Quoted from MaxAsh:
If removing the daughter board is as hard as some people say, should I go for the Piggy Deux workaround board? Or maybe try to find someone local with another 80b and borrow their board just to make sure that's the issue?
If you don't have experience with removing the daughter boards on these MPUs, I'd highly suggest either sending your MPU out for repair or if you think the daughter board connections may be at fault you could try the Piggy Deux. It comes down to a time vs. money vs. risk of damaging the MPU further.
The daughter board is not an easy thing to remove/desolder, due to how it's all sandwiched together. You can't easily get under it with cutters to snip it out. The traces are thin on the MPU and pads don't put up with a lot of heat. Through-holes for the 2.54mm headers they used to connect the boards are sized too small so don't easily clear with a desoldering gun. In-short... it's very likely, if you haven't practiced on other boards, that you'll do some damage trying to remove the daughter board. I tried removing a few of these on junk boards years ago and spent a few hours between removal & then having to fix some pads/traces, and that was even with decent equipment and taking my time. Decided there had to be a better solution so people weren't damaging their MPUs (sometimes beyond repair) and that's when I created the Piggy Deux @ https://www.pinitech.com/products/gottlieb_piggydeux.php.
The Piggy Deux is designed as a plug-and-play fix for daughter board issues. You don't remove the original daughter board & there's no soldering involved. Takes just a few minutes to install (recommended you pull the MPU and set on a flat surface, remove the EPROM from the daughterboard, install the Piggy Deux with eprom into TC1). If the board still doesn't boot, then you've got other issues -- and if you can get the board working 100% without the Piggy Deux, you can save it for the next Gottlieb Sys80B.
Where the Piggy Deux could help is if as you press on the daughter board while powering on the game, you sometimes get the game to boot. Or if the game's booted and you press around on the daughter board, it resets or freezes. That usually indicates daughter board solder connection issues. In that case the Piggy Deux is an easy way to fix the issues that will save you a lot of time/frustration.
Considering what's been posted in this thread, the board was working BEFORE the installation of the NVRAM. Any time you have a working board that you make a change to and it stops working, 9 times out of 10 the problem is going to be where the change was made. If you haven't already dumped a lot of time into beeping things out at the 5101 socket, that's where I'd concentrate effort. If there's a small fleck or solder bridge making a connection between two address, data or other signals at the socket, the board won't boot because signals are shorted.
With the NVRAM out of the board, take some close-up pictures of the front and back of the 5101 socket. There might be something someone catches in those pictures that could help you out. Otherwise, if I was you I'd use a meter on continuity test and beep things out at the 5101 socket -- without any RAM in there. Use the schematic to verify connections and check adjacent pins for address/data lines that SHOULD NOT have a connection.
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NVRAM, Bally/Stern LED Displays & Mods for pinball machines