Fixed ASR33 keyboard, built USB to teletype interface device but still debugging it

MODEL 33ASR KEYBOARD RESTORATION

I partially disassembled and adjusted my keyboard for my teletype model 33 ASR, getting it to work smoothly and reliably. I verified the contacts using a VOM while pressing many of the keyboard keys. It is now ready to be reinstalled in the machine, while I go on to work on the call unit, printer unit, tape punch and tape reader mechanisms.

Restored keyboard module for my ASR33 teletype

BUILDING TELETYPE TO PC INTERFACE USING REFLOW OVEN

The board for the open source TTYLoopDriver project uses many small surface mount components, in addition to a few through hole parts. I carefully put down solder paste and inserted all the components in place, ensuring the polarity of diodes and similar parts.

I ran this through my reflow oven, another open source project by the way. The board came out with solder bridges on three of the tiniest integrated circuits, something I had to clean up with solder braid and manual soldering under the microscope. There are also a couple of skewed parts I can adjust.

Board coming out of the reflow oven, needing tweaks

The large metallic coil in the center was enough of a heat sink that it kept the solder paste from fully flowing. I touched that up with the soldering iron. The small ICs U2, U11 and U9 had solder bridges on the leads, which I repaired by judicious use of solder braid after flooding the surface with flux. Finally, I used the hot air rework tool to remove the capacitor that was pivoted and shorting to the pivoted resistor, then cleaned up the resistor end and manually soldered the capacitor back in place.

The remaining components were through hole parts which I mounted and soldered in place. The final part was the USB board that fits in the upper left. It comes with a right angle header that must be removed. My Hakko desoldering gun vacuumed away the solder and allowed me to remove the only header. I then installed small straight headers as a mount for the USB daughterboard onto the main PCB and cleaned up all the solder.

Finished board ready for testing

After an inspection to rule out any solder bridges or other errors, it was time to do the checkout steps. First is to plug in the USB board and verify that it is supplying proper power to the rest of the board. The board is not properly reporting its ID to Windows (or my Mac either). The RX led is stuck on.

The USB board must be reprogrammed to implement the 45 baud speed and to request 400ma from the USB host, which requires the daughterboard maker's development studio software. I downloaded it but until the USB board is talking properly I can't reload the firmware or do anything else.

It seems to me that the CP2102 daughter card should be talking to the PC even if the connection is not working to the main board. Since I had to desolder the original right angle header and install a straight header, I may have a connectivity failure on one of those pins. I can see that the top side is soldered well, but if the actual signal lead attaches to the underside of the daughter board, there might be problem if I broke the via when extracting the old pins. 

My action plan is to:

1. find the CP2102 schematic and test connectivity from the chips on the daughter board to the pins
2. failing to find the schematic, I will unsolder all the headers, separate the daughter card and solder the pins on the underside. If I reattach it after this change, and the header modification was the problem, then it should work.
3. in parallel I will do more connectivity and short testing of the main board, just in case it is somehow holding the USB card in reset or keeping it busy. 

Teletype stuff

VISITING POWDER COATING FACILITY WITH TTY MODEL 19 METALWORK

Marc disassembled the entire Model 19 teletype, separating all the painted metal parts for restoration. This military unit had been repainted by brush and was quite ugly. The plan is to strip the old paint off and to powder coat the unit to make it appear like new.

We drove it over to the shop to get a quote and to let Marc pick out the color and finish. The price itself was quite reasonable and the staff were clearly able to protect threaded screw holes and other parts that had to stay clear.

Marc is wavering between a blueish-green color and a flat black, but part of the decision depends on the quality of the metal once it is sandblasted clean. If too many scratches and dings, it will need to be a more textured black color to hide imperfections. To the eye, most of the flaws we see are likely to be simply paint chips from all the layers of paint on the object.

The plan is to have the desk and the teletype printer cover sandblasted first, then Marc will come by to inspect the metal condition. Based on that, he will choose colors and have the shop continue to sand and then powder coat everything.

