VOGONS


First post, by analog_programmer

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I found one old and durty HP model C3758A PS/2 keyboard (made by KeyTronic Co.) from Vectra-line PC for few bucks, but it's not in great shape. Actually it's in bad shape. Here are some pictures how it looks when I got it:

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This is how it looks when i got it.
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Bottom.jpg
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This is how it looks when i got it from the bottom side.
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It's stained, it's durty and someone cut the PS/2 cable (I don't know why, maybe this is normal when things goes for recycling/scrap), but since this is very good high quality rubber-dome keyboard I decided to try to restore it and eventually to use it as daily-driver keyboard for my desktop system.

I managed to remove the top plastic without breaking too many plastic clips (I broke two, but used "super glue" and seems fine now). The plastic has become very brittle over time.

Opend.jpg
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Opend.jpg
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Top plastic removed.
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I also removed all keys (on five of them very small pieces broke off) and put them away for good washing. And now I'm here with the restoration process (actually nowhere in process of cleaning):

Opened with removed keys.jpg
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All keys removed.
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And this is one of five slightly damaged keys (damn old fragile plastics):

Broken key.jpg
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One key with small broken piece (a kind of a "pad" for a clip that holds it to not fall when installed).
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I want to ask for some advises:

How to continue further with disassembly process, so I don't damage more things?

How to clean and what to use for cleaner for contact plastic sheets?

Is there any accessible keys that will fit to replace the slightly damaged ones or I have to try some impossible magic with baking soda plus "super glue"?

I don't have the pinout for the cut PS/2 cable, any help will be appreciated. I don't know why there are 6 wires in this PS/2 cable.

Edit: The only problem to solve remains the wiring for 6-pin PS/2 PCB connector.

Last edited by analog_programmer on 2024-02-26, 23:54. Edited 3 times in total.

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Reply 1 of 18, by analog_programmer

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So far, so good. I disassembled the keyboard completely without any new damages. Every bigger part was hold by plastic clips, thus this keyboard it's not designed for repair jobs. This will be the first and the last time when I open and close this keyboard, so I have to make no mistakes on reassembly.

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Fully disassembled keyboard
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This is how looks the PS/2 cable connector on the keyboard's PCB. I still can't find which wire is which to PS/2 male plug.

PS2 connector.jpg
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PS2 connector.jpg
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PS/2 cable connector on the PCB
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I will clean every plastic part with soapy water, then with surgical alcohol (95% C2H5OH). Small parts like keys goes to ultrasonic bath. I'll clean the rubbery sheet with the key's "domes" with distilled water and pure alcohol. I have no plan to "retrobright" this keyboard since I have no experience for this job nor suitable UV-light set. Maybe I'll use some "magic eraser" sponge for slight final treatment on most yellowish parts of the plastic housing.

I think I'm gonna dry-brush the plastic sheets with the contacts from the "inner" sides and to wipe out their "outer" sides (there are no contact pads) with a cotton swabs/buds soaked with pure alcohol.

If there are some suitable keys replacements, please give me some clue.

And the question for pinout for the 6-wire cable/PCB connector is still valid.

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engineer's five pennies: this world goes south since everything's run by financiers and economists
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Reply 2 of 18, by analog_programmer

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If this will be of use, here it is a bigger photo of the 6-pin PS/2 keyboard's PCB connector:

6_pin_ps2_connector.jpg
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PS/2 PCB connector
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The colors of wires from pin 1 to 6 on the J1 PCB connector are:

1 - brown
2 - red
3 - yellow
4 - white
5 - grey
6 - orange

from СМ630 to Ryzen gen. 3
engineer's five pennies: this world goes south since everything's run by financiers and economists
this isn't voice chat, yet some people, overusing online communications, "talk" and "hear voices"

Reply 4 of 18, by analog_programmer

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giantclam wrote on 2023-12-05, 04:43:

Pic of other side of the PCB?

There is some chip on the other side and I'm thinking to trace its pins to the connector and search for datasheet. I'll attach a picture of the other PCB's side later today.

from СМ630 to Ryzen gen. 3
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Reply 6 of 18, by analog_programmer

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giantclam wrote on 2023-12-05, 05:58:

The only time I've seen them wired like that, is when a PS/2 mouse is integral (or plugged into) the keyboard unit itself.

