It's a jumper that tells the machine what size ROMs to expect, in this case that a 2716 ROM will be in position U2. What ROMs do you have in your machine?

Can you post a picture of the lower half of the board showing the U6 ROM and the jumpers to the left of it?

Looks identical to the OE board in the Silverball Mania I recently finished, down to the same wire stripe. I never questioned it...

IMG_6199 (resized).JPG

It is jumpered wrong for those ROMs. Checkout Bally/Stern on pinwiki.com for what jumpers are correct.

E11 to E25 would be setting the board to trigger U2 Pin 20 off of /A14. Is that for 2532 and similar type of masked PROM?? I have seen that jumper done many times, but not really sure why they use it as I would normally always convert right over to the typical 2732 jumper setup we use.

The standard jumpers for 2732 have u2 of triggering with /(vua+q2+a12)+A11.

It depends if your ROMs are proper. Considering ive seen countless MPUs with that jumper setup, it will work in some situation.

If you are locked up and unsure / know about your roms/jumpers are mixed up/good. Then you rejumper the board for two 2732s and get new known good 2732 ROMs.

The board's design works for different design memory chips.

The board requires the jumpers be set to support the type of ROM chips that are in the game.

So 'why is there a jumper'? Because that's what intended to be there
'Is it needed?' - Basically yes, but being there doesn't mean its right. You must have the jumper setup match the chips in use.

That jumper setup won't work with the 9316A ROMs you have. Your board is jumpered for 2716 EPROMs as mentioned above which has different chip enable signalling to 9316A.

See the pic below - note my U6 ROM is a 9316A in ceramic package version. Jumpers you need are:

E1 - E4
E2 - E6
E7 - E8
E9 - E11
E12 - E36
E13 - E15

E31 - E32
E33 - E34
E16A - E19

Bally MPU 9316A jumper setup

That incorrect jumper setup cannot cause damage to the ROMs or the MPU board.
Technically, the CPU would have executed incorrect code that on a one in a million chance could have caused a coil to lock on - extremely unlikely though.

Disconnect connectors J2 and J3 from the MPU board. Does it still fail to go into attract mode?

Someone had a similar problem a month or two ago but I can't find it.

This time disconnect J4 from the lamp driver board - do the displays now enter attract mode properly (alternating between 00 and High Score to Date)?

Which pop bumper is causing the problem?

When the 555 timer had an issue you where probably hammering the CPU with display interrupts and the software would crash.

Find the pop bumper under the PF and clip off the capacitor wired across the switch. If that fixes it the cap was bad. The cap helps the switch be more sensitive, but I have found a properly adjusted pop bumper can be nice and snappy without that cap. If it seems to be missing closures and you don't like the performance add the cap back. 0.047uF (or 47nF)