Frunch thanks for the above and Cheddar thanks for the link below regarding testing the 3081's.
https://pinside.com/pinball/forum/topic/game-plan-mpu-repair-a-shotgun-guide-w-pix/page/2#post-2049837
I finally got around to really getting into this machine, picked up some parts but still can't get the flipper relay to engage during bootup and game play. As before, when grounded to the Q15 tab, the relay engages and the flipper fires.
Tested Q15 (SE9302) and replaced it with a TIP102. Tested each of the transistors in U4 (3081). Based upon the link above, they should each have readings between .65-.75. The following tested good - 16/1; 8/7 and 6/4. 13/14, 11/12, 10/9 and 3/2 (flippers) tested bad. I also compared the results with U3.
Acquired a socket and a new 3081. Put the DMM to the 3081 before installing it and obtained correct readings. After socketing the 3081 and before putting the board into the machine, the readings are still off. The 2nd reading is to pin 15. Again, they are all based on testing per the link above.
Red/Black - Readings
16/1 - .729 and .729
13/14 - .233 and .511
11/12 - .233 and .511
10/9 - .233 and .511
8/7 - .732 and .732 (Right Drop Target Bank)
6/4 - .729 and .729
3/2 - .233 and .509 (Flipper)
Is there a different way I should be testing these ? All readings from U3 are in the .720 to .730 range.
During testing, I had a slight issue with the right drop target bank (Mata Hari), so I replaced all of the transistors, caps and diodes. The bank works. So my install of the socket and chip appears to be successful. Additionally, based on Mata Hari's schematics, 8/7 for the Right Drop Target Bank is the only other used in U4.
All components in the circuit were tested, except for the diode at CR17 which reads the same as others but as I understand needs to be tested out of circuit. I was getting strange readings from CR20 at the flipper relay, so replaced it. There was no change in the readings after replacement. I also tested continuity across the circuit from J4 8 to J3 5.
What am I missing ? Why are my readings off on U4 when I insert the chip ?
I could really use your assistance at this point.
Eddie