Finished up typewriter installation and attempted to run the 1132 printer diagnostics

POWER CONNECTOR INSTALLED AND SEARCH FOR THE MISSING BOLT

I plugged in the SMS paddle card for the power connection to the typewriter. The signal paddle cards are plugged in above the power section, with a long bolt and wing nut holding the connectors in place. I was reinstalling the bolt, which is inserted from the bottom and secured by the wing nut at the top. It dropped out of my hand and disappeared down inside the machine amidst a maze of cables. 

I searched for about an hour, moving cables, shining lights and feeling around. I then began deinstalling items to open up the space. I loosened and moved the connector block that the printer and card reader cables are attached to. I disconnected the raw power supply and slid it partway out of the machine. 

When I finally found the bolt, I installed it from the top, disregarding the IBM method, so that this doesn't happen to me again. The cables were connected and it was time to power up the 1130 and try out the diagnostic using the typewriter.

DIAGNOSTIC REPORTS TYPEWRITER REMAINING BUSY - PLUS MOTOR NOT RUNNING

The diagnostic monitor tests the console printer and loops to try again when the busy bit is on in the device status word. After sixteen attempts without the bit clearing, it waits with 30FA in the System Buffer Register. I pushed the Space button to see how the printer was responding, but nothing happened. That was when I noticed that the motor was NOT running. 

I opened the main fuse section of the 1130 to test the fuse delivering the 115VAC to the peripheral devices. It was then that I noticed that fuse F6 was completely missing, which certainly explained the lack of motor activity. 

FUSE INSERTED, TYPEWRITER COMES TO LIFE FOR BUTTON PRESSES

Once the fuse was back in the machine, the typewriter completed the button press actions I triggered back before I discovered the missing fuse. It responds to those, but the diagnostic still reports it is continually busy. 

SCOPING THE SIGNAL FROM THE TYPEWRITER TO FIND THE FLAW

I put the scope on several signals coming into the 1130 from the console printer. End of Forms indicates when the paper has run out. End of Line should go high as the carrier passes the right margin. The interlock signal will go high during the long operations Tab and Carrier Return. Finally the CB Response should go low during an operation such as space, character print, or other action, returning to high once the mechanism has completed enough of that function that it is safe to trigger a following request. 

Pushing the Tab or Return buttons activated the interlock signal and blipped the end of line signal as the carrier moved through the right margin. The CB Response signal was permanently low, however, which is not correct. This is why the controller logic considered the typewriter to be busy.

CB Response is a series of three microswitches (CB in IBM parlance) that should normally be closed. They are wired in series to pass the +48V supply through to the CB Response line. Thus it should be at 48V when the typewriter is idle, only dropping out during motion of the mechanism. I found this to be an open circuit from the 48V side to the CB Response side.

One of the switches is driven by the print cycle, opening during most of a print operation and closing again after the selection solenoids are free to be selected for a different character. This is called CB2. 

Another switch is driven by the shift mechanism, opened while the type ball is rotating between the upper case hemisphere and the lower case side. It would be closed when the shift mechanism is sitting at either state. This is CB7. 

A third switch, CB5, is opened when the short action operational clutch is activated - for a space operation, as an example. When the operational cam stops, the switch should close again. 

I found that CB2 and CB7 were working properly. CB5, on the other hand, was mechanically opening and closing as it should but no electrical signal was making it through the contacts. I tried some Deoxit but it had no effect. 

SWITCH REMOVED TO CLEAN CONTACTS

I had to remove the switch from the machine to get in and clean the oxidation layer off the contacts. I hunted for ten minutes but couldn't locate my burnishing tool, a piece of metal that looks like a feeler gage with a slightly rough surface that will gently remove high spots of oxidation on contacts. Still, I am comfortable that once I get the switch passing electricity while the contacts are closed, the typewriter will no longer be permanently busy.