Dead Keyboard

discussion of games, software, hardware & emulators relating to the Acorn Atom
JannievanZyl
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Dead Keyboard

Postby JannievanZyl » Tue Aug 29, 2017 4:23 pm

Hi,

/Pulling hair out here

After trying a million DC barrel connectors on my (perfectly working) Atom, I eventually soldered an external power connector onto the PCB.

Now I get the following;

1. Machine starts up and 'Break' initializes the machine. Get the prompt, etc.
2. But I get no response from the keyboard. As if the keyboard is not being scanned?

I'll dig up the circuit diagram and start faultfinding but was hoping for a few quick hints from the experts.

Any ideas?

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oss003
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Re: Dead Keyboard

Postby oss003 » Tue Aug 29, 2017 5:28 pm

First check if the power supply is between 4,95 and 5,25V.
Then you can try replacing the 8255 and/or 7445.

Greetings
Kees

JannievanZyl
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Joined: Sat Feb 11, 2017 8:56 pm
Location: Cape Town, South Africa

Re: Dead Keyboard

Postby JannievanZyl » Tue Aug 29, 2017 5:49 pm

Thanks Kees,

PSU is fine and I've swapped the 8255. Looking for a 7445 to try.

I'm not seeing any activity on the Adress and Data busses. CPU is getting clock and Reset works to all the chips.

But it comes up with the prompt, so the CPU/RAM/ROM must be working, right?

JannievanZyl
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Joined: Sat Feb 11, 2017 8:56 pm
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Re: Dead Keyboard

Postby JannievanZyl » Tue Aug 29, 2017 6:54 pm

OK, sanity check, please.

1. Reset on 6502 stays low UNTIL I press 'Break' when it goes high as long as the key is pressed.
2. My understanding is that *Reset implies it must go low to reset the CPU, not high.
3. When I trace it back, IC 9 is working fine.
4. BUT, the Break key is make-before-break, while the circuit diagram seems to indicate it should be break-before-make. Like all the other keys.

Do I have a dud Break key, or is this correct, i.e. the Break key is normally-closed?

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martinw
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Re: Dead Keyboard

Postby martinw » Tue Aug 29, 2017 7:38 pm

My break key is exactly the same as the other keys mechanically.

Martin

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oss003
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Re: Dead Keyboard

Postby oss003 » Tue Aug 29, 2017 7:53 pm

If you get ACORN ATOM and a prompt, the processor, RAM and ROM are working.
Not sure if all RAM is working ok, but zeropage and video RAM are.

Reset should be high on the CPU and goes low while pressing BREAK.
Only on the 8255, reset is low and goes high when pressing BREAK.
The only chip in the reset line is IC9 so please check if it's working correct.
If BREAK is not pressed, pin 13 and 4 IC9 should be high and pin12 IC9 low.
While BREAK is pressed, pin 13 and 4 IC9 should be low and pin12 IC9 high.


Greetings
Kees

JannievanZyl
Posts: 25
Joined: Sat Feb 11, 2017 8:56 pm
Location: Cape Town, South Africa

Re: Dead Keyboard

Postby JannievanZyl » Tue Aug 29, 2017 8:31 pm

This is super weird.

Confirmed the Break key is now normally closed and goes to about 7KB when pressed.

Checked on another Atom and confirmed it's supposed to be normally open.

So I lifted pin 13 of IC9 where the Break key attaches.

If I now momentarily short pin 13 to ground, the Atom resets and works perfectly.

So, this is crazy. (After a bang or two, it seems) the switch literally inverted. Going from normally open to normally closed.

Now my next question;

1. How do I remove the switch? I tried to unsolder it but not sure how to pull it from the frame it sits in?

2. Would I find a replacement anywhere?

PS: I did check that it's not full moon and no weird eclipse is going on.......

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oss003
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Re: Dead Keyboard

Postby oss003 » Tue Aug 29, 2017 8:50 pm

Do you have an Issue 4 keyboard or an Issue 5?

A key in an Issue 4 keyboard works with springs and it could be that one spring leg is to long and makes contact with the other spring leg.
If you press the BREAK key, the contact is broken and the function is reversed .... but it's a guess.

It is hard to replace a key in an Issue 4 keyboard and also difficult to repair.
There are several topics about replacing Atom keys in an Atom keyboard.

http://www.stardot.org.uk/forums/viewto ... +4#p150665
http://arduinonut.blogspot.nl/2009/09/mending.html

Greetings
Kees
Attachments
Atom Key.png

JannievanZyl
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Re: Dead Keyboard

Postby JannievanZyl » Tue Aug 29, 2017 8:59 pm

Thanks Kees,

Will look at those links.

How would I know which version keyboard I have?

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oss003
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Re: Dead Keyboard

Postby oss003 » Tue Aug 29, 2017 9:07 pm

When you open your Atom, it's printed on the mainboard.

issue.png

Without opening, an Issue 4 keyboard has smaller letters on the keycaps than those on an Issue5.

Greetings
Kees
Attachments
atoms.png

JannievanZyl
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Location: Cape Town, South Africa

Re: Dead Keyboard

Postby JannievanZyl » Tue Aug 29, 2017 10:34 pm

Cool,

Definitely an Issue 4.

I pulled the switch plunger off the Break key and tried to reset the springs. Gave up and soldered a temp switch across the break key to get the system working again. But think I'll give it another go to fix the switch.

In the meantime I'm in the market for a nice clean Atom if anyone on the forum has one going. Would prefer to get a second system.

Also an Electron, as mine seems to suffer from the dreaded ULA problem.......

JannievanZyl
Posts: 25
Joined: Sat Feb 11, 2017 8:56 pm
Location: Cape Town, South Africa

Re: Dead Keyboard

Postby JannievanZyl » Fri Sep 01, 2017 12:50 pm

Hi,

In this design, how is the contact made?

Just the two prongs of the springs touching that middle plate of the plunger?

Would anyone on this group have a spare key I can try and replace?

Atom Key.png


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