Saturday, July 30, 2016

Preparation for VCF, working to install missing jackscrew in 1132 power connector inside 1131


I fired up the system to walk through the demonstrations - running decks exactly as I will on the showfloor. When I powered up and flipped on the motor for the 1132, it began spewing paper even though it was not yet ready and no XIOs had been issued! A power cycle of the system didn't help.

Perhaps this is an artifact of the loose power connector, which I really should take on next anyhow. I have decent access to the rear of the connector bay inside the 1131, to put in the jackscrew that is missing. I will still have a problem - the need for either an extremely thin wall socket or painfully slow tightening with screwdriver blades.

I had better get all the demonstrations set up to work with virtual 1403 printers, in case my 1132 is not going to be dependable. That means alternate decks, since Fortran programs must be written to the specific printer which will be used at execution time.

I have a 1403 only version of the DMS disk, which I will use for testing the alternate decks. This printer malfunction will make it impossible to do my demonstrations booting a real disk since my cartridge requires the real 1132 to print. I need to figure this out and fix it.

It did appear that the 1132 power connector was partially disconnected - if resets aren't properly done, and grounds aren't good the logic can malfunction thus I will fix the connector first and then revisit the printer to see if any problem in fact exists.

My portable air conditioner stopped cooling the garage effectively, which I think is because it has filled with water. I unhooked the air exhaust hose that runs through the wall to vent outside, rolled the unit out and tried to drain some water from it. I will see if it cools any better now. Otherwise, the garage will be too hot to run the computer for most of each day, limiting my testing.

While waiting to see if my AC will recover to cooler temps, I took the metal top parts from the 1130 replica, steel wool cleaned the surfaces of loose rust, then primed them with Rustoleum Rust Converting Primer, That should give me a paintable surface for my texture coat tomorrow and then for the color coats.

My three advertisements for the 1130 were laminated, as were some signs for the various boxes at the exhibit. The card decks that were being run for demonstrations were printed and put in plastic holders for ease of handling (and protection).


I opened the side door and began planning my approach to this repair. It became immediately obvious that the jackscrew for the power connectors is smaller in diameter than the ones used for signal cables. I can't use the one I harvested from the CHI disk controller box.

There is a power cable that runs to my SAC Interface cable although is has limited use with my design. The power cable carries low voltage AC power out from the 1131 and has a pair of wires that complete the power connectivity circuit.

The low voltage AC energizes relays in the peripheral devices to cause them to power up when the 1131 is turned on. I had the fpga inside my box powered through such a relay, but because of the long time it takes the fpga to load its bitstream from flash, the 1131 will have come out of power-on reset while the FPGA is still in an invalid state. Thus, I jumpered around the relay and manually turn on my box instead, waiting until it is up fully before I switch on the 1131.

The power connectivity circuit carries power from the 1131 power system out to the SAC box, back to the 1131 and to a relay that enables the power-on switch to bring up the system. Thus, pin 23 and pin 28 of the connector are shorted up in my box. Now that I am scavenging the small jackscrew from the SAC power cable,

I need to bridge those two pins without a connector installed. I had used a small wire jumper, which I will put back in place. The connector is reinstalled, sans jackscrew, but the cable itself is not hooked up. Instead, the jumper wire is secured in place.

Now that I have a jackscrew, I need to begin installing it into the power connector for the 1132 printer. I can push the front part of the jackscrew in, but I have to turn the 1/4" nut from the back with limited access room. In practice, the big problem was getting the nut into the back of the connector at all.

Perhaps I can make a tube barely bigger than 1/4", stick it to the nut at one end, and push that tube into the connector hole until I can catch the threads from the jackscrew entering from the front. This is challenging, perhaps why the original owner didn't replace the jackscrew when it fell out decades ago.

I finally decided to remove the connector itself, which will pull forward enough for me to install the jackscrew (laboriously). That means, however, that I need to hold onto and extract nuts and bolts without them falling irretrievably inside the wiring tangles back there. I will also need to be able to put the washer and then bolt over the thread when re-installing.

I am going to shop for a strong magnet on a rod that I can use to grab up nuts and washers as the threads come out. I will figure out how to get the parts back on later, but this way I can remove the connector to fix the jackscrew problem, at least.


  1. Hopefully, the nuts and washers you remove are ferromagnetic. I went through a similar exercise attempting to change the mil-spec power input fitting on my HP2116; unfortunately, the fittings were stainless steel and now I have a major cabinet disassembly project ahead of me. Likewise, most DEC fasteners are stainless.

  2. Hi Jack

    The area below the connectors has a sealed metal box and a flat metal bottom, nothing that could be hurt by the parts. As the machine is moved, they may slide to the open metal grille nearby and drop through.