Sunday, December 21, 2014

Console printer restoration creeps along plusb testing progress on SAC interface box


I continued the hunt for the errant spring, meanwhile re-installed the tab gang clear and tab overthrow stop plates which I had removed for better access to the escapement and tab mechanisms while I was fixing the tab issues.

The gang clear plate went on smoothly, but while I was maneuvering the tab stop plate into position, it slipped from my fingers and fell inside to disappear totally from view. With the relative large size of the plate and the openness of this area of the typewriter, I expected it to be easy to see and retrieve it.

However, it vanished as if it had fallen through a wormhole to some alternate dimension. I spent twenty minutes looking carefully and turning the machine, to no avail, before I decided I had to remove the motor. With the motor out, the entire area where the plate fell was accessible with no place to hide. Retrieving the plate, I put it into position on top of the carrier.

It was an opportunity to clean out accumulated oil and grease in the area, before re-installing the motor. It was fairly easy to put this back in place and get it adjusted for good smooth operation.

I then adjusted both of the plates to meet their specs. The gang clear plate has to be within a range of distances from the clear post of the current column on the tab rack. Too far and it won't clear the posts, too close and it will interfere with carrier movement. The tab stop plate must allow the tab mechanism to latch up reliably, but not move so far forward that it can interfere with the tab rack itself.

The adjustments done and the motor back in place, I can return to the carrier return and missing spring issues which are all that remain to address. I put in another thirty minutes of searching and FINALLY spotted the missing spring. It sat in a spot parallel to several other springs which are attached and functional, so challenging to notice it wasn't supposed to be there. All my prodding in the past didn't uncover that fact, as it was wedged in a way that made it seem attached.

Hurray, I thought, as I got my tools on it and lifted it most of the way out of the typewriter. That is when it happened - the spring popped loose and disappeared again into the bowels of the operational clutch area. Again. After five minutes of looking with no clear sign of the spring, I put this aside until the utter frustration dissipates. I wouldn't want to do any damage while under the sway of emotion.

I came back to the typewriter as daylight faded, since this is inside the garage and equally easily searched day or night. I devoted another fifteen minutes of hunting and peering, which of course included the spot that this spring had hidden last time around. No luck, but I will keep at it as much as I can stand each time and return to the Sisyphean hunt each time after the frustration has abated.


I pulled the interface box out of the keypunch and will insert some additional protective devices just in case we have induced voltages on the wiring that are forcing the Arduino to reset. I will put zener diodes on the inputs even though they should only be switching 5V power we emitted, and improve the arc suppression design for the outputs.


I got right to the repair attempt this morning, setting up the board, clamp, heat gun, replacement connector and other items on a table outside. After a few minutes prep-ing the board with flux paste and fresh solder on the pads, it appeared I might be able to solder this down with just my fine tip soldering iron and ordinary solder.

I gave it a shot and was fully successful! I hooked up to a PC, downloaded by test logic to the board and am ready to start testing of the interface box. Very pleased. The cause of all the problems is a malformed cable, the one sent to me along with the fpga board - it won't fit into any microUSB sockets but another cable I had in my supplies slid in easily to both the original and replacement sockets on the board.

The fpga board was put back inside the box on its mounts, the breakout board fitted onto the high density connector and screwed down, then the power and signal connectors were all put into place. A USB cable was the last connection, in order to test the board and update its hardware configuration.

Time for a bench test of each signal pair from the SAC cable connector, ensuring there are no shorts and that the resistance of each pair is an appropriate value for either a receiver or driver circuit. Once it had passed I could connect cables between this box and the 1130 and safely power up.

My initial test program is set up to inject appropriate (off or idle value) signal levels into the 1131, see that the existence of the box doesn't stop the 1130 from operating normally. In addition, it has a mode that will force an interrupt to be taken (on level 4) and show receipt of certain processor state.

I powered the box up in order to load the configuration file, but the loading software reported no valid devices found. It definitely sees the USB link and device, reporting the correct board type, but otherwise can't see the fpga for bit programming nor the flash devices to store configurations.