RESTORING TELETYPES

I brought my model 15 teletype, model ASR33 teletype and model 14 transmitter/distributor over to Marc's house to join his model 15, model 19 and two ASR33s for restoration. I tore the ASR33 down to separate the printer unit, keyboard unit, call control unit, stand and cover, in preparation for restoration.

The baseplate had foam rubber as a sound dampener, but the material had become friable and partially disintegrated. For the most part it did not become liquid and stick to the baseplate, which made cleanup relatively easy. Only the spots where adhesive was used to tack down the foam will take additional work to clean up.

While I was moving my model 15 printer unit around in my garage earlier this week, the work gloves I had on snagged onto a spring on the side of the printer unit and released it. I needed to search for the spring in the garage, but first it was important to know where it was formerly attached.

Using the model 15 at Marc's house as a guide, I identified every spring on the left side of the printer unit and matched against my unit, thus locating the missing spring. It attaches to the carriage return dashpot arm, to restore the dashpot which is an air dampener that absorbs shock from the carriage slamming to the left edge.

Dashpot restore spring, missing on my model 15 printer

The arm will push into the dashpot, converting carrier motion to air compression and spreading the deceleration over a longer interval to minimize G force. The carrier rebounds to the column 1 position and the spring then pulls the dashpot arm out to ready it to handle a subsequent return. I found the spring in the garage where it was pulled off by the glove.

My ASR33 keyboard is not working properly. Each keypress should set the sliding rods to reflect the ASCII code related to the character on the keycap. Lubrication has hardened and gummed up the works a bit. I worked the mechanism, cleaning off old grease and inspecting the condition. 

ASR33 keyboard module

Now I see every character encoding properly on the switch contacts on the side of the keyboard, but I am not happy with the trigger and release that fires the distributor to serially encode the result of a keypress. The keypress pushes on the universal codebar, which trips for every key. I don't see it trigger and then restore properly between button pushes. I will study the mechanism and manuals, then adjust whatever is needed until the keyboard works as it should. 

Worked on 1401 systems at CHM, two fun kits

1401 SYSTEM RESTORATION AT COMPUTER HISTORY MUSEUM

Today we met to work on issues with the 1401 systems, particularly the inability of the German system's 1402 to read cards successfully. During a special visit of the "Fortran Geezers" on Sunday we ran Fortran compilations using a low density tape we had created. We discovered that one of the tape drives would not switch between high and low density.

Investigating the tape drive, Alan Palmer and Marc Verdiell found the contacts of the pushbutton were not working properly. A bit of work corrected that, allowing the drive to switch between Low and High density. At that point, a second flaw was discovered, a bad light bulb in the High Density display; a replacement bulb was put in place.

The card reader has a central shaft that rotates once for each card feed cycle, activating a number of cam based timing switches and the picker knives that grab the bottom card and shove it through the hopper throat and into the maw of the reader. The picker knives are driven by two cams, metal objects with hard plastic molded over them.

Due to improper adjustments in the past, the picker knife mechanism would slam back against the metal frame, applying excessive shock to the picker cams. The plastic was dented, fractured and gouged. This caused the picker knives to move at variable times, leading to the physical card moving out of sync with the rotating shaft and its timing switches.

The reader was disassembled and the bad shaft removed. We don't have a spare for this in our workroom. We have two ways to address this problem. If we can find a machine in the museum storage area that is surplus, thus amenable to removal of parts, we can swap the damaged shaft with a good one. If not, we have to machine a replacement.

To be surplus, the museum must have several of the machine and designated one or more as available for these purposes. Machines with only a single example, by contrast, cannot be touched as they must reflect the exact condition they had when donated.

The card reader mechanism is used in several IBM products, not only the 1402 reader/punch. The 2540 reader/punch and the 088 collator are so similar that they would have the same shaft with picker knife cams. We will explore this next week in the hope that we can repair the 1402 easily.

If we are forced to machine a replacement, it must also have a similar very hard plastic over the cam which makes the fabrication much harder than simple metal machining. 

