Something shorting higher power to those sockets occasionally ? Might be hard to do, but get a meter on it when brightness sizzling happens and see what is going on.

LTG : )

If you can't figure out where the spike is coming from, stick 12 volt leds in there.

LTG : )

If you could measure voltage at the board going to those sockets. Would help sort out board issue or something in the wiring to the sockets causing it.

LTG : )

How do #44 and #47 incandescent lamps behave in the game with the Rottendog board?

That voltage is too high. What is the voltage on your power supply at fuse F3?

-Hans

Schematic shows that's the +18v line which should be pulsed down by the lamp routines to about 6 volts.

9 volts out of it indicates to me perhaps that the bridge supplying this circuit is failing, or the connectors to it is.

overly bright lamps that burn out quickly usually means a blown locked on column driver circuit. They strobe the 18v quickly to get a nominal 6v. When the column is locked on the lamp gets the full voltage.

On an original board I think it goes PIA -> 7408 (blanking)-> 2 transistor cascade -> lamp. Rottendog using mosfets the circuit may be much simpler. From the picture it looks like the PIA may be turning on the mosfet directly through a series resistor.

When I would fix I would pull the lamp fuse and go into lamp test. With a logic probe check the PIA port is pulsing. Check the 7408 output gate is pulsing. If either of those are not working right, replace the part not pulsing. If both the logic stuff looks good I replace both transistors.

Before powering back up inspect the playfield closely for things like a solenoid lug and GI lamp leaning onto a feature lamp. Also I have see a dangling ground braid flopping around in the head touch lamp sockets on the backbox door.