I have been working on the system 6 MPU from a Gorgar project. I have replaced the sockets and am working on it with a test bench power supply. I have installed the diagnostic test rom for troubleshooting. Both LEDs stay lit when powered on. I have checked to see if the MPU is running with a logic probe at legs 9 through 20 and 22 through 33 and all show activity. I have also replaced IC 18 on the board.

IC 17 shows activity on legs 1 through 11, 13 through 17, 19, 22 and 23.

Thanks for any help.

I have been systematically going through the procedure using the latest version test eprom. Here is what I have found thus far.

1) Both LEDs stay on when test bench power is supplied
2) PA6 and PA7 on IC18 stay high
3) All of the address bus signals between IC8, IC3, IC4 and IC1 are identical
4)The input and output signals for IC9 and IC10 are identical
5) The EPROM test chip IC17 pin 20 is high and pulsing, and IC15 pin 7 is high and pulsing
6) IC8 pins 2 and 3 are high
7) IC1 pin 5 chip and IC8 pin 14 are both high

I have not replaced IC11 or IC12 which is recommended if the above steps all check out okay.

I think I have narrowed the problem down but could use some help. To recap, in addition to the above post I have replace IC11 and IC12.

I think the problem is with the reset circuit. I have new CPU with new socket - new sockets elsewhere on the board as well. I don't have an oscillator scope, but the voltages on pins 38 and 39 of the cpu are 1.14 on pin 29 and 2.48 on pin 38 - pin repair site on system 6 boards say they should be at 3 volts. I replaced the crystal but that did not solve the problem. I do not have continuity between pins 38 and 39. I also installed a new cpu chip.

Thank you as always for the help.