QUICK FUN KIT BUILDS

I bought kits from Evil Mad Scientist to build large versions of the 555 timer and 741 op amp integrated circuits, using discrete transistors and other components matching the circuitry on the silicon of the real ICs. These work when wired in place of the 555 and 741 (with some performance limitations due to the large size). Mainly, the look cool and are a fun.

The ubiquitous 555 timer chip

Widely used 741 Operational Amplifier chip

Picking up some teletypes

NEW TELETYPES

I picked up a Teletype model ASR 33 today and brought it home. It is in pretty clean shape, but will need restoration to get it working properly. There is also a front panel and knob missing.

My ASR33 teletype

On eBay I saw a model 15 for sale, actually the military TG-7-B model which is mainly different because it fits into shipping crates for transportation in the field. It had a low starting price and no apparent interest from others, so I placed a bid and won it for $99. I do have to drive down to southern California to pick it up, but it is a great deal even with that.

A TG-7-B teletype

Keyboard of my machine

Finally, I was given a model 15 Transmitter/Distributor (TD) which is a unit that reads paper tape and transmits it as serial data. This will allow me to use paper tape to drive the printer.

Data in parallel from tape on left, serialized by rotary encoder

Working on teletypes, laptop and refrigerator repair

MACBOOK PRO 13" MID 2010 FIXUP

With my disk cloned to the new 1TB drive and swapped into the machine, I could apply maintenance, remove items I don't want and get this system ready for my use. I have the original 250GB hard drive in an external case to protect all my daughter's files.

At noon I noticed that the machine is reporting only 2GB of RAM, insisting that one of the two memory slots is empty. Perhaps dust was in the connector, which might explain the problems with the memory upgrade that I have already sent back for replacement. I cleaned a bit and restored both RAM modules, now the system is back to 4GB, while I wait on the substitute to arrive.

Finally the new modules arrived, but exactly the same results were experienced. Neither module will be recognized in either of the two RAM slots, while both of my 2GB modules work fine. I guess I will abandon hope for an 8GB upgrade and return the new set of boards for a refund.

MODEL 15/19 TELETYPE RESTORATION WORK

At Marc's on Friday to work on the teletypes. Our objectives were to complete two tasks, stripping wiring from the desk of the model 19 and checking out the keyboard assembly.

After we found the complete wiring diagrams for the desk, we were comfortable removing all the wires and receptacles. This took almost three hours, since the wiring is a rats nest of crisscrossing cables, quite a few routed through armored cable with 90 degree caps.

After unsoldering just two wires, we were able to wrestle all the rest out of the desk and complete the stripping down of the table in preparation for repainting. We looked at the large number of parts, wires, sockets, cable trays and switches from the desk, in addition to the large pile of parts from the teletype equipment that sat atop the table.

All the metalwork is loaded into Marc's car, ready to be delivered to the restoration shop which will sandblast and powdercoat everything. The most likely color is black, the same as the military version, but all options remain on the table until the shop begins work.

The keyboard and perforator mechanism is relatively simple and probably can be restored adequately without complete disassembly of all parts. We separated the printer, keyboard/perforator and the motor baseplate units. These come apart easily, held in by thumbscrews and sliding apart immediately.

Rotating the keyboard/perforator mechanism by hand, we confirmed that it moved easily and that the keypresses were converted properly into serial bits as well as setting up the perforator pins as parallel bits. There is dirt and mild corrosion to be cleaned up, but we think this can be cleaned entirely by dunking in Simple Green and scrubbing. If there was resistance or erratic motion, indicating solidified grease, then we might have had to disassemble every part for cleaning.

The motor baseplate also looks good. It has both DC and AC power connections, with the DC line used to operate the 60ma 120V solenoids in printers and reperforators. The AC line simply spins a synchronous motor that will provide the impulsion for both keyboard/perforator and printer operation.

The baseplate is also dirty and will be cleaned. There are some current limiting resistors to clean up and check, but with a freely rotating motor, this is likely to work perfectly as soon as we power it up.

