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ShootTheCore

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I've had a Taito G-Net board sitting in the repair queue for a few months, and I finally tackled it this weekend.

This board had an issue where Coin 1 was shorting to Ground, causing games to constantly reboot with a Coin Error message. Enabling DIP Switch 4 lets you access the Service Menu at least.
IMG_1075.jpg

G-Net uses a Sony ZN-2 for the base board. I know @Hammy does a lot of work on this hardware, so I reached out to him early on. He told me that the 74LS253 TTL logic chips that handle control inputs fail frequently.

I traced Coin 1 from the JAMMA edge, through a few vias, resistors, and capacitors, and finally landed on Pin 3 of IC558.
IMG_1076.jpg

Sure enough, when I tested this pin for continuity with ground, it beeped through on the multimeter. None of the other 74LS253 chips did for the same pin.

I carefully desoldered the failed 253 TTL, and swapped in a fresh one.
IMG_1077.jpgIMG_1078.jpg

Now the Coin 1 input registers correctly. I played a full round of G Darius to test things out, then left it to soak test overnight.
IMG_1083.jpg

Happily, everything still functions correctly one day later. Successful repair! :thumbsup:
 

stj

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nice, but why the capton tape?
the surrounding parts wont be effected by the heat - just get a bit of a reflow :)
 

ShootTheCore

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and get blown away without the tape if you work with hot air.................
Exactly. I’m using hot air to evenly melt the solder on the SMD TTL, and I don’t want any of those tiny nearby SMD resistors and caps to shift.
 

stj

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lol - thats why you turn the flow up and down :)
 
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