I know about PS/2 dual port combining keyboard and mouse through one connector, but no, there's no PS/2 mouse connector in this keyboard.

Maybe two of all six wires are redundant, but anyway I have to find out the four pins that will work for 4-wire keyboard cable with PS/2 male plug (ground pin is easy to find).

from СМ630 to Ryzen gen. 3
engineer's five pennies: this world goes south since everything's run by financiers and economists
this isn't voice chat, yet some people, overusing online communications, "talk" and "hear voices"

Reply 7 of 18, by giantclam

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analog_programmer wrote on 2023-12-05, 07:15:

I know about PS/2 dual port combining keyboard and mouse through one connector, but no, there's no PS/2 mouse connector in this keyboard.

Maybe two of all six wires are redundant, but anyway I have to find out the four pins that will work for 4-wire keyboard cable with PS/2 male plug (ground pin is easy to find).

Could well be, why I wanted to see other side..ie; the no-stuff at CR1/CR2

Reply 8 of 18, by analog_programmer

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giantclam wrote on 2023-12-05, 07:51:

Could well be, why I wanted to see other side..ie; the no-stuff at CR1/CR2

Later when I'm at home I'll make some pictures of the keyboard's PCB. Actually I was mistaken about the controller chip - it's on the same side as 6-pin connector, nut in the other end of the PCB. Anyway this doesn't matter.

I saw some pictures on the internet of old keyboards with RJ-like male plugs instead of male PS/2 plugs, but I can't find any picture of HP Vectra PC with RJ-style keyboard female plug on its backplate. I don't know from what HP Vectra model comes this KeyTronic keyboard, but is there any chance to be with non-PS/2 plug originally?

from СМ630 to Ryzen gen. 3
engineer's five pennies: this world goes south since everything's run by financiers and economists
this isn't voice chat, yet some people, overusing online communications, "talk" and "hear voices"

Reply 9 of 18, by giantclam

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analog_programmer wrote on 2023-12-05, 09:03:

Later when I'm at home I'll make some pictures of the keyboard's PCB. Actually I was mistaken about the controller chip - it's on the same side as 6-pin connector, nut in the other end of the PCB. Anyway this doesn't matter.

I saw some pictures on the internet of old keyboards with RJ-like male plugs instead of male PS/2 plugs, but I can't find any picture of HP Vectra PC with RJ-style keyboard female plug on its backplate. I don't know from what HP Vectra model comes this KeyTronic keyboard, but is there any chance to be with non-PS/2 plug originally?

Could be... tough without knowing which vectra =)

Reply 10 of 18, by analog_programmer

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giantclam wrote on 2023-12-05, 09:15:

Could be... tough without knowing which vectra =)

Or maybe it's something like IBM model M PS/2 cable, but without RJ connector at the keyboard. I have to check the pinout for model M PS/2 six wires cable.

from СМ630 to Ryzen gen. 3
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Reply 11 of 18, by analog_programmer

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giantclam wrote on 2023-12-05, 04:43:

Pic of other side of the PCB?

Here are some more pictures:

Botoom PCB.JPG
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Botoom PCB.JPG
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Botoom PCB under connector	.JPG
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Botoom PCB under connector .JPG
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Botoom PCB under controller chip.JPG
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Botoom PCB under controller chip.JPG
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Controller chip.JPG
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Controller markings:

26923-40-80C31
© 1995
i KEY TRONIC
ⓜ © 1980 L6324379A

This is of no meaning to me, except the year of manufacturing. Maybe it's Intel i26923 / 80C31 analogue, or maybe it's not.

Pin 5 on the 6-pin connector (grey wire) is ground (shielging), but seems lik it's not connected to the controller. I have to check again if it's going on pin 20 (or something like possible Vss - ground) on the controller.

Pin 3 (yellow wire) on the connector goes to pin 40 and also seems to pin 31 (have to check again) on the controller (possibly +5Vdd/Vcc???).

