Model F XT repair - Mystery of nonworking F XT in seeming good condition

[berserkfan]

Hello Folks

Some time ago I bought a Model F XT from someone and it was damaged in transit. The casing was smashed and the keyboard half fell out. Spacebar was broken. I could not get it to work.

I extracted my pound of flesh via Paypal complaint, then left the keyboard to one side. Recently I came back to take a closer look at the F XT.

Firstly, I was surprised at the seemingly good internal condition of the F XT. Apart from the smashed casing and broken space bar, actually the keyboard was in pretty good physical condition inside.

Here's what I found:
No Rust
No nasty tar like substance
No rotten foam
No nasty scratches on PCB
No cracks
No solder joints that appear broken
No visible dirt or corrosion
Cable, grounding cable, all intact and contacts not corroded.

BUT

It still doesn’t work! Figuring that maybe the broken spacebar was causing trouble, I removed it. All the hammers and keys actuate nicely. It still didn’t work!

Took apart the Model F XT, and noted that it was actually in solid condition inside. PCB wasn’t cracked, no clearly broken solder joints or shorted out places or destroyed traces. I managed to put it back together after an hour, minus the spacebar of course. I figured I may as well live with a teeny weeny 1.5x spacebar because at least that is easier to put in. Just in case the fault lay in the cable, I replaced it with another working F XT cable from another Model F XT I have.

And this F XT still doesn’t work! 100% doesn’t work! Not a single key! No HIDlisten response! HiDlisten doesn't even produce a row of dots! I can assure everyone that yes, the cable works, the Soarer converter works, the soarer software has been loaded onto the teensy. I have another F XT that functions perfectly.

What can I do? What’s wrong? It can’t be shorted out; I was testing it in its casing and there were no wires lying about creating contacts that shouldn’t exist. Since I had the opportunity to take it apart, I examined the PCB and there was nothing obviously broken or burnt out.

[dgreekstallion]

Is it possible there's damage to the internal electronics via liquid/rust/oxidation?

Edit: maybe it's a tracing problem, I can't find out if these use a membrane or not?

[ch_123]

Is there a problem with your adapter? What sort of adapter are you using, is it one of Soarer's ones?

[fohat.digs]

Is there a problem with your adapter? What sort of adapter are you using, is it one of Soarer's ones?

He said he had another working XT, the problem is clearly internal.

Did you unplug and re-seat the big connector to the terminal? Is it grounded properly?

[Parak]

One test of interest is to remove the top plate with all the barrels and flippies, and just leave the bare pcb with the backplate connected to the converter. The sense pads respond to thumb presses, and dropping of flippies on them.

However at this point it sounds like something went bork on the electronics side :/

[berserkfan]

a repost of something on another thread:

I have another XT that works ie not XT adapter problem.
For F122, I have two Terminals (M122) that work. So it's also not adapter problem.
These are two separate adapters using two different teensies. I made different adapters so that I can attach ps2 and 240 degree DIN to them respectively.

um, fohat, what's about that grounding cable? I notice not all keyboards have that grounding cable. I don't think it was loose, but I can't be 100% certain. Since that non working F XT came loose (keyboard split and half-came out of the smashed casing) in transit, it is possible that grounding thing had come loose when I first tested the F xT. I did not take apart the casing when I tested it first time round; I shoved it back into the half-broken casing.

Then I took apart the casing to poke around inside.

It remained loose after that because I never tried screwing it back into the casing. (The ground cable or whatever you call it is screwed into the casing normally but since casing was broken I didnt't put it back.)

Is there a problem with your adapter? What sort of adapter are you using, is it one of Soarer's ones?

He said he had another working XT, the problem is clearly internal.

Did you unplug and re-seat the big connector to the terminal? Is it grounded properly?

[berserkfan]

 Ok, I tried again. This time I got
rFF
rFF
for every key when using HID listen.
That’s all. No additional code or stuff. Just these six letters over 2 lines for every key.

[fohat.digs]

At least it is not dead now.

Soarer knows about those hid_listen codes, I have only used them in desperate times.

Keyboards have all different grounds, some integral. I have not had an XT apart in a while and don't remember the setup, except that it does have a very large plug coming in from the cable.

[berserkfan]

wow, very frustrating. Soarer unable to help. Looks like the combined brains of Geekhackery has been unable to find a solution!

[Soarer]

rFF isn't an error code as such, but it probably means that there's a bad connection on the data line somewhere. Possibly in your wiring, or possibly due to damage aorund the cable connector on the PCB.

On the plus side, the main parts of the keyboard (CPU and capsense chip) are clearly working!

[berserkfan]

I haven't actually been able to replicate that - later re-connections and retries with teensy got me nothing.

However, the rff rff was definitely not an illusion conjured up by my desire to have a working keyboard. I tried it on like 30-40 keys. So if you say the CPU and chip are working, that's awesome.

