Working on a Williams System 6 MPU (Time Warp). It was dead when I got it. Replaced the MPU socket and ROM sockets along with the header connections. Found a bad 6810 at IC13 and installed a socket and new 6810. Removed the battery holder and filled in all the solder holes. Powered it up on my test bench with a computer power supply providing the 5v and 12v. The board boots up into audits mode but it won't go into attract mode. If I push the diagnostic button, both LEDs light solid.

Figured the 5101 was bad so I removed it, tested it and it was fine. Installed a socket and an NVRAM. No change.

At this point I put in Leon's test rom. It boots up with both LED's faintly flashing which tells me it's running. If I push the diagnostic button, both LEDs light up, both go out then both light solid, which points to an issue with the 5101. I checked all my traces between the 5101 and the 6810's and they are good. Tried another good 5101 and no change. I thought perhaps the 7408 at IC12 was bad so I unsoldered it and it tested fine. Put in a new one but no change.

According to Leon's memory test, the 5101 pin 7 (A7) should be at 0v during memory test but it's measuring 2.7v and the 6810 pin 11 (A7/CS1) should be 0v but it's showing 1.1v.

Any ideas?

Traces all check out. This System 6 MPU has no small traces coming off the battery pads. I've removed the battery holder, filled in all 6 solder holes with solder and have an NVRAM installed.

One odd thing is I recently downloaded Marco's test rom and ran that on this board and it passes all the CPU tests. I'm waiting on the CPU/single ROM board from Siegecraft as I'm making this an MPU board for my Firepower.

That was it! I had forgotten to plug my diagnostic switch adapter from Siegecraft into the MPU and set the dip switch. Board is now booting up into attract mode just fine on my bench. Thanks for the help!