Problem with a 5251

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AJM

Problem with a 5251

Unread post by AJM » 04 Jan 2019, 22:30

Some weeks ago I got an IBM 5251, which was in really good shape. No rust, nothing broken or bent.
5251.jpg
5251.jpg (746.08 KiB) Viewed 176 times
But the switches were very loose, so I opened it, cleaned it and replaced the foam.
All switches are sitting tight now - and clicking happily.
At last also the xwhatsit controller arrived and I could start trying it out.

But I have now the problem that there is no Voltage Threshold, at which all keys are working correctly.

At 112 all keys have the state "off". If I press keys, nothing happens.
1.jpg
1.jpg (25.69 KiB) Viewed 176 times
If I go higher - starting from the left side - keys start to register as pressed, although I'm not pressing any.
2.jpg
2.jpg (25.68 KiB) Viewed 176 times
Until at 128 the 10 first columns all register as pressed, although I'm not pressing any. And if I press keys of the other columns nothing happens.
3.jpg
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If I continue to raise the threshold, finally keys start to react, when being pressed. Starting in column 23. The higher the threshold, the more columns start working - till column 11 - at a threshold of about 144.
If I go higher, key presses start to trigger multiple spots, until in the end the whole matrix registers as pressed (without keys being pressed).

To sum it up: I can get the columns 11 - 23 roughly working, but columns 1 - 10 are either in state pressed or not-pressed - depending on the threshold, but at no point work correctly.

Does anybody have an idea, maybe?

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Muirium
µ

Unread post by Muirium » 04 Jan 2019, 23:01

Read Xwhatsit’s manual. This is exactly what it’s supposed to do.

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AJM

Unread post by AJM » 04 Jan 2019, 23:46

The first half of your remark was helpful, thank you.

I had missed the chapter "Troubleshooting", where I now found:
The edge connector is misaligned with the contacts on the pad card—look
closely to make sure the connector contacts are centred on each pad card
contact.
Not expecting, that the xwhatsit connector is wider than the pad card, I hadn't paid enough attention during the first installation and it had ended up 2 millimetres misaligned, which messed everything up.

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Muirium
µ

Unread post by Muirium » 05 Jan 2019, 00:03

Also there *should* be matrix positions permanently set to 0 and others permanently at 1. That's how IBM designed it. Their factory controller knew about those and calibrated accordingly. Xwhatsit lets you hand pick them, which is how its his own auto threshold system works. Or you can just go manual.

This is all spelled out somewhere in his documentation. I remember learning all about it when I installed my very first controller. He was still around back then, and often told me to go check in the right place!

SneakyRobb

Re:

Unread post by SneakyRobb » 09 Jan 2019, 15:22

AJM wrote:
04 Jan 2019, 23:46
The first half of your remark was helpful, thank you.

I had missed the chapter "Troubleshooting", where I now found:
The edge connector is misaligned with the contacts on the pad card—look
closely to make sure the connector contacts are centred on each pad card
contact.
Not expecting, that the xwhatsit connector is wider than the pad card, I hadn't paid enough attention during the first installation and it had ended up 2 millimetres misaligned, which messed everything up.
I had a similar issue with my keyboard. I found that first it is easy to not get the xwhatsit correctly set on the board. So make sure it is in place correctly all the way down as you say.

User avatar
AJM

Re: Problem with a 5251

Unread post by AJM » 09 Jan 2019, 17:14

Yes, it sits correctly now and works perfectly. :)

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