I had a Rosewill with the traditional mini-USB connector problem in the past. The mini-USB got desoldered. Of course fixing that was easy. Unfortunately, it doesn't seem so straightfoward with this. There is no clear damage area that screams 'fix me".

But at least we've narrowed this down to data line. So does that mean I should be looking carefully at the leads that correspond with the data line? Which one would that be?

rFF isn't an error code as such, but it probably means that there's a bad connection on the data line somewhere. Possibly in your wiring, or possibly due to damage aorund the cable connector on the PCB.

On the plus side, the main parts of the keyboard (CPU and capsense chip) are clearly working!

[Soarer]

Yeah, the connector inside the XT is pretty robust! Here's the wiring.

But, if you're not getting rFF other times when you plug it in, one of the other connections is dodgy as well - could be any of them.

So, check with the multimeter all the way from inside the XT to the Teensy and see which ones are bad!

[berserkfan]

In my two latest passes:
1)   I got the thing to produce a nonstop slew of rffs. (Ie totally without me pressing anything, and with all keys seated so it isn’t a repeating switch)
At the same time I notice teensy LED was glowing all the way. It never stopped until I got tired of watching rffs and pulled the USB out.

2)   HID listen was not flooded with rffs until I pressed one key, then it started going crazy with rffs. I hit lots of keys, then rffs suddenly stopped and there was nothing else. No dots either.
During this pass I noticed teensy did not glow until after I hit my first key and the rffs started spewing out.
Various checks with the multimeter has confirmed that the data line is definitely dead. And it is definitely not an adapter or teensy problem, so it is definitely to do with the data line/ connections inside the PCB.

But since I’m very new to messing around with electronics, I don’t know what to do, Soarer. I’m happy to take this apart again, since by now I have resigned myself to a new hobby called Struggling with F XT, but what do I do next to test the PCB? I can see the leads and traces that lead from the white data cable input, but how do I test things? What am I looking for? No solder joint looked broken. No trace was clearly cut or cracked.

Do I randomly press one multimeter tip against a solder joint, and a multimeter tip against another solder joint on the power or brown cable? Every single connection or combo of connections appears dead when I do that.

Sorry if I am so ignorant of basic electronics. But Gutz (the guy in my avatar) doesn’t give up!

And don’t be worried about giving me suggestions. My day job is getting very stressful these days, and I use every break to take my mind off things by working on something that redirects my stress elsewhere…

Yeah, the connector inside the XT is pretty robust! Here's the wiring.

But, if you're not getting rFF other times when you plug it in, one of the other connections is dodgy as well - could be any of them.

So, check with the multimeter all the way from inside the XT to the Teensy and see which ones are bad!

[berserkfan]

OK on my latest try I did something different. I connected the keyboard cable to the PCB alone. (Strictly speaking, PCB on Membrane on Backplate on Keyboard metal back casing).

What I found: no random spews of rFF
When I took a hammer and started making contact with the PCB contacts, it started producing rFFs in a controlled fashion. If I held down the hammer, lots of rFFs. If I hit several contacts several times as though I was typing, rFFs appeared in the speed and order in which I made contact. When I made no contact, no rFFs or dots appeared.

Unfortunately I really can't find any visual flaws on the PCB, so I have no way of figuring this further.

[berserkfan]

OK, now I've tried switching pCBs. now both XT keyboards don't work. this is really a lesson in patience.

[fohat.digs]

The inner workings of the IBM Model F are a bold place to begin for someone who is not already comfortable at the workbench.

[berserkfan]

The inner workings of the IBM Model F are a bold place to begin for someone who is not already comfortable at the workbench.

How do I insert an image or upload to GH server? Drag and dropping from my pictures folder doesn't work. I don't know HTML and don't know how to link. In the past I put links to my imgur account, but now I want the photos directly displayed like how everybody does it!

ANyway, fohat.digs, my Avatar is GUTZ and this anime character is notoriously stubborn. He's supposed to represent human willpower in fighting overwhelming odds. I think the F XT is pretty underwhelming where overwhelming odds are concerned, but that doesn't change my frustration! 

[Game Theory]

Add as an attachment

[berserkfan]

k great, thanks, modified the OP.

but now I have two new problems:

1) I have another teensy, so I wanted to build an adapter with an AT female connector for the F XT. We already know from soarer.docs which hole carries what lead. But what about the wires that emerge from the back of the AT female connector? Which is which?

And how do I test? I tried doing a continuity test using a multimeter, but I have no idea what I am looking for. There was no current between any of the leads and the front holes, but I don't know if the multimeter tip was able to make contact when I pressed it inside the holes.

2) Another challenge that I now face: I broke my multimeter. Yes, that's Gutz for you. If you watch the manga/ anime you will know that this is 100% characteristic of Gutz. Note I broke my multimeter lead AFTER ALL THE TESTING WAS DONE AND I WAS PUTTING AWAY MY MULTIMETER. But how do I fix this?

