'81 keyboard error - all keys in columns 5&6 and below

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Trevor_B
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'81 keyboard error - all keys in columns 5&6 and below

Post by Trevor_B »

I'm resurrecting one of my old '81s.

I've made sure it's working with the exception of a couple of key columns. I get the K prompt, can run simple progs, but any key/function under numbers 5 & 6 doesn't work.

Am correct in suspecting a duff resistor on RP3 ("slot" 1)? I bought some replacement resistor arrays a few years ago, but before desoldering/resoldering I'd like some opinion about if it's the right thing to do - or alternatively some way I could test before I get the solder sucker out?

I have plans to put in a new VLA, 32k ram upgrade, composite video and UDG, but before I start, I want to make sure it's working properly
Lardo Boffin
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Re: '81 keyboard error - all keys in columns 5&6 and below

Post by Lardo Boffin »

Have you replaced the keyboard with a new one? You can get them on Sell My Retro for around a tenner.
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Trevor_B
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Re: '81 keyboard error - all keys in columns 5&6 and below

Post by Trevor_B »

Hi Lardo

it's a new keyboard and proven working (tried it on the minstrel 3 - works fine).

tbh I knew about this issue a few years ago, hence buying the replacement resistor packs. I just wanted an opinion if it's the right things to swap, or to look elsewhere. From the keyboard matrix diagrams I can see that both columns link back to the same keyboard connector(the mtherboard connector is fine - have checked that already.

Trev
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1024MAK
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Re: '81 keyboard error - all keys in columns 5&6 and below

Post by 1024MAK »

Have you tested the existing resistor array (RP3) with a multimeter?
With the ULA removed (if its in a socket), test between +5V and then each pin on the five pin keyboard connector. Each should measure 10kΩ. If the ULA is not in a socket, but is soldered in you can still do the test, but the ULA will affect the results a bit so the resistance will be lower.

Or with the board powered up, measure the voltages on each of the contacts in the five way keyboard connector. They should all be the same voltage. Unless a key is pressed.

You can also use a piece of thin solid core wire (e.g. fixed telephone wiring or network cable) with the insulation stripped from the ends, poke one end in one keyboard connector so it touches one contact, then do the same in the other keyboard connector.

If you still have problems, it could be a faulty ULA.

Mark
Trevor_B
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Re: '81 keyboard error - all keys in columns 5&6 and below

Post by Trevor_B »

I tested the resistor pack (ULA is soldered on this board)

4 connections showed ~6.25kΩ, one showed ~10kΩ (looking from underneath the board, the furthest right connector is roughly 10k, the other 4 were roughly 6.25 - within a few percent for both).

tbh I'm not sure what this means now; as Mark says, they should all be similar but the variance of the last connection - even though it's 10k as per the resistor value - has me wondering if the problem is within the ULA as Mark says.

I'll see if I can get hold of another ULA (VLA-81 - once SMR has them back in stock), unless anyone has any suggestions otherwise?

Trev
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1024MAK
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Re: '81 keyboard error - all keys in columns 5&6 and below

Post by 1024MAK »

Yeah, either the ULA or the solder joints or PCB tracks.

Test on continuity between the ULA pin and the keyboard connector pin.

Mark
Trevor_B
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Re: '81 keyboard error - all keys in columns 5&6 and below

Post by Trevor_B »

I've ordered a new ULA - VLA-81, hopefully winging it's way from NZ as I type. This'll be the first upgrade and assuming it fixes the issue it will hopefully be followed by a 32k internal upgrade - when I can find some reasonable instructions.

I'm having a few issues posting on here today - I keep being told my IP address is blacklisted (any ideas folks?). Posting via VPN and different IP address
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1024MAK
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Re: '81 keyboard error - all keys in columns 5&6 and below

Post by 1024MAK »

Trevor_B wrote: Mon Dec 14, 2020 9:43 pm I'm having a few issues posting on here today - I keep being told my IP address is blacklisted (any ideas folks?). Posting via VPN and different IP address
Is this via a PC or via a mobile signal? Which service provider are you with?
Also try logging off and back in, or if using a mobile connection, going to airplane mode (off-line) and then waiting 30 seconds before trying to reconnect. Then try again.

Mark
Trevor_B
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Re: '81 keyboard error - all keys in columns 5&6 and below

Post by Trevor_B »

It's PC via BT; Have rebooted started the router (trying to grab a different IP address at the router level - failed). I'm sure it's temporary, and by posting this update I'm sure to find out!

..yep - now back to normal
Trevor_B
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Re: '81 keyboard error - all keys in columns 5&6 and below

Post by Trevor_B »

New VLA-81 arrived today - now to unsolder the existing ULA.

I'm going to solder in a socket for the new VLA and I'm just waiting for it to be delivered.

So - back to being quiet again for a while.

Happy New Year all - it's the 40th anniversary year for the zeddy!
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