Have an escape from the lost world mpu that I am trying to fix. I had no led flashes at all, replaced 6803 and both pia chips. Now the led flashes erratically. Sometimes it will flash a few and get stuck other times it flashes more than 9 times. Seems like it is boot looping. Tried replacing 6116 with nvram but flashing became quicker and more erratic so I put original back. All test points have correct voltages. Test points on power board all good. All power board fuses good. Nothing from displays. Gi lights and some flashers come on with power. Sound board boots and plays sound with test switch... help!

#2 4 years ago

???

silen7ce

Pinside member

Easton, MA

6y 50,600 309 11

I was thinking to try replacing u2 u3 game roms next...

#3 4 years ago

???

pinworks

Pinside apprentice

Taylorsville, NC

11y 14,150 26 1

I would suspect the sockets with that kind of erratic behavior Are the socket contacts nice and shiny? Are any of them closed frame Scanbe?

Also check the /RESET circuit. Pin 40 of the cpu should be low for a few hundredths of a second then go high. If it is constantly cycling from high to low, the cpu reboots each time it goes high. One way to test it should be to take a jumper connected to 5 volts and press it to pin 40. If things stabilize, the reset circuit is the problem.

I suggest you get Leon's test chip and follow his routine for testing the board. That will give you a systematic approach to the problem.

Good luck

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