Repairing fault-handling of the Burroughs Portable adding machine

With the subtract-function fixed and columns 7 & 8 re-activated, this Burroughs Portable performed all calculating functions flawlessly. What however did not work at all, was the catching of faulty, incorrect input conditions. (Because this doesn't impact the normal functioning of the machine, this a 'malfunction' that can remain completely unnoticed. The machine did not dis-engage and simply completed a cycle, with possibly incorrect results.)

This now also repaired and re-activated.

Looking back, this functionality was probably broken from a combination of wear to parts and from parts getting bent by handling without its case/base. And made worse from my injudicious handling of the keyboard-module during cleaning - learnt for a next time that the exposed brackets are 'soft' and critical to timing.

Most adding machines have interlocks to prevent wrong operation that could cause incorrect results or damage to the machine. E.g. the keyboard is blocked during a cycle or it's made impossible to reverse half-way through a cycle. The Burroughs Portable has plenty of such safety interlocks. It however also has two fault conditions that are not blocked, but that are prevented by dis-engaging the handle and in that way prevent completing a cycle.

The two conditions that should trigger the handle dis-engaging are trying to start a cycle with:

• Depressed total or sub-total and a value set on the keyboard.
• Depressed total or sub-total and the machine set to subtraction.

Reading user instructions confirmed that the machine should catch these fault conditionsa and then reset. (Scans of these original instructions very kindly provided by Mike Hancock who created the very informative Burroughs Info website.) 

Reading further in the very extensive US patent 1,853,050 by Mr Horton covering the Portable gave more background on these two exceptions, how they are caught and what should then happen. The two conditions have their own specific 'trigger' that both then lead into activating the same dis-engage & reset mechanism.

To start with, the mechanism to dis-engage the handle from the mechanism is shown in Fig. 3A of the patent (here below). This is a detail of the left-side of the machine shown in Fig. 3 that is mostly dealing with the electric drive arrangement. The axle actuated by the handle (91, orange) is inside another hollow axle that drives the machine. (Actually, it pulls the machine via springs with the dashpot limiting the speed; a lot of thought & experience went into this design.)

To give the short (...) summary: The handle drives the rod 91 that has mounted on it the hook 89, this pulls along the machine's mechanism by contact-surface 87 onto hook 83 that is fitted to the machine's mechanism. At the same time, the rod 191 moves rearward (locks the keyboard among other things), the stud 194 moving in the slot 210 then rotates the extra hook 212 out of the way. That's normal operation. When an exception is detected, the rod 191 does not move all the way rearward and the hook 212 is left in the path of face 86. This then smartly pulls hook 83 away from 89 and the handle is dis-engaged from the mechanism.

In an actual machine, without electric motor, the relevant parts can be seen much clearer.

This dis-engaging should happen after the keys-reset lever is dropped behind its position on rod 191 on the right side of the machine AND it should happen before the pawl of the full-cycle mechanism clicks in its first stop (red arrow) on its cam 76 inside the machine. Then the mechanism will jump back to its rest-position and clear all keys. Simply moving the lever back to its start position will re-engage and the machine is ready again.

Probably due to wear, the dis-engaging happened AFTER the first full-cycle stop clicked in - that meant that a fault-condition would truly disable the machine. It would need opening up and manually resetting, continuing a cycle or forcing a clearing via manipulating by hand rod 191. (This wear and fault may have been a reason long ago already for the machine to be 'retired' and may also be why the baseplate of the machine was loose. It was not fitted to the mechanism, the machine sitting loose on top of the 'pan' so easy access to the parts that need twiddling.)

To compensate wear and move the timing of the dis-engaging before the full-cycle stop, a shim was added onto face 212. A bit of a kludge and too large, but this way the 3mm brass clamps itself on the back of the pawl. Fixated with cyanoacrylate, it only needs to keep it 'still' and the glue does not have to take any force. It also makes it reversible; applying heat (soldering iron) will disintegrate the glue.

The tip of the brass 'shim' was filed down to about 0.5 mm to slightly advance the timing. Another tweak was adding a bush around stud 85 (not visible itself, it's peened into the oval covering of part 87), this pushes out the hook 86 a bit further and makes it easier to dis-engage.

Brass is really too soft for this kind of function, but great for filing to shape when experimenting. In any case it's a 'kludge' and should not see much action - it is exception handling for faulty use.