It worked fine with just the fpga board, but with the XM105 breakout board installed it is failing. That is the clue - something is wrong with the JTAG chain that is used to detect and program devices. I remember reading somewhere that if the chain is open, the signal won't wrap back to the sender which may be what is happening, if the fpga board opens the chain when the HPC connector is installed.

Without having logic set up by my program, the outputs are not driven to zero, instead defaulting to their 'on' condition. Thus, the 1130 reported interrupt requests on all four levels, but didn't show any signs of distress otherwise. Once I fix the program with the JTAG chain and can configure the logic of the interface, I should be able to test steadily.

I found that my fpga board checks a signal called FMC-Present which is one when the breakout board is installed. When on, it breaks the connection of the JTAG chain, allowing the user to insert additional devices on the breakout board. All I need to do is connect the JTAG signals TDI to TDO on the breakout board and this should work fine. Made up a jumper and installed it. Worked fine now.

I am able to receive and properly interpret all the signals arriving from the 1131 to the box, but my signals requesting interrupts are being ignored. I may have jumpered something in the 1130 to block these in my earlier restoration and debugging, or I may have a problem with the circuits that drive input to the 1131 from my box. I am going to monitor the voltages on one of the signals to see what is actually occurring on the cable.

The output voltage stayed high, although it should have been pulled down to near ground when I activated the request. I had an LED indicating the state of the signal I believed I was sending to that circuit and it faithfully matched what I set with the fpga board switch. I moved the voltmeter to the input of the circuit which should be driven by my fpga, yet I saw no change in voltage as the request changed between on and off.

Any number of problems could be causing this:

  • mis-wired connector or confusion over which connector pin is emitting this signal
  • problem with configuration of fpga resulting in invalid voltages driven into circuit
  • my wiring of the SAC interface connector did not connect IntReq Lvl4 to this circuit
  • unknown flaw in the circuit
I will be investigating as many as I can tonight, since daylight is fading rapidly, putting an end to my testing today. I am satisfied with the progress now that I have a working programming link to the fpga board. I have an idea of some additional debugging logic I can insert that will allow me to do some bulk verification of the correctness of the wiring of the inbound signals from the 1131. 

Saturday, December 20, 2014

Futile hunt for spring lost inside mechanism of console printer, plus prep to repair FPGA board


My first act was to hunt for the spot where the spring fell off, as that might be a cause of the failure to consistently release the margin rack when carrier return operations start. I discovered it belonged on the pivot that twists the tab torque bar, to keep the link from pulling on the torque bar when it is in its inactive state.

The spring is challenging to fit into place, as it is strong, has the ends bent into an almost complete circle requiring force to push over brackets, the bracket and lever are both thick, and the two holes are deep inside the machinery. I had to use forceps, spring hooks and other devices to try to attach it.

Boom - the spring snapped out of the forceps and flew to an unknown location. I wasn't even sure whether it stayed inside the typewriter or flew elsewhere in the garage. After a sanity break, I continued my search and discovered it deep inside.

However, retrieving it was not the piece of cake I expected (you would think I would know better and harbor deep pessimism, but no . . . ) and it lodged somewhere down inside the mechanism. I spent somewhere between three and four hours (yes, hours) patiently looking, probing and testing but as of mid afternoon I still don't have the spring.

For a diversion, I watched the carrier return mechanism, focusing specially on where the mechanism tilts the escapement torque bar and pulls the link that releases the margin rack to the right. The issue is that a part of the latch assembly is not restoring all the way to its rest position, most likely due to sludge but we shall see what actually causes this.

At some points the carrier return latch is not releasing so the cycle starts over and over - the errant spring is likely somewhere in the path of the clutch latch or release, but it could be a random coincidental new malfunction.

It is maddening to feel that, if I can only find and install that lost spring, I will be able to quickly finish the tweaks and put this printer back together. Depressing to think that I have two different peripherals suffering from a lost item in the mechanism, devilishly hard to locate, without which I can't put them back under power or finish their restorations.


