Hello! Ive been restoring an EBD. New hardtop playfield...LED kit....i serviced it all and it works beautifully except for 1 issue. This has been tearing me apart as I understand why it can happen but I don't understand why it is happening. I am hoping someone here can give me some insight. On to the issue:
The issue is simply this, when the signal for the 4 drop target reset happens, it resets the 4 drop targets as normal but simultaneously fires the 2,10 drop target. In test mode, the 2,10 will fire normally alone and not cause the 4 drop target to fire. Only happens when the 4 drop target solenoid fires does the 2,10 fire erroneously.
Here is what I did:
I know that those 2 solenoids share a connection and the relay will switch between. A bad diode could cause this symptom. So i started probing. checked solenoid expander board. 555 incandescent bulb is working(i did not swap this particular one to LED). All GI is working and relay is switching. I believe the relay was changed at one point(not by me). I cant confirm it was changed but it looks way too new to be original. Reflowed all connections on SEB for good measure and checked diode which was good. I checked the 2 diodes on the 4 drop target reset solenoid and the 2 on the 2,10 drop target. All checked out normal....i replaced them anyways. No change in result. Checked diodes on SDB for the hell of it, all checked fine. Checked the driver transistors even though I didnt think they were the issue....all checked out ok.
I'm confused as to what is wrong. It isnt that complicated of a circuit and it is driving me mad as to why I cannot seem to understand what is happening here. Could someone help me end my madness?
Edit: picture of the schematic. Anotger bit that is confusing me here is the image of the SPDT relay switch. Im reading this as the normally closed position which should be keeping wire 67(i dont have the wire color code handy) active and when energized activates line 81. When I was in the test mode it was reversed as to what the schematic says.