Thanks again to everyone who posted replies!

[fohat.digs]

Bummer about the multimeter!

On mine, I found that I was needing a thinner probe, so I soldered a sewing needle to the tip of one side, so that I could plunge deep into tiny holes like pin connectors.

If you cannot re-attach the handle, you could always just strip some wire and attach a pin to that lead.

Otherwise, you can stick something like a paper clip into each hole and test that against the wires at the other end.

[Soarer]

Looks like the kind of probe where the tip unscrews, so it might be fixable!

Soldering on that Teensy might be a problem, the +5V in particular looks iffy. There's far too much solder - too much to even see if it's flowed onto the pads! Be very careful when you rework it, because it's easy to pull up a pad if you pull on the wire before the sodler has _completely_ melted!

There's a lot of bare wire showing as well, which risks shorting out. As a temporary thing it's OK as long as you take care with it, but really you should push more through the hole, solder, then snip the excess off.

The IBM PCBs look fine.

[berserkfan]

all very important tips and guidance, o elevated elder! I will heed your advice. but I find doing it right very, very hard. i really, really suck at soldering and am even worse at desoldering. somehow things never turn out right.

Looks like the kind of probe where the tip unscrews, so it might be fixable!

Soldering on that Teensy might be a problem, the +5V in particular looks iffy. There's far too much solder - too much to even see if it's flowed onto the pads! Be very careful when you rework it, because it's easy to pull up a pad if you pull on the wire before the sodler has _completely_ melted!

There's a lot of bare wire showing as well, which risks shorting out. As a temporary thing it's OK as long as you take care with it, but really you should push more through the hole, solder, then snip the excess off.

The IBM PCBs look fine.

[fohat.digs]

If there is a electronic supply store nearby, get a small roll of "soldering wick" which is flat braided wire that soaks up molten solder.

You press it against the solder with the hot iron, and capillary action makes the liquid solder draw up into the wick. Then you cut off a few mm and discard, exposing a fresh end.

Also, keep a wet sponge on the table and wipe the soldering iron on it often to keep it clean.

[Soarer]

I hate that wick stuff - can never get it to work nicely
A spring-loaded sucker (like bezerkfan has) works better for me.

Sponge should be only damp - on the verge of drying out is good! Too wet and it takes heat from the tip, too dry and it burns.

After cleaning the tip, just before making a joint (heh), get a tiny bit of solder on the tip - this will help transfer heat into the parts you're soldering. Then put the iron on the parts for a couple of seconds before applying more solder - a little at a time! If the solder all flows onto the iron, ditch it on the sponge and start over.

[fohat.digs]

I hate that wick stuff - can never get it to work nicely

Soldering wick is certainly crude, but it is cheap and quick. A "solder sucker" is much better if you want to spend a few more bucks.

All this stuff will get far easier with a little practice.

[berserkfan]

Yes, I tried that, but it seemed as though the wet sponge was burnt. Are you talking about a natural sea sponge, or a standard 3M sponge for dishwashing? (Mine is standard 3M).

If there is a electronic supply store nearby, get a small roll of "soldering wick" which is flat braided wire that soaks up molten solder.

You press it against the solder with the hot iron, and capillary action makes the liquid solder draw up into the wick. Then you cut off a few mm and discard, exposing a fresh end.

Also, keep a wet sponge on the table and wipe the soldering iron on it often to keep it clean.

[berserkfan]

Apart from sanding the soldering tip, I find it very tough to 'tin the tip' as some people suggest. Solder either refuses to stay on, or it refuses to leave after it gets stuck. I really have little control over this process because I suck so bad at it.

I know that theoretically only a small amount of solder is needed. In practice it doesn't work for me. I broke more than a few solders because they weren't tightly soldered enough. I really don't know how you guys can use a bit of solder and still have the wire tightly soldered.

In any case, that happens to be my worst soldering attempt. My other soldering attempts were better (though not by any means remotely close to professional standards!)

My solder suckering skills really suck. On a PCB that Ivan Ivanovich gave me (for practice) I managed to remove a number of solders, but have a lower than 30% success rate. For teensy, it's even worse. I'm also always afraid of burning the teensy since it's so teensy-weensy.

I hate that wick stuff - can never get it to work nicely
A spring-loaded sucker (like bezerkfan has) works better for me.

Sponge should be only damp - on the verge of drying out is good! Too wet and it takes heat from the tip, too dry and it burns.

After cleaning the tip, just before making a joint (heh), get a tiny bit of solder on the tip - this will help transfer heat into the parts you're soldering. Then put the iron on the parts for a couple of seconds before applying more solder - a little at a time! If the solder all flows onto the iron, ditch it on the sponge and start over.