My parts had not yet come and I can't do any testing until I repair the micro USB connector on the fpga board. I think I get everything on Monday at which point I can do the repair and start some testing.

Tonight, to my surprise, the micro USB connectors arrived and I put together the plate which I will use to hold the part in place while I solder it down. I intend to use the QuikChip solder, a special formula which liquifies at a very low temperature. By using my hot air rework gun to heat the connector with its paste underneath, I should get that new solder flowing without the rest of the parts on the board loosening. Tomorrow is the day I give it a try.

FPGA board with missing USB connector right edge mid height

Spare micro-USB SMT connectors

Jig to hold down part during soldering

Friday, December 19, 2014

Ruined disk heads removed from Diablo drive (external drive, not primary 1130 disk), console printer adjustments


The main problem appears to be sticky behavior of the margin rack which should be popping to the right when a carrier return begins in order to be slammed left as the carrier reaches the left stop. I am also a bit uncertain of the adjustment for the linkage that will release the rack, as that might not be ensuring the release is made every time.

In hand cycling to test this, I saw the machine begin to operate poorly in another area I thought already resolved - tab movements. The tab mechanism on the rear of the carrier should be locking up until it is released by a set pin at some target column, but instead is not locking so the tab movement ends prematurely or is only a few spaces long.

This appears to be the sludgy old lubrication still causing problems, alas. I am working with 99% Isopropyl Alcohol to clean some of it out, everywhere I can get to in these mechanisms, and then replace the lubrication with an appropriate light oil (Mobil 1).

I removed the tab overthrow stop and gang clear plates from the rear of the carrier, which leaves the escapement, backspace and tab mechanisms clearly visible and accessible. I was able to carefully observe the operation of the mechanisms which led me to the likely cause of my erratic tab movement.

The tab torque bar is twisted by the cam and levers on the right rear of the machine when the tab operation is selected. The bar pushes the tab lever toward the rear, pulling the escapement and backspace pawls out of their racks to allow rightward movement of the carrier. The tab latch should set, keeping the pawls out of the way until the tip of the tab latch strikes a set pin on the tab rack, which pivots the latch, releasing it.

The latch is not setting - but if I push the linkage to rotate the tab torque bar myself I can make it reliably latch. Thus, I think that I can shorten the linkage, which has a turnbuckle for adjustments, to ensure that the tab latch is pushed far enough to reliably engage.

The failure of the margin rack to be released to the right when a carrier return operation begins is a similar situation - a lever pulls a linkage that releases a latch on the right of the margin rack. I will adjust that turnbuckle to make it shorter, thus moving the release arm further on the margin rack release mechanism.

After adjusting the tab torque linkage, the tab latch is setting reliably. Whenever a tab is commanded it latches and moves to the right, only resetting when it hits a set pin on the tab rack. Excellent behavior. One major problem resolved.

I shortened the linkage to release the margin rack but it isn't so reliable. It appears that the range of movement is too short for the lever that pulls on the linkage. I am going to dig further into the mechanism and adjustments to sort out why and what to do about this.

I did find that if I am doing a right tab and it runs into the right margin, it isn't releasing the tab latch. I need to see how this is supposed to occur before I can sort it out. It may be related to the problem with the rack release, or not.

I did find a spring under the mechanism, undoubtedly fell off the typewriter somewhere. I need to figure that out and replace it, needless to say. My first spots to check will be the carrier return and tab sections of the operational shaft, about where it fell, as these could be the cause of my two remaining problems.

After investigating the theory of operation manual, I realized that the tab latch will remain set when the carrier runs into the right margin stop. It is when the carrier return operation begins that this is resolved, because the escapement torque bar is turned by the carrier return mechanism in order to keep the escapement and backspace pawls out of the escapement.

If that didn't happen, the carrier would make a ratcheting sound as the escapement pawl skipped over all the teeth on the escapement rack. The twisting of the escapement torque bar also swings part of the tab latch mechanism out of the way, releasing the latch. Therefore, the right hand margin behavior is not a problem.

