System 11b mpu conversion to 11a.

[Goingpinsane]

Hey guys. Been having some trouble with my tomcat mpu not booting. Not getting 5v at test point. Taken it to a tech (Tv repairer as its all I have locally) and he can't work out what's going on. Not sure where to point him to start looking. Problem started with the pop bumper transistor blowing. Had a coil short.  Slings started firing on start up. Then nothing. Dead!

 If I can't repair that board I have a system 11b mpu out of an earthshaker. Can I convert that board to suit my tomcat 11a? I know I have to convert the audio section but wasn't sure if anything else needed changing.

Cheers  for any help.

[Steevsee]

11b will work fine in 11a,  once missing sound components, including the 1J-15 connector, are installed.

[Steevsee]

Regarding the original being "dead", did you check all fuses?

Pretty sure the bumpers and slings are part of the special solenoids section on system 11.

[Goingpinsane]

Cheers for that. Checked fuses. Can't get it to boot up. Took board out of machine and hooked it up on test bench with a different power supply. Only getting 3v at 5v test point.

[Steevsee]

Were the blown transistors replaced?

You can easily test the large TIPs on the bench with a continuity meter. 
With power off, check for continuity between ground and the metal tab of each transistor.

[Goingpinsane]

All checked. Left sling and pop bumper tip blown. Replaced both and the smaller pre- driver. The next buffer chip along the line changed also. I think it was u44. It had a short also.

[Steevsee]

Sounds like you've got it pretty much well covered.

Could also be a bad Pia if locking on problem remains.

Also assume you replaced the shorted coil, or at least removed it from circuit?

Ensure all  fuse values all correct also.

Does the voltage problem persist?

[Goingpinsane]

We still can't work out the voltage drop. Will a bad Pia draw down the voltage? One thing, the game rom at u26 or 27 was really hot. Can't remember which one. Is this pointing to a bad rom or could something else be causing this? I removed the coil. I got the machine as a project and the pop bumper was not connected. Maybe the last owner knew something and left it out?

[Steevsee]

Have you tried testing with the hot rom chip removed?

  Not sure, but i think PIA more likely to lock-on or disable your coils if it's bad.

Also how are the mpu header pins for the power connectors?

Any sign of cold/cracked  solder joints?