KITCHENAID BUILT IN REFRIGERATOR FAILURE AND REPAIR

Our kitchen has a 42" wide Kitchenaid built-in refrigerator, with panels on the front that match the custom cabinet work. Because of the wood panels, which are cut specifically to the size of the year and model refrigerator I own, I couldn't use them on a replacement refrigerator. To maintain the look of the kitchen I need to keep this machine operating.

Several years ago it began to report errors and didn't keep the freezer and refrigerator sections at their target temperatures. The repair service sent by Kitchenaid informed me that the maker of the mechanism, Whirlpool, does not stock replacements for these boards although they fail often.

A refurbished unit was placed in the refrigerator and that restored operation until recently when I began to see the temps climb in the freezer portion. Rather than maintaining the 0 F target temp, it would climb to 6 or 7, go back to zero, then soar to 22 or as much as 42 when it began beeping its alarm.

Shutting it down for 15 minutes would sometimes get it to cool back down, but anytime it got into the mid 70s or higher outdoors, this would start again. Lots of food had to be thrown out each time it let the freezer get too warm. We scheduled a repair service, hoping that they still had refurbished units to install.

Today the repairperson arrived, swapped out the board and restored the unit to proper operation. I know that I have a reprieve of at least a year, since they offer a one year warranty on the fix. 42" wide built-ins run from around $7,000 to well over $10,000, in addition to losing the wood panels that match the kitchen cabinets.

For just a bit over $700, I deferred a much larger expense, hopefully for quite a few years. The repair service was well worth it. There are internet based repair services for less, who will refurb the board but I have to remove it, mail it to them and wait for it to return; all during that time the refrigerator will be inoperable.

Restoration of 1401, MacBook Pro, Mac IIci, and work on Documation USB interface

MACBOOK PRO 13" MID 2010 LAPTOP WORK

This morning I dealt with the passwords on the system, many of which my daughter can't remember since years have passed since she used it. The solution was to boot to single user mode, remount the root partition to be writable, and delete the file that tells OS/X that it had completed setup.

With that file gone, it took me through a fresh setup dialog, including the chance to create an administrator account with a known password. From there I could replace all the other passwords, giving me the ability to do anything I need.

The existing system has 4GB of RAM and a 250GB internal hard drive which is choked to saturation with my daughters files. Once she has retrieved the files she wants I can clean up and have room to apply necessary updates.

8GB of RAM is inexpensive enough that I ordered it, along with a 1TB 7200 RPM hard drive. We shall see how well it performs, with those upgrades installed. I did get the upgrades and cloned the internal disk to the 1TB replacement, but the 8GB of RAM did not work. After trying everything suggested by the vendor's tech support staff, there is a replacement on the way.

DOCUMATION CARD READER USB INTERFACE WORK

I got the replacement FTDI based USB to parallel port boards and began to replace the damaged boards on my two interface PCBs. First step after installation was to verify that they communicate reliably with the PC side program, before wiring one into the card reader. Sadly, I damaged the first one while removing the original right angle header pins.

I worked more carefully on the second board I just received. Getting the old pins out was no problem but placing the new straight header pins took quite a bit more time. Although the soldering was fine, for some reason it wasn't able to communicate to the PC.

I did some continuity testing on the USB daughterboard and found that the external pin for signal D7 was not connected to the same signal pin on the FTDI chip onboard. The solder joint looked good and the trace was seemingly undamaged, but no connection.

Apparently good solder joint and trace leading from it

I scraped off a section of the trace at an accessible point on the edge of the board, verified connectivity, and then soldered a jumper wire. Now, D7 from the FTDI chip is connected to the external header.

Poorly focused but exposed trace where jumper will be soldered

Jumper in place to restore connectivity for D7 signal

Alas, testing this still didn't result in communication between the PC side and my interface board. Since I verified the connection of every external pin to its source on the FTDI chip, any connectivity problem must exist on my main interface board. That is, unless somehow a chip is blown. The PC sees the USB device and sets up the serial COM port for communication, making the daughterboard appear to be working.

