Back from trip and visitors, worked on relays, regulator and a 1053

END OF TRIP A BIT MORE THAN I HAD EXPECTED

After I attended the Vintage Computer Festival East and stopped off at the System Source Museum in Maryland, I drove to Virginia to board the Amtrak Autotrain which would transport my car and me back to Florida overnight, retracing the route I took to come up to New Jersey for the event.

I handed my car over a bit after noon, checked in and was waiting to board the train at 3:30. I had a bedroom where I would receive my meal and then sleep until arrival the next morning at 10AM. I paid for Priority Unloading, which would ensure that my car was one of the first sixty (of hundreds) of automobiles to be unloaded in Florida the next day. 

However, at 3:06 they announced that two freight trains had crashed in Georgia, blocking the main rail line, thus the Autotrain was cancelled for the day. I was able to get a refund and planned now to drive halfway home this afternoon and evening, stay at a hotel I booked in South Carolina, and finish the trip the next day. All I had to do was wait for the my car to be offloaded.

Apparently they have never had to unload cars from a cancelled train, although they have operated this daily since 1984. I won't give all the details of watching a large group of contractors stand idly for three hours while managers and others argued in meetings, nor the original scheme which would have involved almost thirteen hours of turning around the rail cars one by one until all 17 were unloaded. After some revisions and creative work, my car was finally handed over to me at 8:30PM, more than five hours after the cancellation. 

I could no longer safely make it to South Carolina, thus wasted the hotel expense and had to find a new stopping point just south of Virginia which I reached around 1AM. I started out the next day and drove another eleven hours until I got home. 

My visitors arrived the following day and I spent two whirlwind days escorting them through Cape Canaveral and the Kennedy Space Center. They left this morning and I had the opportunity at last to get back into the shop.

REGULATOR ISSUE TRACED TO A FAILED IBM 086 TRANSISTOR

I worked out a way to power the regulator on the workbench, which might not sound complicated but the way IBM powers this is with both a raw DC supply and an AC bias voltage, derived from a circuit like this:

The wire coming from one side of the transformer primary is rectified by the one diode on the right and powers the circuitry that generates the reference voltage, using zener diodes, that will drive the regulator to produce exactly the correct output voltage. The center tapped full wave rectifier on the left generates nominally 7.8V DC to power the regulator, but the tap is a half wave rectifier to power the reference voltage generation. 

Once I fed it 7.8VDC with one supply and -7.8V through the diode as the bias voltage, I could watch its operation and probe various points on the SMS card that has most of the regulation circuitry. The regulator begins producing a slightly high output, about 3.27V for a fraction of a minute and then ratchets up higher and higher at an increasing rate. I had an electronic load to demand only 1A from this regulator that is capable of delivering 20A, so having the voltage race over 6.5V did no harm. 

Examining the circuit, I saw that a differential pair of 026 transistors compared the reference voltage to the actual delivered voltage and fed  the difference to an 086 transistor. That produces a drive current, which is amplified by emitter follower stages of an 028 and then a 108 transistor before it drives the four parallel 108 transistors that are the output stage. 

I had tested the four output 108 transistors and the two amplification stage transistors, 028 and 108, but they were working properly on the curve tracer. I probed the voltages delivered to the 026 differential pair and the voltage drop their output produced on a resistor leading to the 086 transistor. Since they looked reasonable, I came to suspect the 086 and desoldered it from the PCB. 

The curve tracer showed the same pattern, that even with a collector voltage of just five volts it would show decent curves for tens of seconds and then begin to run away with steep distorted output curves. This is a smoking gun and my next move is to replace the 086 transistor. 

The IBM Parts Department no longer carries 086 transistors, of course, and reference materials for the transistor specifications are unavailable as well. Texas Instruments, who manufactured this, does not list the IBM private part numbers in their catalogs or spec sheets. I dug through all my spare SLT and SMS boards looking for an 086 I could extract, but had no luck.

This is an NPN Germanium transistor, one with a relatively low beta of 20, the ability to handle about 100mW of power, suitable for the 8+ volt levels of the regulator and the single digit milliamperes of current it has to provide to drive the 028 transistor that is the first amplifier. Some informal substitution charts exist which list some non-IBM part numbers that are claimed to be a decent replacement. In t the case of the 086, it listed the 2N557 and 2N214 which are indeed both NPN Germanium transistors of appropriate specifications. 

I couldn't find any IBM 086 nor 2N557 on eBay but did find a listing for a small batch of 2N214 which I purchased. After I put the through their paces on the curve tracer, I will solder one onto the board and test the regulator again. 

WORKED ON FULLY RESTORING TWO SEQUENCER RELAYS

One of the sequencer relays (R1) had a relatively high resistance for one normally open contact. I used my burnishing tool to remove oxide and make the contact almost zero ohms again. 

The other relay (R3) had the frozen armature due to rodent urine causing rusting. I carefully desoldered the wires going to the relay and unmounted it. I color coded each wire to the contacts and then again to the two sides of the relay coil.

color coding contact wires

color coding coil wires

I was able to free the armature, clean up the pivots and put it back together. When it was soldered back into the power box circuitry, I tested. I plugged in a lamp to the convenience output, turned on the main circuit break of the 1130 and heard a somewhat dramatic click and a hum from the big convenience outlet transformer. The lamp lit up, proving that the relay was now repaired. It is still noisy as it clicks on, due in part to the roughness at the pivots left by the oxidation. 

BEGAN CLEANUP OF VERY OXIDIZED MODE SWITCH AND COVER PLATE

There was substantial rusting of the top of the rotary mode switch cover and the knob itself was encrusted and looked very damaged. I took the plate off the machine and removed the switch and knob.

I was able to remove a heavy film of filth from the knob so that it doesn't look to bad at all. I was surprised that it was in such good condition as it had appeared almost melted originally. 

The plate had the loose oxide removed. It needs to have the oxide converted to an inert covering, then get primed and color matched to the rest of the cover. 

SSM 1130 SYSTEM 1053 BROUGHT BACK HERE FOR FIXES

During the VCF East show, the System Source Museum 1130 was demonstrated as part of their exhibit. The metal rotate tape on the typewriter failed on the last day, snapping at a point where it had previously had a kink. The particular demonstration was repeatedly typing the same character, one with the maximal rotation tension, which seems to have flexed the point with the kink until it broke. 

removed rotate tape fragment

I brought the 1053 back here to replace the tape, after which it can be returned to the SSM for reattachment to their machine. In the process of removing and transporting the 1053, one of the paddle cards was broken. I will repair that as well. It needs epoxy to repair the break and some wire jumpers to bridge the break. The affected pads are for +12, +48 and frame ground, not the 115V for the typewriter motor.