Replace the 5101 socket

It common for the U8 socket to fail due to corrosion from leaking battery or just from age, as pinben suggested, replace the socket. Be careful when handling the 5101 IC, they are very sensitive to static electricity.

Yes basically. The 5101 plugs into a socket at U8.

With a logic probe you can test the socket. With the ROMs removed, all pins should be pulsing except CE2, Ground and vcc (+5v). Probe on the 5101 leg while plugged into the socket. Just note pressure from the probe lead could make continuity.

You have to get that battery corrosion cleaned up before anything is going to be reliable on that board.

DEN, you don't need a kit, this thread is a great step by step guide!

https://pinside.com/pinball/forum/topic/stripping-battery-corrosion-with-a-strong-acid

Bleach is an alkaline with a high PH number about 12. It is similar to the battery leakage that caused the damage to the board.

You need to find an acid based liquid. If you examine the various toilet bowl cleaning products you should be able to find one that is HCL (hydrochloric acid) based. Vinegar is also a weak acid that has been used in the past for neutralizing battery corrosion.

The HCL product that is recommended is a jell like substance that doesn't run easily. However with care and multiple applications you can use a runny acid product to clear the corrosion.

Also, you can use Muratic acid associated cleaning concrete.

Using a strong acid is dangerous and extreme care must be exercised in use.

Using an acid based product to remove and nutrialize alkaline corrosion caused by battery leakage will not
damage potted chips, resistors, ceramic capacitors or diodes. Do not get acid on electrolytic capacitors or
relays.

So you have to use care in the use of acid on your circuit board. Alkaline corrosion follows the tin/lead traces
and creeps up the legs of chips and can get internal to chips and other parts in serious corrosion conditions.

So that is why chips, resistors, sockets and other components in corrosion areas need to be replaced.

Products do not usually indicate the PH number but list components. So you are looking for a product with
HCL as the main component and is usually indicated as a percentage of the total product, such as a 5%.