The more complex side of the mechanism to detect the wrong setting is on the right side; that's where all the control mechanism is. That's where the push-bar is that is pushed forward a smidgeon further if total and a key are pressed at the same time. The keys detection goes via the U-section bail at the top of the keyboard to that push-bar.

That bail (in green circle) is the stop for a push-bar 185 that is pressed downward by the total or sub-total keys, changing its stop-position. This push-bar has an opening around the rod 191, thus limiting the travel of 191 and thus triggering the dis-engaging. (All this took a while to figure out...) With the dis-engaging mechanism again working, this fault condition triggered correct again.

The dis-engaging when a totals is depressed and the machine is in subtract still did not work - the handle did not dis-engage and a cycle was completed (with possibly wrong results).

The detecting of subtract-mode and a total key is a different mechanism to trigger the same dis-engaging mechanism. To make it interesting; the actual machine is different from the patent drawing in just this detail! Other than this subtract-lever detail, the machine is exactly as shown and described in the patent:

Instead of the forked extension to the front of the subtract-lever around rod 191, there is a separate part slotted over rods 191 and 122 with an upward forked-extension that interacts with a stud on the subtract-lever. During a cycle, the rod 191 is swiveled to the rear, raising this upward extension into the path of the subtract-lever's stud; this prevents operating the lever during a cycle - a safety interlock.

This part also plays a role in the detection of the fault-condition - that is done by preventing the subtract-lever reaching its end-position. When a totals is depressed this pushes forward a tab 223A about a sixteenth of an inch, and this tab blocks the subtract lever from reaching its end-position.

This sixteenth of an inch (well, approximately) should make the difference between the stud of the subtract lever sliding past the upward-fork or catching and stopping it. This no longer worked, probably because I accidentally (clumsily) bent the rod 191 assembly during cleaning of the keyboard module - the brackets may all be fairly heavy-gauge, but are soft. To repair this, applied another kludge; an angle-piece shaped from a steel nail was added to the side of the forked-extension. This now makes it catch on the stud when a totals key is depressed in subtract-mode - and move free when no totals key is depressed.

The left image shows it clearing the stud, the right image shows it catching on the stud (and triggering the dis-engagement of the handle, the machine jumping back to start and clearing all keys).

Overall, detecting these 'fails' and finding out how they were supposed work (and then figuring out how to repair) gave extra insight into the whole working of the Burroughs Portable adding machine. With its fairly modular build-up it is not the most difficult or complex of adding machines, but still (or because of that) contains a remarkable amount of ingenuity!

The patent is perhaps a bit unusual, in that a single patent document contains the full description of a whole machine - more often there are multiple patents documenting different features (inventions) of a machine. Absent a full repair or service manual for the Burroughs Portable of the 1920s, this patent is a pretty good resource. To give an impression of the patent; it contains a full 20 pages of detailed diagrams, followed by 28 pages of terse technical explanation.

To note though that there are some detail-differences with actual machines (e.g. the subtract-lever) and it was not written for a repairman. It e.g. glosses over some details that will be important when servicing. For example, what it states is true; the keyboard can be lifted off after removing two screws and sliding it rearward. But you also must unhook two springs and use a finger to keep rod 191 pulled all the way forward to take it off without breaking anything! (I've taken the keyboard off about a dozen times by now; that little spring that holds the reset-push-bar is easy to miss.)

These Burroughs Portable adding machines are pretty common and not all that sought after today. The reason these are common is I think not only because Burroughs had a great sales organisation, but also because it was a very good, low-cost and fit-for-purpose design - it sold in large quantities:

Office Appliances, November 1926

Advanced digital computing technology of the 1920s!

For the mechanically/technically interested, these are absolutely worthwhile machines - and repairable too :-)

Type cleaning on the Burroughs Portable adding machine

Just like typewriters, the type on an adding machine can get clogged-up with old ink or dirt from the ribbon. The Burroughs, like most adding machines, has a rising-segment printing mechanism; the trick is to first get good access to the type for cleaning.

On the Burroughs it is relatively easy to remove the platen, by taking off the top-assembly. Removing 3 or 4 screws should allow this assembly of platen and ribbon-spools to lift off. To then make the segments pop-up, enter 9's in all columns and stop mid-cycle.