Found another suspect solder joint on a different cable, which I cleaned up. Still no communications, but it seems I am getting closer and closer. As long as it isn't a bad chip I will eventually get this chatting with the PC. In the meantime, I worked with the other board that I completed, which does talk to the PC reliably it appears.

The card reader does not appear to be working properly - which may be an issue with my wiring or something that was already wrong in the reader itself since I hadn't done a full test of this device before. I can see the EOF signal go on and off, as well as reliably reflecting the front panel status conditions such as Hopper Check, Pick Check, and Read Check.

What isn't happening properly is reading. I see the program issue a Pick and the card moves through the machine, but the software is still waiting with the pick active. I need to put the scope on the reader to verify that it is delivering the response that the controller expects to the pick, which is BUSY signal going true. That signals that the leading edge of the card has reached the photocells.

Sometime after BUSY goes true, we should see 80 Index Marker (IM) pulses which tell the controller to sample the 12 data lines. The controller design by Brian Knittel ignores the BUSY line, thus the only way the controller chip could know that a card has been read is to see the IM pulses.

All of this suggests that I am missing the IM pulses, so that is first up on the diagnostic priority list.

COMPUTER HISTORY MUSEUM RESTORATION WORK

Today we verified that the spurious Reader Check and Validity Check errors on the German 1401 system were indeed caused by the SMS card I identified last week. We ran the machine for quite a while without errors, after which I put the suspect card back in and began to see the same errors again. The good card was reinstalled and the machine run for quite a while with no errors.

The software archiving group brought a donated Mac IIci to me to restore, allowing them to archive a large batch of Mac related software. I helped them make a list of replacement electrolytic capacitors and CMOS battery, which they ordered from Mouser and handed to me this morning.

There were a few axial through-hole capacitors but most were surface mount cans. I used my vacuum desoldering gun and hot air gun to remove all the original capacitors. We cleaned the board, particularly the spots where leaking capacitor fluid were found.

I didn't think to bring solder paste, so I had to attempt to solder the SMT capacitors to the board using a regular soldering iron and careful technique. The through -hole were easy, of course. The machine sprang to life and works perfectly now.

MacBook Pro repair

APPLE MACBOOK PRO 13" KEYBOARD REPLACEMENT

My daughter had a MacBook Pro, a mid 2010 13" model, from when she was in college. It wasn't working, a couple of keys were broken and she handed it to me for disposal. I did a bit of research and found that I could buy a replacement keyboard mechanism for under $17 including shipping, if I could get it working.

I forced a reset of the management controller and it came up. Based on that, I ordered the keyboard and waited for it to arrive yesterday. I researched the process of swapping the keyboard and discovered that it requires removing essentially every part of the body of the laptop before you can get to the keyboard. Yikes!

I set the laptop up on my workbench, with the teeny phillips, Torx and tri point Y00 screwdrivers that would be needed. Taking plenty of pictures and working slowly, I filled a large egg carton, cell by cell corresponding to each step where screws are removed, and the other parts placed in order.

The keyboard itself was screwed to the case with 54 Phillips 00 or 000 screws (very tiny screws). I removed them all and put the replacement keyboard into the case. Tweezers and screwdriver in hand, I placed and tightened all 54 screws. Next I had to replace the backlight for the keyboard.

Layer by layer I put the laptop back together, sliding ribbon cables into their connectors and plugging in a myriad of other connectors until everything was together. While opening the laptop I realized that one of the two memory boards was loose, not properly seated in the machine. Having 2MB rather than 4 would certainly contribute to the slowness my daughter had experienced.

The laptop came right up, performs well (for a 4GB mid 2010 era machine) and every key works properly now. However, my keyboard backlight isn't working. When I next open the laptop I will reseat the tiny ribbon cable, as that may be the problem, but even without backlit keys it is a perfectly usable system.

I will now look into buying larger DIMMs to increase the memory to its max of 8GB (two at 4GB), plus perhaps a larger internal disk or SSD. First I need to work with it a while to decide if it is fast enough to be worth the upgrade. Meanwhile, there are some old files my daughter wants to retrieve before I do a clean install onto the machine.