Pin 1 on the connector (brown wire) goes to R2 (50 Ohm) resistor and the other end of R2 goes to pin 36 and 38 on the controller (possibly data output +DATA).

Pin 2 on the connector (red wire) goes to R1 (50 Ohm) resistor, other end of R2 goes to R3 (2 kOhm) resistor, other end of R3 goees to R9 (27 kOhm) resistor, and finally other end of R9 goes to pin 32 on the controller.

Pin 4 on the connector (white wire) goes to some capacitors (C1 and C3 maybe decoupling caps) and also to anode of the diode CR3 and to R8 (23.3 kOhm) resistor, the other end or R8 goes to diode's cathode and then to pin 9 on the controller

Pin 6 on the connector (orange wire) - can't trace it back with the multimeter, but seems like its trace goes directly to keyboard's plastic contacts sheets connector.

I have no idea which ones could be for +DATA and +CLK.

from СМ630 to Ryzen gen. 3
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Reply 12 of 18, by analog_programmer

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It would be much more easier to trace back the PCB connections to 6-pin cable connector if I remove the metal "clip" that holds the plastic contacts sheets to the PCB, but I don't know how to do that without risking to break something. There was a plastic locking post through PCB and contacts sheets and I removed It, but I didn't dare to pull the sheets from under the metal "clip" lest I tear them.

from СМ630 to Ryzen gen. 3
engineer's five pennies: this world goes south since everything's run by financiers and economists
this isn't voice chat, yet some people, overusing online communications, "talk" and "hear voices"

Reply 13 of 18, by giantclam

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M'kay....don't futz with that connector, I think I see enough...

The shielding is analog ground, pin6 you say -- whatever pins connect to either end of of C1, will be your +/- pins.

Might be polemical as to whether this is AT DIN-5 or PS/2 ....

Looks like that controller is from this base design -> https://www.keil.com/dd/docs/datashts/intel/8 … bh_87c51_ds.pdf

Now that you have shield, power, ground, ... beep out which pins on the IC, connect to the remaining pins for the cable ....might lend a clue =)

Reply 14 of 18, by analog_programmer

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giantclam wrote on 2023-12-06, 09:37:
M'kay....don't futz with that connector, I think I see enough... […]
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M'kay....don't futz with that connector, I think I see enough...

The shielding is analog ground, pin6 you say -- whatever pins connect to either end of of C1, will be your +/- pins.

Might be polemical as to whether this is AT DIN-5 or PS/2 ....

Looks like that controller is from this base design -> https://www.keil.com/dd/docs/datashts/intel/8 … bh_87c51_ds.pdf

Now that you have shield, power, ground, ... beep out which pins on the IC, connect to the remaining pins for the cable ....might lend a clue =)

Thank you very much for the link with datasheet, that will help a lot to trace the signals at 6-pin cable connector.

The pinout diagram from the document confirms that yellow wire is Vcc (controller's pin 40). But why is that pin 9 on the controller (RESET) connected to white wire, is it for +CLK signal? And which one can be +DATA, controller's pin 11 TXD (nope pins 11 and 10 are for connection between two controllers) maybe I have to search for some of the register pins on the controller? Pages 4 to 6 gives explanation to controller's signals, but I can't figure out which signal names correspond to PS/2 plug names +CLK (clock) and +DATA.

P.S. In my case there's no matter if the original cable plug was DIN5 or PS/2 since their signals correspond without transducers. I think HP Vectras from 1995-96 don't use DIN5 pugs for their keyboards. I intend to use a 4-wires PS/2 cable or if I find one with 6 wires to use the shielding as well (and there will be one redundant wire left).

P.S.2 I found another datasheet for 80C31 controller that seems more specific: https://www.nxp.com/docs/en/data-sheet/80C31_80C32.pdf (from 2000) and https://pdf.datasheetcatalog.com/datasheet/ph … 80C51BCGN40.pdf (more period correct from 1996).

I think I found some clue for PS/2 CLK signal:

XTAL1-dia.jpg
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XTAL1.jpg
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This XTAL1 pin is used for external clock signal by the controller when is not used its internal clock generator. I think I have to check this one (pin 19 on the controllr) for connection to 6-pin PS/2 cable connector. If this is correct, then I just have to figure out which pin of the controller corresponds to +DATA on the PS/2 connector.

