Sinclair ZX80 / ZX81 / Z88 Forums

Andy Rea wrote: ↑Sat Nov 18, 2017 7:39 pm I would check for shorts near the data pins of the cpu, the track clearances are quite close around there, also the diodes near the keyboard connector some.of the traces run very close to the diode pads.

Other than it not working it looks very nice, good job so far.

Regards Andy

Cheers Andy. I will get the magnifying glass and continuity tester out later.

Logic probe £5 from Maplin. Nothing fancy, just shows if a pin is high, low, hi-z or pulsing. S'all you need.

El cheapo logic probe for 5V TTL logic...

If you have a spare 74LS14 or 74HCT14 logic chip, connect a test probe to a resistor (100 ohms to 180 ohms for a 74LS14, 330 ohms to 820 ohms for a 74HCT), then connect to any of the chips input pins.
On the relevant output, connect a RED LED via a 390 ohm or 470 ohm resistor to +5V. LED anode to the resistor/ +5V side.
Then connect this same outputs to another input pin. On the relevant output, connect a GREEN LED via a 390 ohm or 470 ohm resistor to +5V. LED anode to the resistor/ +5V side.

Connect a ceramic capacitor (value not critical, preferred value 100nF) across the +5V (VCC) pin 14 and 0V (GND) pin 7of the chip. These also have to go via mini clip probes to the supply lines of the circuit under test.

Mark

I wimped out and bought one - I would have had to buy some bits in order to make my own.

I got new sockets from Sell My retro:-

https://www.sellmyretro.com/offer/details/3473

They have four legs rather than the three in use on the zeddy. Do i just fold the unwanted one under or do i need to remove it? Currently I have reused an old one.

Lardo Boffin wrote: ↑Sun Nov 19, 2017 2:59 pm I wimped out and bought one - I would have had to buy some bits in order to make my own.

No shame in that! You have enough on your plate

Lardo Boffin wrote: ↑Sun Nov 19, 2017 3:50 pm I got new sockets from Sell My retro:-

https://www.sellmyretro.com/offer/details/3473

They have four legs rather than the three in use on the zeddy. Do i just fold the unwanted one under or do i need to remove it? Currently I have reused an old one.

Remove it or just cut it off. It's not fitted on the sockets that Sinclair used. Hence not needed.

Mark

Yes - I think this product have been upgraded with a fourth leg in the last 30 years.
Cut it with a side cutter.

PokeMon wrote: ↑Sun Nov 19, 2017 10:14 pm Yes - I think this product have been upgraded with a fourth leg in the last 30 years.
Cut it with a side cutter.

So I’m finally armed and dangerous with a logic probe (that thing has a wicked sharp tip!).

Its an LP-2800 from Maplin.

Now what?....