://www.datasheetarchive.com/pd...df521f241dbd9effe52&type=M&term=HYB39S16320TQ

I really appreciate any help anyone can give.


IMG_20200125_171300991[74].jpg
 
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TobyRieper

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Successful- swapping the IC for aforementioned part works. Now have beautiful non corrupted graphics in all its glory. If anyone has a similar problem with one of these SGRAM boards looks like there's a few alternatives from the original. As long as it has the same memory and timings :)
 

Darksoft

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Hi,

looks like you found the problem to your issue. That guide that you linked to is very nice and I'm sure it will be very helpful on repairing some more model3 Video boards. These fail A LOT, so any help is always good.

Pinging @irepairsega
 

TobyRieper

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Thanks I hope it helps others :), I am now troubleshooting the DBS2 board. I've tested all the connections apart from the volume pot and the conductors going from the coin box to the cab. I've got power around 4v on the board and the 4 LEDs light up. No problems hearing the sound effects, crowd , car engines etc.
 
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