Author Topic: CPC 464 Keyboard Repair tip  (Read 1407 times)

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Offline TheCorfiot

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CPC 464 Keyboard Repair tip
« on: 01:10, 09 March 13 »
Hi forum chums....

I was repairing a shortboard 464 for my friend BluesBrothers this evening and found something which maybe common out there.

There was a problem with the keyboard, quite a few keys were being ignored.

Continuity checks between the keyboard connectors and the sound chip found three open circuits on pins 11,12,13 of the chip.

The tracking routes wierdly in that it goes from keyboard connector to joystick port to sound chip and here lay the problem as the pins for the joystick socket also double up as vias, passing the signal from one side of the board to the other.

Exerting above average force on the joystick connector had caused 3 micro cracks in the tracking just at the point between the through hole solder connection and the track heading off to a via..
Careful removal of a small amount of solder resist at that point and then resoldering the joystick pins allowing the solder to flow over the crack sorts things quite tidily and easily....

Just wanted to share as it could be common when the joystick port has suffered abuse.

TC  :)
« Last Edit: 01:13, 09 March 13 by TheCorfiot »

Offline Bryce

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AW: CPC 464 Keyboard Repair tip
« Reply #1 on: 14:41, 09 March 13 »
Great tip, sounds like one of those faults that could keep you looking for hours. Do you think the solder bridge repair will survive regular joystick pluging? I would have gone for direct wire links.


Offline TheCorfiot

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Re: CPC 464 Keyboard Repair tip
« Reply #2 on: 15:37, 09 March 13 »
It has some reinforcement due to the larger solder base...
I gave it some good flexing too, any more and the socket would break...

I agree about hardwiring it, would be nice to keep the board look original though...

Will think about it  ;)

Offline Velktron

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Re: CPC 464 Keyboard Repair tip
« Reply #3 on: 01:49, 23 March 13 »

I must have stumbled upon this very same problem with my "new" 6128 as detailed in this post. In addition to having a dead keyboard line (the membrane tested OK) I also get no sound output and garbage joystick input (moving the joystick around generates bogus keystrokes).

What do you think? Could it "simply" be a matter of trace continuity, or is the AY chip busted?  :'(

Offline db6128

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Re: CPC 464 Keyboard Repair tip
« Reply #4 on: 04:27, 23 March 13 »
The AY is controlled via the 8255 PPI (Parallel Peripheral Interface), which also takes care of input from the keyboard and joysticks, so you may well be on the right track. Hopefully someone with more in-depth electronic knowledge can advise.
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