Got a Bally Party Animal that will not boot(this is a new problem, game was working good). Upon boot up I get 3 flashes from led. According to Pinwiki, there is a RAM issue. I installed NVRAM sometime ago, but got a replacement and installed with no change.
I then pulled MPU and connected to test bench, and had a friend burn Leon's test chip. When booted up with test chip, led just lights and stays on steady. I then started going through Leon's test procedure. Removed both eproms(U2,U3). Checked Reset signal-OK, next checked Clock signal Supposed to be 1v @ U1 pins 2/3, got 1.2v @pin 2, and .5v@ pin3(?) I thought this was odd, and rebuilt the whole clock circuit(crystal,C2,3,4,5) with no change upon retesting. Decided to continue on- checked address lines and all seems good. Reinstalled test eprom, and checked U3 eprom signals. Here is where I get confused, the test procedure says I should have .5v @ U3 pins 21,23,24, I got 4.2v. Now these 3 pins are connected to pins 26,27,28 of U1 cpu. In previous test procedure, it is stated I should have between 2-4v at U1 pins 21-40. So If U1 pins 26,27,28 are supposed to be out putting 4v, and are connected to U3 pins 21, 23,24, how are they supposed to test at .5v?
Also replaced ICs @ U5,U6,U9,U10. Still no change. Test eprom still will not flash boot led, nor will reinstalling game EPROMs get it to boot past 3 flashes?.
Can someone help me find what I am missing?
Many thanks for any ideas