Bench test of 1132 printer power box - part 2

DISCOVERING MULTIPLE WIRES THAT HAD BEEN GNAWED

As I was preparing to reinstall the contactor, having epoxied the new wire into place on the side of the coil, I noticed a wire whose insulation was gnawed off leaving a long section of bare wire. I could see what appeared to be more bare sections of wire below. The box had to be opened up to allow me access to check all wiring and replace any that have exposed wire strands. 

I had to drill out one of the screws because it was too rusted to break free, the others could be removed after some percussive rotary moment was applied to them to start them moving. I could tilt out one of the sides of the metal box. 

To gain access, I had to detach some wires that were too short to let the side tilt out fully. I marked each and finally could look at everything. Lots of wires with gnawed off insulation, one of them barely able to conduct electricity. 

The solution is to replace all the ruined wires and reassemble the power supply box. I had a good supply of heavier wire but had to go to the local hardware store to buy 22 feet of 14 gauge for the medium current wires. I began rewiring but didn't finish before I had to leave for a dinner with friends. 

TESTING SECTIONS FOR SHORTS

I did safety checks on all portions of the power box and the printer to identify any short circuits, such as a bad transformer primary, prior to doing any testing under power. Another important test was a set of dedicated wires in the cables from the 1130 that delivery 115VAC to spin the fans whenever the 1130 system is powered on. It was important that the blower motor not be shorted. This is on the wires attached to TB1-7, TB1-13 and TB1-14. 

Input to power supply

Blower circuit

To accomplish some of the short tests, the meter is attached to the wire harness that was disconnected, since items like the blower motor are outside the power supply box. I did validate as much of the external circuitry as feasible during this exercise. 

VERIFYING UTILITY OUTLET CONNECTIVITY

A dedicated set of wires in the power cable coming into the 1132 delivers unswitched 115VAC power to feed a utility wall socket for customer engineer use. I checked that we had proper neutral, hot and ground lines with no shorts. The test was on the wires hooked to TB1-16 and TB1-17.

Once again, this is mostly done outside of the power supply box, since the incoming wires from the cable and the outlet box were both external, attached to the terminal block. 

Everything was good with this verification. 

CHECKING CE POWER SWITCH CONDITION

The wires on the power cable delivering 208/230V to the printer pass through a toggle switch on the power supply.  When switched on, as it normally would be, the power then passes through the contacts on the contactor K1 before energizing the primary of the main power supply transformer. Simultaneously it drives the main motor for the printer and the usage meter power supply in its separate box. 

The switch was working perfectly.

CHECKING MAIN AND CARRIAGE MOTORS FOR SHORT OR OPEN CIRCUITS

I couldn't spin the main motor since the 403 print mechanism is gummed and frozen with congealed old grease and oil. However I wanted to ensure that the windings all had continuity without any short circuits. This done with the wires that attach to TB1-3, TB1-4 and TB1-12 since the motor is outside of the box we are testing. 

Similarly, the carriage control motor which advances the paper was not moving freely due to old lubricants, but its windings could be checked at this point. It is supplied by 48V while the main motor runs on 208/230V. It is checked via the wires that attach to TB2-1, TB2-4 and TB2-9. 

Both motors had appropriate DC resistance and no shorts to ground. 

SHORT TESTING THE LOGIC GATE

I tested the power rails for shorts and found none. The +6, +3, -3, +12 and +48 were all good on the gate. I tested the magnet driver circuits superficially and found no shorts there.