IBM Model F 4704 - character ghosting?

[HighPlainsDrafter]

Greets, all.

Picked up a wonderful Model F, the 107-key 4704 with the all-metal casing. Crisp and pingy.

Noticing an extra character (or a burst of several characters) at seemingly random intervals. For example,
I typed the letter "F" but instead, the result produced:
FHJ:"
It could be once in 24 hours, or several times within a few moments. Last time it occurred (several bursts the same moment), I picked up the board, tilted it from side to side, gently shook it, and it returned to only occasional ghosting.

Things I tried before that:
- Disconnected the wires from the solenoid to the xwhatsit controller.
- Adjust the following settings in the Xwhatsit controller GUI utility to
  * Expansion Header tab: set to Disabled" (after earlier setting it to 255) under the Expansion Header tab, to disabled the solenoid/buzzer in the utility GUI.
  * Column Skips tab: was sure to checkmark box 16, signifying GROUND.
  * varied the voltage threshold (in the GUI). Placing it right up to the max it I can (around 137) before it does the opposite -- dropping characters.
Shot compressed air through some of the barrels of the keys, but not all, and didn't do so with the top cover off to really give it a go.
Rebooted the (Windows 7) pc. Tried a different USB port on the pc.

Things I haven't tried: another pc, another physical location (in the small chance EMI is somehow getting past the metal casing), nor another operating system.

My typing speed isn't unusually fast: 70-90wpm. My hardware skills aren't impressive, so wouldn't be up for major surgery.

Dropped (missing/unregistered) characters only occur if I raise the voltage threshold too high or introduce a solenoid value to prevent some characters showing, so, not an issue. It's the extra characters I'm trying to troubleshoot. The characters seem random. Ideas? Or best to swap out the innards? Any suspicions it's likely limited to this model, having a solenoid (even though mine's disconnected from the xwhatsit and disabled in the utility)?

Thanks to all who contribute to this fabulous community.

[snoopy]

hi there,

did you buy it with the controller already build in?

this is a good thread for research on dt: http://deskthority.net/for-sale-f55/xwhatsit-s-grand-unified-ibm-capsense-usb-controller-thread-t7993.html

Not sure if xwhatsit is regularly browsing through all the gh forums, but you could try to ask him directly somewhere. He always has good ideas concerning troubleshooting.

[Xonar]

The same thing is happening to me on both my Unsaver and my 4704 107 key. Oddly though, only the spacebar on the 4704 seems to be problematic. All other keys are fine. A lot of keys on the Unsaver have the issue. Orihalcon told me that on the 4704 there may be some dust on the capsense PCB that shifted during shipping and is causing the ghosting issues, but I haven't had the chance to disassemble it and figure that out yet.

[CPTBadAss]

I had problems with this because my 4704 wasn't grounded properly. You might want to doublecheck that the grounding wires are all in their proper spot.

[Melvang]

Couple things that can help with this issue.

Disassemble, clean with iso

Check grounding

Also double check the voltage settings on the firmware.  Sounds like it might be a touch high.

[Ellipse]

One possible solution that worked for someone's unsaver over on DT:  it involves replacing the firmware with one containing an alternative debounce filter.  Here's the firmware:  http://deskthority.net/for-sale-f55/xwhatsit-s-grand-unified-ibm-capsense-usb-controller-thread-t7993-900.html?hilit=debounce#p209360

[joc]

One possible solution that worked for someone's unsaver over on DT:  it involves replacing the firmware with one containing an alternative debounce filter.  Here's the firmware:  http://deskthority.net/for-sale-f55/xwhatsit-s-grand-unified-ibm-capsense-usb-controller-thread-t7993-900.html?hilit=debounce#p209360

This alternative firmware also fixed the issues HighPlainsDrafter was having with his F107. I think he's still testing the firmware so he hasn't posted any public updates yet.

[HighPlainsDrafter]

Joc, enough time has elapsed successfully testing your hex patch to confirm it is the solution for my situation; thanks very much.

[orihalcon]

Has anyone had this problem with one of my controllers? They are the ones with blue PCBs. I paid quite a bit more to upgrade to higher quality components with lowest possible tolerances, but don't know if that made a performance difference or not.

[joc]

Joc, enough time has elapsed successfully testing your hex patch to confirm it is the solution for my situation; thanks very much.

That's good to hear. Thanks for posting an update.

Has anyone had this problem with one of my controllers? They are the ones with blue PCBs. I paid quite a bit more to upgrade to higher quality components with lowest possible tolerances, but don't know if that made a performance difference or not.

