HP 9845 workstation keyboard (ITW Magnetic Valve)

Anakey

06 Sep 2019, 01:02

I first saw this board placed for sale by tentator in his recent sales thread and instantly thought it looked cool, scientific numpad, thick doubleshot keycaps, an Execute key and at an acceptable price, The original listing was unknown switch type, however with some digging through the wiki thanks to the recognisable swith pinout I saw they were likely the early version of ITW Magnetic Valve switches. I went along with the purchase and then it arrived on Monday.
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Keycaps are thick doubleshots and are Microswitch hall effect compatible HP cap on Left, Microswitch cap on the right
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HP cap on Microswitch and Microswitch cap on Magnetic Valve
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When i first saw the pictures in the sale thread something cought my eye as strange, the arrow cluster in the top middle of the board was on a daughterboard that was offset from the main pcb. Upon desoldering the board so i could thouroughly clean the switches, plate and PCB I discovered that the cursor keys were in fact double action.
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The double action switches have 6 pins as can be seen in the pcb through holes for the switch legs.
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As you can see there are 2 ferrite cores at different levels on the lower part of the stem. The upper part of the stem houses a small spring shown by the brass colour in the centre of the stems that passes through the hole on normal switches. This second spring is compressed after the normal larger spring has compressed so the switch has twice the travel distance of a normal switch for both actuations.
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The switches in the arrow cluster needed to be on a daughterboard because of the increased length of the double action switches. The switches that are not double action in the arrow cluster have extended pins that match the extra height of the double action switches.
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I still need to clean the switches using an ultrasonic bath to hopefully remove any dust that may have gotten inside the swiitches. My biggest hurdle is going to be attempting to convert this. I have none of the logic circuitry, this was obviously handled on the main system this board was originally a part of. Any help from the Dt community will be much appreciated.
Last edited by Anakey on 07 Sep 2019, 01:05, edited 1 time in total.

MMcM

06 Sep 2019, 21:04

There might be some information on http://www.hp9845.net/.

Anakey

07 Sep 2019, 00:50

MMcM wrote:
06 Sep 2019, 21:04
There might be some information on http://www.hp9845.net/.
Wow thank you for that link, i did try the number before but tried the whole number rather then just the first part looks like the main machine would have been quite a major investment and probably used for many years. I shall drop them a link and see if i get a reply.

MMcM

07 Sep 2019, 05:40

Also check out http://www.hpmuseum.net/collection_document.php. It looks like maybe 9845B_SchematicsByTonyDuell_152pages2.pdf has the hand drawn(!) schematics, including the keyboard assembly.

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DMA

26 May 2020, 08:11

Mmkay, you probably didn't succeed with conversion. The rows that go to daughterboard probably were too unstable - may be tripping adjacent rows, may be tripping 4 columns instead of one.

I had a tall ITW board with long traces, which had the above symptoms. Ended up cutting ALL the traces and handwiring, using PCB for structural support only.

Once I did that - it all magically worked, PERFECTLY. Can press 20 keys at once and still get no keyspam with debouncing as low as 2.

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