Before pulling the handle, it's a good idea to set the machine to non-printing; without a platen present the printing hammers would only try to knock the segments out of their guides. I.e. slide the little tab to the left:

Then pull the handle forward, but not all the way. The full-stroke mechanism has several 'clicks' that lock the handle and prevent it going back before completing a full stroke. Leave the handle at the last  'click' before completing a stroke. This will leave the handle in the forward position and the type segments raised to their full extent.

The housing doesn't need to come off, but could be easily lifted off after removing the two screws in the front.

Cleaning of type is exactly the same as with typewriter slugs; a sharp needle to pick-out the caked-up areas and a brush to clean the type. A rag to prevent the dirt dropping out of the type falling into the mechanism.

After cleaning, the stroke of the lever can be completed - and the segments drop back to their rest position again. The machine is then re-assembled, i.e the platen and spools module placed back - followed by a quick test of all numbers on all columns. The rock-hard platen is now probably the limiting factor for print-quality - nevertheless, all clean and readable :)

New 7/16" ribbon for the Burroughs Portable adding machine

Even though it all works with a standard half-inch ribbon, the Burroughs is actually built to take a 7/16" ribbon. These are not too common anymore, but can still be bought. They can also be found in some cassettes for more modern printers or cash-registers. In this case, a cassette for an Olivetti PR4 was opened up.

This cassette contains a 7/16th ribbon in an endless loop. First thing is to find the splice, i.e. the spot where the ribbon was welded together to make a loop. To avoid having a 'hard bit' somewhere halfway on the ribbon, that's the spot to cut it.

Then the new ribbon is wound on a spool or simply onto a toothpick. This helps to remove any kinks from having been zig-zagged on the cassette. It also be convenient for re-inking the ribbon.

These cassette ribbons were probably not very heavily inked to start with, especially when intended for a pretty aggressive needle-printer. These cassettes often are old stock, so perhaps already dried out as well -despite the cellophane wrapping. (Probably not actually cellophane, but whatever transparent plastic material it is; it probably isn't fully airtight.)

To work well in an adding machine, a ribbon needs to fairly heavily inked. (Same for a Hammond, but an Oliver could be fine with a lightly inked ribbon as it packs quite a punch.) To add more ink, ideally a little inking-machine should be used. Proper inking is done by first fully soaking the ribbon and then squeezing out excess by feeding it through pressure-rollers. Level of inking is regulated by the pressure on the rollers.

Not having such a machine (not yet :) the inking was done by hand. Either place droplets of ink onto the coiled ribbon and let it seep in, or apply drops/streak along lengths as it is wound from spool to spool. Stamp-pad ink, either 'water' based or metal-stamp ink that should be oil-based. It can help to leave the ribbon a day or two after applying ink to let it all even -out and properly soak in the fabric.

Whichever inking method was used; a final and messy step that is essential for a usable ribbon is to squeeze and spread-out the ink. To do this manually, the ribbon is wiped with a bit of absorbing card or towel over paper. As lengths of ribbon are pulled through this wiper, excess is removed and evened out. It's messy, but not hard and makes a lot of difference. 

With the little Burroughs spool full, the ribbon cut to length and firmly fixed to the other spool. Note that the Burroughs Portable -like many other adding machines- uses tension on the ribbon to reverse the ribbon-transport. That means it should be very firmly fixed to the spool - e.g. tied to the spool-core with a knot. Double knot.

The spools with freshly inked 7/16th ribbon then placed on the adding machine. The ribbon winding directions are obvious from the spool driving ratchets, routed around capstans as shown below.

Net result: a better fitting ribbon and a legible printing line on the Burroughs Portable adding machine.

Carriage cleaning of the Burroughs Portable adding machine

This Burroughs Portable adding machine has the wide carriage option; a 12 and a quarter Inch carriage with tabulator stops.

The brightwork on this wide carriage was very dirty and/or corroded. Most of the brightwork originally would've been shiny nickel-plated, but now with the dirt of decades and some spot-corrosion:-no longer very bright. One of the tabs below cleaned back to a shine proved it was mostly dirt.

This wide carriage of the Burroughs turned out to be not so easy to take apart for cleaning. Several collars are pinned onto their rods and even the platen-rod has a ratchet-wheel doweled in-place. Taper-pins are very hard to remove. So for now only limited cleaning of the most exposed (and reachable) parts. Removing side-plate mounting screws allowed the side-plates to be shifted just enough for the tabulator rack to come off.