EDIT: I think I have to look for PS/2 DATA connection to some of the 0 to 3 ports pins on the controller as it is bi-directional connection.

80C31 ports pins.jpg
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80C31 pinout.jpg
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from СМ630 to Ryzen gen. 3
engineer's five pennies: this world goes south since everything's run by financiers and economists
this isn't voice chat, yet some people, overusing online communications, "talk" and "hear voices"

Reply 15 of 18, by analog_programmer

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Pin 1 to 6 on the J1 PCB connector according to colors:

1 - brown = pin 37 (port 0.2) of 80C31
2 - red = pins 38 and 39 (ports 0.1 and 0.0) of 80C31
3 - yellow = +5Vdd/Vcc (pins 40 and 31 of 80C31)
4 - white = GND (pin 20 of 80C31)
5 - grey = Shielding
6 - orange = ?? (can't trace this one)

Actually pins 18 (XTAL2) and 19 (XTAL1) of 80C31 are connected to GND through 3-pin tantalum capacitor oscillator (giantclam corrected me), so the XTAL1 (pin 19) can't be +CLK from PS/2.

I think now I can try the brown and the red wires for +DATA and +CLK signals with 4-wire PS/2 cable-without any problems and if it doesn't work at first try I'll swap the two wires.

Last edited by analog_programmer on 2023-12-09, 11:56. Edited 2 times in total.

from СМ630 to Ryzen gen. 3
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Reply 16 of 18, by giantclam

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analog_programmer wrote on 2023-12-09, 11:03:

Actually pins 18 (XTAL2) and 19 (XTAL1) of 80C31 are connected to GND through 3-pin tantalum capacitor, so the XTAL1 (pin 19) can't be +CLK from PS/2.

That component is an oscillator, not a 3-pin tantalum capacitor =)

Reply 17 of 18, by analog_programmer

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giantclam wrote on 2023-12-09, 11:40:

That component is an oscillator, not a 3-pin tantalum capacitor =)

That also seems legit. I didn't inspect component's markings with magnifying glass, so I decided, that these pins are connected to ground through capacitance for some filtering and the internal chip pulse generator schematic is unused.

Anyway, this is not related to CLK signal of the PS/2 port.

P.S. Yep, I forgot that C3 is under the paper label on this picture: download/file.php?id=180183 , so "Y1" for sure isn't for capacitor. My mistake, Y1 is an oscillator.

I'm searching for spare 4 or 5 wire PS/2 cable to try this connection:

1 - brown = +DATA (pin 37 - port 0.2 of 80C31)
2 - red = +CLK (pins 38 and 39 - ports 0.1 and 0.0 of 80C31)
3 - yellow = +5Vdd/Vcc (pins 40 and 31 of 80C31)
4 - white = GND (pin 20 of 80C31)
5 - grey = Shielding
6 - orange = no connection

If it doesn't work I'll change signals for wires 1 and 2. I hope there will be no problem for the controller chip if these two signals are swapped for test.

from СМ630 to Ryzen gen. 3
engineer's five pennies: this world goes south since everything's run by financiers and economists
this isn't voice chat, yet some people, overusing online communications, "talk" and "hear voices"

Reply 18 of 18, by analog_programmer

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I totally forgot to update this topic with the results from restoration.

I've connected five internal plug wires (out of six) to PS/2 male connector and now the keyboard is fully working. My last suggestion for the wires was correct.

Once again already tested and working connections by color:

1 - BROWN = +DATA
2 - RED = +CLK
3 - YELLOW = +5Vdd/Vcc
4 - WHITE = GND
5 - GREY = shielding
6 - ORANGE is disconnected

Now I have to spray-paint the yellowed casing plastics (I'm thinking of black mat spray can) and restoration of this old HP keyboard will be completed.

Special thanks to giantclam for the help!

from СМ630 to Ryzen gen. 3
engineer's five pennies: this world goes south since everything's run by financiers and economists
this isn't voice chat, yet some people, overusing online communications, "talk" and "hear voices"