I think the root cause of the problem of key chattering is the stock firmware's debounce implementation and not component quality. Although, dirty flippers/PCBs and bad grounding can also cause problems. I'm surprised more people haven't noticed this problem because I think all xwhatsit controllers running the stock firmware should be susceptible to key chatter. On the other hand, the seller of HighPlainsDrafter's F107 didn't notice any key chatter when he retested the keyboard so maybe not everyone notices the problem for what it is.

The stock firmware uses an integrator debouncer similar to this one to filter the key-press signals. Using an integrator debouncer shouldn't cause any problems if the debounce time is relatively long and/or the sample frequency is relatively low. Unfortunately, the stock firmware uses a relatively short debounce time (max of 4.8ms for press and 8ms for release) and relatively high sample frequency (min of 625Hz) - this hinders the integrator algorithm's ability to filter out noise. Even Soarer was skeptical of this debounce technique.

[Janeiac]

It may be that firmware, or grounding, is the issue; however, the first order of business for this kind of keyboard is to crack it open, pull the keys (not the spacebar) and clean everything thoroughly. Snap some cell phone photos before you begin-- seriously, it's amazing how easily one can forget something small. Drop all the keys into a cup of warm water and liquid dish detergent and soak them overnight. Rinse them off thoroughly in a strainer and address any stubborn gunk with a Q-tip and some 90% isopropyl alcohol. Meanwhile, blow out the body with canned air, clean everything, and including  between the barrels with Q-tips and alcohol. Turn it upside down and gently shake and tap it with the heel of on hand to free any grit. If you have HEPA vacuum with a dusting brush, use that.
If there is one key that is the problem, try wiggling and slightly (don't pull it out) stretching the spring, and pay special attention to getting it clean. It could be a minuscule bit of crud that is causing the electrical signals to be incorrect.
Do the easy and simple thing first. Your keyboard should be cleaned this way periodically regardless. Good luck, and let us know how it turns out for you. It's always useful to see what works for others. Cleaning has worked for me in the past.

[Xonar]

I flashed joc's firmware on my 4704 and Unsaver, and it solved the issue entirely. Thanks joc, as well as everyone else who offered their advice!

[Melvang]

It may be that firmware, or grounding, is the issue; however, the first order of business for this kind of keyboard is to crack it open, pull the keys (not the spacebar) and clean everything thoroughly. Snap some cell phone photos before you begin-- seriously, it's amazing how easily one can forget something small. Drop all the keys into a cup of warm water and liquid dish detergent and soak them overnight. Rinse them off thoroughly in a strainer and address any stubborn gunk with a Q-tip and some 90% isopropyl alcohol. Meanwhile, blow out the body with canned air, clean everything, and including  between the barrels with Q-tips and alcohol. Turn it upside down and gently shake and tap it with the heel of on hand to free any grit. If you have HEPA vacuum with a dusting brush, use that.
If there is one key that is the problem, try wiggling and slightly (don't pull it out) stretching the spring, and pay special attention to getting it clean. It could be a minuscule bit of crud that is causing the electrical signals to be incorrect.
Do the easy and simple thing first. Your keyboard should be cleaned this way periodically regardless. Good luck, and let us know how it turns out for you. It's always useful to see what works for others. Cleaning has worked for me in the past.

With an F, I personally don't recommend the turn upside down and tap/shake.  With the age and the type of foam used, chances are you will introduce more debris into the cavity between the PCB and the flippies.  I also don't recommend compressed air either.  The one exception is if the keyboard in question has had a recent mat replacement.

That being said, if one is going to take the time to take one apart, do the mat replacement, and clean with ISO, 90% or better.

[joc]

I flashed joc's firmware on my 4704 and Unsaver, and it solved the issue entirely. Thanks joc, as well as everyone else who offered their advice!

Great, I'm glad it worked out for you also.

[0100010]

Necro; but I flashed my F107 with this debounce filter today after being unable to resolve a spurious ghosting issue with my left bracket key.  Will monitor for it for a couple weeks.

[0100010]

Replying to myself, to update after some time with the debounce filter.  It is flawless!  No more ghosting left bracket.  Anyone with an intermittent, but persistent ghosting key or two, needs to load this build.

[bryanluman]

Sorry if this is a bit off-topic but where can you pick up a 4704? I've been searching ebay and the classifieds here but haven't seen anything yet. I need one of these giant metal beasts!

[0100010]

Haven't seen any left recently, on ebay, GH or DT classifieds.  You could IM orihalcon or ellipse, see if they have any left.

[pr0ximity]

I believe there are a couple on DT somewhere

[bryanluman]

Thanks for the info, I followed up with orihalcon and have one on my way! I think he still has another if anybody is looking.

[fxxk7692]

I have the same problem before with my model f XT. I fix it by cleaning up the rusty grounding wire and the part of the backplate where it's connected to with wd40 + diamond file