As can be seen in the image below, the main spacer-rod behind the paper-tray was not removed and still has a brownish hue. However, the tabulator bars and springs did come out quite nice. (And no longer look like you'd catch something off them at five feet.)

One detail when re-assembling the carriage is the positioning of the ratchets. The Burroughs has two; a driving ratchet wheel and a holding ratchet wheel on the platen rod - both visible right next to each other in below image. The holding ratchet wheel is fixed in position on the platen rod by a screw.

This holding ratchet wheel must be adjusted so that in the holding rest-position the driving pawl on the driving ratchet-wheel is only-just released and drops free again after a line-feed.

This was the cause of the carriage line-feeding issues of the machine. It would only do a line-feed when set to dual-spacing and block the platen from reversing using the knobs. That was because the pawl could not drop free, but was kept under pressure (and failing to fully advance the platen). Very likely this was not adjusted at the machine's last servicing - perhaps in the 1960s still. After assembly it was set to dual-spacing and the carriage did feed, so no more attention given.

During cleaning; one little artefact of the manufacturing process of screws; the slots of screws were cut. On this one screw (right), the slotting-machine must have been set a little too low, neatly splitting the entire head.

Cleaned and carefully tightened back in place. The split head makes it a weak screw, but it held the paper-roll bracket on for 97 years and should do so for another 97 years.

New gasket for the Burroughs Portable adding machine

Many Burroughs Portable adding machines don't have it anymore, but originally there would have been a rubber gasket between the top housing and the base-plate. It may have perished (as rubber can do), or maybe it simply wasn't put back after a servicing. This U-section rubber gasket is shown in the patent image - circled in red.

A length of suitable, rounded rubber U-channel of 6 x 6 mm with a nominally 2 mm slot could be sourced, found online.

With a hole-punch, half-circle cut-outs were made for the gasket to clear the threaded-bush of the front-mounting screws. Then pressed onto the sides, cut to length at the back and the ends glued together.

Before fitting the new gasket, a nut was soldered in as replacement for the missing front right threaded bush. No idea what thread it is, but fortunately two screws and a nut of the correct thread were in the tin-with-bits salvaged from a 1940s Underwood.

The top housing now fits very snuggly on top of the baseplate - the rubber will help against dirt and dust getting into the machine (and maybe against noise, but I doubt it).

The spool-cover tops are already re-painted and the spool-nuts spruced up. The rusty tops of the spool-covers were sanded completely back to bare metal and re-painted. To mimic the textured lacquer finish, some 'meandering' was added with a fine brush on top of the base layer of flat-black paint. Then the spool-cover was finished with a satin gloss. When viewed from a distance, this blends in well-enough with the original finish of the machine.

The carriage still needs to be cleaned-up, but this Burroughs Portable is starting to look very solid and dependable already (it would feel right at home in a bank ;-)

Tune-up for the wind-up gramophone (and playing records)

Spending some time last weekend playing records, the bright colors of some labels do impress. From the way these were stored, they'll have been shielded from sunlight. Sleeves are usually a bit faded, yet these orange labels really stand out.

The records from the 20s and 30s found here in the low countries are quite international. Much is relatively local, German, British and French, but this Crown is a US record and e.g. the Odeon is from Argentina.

The sleeves make a point of the music having been electrically recorded. This was something new that quickly became the standard from the late 1920s. 

And also the below Dutch record sleeve proclaims; "The latest invention is the Homocord Electro - the electrically recorded disk".

Electrical recording really did improve the quality of the sound. Playback was still mostly without electrical pick-up (that started emerging in the late 1930s for (expensive!) home equipment). These ~1930 records would've been expected to be used with an acoustic reproducer. For example on a portable wind-up gramophone, like this 1929 HMV model 101.

During playback however, some louder sections of the record suddenly sounded 'off'. The gramophone was not keeping speed. As it had been a while since servicing, very likely then that the motor badly needed a tune-up. Maybe even a re-greasing of the motor spring.

To do a service: slide off the circlip, switch the brake to 'off' and lift off the turntable. Give the motor time to fully unwind - when servicing a wind-up motor there should be no tension left in the spring. After removing the four screws in the corners of the motor board this can be lifted out, front up first and sliding the motor 'block' from under the rear deck and forward.