I reached the end of the evening without a clear diagnosis of the problem with the carrier return mechanism. I will study the theory, parts and adjustment information, plus review some video training on Selectrics, preparing to tackle this again tomorrow.


I removed the disk heads from the Diablo drive that came in the CHI rack - they show major damage from a head crash and are unusable as they are. They have crashed into the surface of a disk, ruining both the disk cartridge and the heads.

Head crash damage visible on the heads - scrapes on metal plate and magnetic oxide wedged in scratches

Rectangular slow beside upper holes, to side, with brown iron oxide coating from disk packed over ceramic head inside
You can see lots of scraping on the shiny metal surface of the head, caused by various particles which were embedded in the disk surface which rotated under the head. Also, you can see significant brown ferromagnetic coating material from the disk surface has been packed in the rectangular gap which exposes the ceramic part of the head and its metal poles that do the actual reading and writing.

First, the oxide material has to be cleaned out of the gap, then the condition of the underlying ceramic and electromagnet poles must be assessed to see if they can be saved or need rebuilding/replacement.

The metal plate has to be removed from the arm assembly and the internal ceramic, coil and pole magnet assembly which is the functional part of the head has to be removed from the plate and set aside.

Next, the metal plate would have to be polished to remove the scratches, perhaps with a new layer of the chrome-like surface added.

After removal of scratches, the metal surface must be returned to the curvature it needs to fly aerodynamically on an air cushion at a target height above the rotating disk surface, without wobble and certainly without oscillating vertically in a way that might bring it into contact with surface irregularities or the disk itself.

When all else is done, the ceramic/coil/pole part has to be put back onto the plate at the right alignment and depth, the plate affixed by microwelding to the arm in the proper orientation, before it could be put into the drive and used again.

As you can tell, rebuilding a head requires special equipment, skills and quite a bit of care. Years ago there were several services which did this processing, taking damaged heads like these and returning assemblies that were rebuilt to be as good as new. Once the arm and head began to be built into the disk drive itself, users no longer removed and replaced heads as a maintenance activity - without that process, the need for head rebuilding services evaporated.

If I am lucky I will find a service that still is able to do this. There may be a tiny market handling repairs to systems that must remain in service even though they are decades old and no longer have spare parts availability. Defense systems are just one example of situations where really old technology is still being used with the need for repair/rebuild services supporting an ecosystem. The cost of replacement of the technology with more modern tech is so high in these cases that is justifies high charges for service and rebuilding, even at the extraordinarily low volume of such activity.

If anyone knows of a service or person who can rebuild the heads, please let me know. If you know of someone who has replacement heads for the Diablo Series 30 disk drives or something compatible, also pass along the information.


I will try to solder on a replacement microUSB connector onto the fpga board. Digilent replied but does not do repairs. They offered to process a warranty claim but it is clear damage by me, not a defect, so that is off the table. I ordered the receptacle from Digikey and should have it in a couple of days, slight delays due to heavy holiday shipping volumes and of course a few actual holidays where packages stop moving.

Wednesday, December 17, 2014

Fighting the last problems with the printer

As I had mentioned, I spent time meeting friends from the 1401 Restoration Team at the Computer History Museum and then had my haircut in the afternoon, but did get into the garage for a few guilty stolen moments.


Wrestled the C2 contacts into position to give the intended timing, breaking the circuit as the print cycle hits 20 degrees of rotation and making it again as we pass 120 degrees on the way to completion at 180. This timing is related to the realities of the selection mechanism, which has released the various latches before 120 degrees, at which point the type ball is rotated, tilted, locked in place and just about to strike the ribbon/paper.

If the print solenoids are activated at this point, they will lock in the next character but not interfere with the remainder of the current print that is in process. However, the cycle clutch latch won't stop the rotation, allowing the machine to continue smoothly into another print cycle based on those solenoids which were activated late in the prior cycle. This maximizes the print speed of the machine and reduces stop/start shock.

