Finished cleaning raw DC supply, assembled and tested it; partially reinstalled line filter

REMOVING FINAL DIRT, GREASE AND MOUSE URINE FROM THE DC SUPPLY

Everything else had been cleaned. I wiped off the transformers and then wiped down the length of all the wires to remove any surface grime. The wire brush treatment had removed the thick brown areas to the point that I didn't think I needed any further cleaning or treatment of the metal. 

REASSEMBLY OF THE SUPPLY

The metal enclosure has markings with the capacitor numbers that match the schematics. Since I had stacked the capacitors in the same relative position as I removed them, that was really just a backup verification. The holes in the box also hint at the part placement. Finally, I had my pictures from before it was disassembled to guide me. 

I found that I had to back up a couple times to work out the best order to install parts in order to reach the spots for every screw to be reinstalled. I used the schematics as a check for the wiring which for the most part is obvious because all wires are cut to length and sitting in the proper position. A bit of beeping out with the VOM was the last check.

SET UP FOR BENCH TESTING THE SUPPLY

It will be some time before the sequencer box is rewired and operational, but I can test this unit out of the machine right now. I set up a step-up transformer to give me 230VAC that I could wire to the primary of each of the two transformers. The design of the supply is modular enough that I could test portions at a time, one transformer and then one voltage output section. 

One of the transformers is a ferroresonant type, which takes advantage of some magnetic properties to make a transformer whose output voltage is almost unchanged as the input voltage swings up and down. It has a separate primary winding with a capacitor, producing a resonant circuit that puts the magnetic field of the transformer in an oscillation that almost completely saturates the laminated iron core. This leaves little opportunity for primary voltages swings to change the magnetic field, thus the induced voltage in the secondaries is almost unchanged. 

This transformer is used to generate the +12V and +48V DC power. There is no additional regulation. The outputs come from a half-wave rectifier and some filter capacitors. Each output is isolated from the other and fused. The supply also generates 24VAC across two terminals for use by the Serial Communications Adapter (SCA) option to produce its RS-232B voltages, although this machine is not configured with SCA. 

Modular section for 48VDC

Modular section for 12VDC and 24VAC

A second transformer is an ordinary type, since the voltages produced by this transformer will all be passed through regulators that ensure stable and precise voltages. The ferroresonant transformers are bigger, heavier and burn more power than a traditional supply, thus only used where the regulation is needed. It is not necessary in this section.

This supply must simply provide 7.8VDC to the regulators producing +3 and -3, as well as 12VDC to the regulator producing +6V. It also has an output of 7.8VAC whose two legs are used as a bias input to the +3 and -3 regulators, respectively. These are also half-wave circuits with filter capacitors for smoothing. They do not have fuses in these circuit, but the regulators that consume the power have circuit breakers. 

RESULTS OF THE TESTING

I connected an autotransformer, a device that plugs into the wall and produces a range of AC output from 0 to 130V, to the input of the step-up transformer, thus I could swing the input voltage to observe the intrinsic regulation of the +12 and +48 outputs. I saw raw voltages of 14 and 52 with the nominal 230V input and the variations as I moved the input up and down was very minor. In fact, the output peaked when the input voltage sagged to about 205V but the changes were very small. 

I disconnected the autotransformer when testing the other transformer's circuits as it is not regulated in any way. At nominal 230V input voltage, the sections were producing about 9VDC for two sections and 13V DC for the raw supply for the +6 regulator. There was also AC across the bias contacts and 26VAC on the terminals that would feed an SCA were one of them part of the configuration. 

This supply is ready to be energized when the rest of the 1130's power system restoration is completed. I reinstalled it in the machine but left the regulators unconnected. This means we will not generate any SLT logic voltages and therefore the sequencer will not delivery the 12 and 48 either. I will be able to verify one more time that the voltages are all correct and in the proper polarity before moving forward.

MACHINE HAD BEEN WIRED FOR 208VAC, MUST CHANGE OVER ALL SUPPLIES

The jumpers tell me that this machine had been configured for 208VAC which is a connection across two phases of three phase service. It will be used with 240, single phase. The various power supplies in the 1130 system have jumpers to configure them for 120, 208 or 240. There are quite a few places where the jumpers must be switched, even inside the tamper resistant usage meter power supply. 

REINSTALLING THE LINE FILTER AND NEW POWER CORD

The line filter box was put back inside the 1130 and the wires reconnected from the machine to the filter. I have a new power cord fitted, with the two hot leads already installed. To finish this, I have to connect the ground wires on both sides, which completes the fastening of the filter box since the same nut that fastens the box also provides the ground connection. When the two top plates are reattached it will be ready for power as soon as I finish the restoration of the sequencer box.