PDP-11/05 GT40 Restoration


We removed the power supply so we could check the leakage in the capacitors.

All of them worked OK.

We powered on the chassis without the power supply installed, and found that the fan for the processor and graphics boards was not working.

Wiggling the wires on the fan fixed that issue.

We connected a DC power supply to the input capacitors and were a little surprised to see that all of the voltages regulated correctly.

We reinstalled the power supply and powered on the chassis.

The transformer was hummed loudly, the fans didn't spin, and the circuit breaker popped.

The KBPC25-02-5 diode bridge on the input of the power supply was shorted.

We borrowed a diode bridge from another broken power supply, and now this power supply works correctly.

The system powers up, and some of the LEDs on the front panel light up.

None of the front panel switches do anything, so we need to make sure that the panel lock gets deactivated.

We found a broken 390 Ohm resistor on the M7014 Bus Control & Bootstrap board, so we need to replace that.


We looked at the unresponsive front panel

The +15V and +5V at the backplane were a little low, and about 20mV low at the chips.

The -15V was OK.

We increased the voltages at the power supply to compensate for the losses in the little wire harness

We checked the microwitch for the panel lock switch, and it works OK.