Remaining tasks for the 1053 are:
- Install faceplate on printer
- Hook up tab set/clear rod
- Set tension for red ribbon shift tape
- Hook up forms empty switch from cover
- Install cover
- Pull cables back to allow printer to sit on its stand
- Put printer in final position
Before I drove over to the Computer History Museum to work on the 729 tape drives, I completed the first two tasks in the 1053 list. When I get a chance to load the typewriter diagnostics into the 1130 I will use it to adjust the ribbon shift tape tension, then wrap up the remaining tasks.
|Moving along with reassembly of console printer|
CHM 729 TAPE DRIVE MAINTENANCE
I replaced carbon brushes in six brush blocks, then began working on the one drive that has not had all its brushes replaced. To do this, we moved the remaining drive to the end position in the string, so we could keep that powered down while the rest of the system was usable.
Each brush block has two cylindrical carbon brushes that ride on circular slip rings on the pulleys in the tape drive. They transfer power onto the clutch, which is rotating on the pulley. The clutch will cause the common axle to rotate with the pulley it clutches. The axle has two pulleys, one rotating clockwise and one counterclockwise. The clutches choose whether the tape hub with the reel of mag tape will rotate clockwise or counterclockwise.
Each brush is a cylinder of graphite, with a wider lip at the bottom to keep it inside the holder. There is a copper braided wire soldered to the cylinder, which passes through a spring and is soldered to a terminal on the holder. This allows the brush to move in and out to accommodate variations in the slip ring height and also adjust for wear over time.
There are six holders on a tape drive, each with a pair of graphite brushes. I had to unsolder the worn brushes, use new ones we had made, while reusing the spring and soldering the replacement back into the holder. Each block has a capacitor across the terminals in addition to the connection that supplies power through the brushes to the clutch.
Putting a restored brush holder back in the drive is a procedure that must be done slowly and carefully. If a brush pops off the slip ring and the brush block is moved, it can crack the brush off. We have various homebuilt tools that fit on the block, holding the twin brushes depressed. This gives us clearance to slide the holder into place, tighten mounting screws and verify correct placement before we let the brushes pop out.
A problem on a different 729 drive was finally traced to pitted points on a relay. The relay feeds power through the brushes to one of the clutches. In this case, it was the takeup reel axle clutch that drives clockwise rotation. This will pull the tape upwards from the vacuum column and wrap it on the reel.
Our defect was that the takeup reel was sluggish in rotating clockwise, so that the tape loop dipped below the lower vacuum switch in the right vacuum column and sometimes dumped - when the tape loses vacuum and piles up at the bottom.
When Iggy traced the problem to the relay, he cleaned the points which restored crisp rotation to the takeup reel and eliminated the dumping. We did not complete the brush installation on the last drive, planning to finish it up next week.
EMM CORE MEMORY TO UPGRADE 1130 TO 32K WORDS
I picked up the two 80 position connectors that will connect my EMM 3200 memory module to the rest of my circuitry. I have to wire up the signals with twisted pair cabling and route it to a spare FPGA which I will use to test out the memory. Once I know it is working, I can build the interface board to hook it into my 1130 and give my system a full 32K words of storage.