Beginning restoration of main power box in Infoage IBM 1130

OVERVIEW OF RESTORATION PROCEDURE

The main power box is the enclosure for the main system circuit breaker, the power controlling relays, the time delay reset relay, the fuses, a contactor, a small transformer and the main AC interconnection terminals. It sits under the disk drive on the right side of the machine. 

This system had evidence of a rodent infestation that left many wires with insulation gnawed completely off, some remaining cotton nesting material, and rust/corrosion at the bottom of the box that appears consistent with the effects of urine. There is unknown effect on relay windings and contacts, but nothing was obviously damaged. 

I don't want to try to patch wires around with so much damage and the potential for other spots that I can't see where the insulation is damaged or split open. The safest thing is to completely rewire the box. 

IBM laced their wires into one major bundle where every terminal naturally falls next to the screw where it will be affixed. The wires stay together as a rope which is far preferable to a 'rats nest' of individually routed wires. Smaller bundles are also used, such as the neutral wires running through a different opening in the rear of the box from all the hot wires. 

I will document and verify all the connections, then remove all the bundles and take them out of the box. They will remain intact as a template for the creation of replacement bundles. 

Other parts will then be removed and cleaned up, leaving the bare metal box. I intend to wire brush all the rust and corrosion away. I will then treat the rusted areas with Naval Jelly, which converts the rust into a solid that also blocks oxygen entry for continued rust formation. Once the box is in good shape, the parts go back into it so that everything is ready for wiring. 

MANUFACTURING REPLACEMENT WIRE LOOMS

My plan for building replacement bundles is to use the existing bundles as templates. Where damage makes that a challenge, I will have access to the intact bundles in my own IBM 1130 system that I can measure. 

Essentially, every connection in the bundle is a single wire with a terminal on each end, usually ring terminals. The existing bundle will show me the length of each wire, guiding me to cut wires just a bit longer and to put a terminal on only one end of the wire.

I will line up the wires with the terminals in the existing bundles, then begin lacing the wires into a new bundle. The goal is to have the terminals fit exactly to the destination screw, matching the IBM built part. 

As I reach the far end of each wire where it emerges from the lacing, I will match that to the second terminal on the existing bundle. Cutting my oversize wires and installing a terminal will produce the second terminal on the wire at the correct position to connect to its target screw. 

I should end up with a bundle that I can fit into the box where all the terminals sit over their destination screw. A check with a continuity meter will ensure that the terminals on one side reach the correct terminal of the other side. At that point, they are all screwed down on to their terminal blocks or soldered to their relays or other objects. 

TESTING THE POWER BOX

The goal is to step by step verify the correct delivery of power to the circuit that should be energized without powering any other circuit. I will walk you through a beginning set of tests to show the various paths that must be checked.

Main CB open

In the first case above, with the main circuit breaker open, no circuit in the machine should be energized. Every other terminal is tested for continuity to either of the input legs. 

Only the CB is on

In the case above where only the circuit breaker is switched on, but the fuse F5 is missing, we should not have any power delivered to the transformer T1 nor to any other circuit in the machine. 

CB on and fuse F5 is in

Now we deliver power to the first part of the machine. In this case, we energize transformer T1 which steps down the voltage to produce 24VAC. The 24VAC is only routed to the system power on switch and emergency power off switches. No other circuit should receive any connection to either leg of the input other than the primary windings of T1 and the secondary winding of that transformer should only be connected to the lines that run to the EPO and power on switches. 

At the same time as the CB is potentially energizing transformer T1, there is also a path down to energize transformer T3 for the convenience outlets on all boxes in the system. We will look at that below. 

CB on but relay R3 not activated

Unless relay R3 is activated, the power from the CB will not be delivered onward to transformer T3. R3 switches on when the 24VAC from transformer T1 is not blocked by a pulled emergency power off switch, whether or not the system power switch is flipped on. We have convenience power as long as the CB is on, normally.

CB and R3 but fuses F3, F4 open

The fuses at F3 and F4 have to be intact in order for the power to flow through the CB and through relay R3 onward to the transformer T3. It is only when all of those are present that the convenience outlets on each box have 115VAC power, stepped down from the 230 line voltage by transformer T3. 

power flows to T3 and onward to convenience outlets

If this path is active we should only have connectivity to the outlets and nothing else inside the machine.

T3 output to convenience outlets only

Meanwhile, the main contactor is what is required to deliver power to most of the rest of the circuits in the machine. It is activated when the system power switch is flipped on, delivering the 24VAC through the Emergency Power Off switches (as long as they were not pulled) to the contactor solenoid. 

Contactor must be turned on to deliver most power

Time Delay relay TD1 will allow the power on switch to energize the contactor but when it times out in a few seconds, if the power sequencing circuit did not detect proper voltages present from +3, +6 and -3 volt supplies, it will drop the contactor and turn off the machine. This is a very confusingly drawn circuit and hard to illustrate. The point is simply that the power switch turns on the contactor and it remains on only if the power supplies deliver good voltage levels. 

Contactor delivers 230 to rest of machinery

The contactor feeds 230V directly to a few peripherals that have fuse protection in their own boxes, such as 1442, 1132 or 2501. It also feeds transformer T2 directly, with no intervening fuses. T2 will step the 230V down to 115VAC which is used by devices such as the fan blower motors and any peripherals powered through the SMS power connectors. 

Note that you can see connections to some fuses. The fuses F1 and F2 feed the main power supply and F7 feeds the lamp power supply. Fuse F6 protects the 115VAC from T2 delivered to peripherals through the SMS power connector, which include the 1053, internal disk drive motor, 1134 and 1055 paper tape and the 1627 plotter devices. 

At this point the testing continues, essentially removing all but one set of fuses at a time and validating which circuits are energized and which are left dark. 

Most of this can be tested independently, except that we need the power sequencer to leave the contactor energized if we want power flowing through there to TB2 for fans and through Fuses F1, F2, and F7 to power supplies.