Creating Wilf Rigter's ZXKBD v3

[mrtinb]

Using a transistor or an analog switch, one key can "press" multiple ZX81 key at once.
Here is an example I use to have "Backspace" (BS) and "/" on a single key:

http://forum.tlienhard.com/phpBB3/viewt ... sten#p8838

I looked at the Maplin instruktions yesterday evening and found that two 4066 would do the trick.

/Martin

[mrtinb]

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Now comes the soldering part.

/Martin

[mrtinb]

I finally found my ZX81 in the basement.

I didn't power it up for a day, to make it adjust for the temperature.

When I powered it up, the great [K] apreared. After 5 minutes the [K] disapeared and the screen was white.

Somehow my dear computer only worked for 5 minutes.

I found a diagnostics page http://www.worldofspectrum.org/hardware/rep3.html and ordered a digital probe to figure out which IC is broken.

Project is set back another month.

/Martin

[PokeMon]

Maybe it is just the power regulator (7805).
This could get some hot.

[mrtinb]

Maybe it is just the power regulator (7805).

I've used a volt-meter on it this evening, and it looks ok. I'll have to wait until the digital probe is in the mail, so I can test the ICs.

/Martin

[mrtinb]

It's the soldering going on here. I have 3 prints: Left keyboard, right keyboard and controller.

Soldering on the edge-connector from Pokemon, I realized a design flaw. There is not space for the ICs when the board is connected to the ZX81.

I'm trying to desolder the edge-connector. (Desoldering the edge-connector is not easy)

IMG_0057.jpg (48.66 KiB) Viewed 4310 times

And I'll add pin headers (maybe multiple) before adding the edge-connector again. This way the print will be longer away from the ZX81, and the ICs will fit there.

[1024MAK]

You could use one of these http://www.sellmyretro.com/offer/details/2738 (when PokeMon returns back from holiday).

[mahjongg]

or perhaps the board will fit if you use the IC's without a socket. its far easier to remove the IC sockets without damage to the PCB than the edge connector.

[1024MAK]

I'm trying to desolder the edge-connector. (Desoldering the edge-connector is not easy)

Do you have an electric hot air gun (the type sold in DIY stores for stripping paint)?
If you are careful, you can use a metal vice or similar to hold the PCB vertically, then gently warm up the solder side using the hot air gun. Sweep from one end of the connector to the other, back and fourth. As soon as you see the solder start to melt, use a pair of pliers to gently pull the edge connector (hold the middle). Continue moving the hot air gun to apply heat to all the solder joints. Very soon the whole edge-connector will come free.

As long as you don't hold the hot air gun in one place for too long, the PCB will not be damaged.

I have done this a number of times now, either to desolder a large DIL chip, or to recover edge connectors from old computer boards.

Mark

[mrtinb]

or perhaps the board will fit if you use the IC's without a socket. its far easier to remove the IC sockets without damage to the PCB than the edge connector.

Continue moving the hot air gun to apply heat to all the solder joints. Very soon the whole edge-connector will come free.

Thanks for your suggestions.

I think I'll try to get a ZX81XT from Pokemon first.