This time the motor was kept on the board; the whole board was placed upside-down on the rims of a baking-tray with a towel for protection. Removing three small screws allows the motor cover to be taken off. Then another three larger screws out of the pillars allows the motor plate to be taken off.

Again; take care to not loose the small bearing-ball under the main turntable-shaft (likely held firm in its grease, but still). Also note the washer between the arbor-shaft and bottom-plate - it will have stuck to either the motor or the plate.

The gears were very 'gummed up'; the brass of the intermediate gear had turned green and the teeth filled with 'gunk'. Slowly growing corrosion in the gears mixed with grease could also make a motor lose power - and of course the governor was in dire need of fresh oil on the friction pad. Seeing these issues, decided to leave the spring itself alone - its greasing of ~10 years ago likely still good enough.

The gears were all cleaned, stubborn dirt removed with wooden tools (not scratching). New grease with this time also some graphite applied to the gears. 

The pressure angles of the gears driving the governor are really steep; will need good lubrication. For speed control the governor's friction pad and disk need to be well oiled - and the sleeve-with-disk that is moved by the three weights should move on the shaft without friction for proper speed-keeping.

The motor and gramophone put together again, it seemed to run just a little bit smoother. With 50Hz incandescent lamps becoming rare, strobe disks are getting more of a hassle to use for adjusting the speed. Today however a small application transforms a smartphone into a modern instantaneous speed tester. Nifty!

Testing with a record too (extra drag), the gramophone is again able to keep speed - no more false notes.

Placing another record on the instrument.

Plays great!

Electrically recorded in July 1931 in New York - played back mechanically in May 2025 in Holland.

:-D

Re-activating column 7 and 8 on the Burroughs Portable adding machine

When entering numbers, all columns seem to work. For example, entering 7777 on the left-most columns makes all segments rise and print as they should.

When then doing a total, the columns 7 and 8 segments do not rise and do not print, but the column 6 and 5 print, as does '*' (total sign) on the right-most printing column.

The print-out confirms that columns 7 and 8 are not working in totals.

That was an interesting fault - when the machine was taken apart earlier, the register wheels were spinning freely; no binding. That they print fine when simply adding confirmed the problem was not in the register itself.

Staring at the operation of the machine (with covers off) during adding and when a total is taken, tracing how the parts move, pointed to the problem being in the keyboard. The differential-bars slide under the keyboard for every column.  In adding it is stopped by the peg of a number-key at the right position to cause that number to be added to the register.

At the front of the machine is a rocking bracket for every column - this is rotated out of the way if a number is entered or when a total is taken. When a total is taken, the differential bar (and connected segment etc) needs to slide all the way until stopped by the register-wheel - that's how the value on the register is retrieved for printing a total.

The rocking brackets for columns 7 and 8 did rotate their 'stop' tab down far enough for the differential bar to slide over them. The columns 7 and 8 were snagged and thus always a zero was registered as the totals-value on columns 7 and 8.

Some more peering at the mechanism revealed that very probably the tab that holds the rocking brackets in the keyboard key-locking-bar was bent for the columns 7 and 8. They were angled slightly different from the rest.

These rocking brackets are exposed when the mechanism is out of the case. Looking at this, actually it's likely that this fault was accidentally created by me when working on the mechanism- perhaps when giving the keyboard a thorough scrubbing to clean the keys, dod not take enough care to not put any pressure on these exposed bits.

Slowly and carefully bending these tabs back so that the differential bar just clears the little stop-tab re-activated the total working correctly. As seen in the print-out of all sub-totals for testing if the bending was far enough - first column 8 re-activated and then column 7 came back too.

Just to be sure, adding 333 and 222 indeed gave 555 back in the left-most columns. 

Feeling confident enough to test the tens-carries; multiplying 12345679 by 8 - that also worked fine and printed the expected answer.

(The printing line is a bit obscured by the ribbon. That's because the machine is now fitted with a standard half-inch or 13 mm ribbon. This fits and works, but the machine is made for a 7/16" or ~10 mm ribbon, just like a Hammond or an Oliver. We'll have to see if a well-inked 10 mm ribbon can be arranged for this machine. Until then, a regular 13 mm ribbon does the job.)

This machine is proving to be a grand puzzle, and very much understandable/repairable - more cleaning and some restoring to do.

:)