IBM 5110/5120 keyboard conversion

User avatar
JP!

05 Dec 2018, 05:07

Also I believe this was what Snuci was trying to revive:
http://www.computerhistory.org/collecti ... /102665239

Al Kassow is a software curator at the Computer History Museum so hopefully someone can help with this.

Sprague capacitors catalog:
http://bitsavers.org/components/sprague/

User avatar
lucar

05 Dec 2018, 18:28

snacksthecat wrote: Hi Guys,
I have some questions about capacitors, and it's entirely possible that no one here knows the answer but I figured it can't hurt to ask.

The keyboard has two of these square capacitor thingies (at least that's what I understand them to be):

#1
Image
I believe that those are IBM SLT circuits
https://www.ibm.com/ibm/history/exhibit ... V3081.html

http://www.chipsetc.com/the-ibm-slt---s ... ology.html

and I just SUPPOSE, total guessing here, that they implement the two clock OSCillators.
Try to roule this out.

Luca

Engicoder

05 Dec 2018, 21:49

All the silver ones are hermetically sealed, axial electrolytics, probably tantalum. The yellow ones are either polystyrene film or old avx molded ceramic; 12nF from code ('123')

User avatar
snacksthecat
✶✶✶✶

06 Dec 2018, 01:55

lucar wrote: I believe that those are IBM SLT circuits
https://www.ibm.com/ibm/history/exhibit ... V3081.html

http://www.chipsetc.com/the-ibm-slt---s ... ology.html

and I just SUPPOSE, total guessing here, that they implement the two clock OSCillators.
Try to roule this out.

Luca
Engicoder wrote: All the silver ones are hermetically sealed, axial electrolytics, probably tantalum. The yellow ones are either polystyrene film or old avx molded ceramic; 12nF from code ('123')
Thank you, fellas

User avatar
snacksthecat
✶✶✶✶

06 Dec 2018, 22:06

I know Pillenwerfer said that an ESR meter would only be good for testing the electrolytics but is that truly the case? I ordered one anyways since I've run into capacitor issues a couple times in the past.

Well the meter arrived and I tested a few of them. The yellow ones (which I suspected as bad since one was starting to open up) both read '-' on the meter. According to the instructions, this means a reading over over 99ohms. I don't know exactly how to use the meter yet but this reading is certainly above all of the graph lines in the chart that the manufacturer provided (above the graph line indicates a bad capacitor).

I also tested them with a simple multimeter set to high ohms and got basically the same result.

Does this mean I'm using the wrong tool for the job or are these guys toast?

Image

User avatar
ThePillenwerfer

06 Dec 2018, 23:33

I can't really comment further as I don't know the size of the cap you are testing. I've tried checking new ones for ESR and can't get a reading on ones smaller than 0.01µF.

To put it simply a capacitor lets AC through it but blocks DC. As they get old they can start to Leak, ie let DC through. If one in your keyboard has started to open, damp will have got in causing it to leak. If one has opened enough to see there's a good chance the others have to a degree. If a capacitor is connected across rails for de-coupling and it starts to leak it will draw DC current and pull the rails down.

I don't know what equipment you've got but you can test for leakage by connecting the cap in series with a battery and a milliammeter, or a multimeter on milliamps.
Image1.png
Image1.png (6.9 KiB) Viewed 579 times
The battery should be as near to the rated voltage of the capacitor as possible. The meter may twitch while the capacitor charges but should then read zero.

User avatar
snacksthecat
✶✶✶✶

07 Dec 2018, 05:07

ThePillenwerfer wrote: I can't really comment further as I don't know the size of the cap you are testing. I've tried checking new ones for ESR and can't get a reading on ones smaller than 0.01µF.

To put it simply a capacitor lets AC through it but blocks DC. As they get old they can start to Leak, ie let DC through. If one in your keyboard has started to open, damp will have got in causing it to leak. If one has opened enough to see there's a good chance the others have to a degree. If a capacitor is connected across rails for de-coupling and it starts to leak it will draw DC current and pull the rails down.

I don't know what equipment you've got but you can test for leakage by connecting the cap in series with a battery and a milliammeter, or a multimeter on milliamps.
Image1.png
The battery should be as near to the rated voltage of the capacitor as possible. The meter may twitch while the capacitor charges but should then read zero.
Thank you so much for the tips. I'm going to try the multimeter + battery that you explained.

User avatar
snacksthecat
✶✶✶✶

10 Dec 2018, 01:38

snacksthecat wrote:
JP! wrote: Have you tried giving Al an email @ bitsavers? It is possible that there is still documentation that has not yet been digitized yet.
That's a great idea. I hadn't thought to try that.

Can anyone help me identify the other capacitors?

Image

#1, #2, #9
Spoiler:
Image

Image

Image

Image
#3, #5, #6, #7, #8, #11
Spoiler:
Image

Image

Image
#4, #10
Spoiler:
Image

Image

Image

Thank you guys
I think I would like to go ahead and replace all of the capacitors. Could anyone be a pal and help identify the values of these? Engi already pointed out that the yellow one (#4, #10) is 12nf and I've gone ahead and replaced those two already.

User avatar
lucar

10 Dec 2018, 10:53

snacksthecat wrote:
snacksthecat wrote:
JP! wrote: Have you tried giving Al an email @ bitsavers? It is possible that there is still documentation that has not yet been digitized yet.
That's a great idea. I hadn't thought to try that.

Can anyone help me identify the other capacitors?

Image

#1, #2, #9 #3, #5, #6, #7, #8, #11
Spoiler:
Image

Image

Image
#4, #10
Spoiler:
Image

Image

Image

Thank you guys
I think I would like to go ahead and replace all of the capacitors. Could anyone be a pal and help identify the values of these? Engi already pointed out that the yellow one (#4, #10) is 12nf and I've gone ahead and replaced those two already.
Check this out:

#3, #5, #6, #7, #8, #11 -> 39uF , 10V, 10% , electrolytic

https://www.ebay.com/itm/10pcs-Kemet-39 ... :rk:1:pf:0

User avatar
snacksthecat
✶✶✶✶

11 Dec 2018, 23:25

Thank you guys again. I'm having trouble with these last two:
#1, #2 #9
Markings: 7734+
124
581+
+/-10%
7743+
124
587+
+/-10%
My Measurement: 0.63uF 7.23uF

User avatar
snacksthecat
✶✶✶✶

14 Dec 2018, 02:01

Well I think they're both supposed to be 0.12uF based on the "124" so that's that I bought. No clue why the measurements don't jive with the markings but since the keyboard senses based on a lower capacitance when a key is pressed, I'm hoping that this is just a sign that the old ones were bad. We'll see how this goes. I'll post an update once I get the new ones installed and test it out.

User avatar
snacksthecat
✶✶✶✶

21 Dec 2018, 17:41

Finished switching out all of the capacitors and the board is behaving exactly the same.

I still think that something is making it register as if that slash key is being depressed. I'm not sure how to track down the problem from here though. I've tried poking around with the multimeter but don't have any good ideas yet. Is it a problem that I'm powering the keyboard using a 5v->9v voltage regulator?

User avatar
lucar

21 Dec 2018, 17:44

Are you testing the keyboard with the switches mounted or teared down?

Post Reply

Return to “Workshop”