The device adapter logic in the 1130 is responsible for monitoring the circuit that goes through C2, holding off until the 120 degree point before commanding the next print operation. If electronic hardware were not so expensive at the time these systems were designed and built, a digital buffer inside the 1053 could have accepted the command for the next character and held it until it was time to activate the solenoids, simplifying the requirements for device adapter logic in systems like the 360 and 1130 that drive these printers. Instead. the 1131 directly drives each solenoid and must monitor mechanical state of peripherals in order to time activities correctly.

I have a selectric based mechanism in a Dura word processor that I will restore to act as a 2741 terminal on my 1130 system, but it does have a motor pulley of the same type as I need. I will 'borrow' this one and back-fill with a replacement part I can put back on the Dura. Installed now on the 1053 and working well. I still have some motor vibration, not sure why, but it is not the pulley slots anyway. Quieter and more gentle, so progress for sure.

The carrier return issue with zooming past the left margin stop is still here, at least under power. I need to do more research to figure this out and stop it, now that the printer is so close to operational again. By the end of the evening, I still didn't know why it was hit or miss. Time to step through the adjustments for the high speed carrier return starting at step 1.


I decided to pull the read/write heads from the Diablo disk drive in the CHI cabinet, in order to find someone who can restore them to working condition. There had been a number of businesses that did this with disk heads, back before the heads were permanently integrated into the drives and not worth rebuilding. If I can find any that still exist, I can get the Diablo drive back into operation.


Still looking for a way to get those four leads soldered onto the fpga board, particularly the three that are side by side and thus can't be individually attached (the soldering iron loosens adjacent wires). Ron Crane had some good ideas for how I can proceed, will try them out.

Tuesday, December 16, 2014

Console printer adjustments and restoration almost complete

Tomorrow I have obligations at both the Computer History and Digital Game museums, plus an appointment for a haircut, really constraining my available time with the 1130, but I should be back at the machine in earnest on Thursday.


It dawned on me that my assumption for the restoration, that this was properly adjusted before it sat in storage, is not correct. I see the typeball triangle on the top plate, which should point directly at the platen when at rest, is rotated 5-8 degrees to the right instead. This is undoubtedly causing the issue where the detent bar can strike the tip of the tooth and not enter the proper notch on the typeball rim.

Incorrect home position of typeball, rotated a bit to the right
My early operation of the console, which yielded the correct characters for every position on the ball, lulled me into believing my assumption of correctness. Visually, however, I see it isn't so.

Print shaft gear with setscrews, adjust rod to proper position then tighten these up
The rotate arm should be directly vertical when the typebar is in the home position (at rest), but it is tilted so the top is a bit to the right of the pivot at the bottom, leading to the incorrect home positioning. The adjustment for the rest position is a turnbuckle on the rod that connects the mechanism selecting the rotate amount to the rotate arm.

I hate the idea that I might start adjusting the rotation position but have ignored some 'earlier' adjustment which may be off spec. I believe I have to at least do a quick validation of the adjustments starting at step zero, in sequence, since each adjustment builds off prior ones. Adds a bit more time to this particular restoration but ultimately worth it.

I also see the belt and motor oscillating, showing that the corroded slots on the motor pulley are not allowing the belt to fit into the slot. This raises the belt as the pulley rotates to put the bad slot at the furthest point from the main pulley, increasing tension on the belt, bending the motor forward on its shock mounts, and thus generating the oscillation. It has to be replaced by a good motor pulley - fortunately that replacement will not require any disassembly of other parts of the printer, only loosening of the motor mount screws.

Several hours of careful work gave me proper timing for tilt/rotate, print and filter shafts and everything else except for the C2 contacts that indicate when the mechanism is busy during a print cycle - it should break the connection at 20 degrees of rotation and restore it at 120 degrees.

Timing of C2 contacts
C2 contacts in situ, continuity tester connected by colorful alligator clips at bottom
Adjustment screws - oval slots but no positional adjusters, just hand movement
Another view of contacts
The contacts were a bit oxidized, only conducting sporadically. I used my burnishing tool to strip off the oxide layer, restoring proper operation. Adjusting the contacts to make and break at the proper degree positions was challenging. I could get one or the other point working, but the opposite state change would be too far off its target. I ran out of time today but will be attacking this further in the coming days.

Burnishing tool for oxidized contacts
I found the cause of the carrier return problems - I had dressed some wiring with a cable tie which interfered with a rod used to absorb the energy of the carrier hitting the left margin. This machine has a special feature called High Speed Return installed, rather than the usual mechanism and return speed. It works fine now.

I included pictures of some special tools used to work on Selectrics - the Hooverometer, a spring hook which is used to install and remove springs, a set of bristol wrenches and a circlip installing tool. It is easy to mistake the bristol wrench openings for allen wrench openings, but using the wrong tool rounds off the points rendering the screws useless.

Hooverometer to measure separations and heights

C-clip tool, spring hook and bristol wrench set

I attempted to solder the teeny wires to the teeny pads on the fpga circuit board, but continued to have problems with each method I attempted to hold three wires simultaneously and rest them on their respective pads less than .01 inch apart.

I also contacted the maker of the board, based on comments in some of their documentation that suggests they can make repairs to the board, giving me a backup if I can't get this wired up myself. I found that the board I bought just 30 days ago is now discontinued, removing the option of tossing a few hundred dollars away on a replacement.

Monday, December 15, 2014

1053 Console Printer work

Some health problems have arisen with my father-in-law that took up some time today and likely will take me away from the 1130 restoration from time to time, but not continuously.


I realized when I started on the 1053 this morning that I had two adjustments left to make, not just one. After I set the final print shaft timing, I need to set the contact switch that gives feedback to the adapter electronics about when the print operation is complete to the point where another character or operation can be requested.

Shift interlock cam on filter shaft 

Escapement cam - spaces after each character printed - on filter shaft
The print shaft timing involved setting the timing for when the detent first contacts the notches along the bottom of the type ball, so that it is safely inside the notch but on the side - this gives the detent a 'wiping action' as it moves to the center of the notch with continued rotation of the print shaft.

Gear train - print shaft on top (smaller black pulley)

Print shaft going into carrier at right, cycle clutch and drive belt visible below

Black detent bar entering notch in typeball, barely visible 2/3 of way to right along bottom of pic

The C-2 contacts ride on the cycle shaft gear body, ensuring that the timing of the cam climb point and slope is synchronized. However, the vertical position of the contacts determines exactly where the switch closes and opens relative to the rotation of the cycle shaft, as it moves up or down the slope.
Carrier from top while standing behind printer, sliding on print shaft and along escapement bar

The open and close points are easy to set by reference to the degree wheel affixed to the left end of the cycle clutch shaft - sits at 0 when at rest, then marked in single degrees for the 180 degrees of one cycle.
Degree wheel mounted to end of cycle clutch shaft
To adjust the print shaft timing, I put the Hooverometer in place to block the cycle clutch at the halfway point (half-cycling a character), selected a specific character by pushing the appropriate solenoid arms down, then rotated the hand crank wheel. The gear on the end of the print shaft is held in place by setscrews; loosening them allows the shaft to be turned to advance or retard it compared to the cycle shaft position.

With the machine stopped at the half-cycle point (registering 90 degrees on the degree wheel which matches the state of the clutch shaft), the print shaft is turned to spot the point where the detent bar engages the teeth of the typeball.

However, as I did this, I could see that the ball was not properly rotated. The notch of the teeth was offset so that the detent bar could land directly on the crest of the tooth or even snap into the wrong notch, depending on the rotational play of the typeball.

Now I have to go back and validate the rotation mechanism settings, before moving ahead. The current mis-positioning can cause breakage of the typeball teeth or damage to the typewriter mechanism.

Rotation of typehead controlled by movement of this vertical arm, thru the rotate tape on pulley

Tilt of the typeball controlled by this vertical arm, thru the horizontally mounted pulley for the tilt tape
Selection mechanism that converts various solenoid latches into movement of the tilt and rotate arms

Another anomaly I see occurring is sporadic failure of the left margin to stop the return of the carrier, which seems to be caused by sludge in the margin bar and sliding components attached to it. I exercised them a bit and seem to have a more reliable left stop now, but will keep my eye on it.

Under power, the motor still vibrates a bit which is caused by the corrosion on the motor pulley, such that the belt does not slide into the corroded slots as fully as the normal ones. I need to locate a good replacement and install it before the new belt also is damaged. I think I understand why the typewriter was modified with a power switch on the front panel - the vibration and miss-adjustment of the typewriter would be objectionable but turning off the motor removed the problem symptoms (but the console printer could not be used in this case).

Sunday, December 14, 2014

SAC interface work and 1053 typewriter repair progress


I found the part that must move to adjust the backlash and began adjustments. I can get it well engaged but the backlash of the print shaft to the idler gear is still more than the .001 to .005" that is recommended even with the idler stop as far as I can move it.

I will look at some other machines I have to check the backlash they experience - if it is consistent then I can move on to adjusting the cycle clutch latch holder height, otherwise back to fiddling with the idler gear position.

There are about seven more adjustments to make, some of which I know are quick and easy (e.g. the cycle clutch latch holder height). I continued with the work, getting the backlash into a good range. I then did the height of the cycle clutch holder, using the Hooverometer, a special tool to use with Selectrics.

Next up came a check of the cycle clutch spring and overshoot adjustments, which were within the proper range. As well, I verified the bite of the clutch latch lever was in tolerance.

The next two adjustments are the timing of the filter and print shafts relative to the cycle clutch mechanism. These must move in synchronization which is accomplished by the gear train, once their relative position is set properly.

I loosened setscrews in the gear at the end of the filter shaft and rotated the shaft while the cycle clutch was in its 'rest' position, putting the escapement and shift interlock cams at the proper rotational position.

Before I touched the print shaft, I decided to adjust the motor tension because the belt was skipping cogs on the motor pulley, producing a little 'jump' on each turn. The usual cause of this is that the belt is too loose, plus I thought that the spare belt still had a slight deformation from the way it was stored over the years which would ease out with use.

However, even tightening the belt (by loosening the mounting screws then  pulling the motor) didn't help. I removed the belt from the motor pulley and looked closely, finding a chunk of old belt rubber wedged into one of the slots of the pulley. That caused the slip on each rotation. I removed the pulley and scraped the old rubber out of the slot.

Rubber wedged in slots of the motor pulley
I could see that the bad slot and the two adjacent ones had some corrosion, so they didn't clean up as well as I wished even with a lot of scraping. In spite of having amassed several cubic feet of Selectric parts, for almost every model including Composers and other such rare ones, I had no spare pulley.

Corrosion of pulley after as much scraping and cleaning as possible
I reassembled it and tightened up the tension, happy to feel it rotating smoothly and without any hitches. I believe the wedged up slot and resultant skipping was what caused the failure of my previous replacement belt.

I will finish the adjustments tomorrow with the last step, the print shaft timing. I can then test the printer, reassemble the covers and put it back in place.


I found the pin-out for the wiring of the micro and standard USB connectors, allowing me to attempt to solder the cable from the front panel USB connector to the fpga board. As I typed this, I realized that I would be permanently tethering the FPGA board to the enclosure if I just soldered the connections directly, so I will look for a suitable set of connectors to put in the middle of the cable for disconnection when the board must be removed.

The pads are so small that I have to use 30 gauge wire wrap for the connection on the board then make a joint to larger, more durable wire for the connector I chose. I began soldering these onto the fpga board but the spacing is very close and I found that my soldering iron would release the adjacent wire when I tried to solder a wire on another pad. I need a method of securing all four wires at precisely the right separation, and a means of holding them in position, such that I can solder all of them simultaneously.  This is fussy work and will take some time to figure out a suitable set of jigs.

In the meantime I reinforced the connector plate for the power cable, as the steel is fairly thin and flexed too much with the heavy cable connected. I improved it quite a bit although the receptacle itself does some flexing which I can't avoid given the current thin plate to which it is secured.