AFM Strobe Troubleshooting Tips.
If you have already replaced the bulb and that didn’t fix the strobe or you suspect that the
bulb is not bad, then here are some suggested troubleshooting steps. Use these steps to
find and replace bad components. Do not attempt this if you cannot use a meter or are
unable to solder.
My strobe circuit card had three problems. There was a bad resistor (R1), bad capacitor
(C1) and a broken lead on T1. I replaced R1 and C6 and carefully solder bridged the lead
on T1. All three were found without any power-on testing.
Two things to remember! The capacitors discharge in about one minute from the time
you turn the machine off. The strobe will not work with the coin door open.
1) Look and the solder joints on the strobe xenon lamp bulb itself. Notice that the
lamp’s “anode” and “cathode” solder pads are actually on the component side of
the circuit board. When you solder this lamp, make sure you flow enough solder
through the circuit board to cover those pads or carefully solder from the top
(component) side of the board. Do not touch the lamp’s glass, as the oil from
your fingers will make the lamp fail early.
2) Remove the main strobe circuit board from the machine. The strobe board is
located on the back of the playfield backboard. Remove the box that shields the
board. The board can then be unplugged and popped off it mounts.
3) At your workbench. Examine the board and look for anything obviously burnt or
blown up. Look very closely at the leads on T1. They are very small and you
will probably find one that is broken. Use a magnifying glass! I was able to
mend my broken lead with a careful solder bridge. Epoxy T1 to the board if it is
not already. Pinball Resource sells T1 replacements.
4) Using a multi-meter, verify the resistance of each resistor on the board. There are
no problems with parallel resistance on this card, so all of the resistors should
read within 10% of their specified value. R6 and R7 will take a little while to
stabilize at 100K ohms while the meter charges up C3 and C4. If R6 or R7 test
much less than 100K ohms or do not exhibit a slow charging through the meter,
then C3 or C4 is probably bad. Swap the leads and watch the caps charge the
other way until the reading gets near 100K again. (R1 was bad on my card, it
measured infinite ohms. R1 should be 120 ohms, not 51 ohms as shown in the
5) Using a multi-meter on the diode test setting, verify all of the diodes on the board
6) Using a multi-meter verify the path through the transformer T1 is good. The
transformer should be a dead short on an ohm meter (close to zero ohms). Make
these reading from the solder side of the board to verify there is no break in the
7) If you are lucky enough to have a capacitor tester, you can de-solder one leg of
each capacitor and test the caps. Cap testers are not as accurate as resistors –
ballpark is okay here. Capacitors will not test properly while both legs are
connected in this circuit. (I tested my caps with one lead lifted and C6 was bad.
It measured 3.3 pF; it should be .22 uF. C5 measured the proper .22 uF.)
Testing with power on.
Due to the high voltages present on the strobe board, I suggest switching the machine off
and waiting for discharge one minute before repositioning the meter probes. Clip meter
probes securely to the component(s) to be tested (where possible), set the meter to the
proper voltage type and range, then turn the machine back on to make the measurements
“HANDS FREE”. Turn the machine on, take the measurement and turn it off one
minute. Repeat this for each measurement listed below, do not move probes with the
machine powered on. There are big capacitors on this board, if you short something the
resulting spark could burn the hell out of a component or wire lead in a split second. Not
to mention that it is dangerous. Also, do not probe the trigger output from T1 unless you
are looking to blow up your meter.
Raise the playfield and find the harness hanging down. Connect the strobe board to its
harness on J1, then place the board on an insulated (rubber- not an ESD bag!) surface
before connecting the meter and powering the machine on. You can also do this with the
board mounted on the backboard, but it is a little harder to see.
Verify the following measurements on the strobe board with machine powered on and
coin door closed. LED 1 should be dimly lit and kind of flickering. Do NOT run the
strobe test diagnostic during this except if you are testing the input to the MOC3011 chip:
1) ~150 volts DC across C3.
2) ~150 volts DC across C4
3) If C3 and C4 test bad, check for 50 volts a/c between J1 pins 3 and 5.
4) ~150 volts DC across C1
5) ~75 volts DC across C2
6) ~70 volts DC across C5
7) ~130 volts DC across C6
8) ~12-16 volts DC from pin 1 of the MOC3011 chip to any ground strap in the
9) Connect meter between pins 1 and 3 of the MOC3011. Power up and go into the
tests menu and run the strobe test. The strobe test is the second from the last test
in the solenoid test menu. You may be able to see the pulses depending on your
meter’s speed, but an oscilloscope is really handy here. These will be 12-16 volts
See schematic below: