No 6th flash is the display interrupt generator. The computer looks for the display interrupt to be pulsing at a PIA leg. If it does not see that pulse it will not flash the LED the 6th time.

Make sure IC12 is connected to ground. Make sure the 1k resistor is properly connected. Make sure the .1uF chicklet cap is connected properly. The board looks a bit beat in that area.

After that put use your logic probe on the display interrupt pin of the PIA. It should be pulsing. The schematic says average dc voltage should be 4.5vdc. The display interrupt should always be pulsing from the moment the board is powered up.

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marked where i'd check for ground connection.

Also check that the IRQ pin from the CPU is connected to both PIAs(p37 of PIAs).

Woot! you're welcome & have fun

Resuscitating this thread as my Medusa is having the same problem now.

Game worked fine in a tournament last weekend, towards the end of the weekend it started having an issue where the flippers would suddenly stop working, at first intermittently, then until the game was restarted.

When I got it home the flippers were fine, but after a couple of games the ball would no longer eject from the upper pf saucer, though the switch would register. Once again, restarting the game would kick out the ball.

Finally the game stopped booting altogether, only shows 5 flashes so not getting the 6th. I tested pin 40 on U11 with my logic probe and it is pulsing. I swapped in a spare U11 chip from another board (not certain it is good though), and still no 6th flash.

Board is very clean, no battery damage, verified continuity between u11 topside pins and the traces under the socket as well.

Bad U11?, or is there something else I can check?

Interesting data-point. Tried swapping in a working Alltek mpu board and it also stops booting after the 5th flash.

Thoughts?

something external can force a PIA port high / low making it fail the POST... like a bad display. I would unplug everything but MPU j4 and try again.

Hear hear for Andrew. Great support mate to fellow pinsiders here, good stuff!

So I feel like a fool, F4 fuse was blown.

I notice now that my Shield of the Gods solenoid isn't firing so could be what caused it.

When in doubt, plug it in...

Thanks for the fast response!

Ahh okay, you where missing flash 7 then.

The playfield fuses are protected by a 1 amp slow blow fuse, but the knocker, coin door, and any other non PF solenoids are only protected by the 5amp fuse on the rectifier board. When the rectifier board fuse blows and not the PF fuse, it is usually caused by the knocker it seems (or chimes in an early game). If a PF solenoid made the rectifier board fuse pop, but not the PF fuse, someone probably stuck an overrated fuse for the PF solenoids.

Reviving old thread...
I just purchased a used but nice Fathom -35 MPU to use as a replacement for my Space Invaders project. I know I have to rework the jumpers, but I noticed resistors at C8 C11 and C81 on the Fathom board where the SI board had small caps. Weird. Any ideas? Haven’t got to the point where I am ready to power it, but looking to avoid issues.

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Those are .01 uF color coded capacitors.

they are all capacitors

brown = 1
black = 0
orange = 3 (add three zeros)
the extra bands are probably tolerance, class, ratings etc which isnt critical for these simple bypass caps.

So that would translate to a cap with a 103 marking so it is 10,000pF or 10nF or 0.01uF.

Thank you both! I was scratching my head for sure.