Random keypresses from IBM Model F XT with Soarer's


11 Nov 2018, 22:12

So here's something which has been bothering me for ages: I've got a Teensy with my favourite Soarer Converter XT shortcuts in it which is completely built into the keyboard.

When I leave the keyboard connected to my PC for 5-10 minutes while I'm switching between keyboard and mouse, I sometimes start seeing my computer freak out because it's receiving random keypresses from the keyboard. When I keep Aqua's Keyboard Test open instead I can see that there are brief make and break signals being sent from all over the keyboard: alphas, Control or Alt keys or even combinations with the F1-F10 keys.

I've tried soldering in some pull-up resistors, but it's only afterwards that I thought about adding a wire to connect the back plate to GND similarly to how the original cable does it.

The grounding wire did avoid some interference which I spotted when my mouse's USB cable came close to the keyboard, but so far no luck: this Teensy appears to be having issues with either one of my XT keyboards.

Has my Teensy got busted I/O ports or do my XT keyboards just happen to have the same flaw? I don't know, but I would like some feedback from others.

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12 Nov 2018, 01:27

I’ve made several converters (about five Teensy 2s and one Pro Micro) and never had this kind of problem. Not even on an XT, which was my first Soarer conversion and got a lot of use as my only mechanical at the time. Random presses like that would have woken up computers and unleashed all kinds of crazy that I would have surely noticed. No such hauntings here! In all my use of the converter, I’ve seldom had any issues at all. Nothing worse than a rare missed modifier or a very rare stuck key a power cycle fixed. I’m picky, I couldn’t stand what you’re seeing!

Try another Teensy, or a clone. The fact both your XTs are triggering it suggests a problem there.

A word of warning about Pro Micro Teensy clones: I found my AT wouldn’t work. It drew too much power, playing dead until I put a real Teensy in there instead. Likely to be a similar issue for the XT, so I’d go for a real Teensy in your case.

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12 Nov 2018, 01:46

@JBert: Interfering external signals perhaps? Do you have ferrites on your USB cables?

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12 Nov 2018, 01:52

If you have a multimeter it would be worth checking to make sure the voltage looks right.

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12 Nov 2018, 11:29

If it was a usb problem, I’m guessing the host would sputter through connect/disconnect cycles instead of spurious keys. Wiring is worth a check, though especially on the Teensy to keyboard side.

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12 Nov 2018, 12:46

I had similar issues with my internal Soarer Converter for my M122, but with a Pro Micro. Modifiers pressing every time and "latching" keys. I took apart the wires, soldered all again and by the same way it started, with no explanation, worked fine.
Mine even was causing some strange lag to my PC.


26 Nov 2019, 20:43

News about this Issue? I have same random keypresses when i connect this model f xt, but this problem disappers after 5 minutes.
If I disconnect and reconnect nothing appears but if leave the keyboard for a while the problem recurred for these 5 minutes. I don't know how to solve this situation.


29 Dec 2019, 18:06

I've got no news for you. I have disassembled my model F at one point and actually haven't put it back together again...

It seems I need to get a Round Tuit.

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29 Dec 2019, 19:23

I did an internal Pro Micro-based conversion of my Model F XT last night, and I had similar issue too. Although as well as getting random characters when doing nothing, it triggers constantly if I type too vigorously. In fact, I could trigger it by tapping the part of the case where my converter sits.

Not knowing exactly what the issue was, I tried a bunch of stuff this morning and it worked for me:
  1. Reworked my solder work like PlacaFromHell tried: removed old with wick, readded solder to the pads, and then heat up the solder to slide my male dupont pins in.
  2. Added numerous cable clips to ensure none of the wiring can slide about - I placed three in total, with two being a reversed pair before the USB cable leaves the case and one for the header wires. I know the USB cable is unlikely to be the issue, but I wanted to ensure as many variables as possible were eliminated.
  3. Underneath where the Pro Micro sits, I made a dampener out of some tape and a double-sided sticky pad.
There's still more that I could do/you could try if you haven't done so. Like my duponts are still very loose on the header of the logic board - whilst the clip acts like a tug dampener, I am going to order a 69176-014LF connector so that my Pro Micro-logic board bridge can use the clips on header. You could take the connector I need off of the XT cable that came with the keyboard. But in my case whilst mine is quite a temperamental cable (hence why I did the conversion), it could be useful in the future.

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