Reading this thread with a system 11 power board in front of me, another coincidence. +100v is ok -100v reads -130v and is like nino mentioned, affecting the display. Just began testing last night. Havent played much with sys 11's but learning my way around quick. Anyone point the finger at the above culprit before I test all components? Thinking it may be a cap.
I had a similar issue on a my JP (Data East) ... Similar setup.
There are a couple of things to check - R1 and R4 should be 39K. Measure them as a starting point.
There are two zener diodes (ZR2 & ZR4) that drop the voltage to -100V and +100V. They are 1N4764A from memory..You can use another diode 1N4763A to drop the voltage to -91V and +91V - this prolongs the life of the display.
That's where I would start.. From a hobbyist's point of view, I just rebuild these HV sections as a general rule.
Would need a second opinion - as I have not worked on a system 11 for YEARS
I would just rebuild any High Voltage power section as a rule of thumb... Years ago I used to just replace the faulty part, only to find that something else would fail within a few weeks.
So, in the High Voltage section of any pinball board, I replace all active components - Transistors, Diodes, Zener Diodes and Bridge Rectifiers - and also the capacitors (capacitors dry out, and then cause their own problems). It's always a good idea to check the resistors and make sure they are in spec - many resistors have a 10% tolerance, so if they are out of this range, replace them. For some resitors it is a good idea to use "Flameproof" resistors... these are usually a "Metal Film" type, but are specifically designed to be flameproof. I have seen a few catch fire!
