Sinclair ZX80 / ZX81 / Z88 Forums

Seeing as this is such an active topic I've spent some more time on it. Attached is the results of my labour. I wanted to make sure that I hadn't fluffed up the board due to a schematic or routing error.

I checked the schematic against the PDF version at least a half dozen times. I painstakingly re-laid out the PCB according to the design in the PDF. I spent an hour tweaking the layout in eagle and laying it over a scan of the PDF to ensure that it's as accurate as it needs be.

I've included the eagle files & exported PDF of the board in case anyone wants to make their own. I've made a silk layer if you're that way inclined. I've included the GIMP source (layered) files showing the over-laid eagle export, in case you want to check I'm not cheating. I've included a PNG for the less untrusting You will see that there are minor differences in component sizing - specifically the caps - but I left that as-is because metric system. I've also left a particular part of the routing spaced a little more generously as the original version was a little too close together for my liking. You can see that around the south west side of the IC, north of the LED.

I'm happy that the board as built by Lardo is electrically consistent with the original as it's from the same eagle schematic as this version.

I made a new board using the PDF pattern if anyone is interested in making one up - Mark?

If you are offering, who am I to refuse?

The standard E12 series resistors I already will have in stock. I should have some 10nF ceramic capacitors and have lots of 100nF capacitors. I also have 1N4148 diodes and red LEDs. I'm sure I have a LM324AN somewhere...
So that just leaves the remaining resistors (1.1k and 24k).

While perusing the datasheet for the LM324AN, I did notice that TI recommends having 100nF ceramic decoding capacitors between the power supply pins, close to the chip. So it may be worthwhile adding the provision to any production PCB.

Also, the use of a 14 pin turned pin type DIL socket may be wise.

Mark

On its way.

There was a little scaling issue with the print I made of the PDF which meant that I was off by a few percent. This meant in turn that I had to slightly alter the stance of the socket used for the chip. Not turned pin m'fraid, it wouldn't have worked. It's a quality dual wipe though - not to be sniffed at

I have a complete second set of parts I’m happy to send on.

If Mark wants first dibs on the parts then that's cool - if not I'll make another board so I can offer up a second data point.

I'll be happy to then send the completed board back to you. I don't do tapes

1024MAK wrote: ↑Sat Feb 03, 2018 11:53 am
Testing the LED
===============
Remove both cells (batteries) from their holder.
Connect the positive terminal of a 3V or a 9V battery to a resistor (see below for the value). Then connect the resistor to one of the LED connections. Connect the other LED leg to the battery negative connection. If the LED lights, mark the LED leg connected to the battery negative with a black marker pen (or mark that side of the LED body).
If the LED does not light, try the other polarity.
If the LED does not light at all, disconnect it...

Just for my sanity (I know you have already said that you have done this), can you do the checks and tests as per this picture:

Mark

The LED did not light up at all on the PCB. Once removed it lit up fine and was inserted correctly.

I rechecked for shorts and continuity where suggested and all is good.

I have pretty much run out of time on this for now - the people who are buying my house and have been faffing on for months got in touch Friday and asked if they could move in next Friday! How we laughed...
The upshot of this is that I have got to do some extreme packing and a lot of stuff (including all of my retro stuff) is going into storage for a couple of months while the house we are moving into is built.

Happy days.

sirmorris wrote: ↑Sat Feb 03, 2018 10:36 pm If Mark wants first dibs on the parts then that's cool - if not I'll make another board so I can offer up a second data point.

I'll be happy to then send the completed board back to you. I don't do tapes

I’m happy to send to whoever! I of course only ever use my ‘spand and never go near tapes.

This certainly didn’t arrive today...

sirmorris wrote: ↑Sat Feb 03, 2018 4:34 pm Seeing as this is such an active topic I've spent some more time on it. Attached is the results of my labour. I wanted to make sure that I hadn't fluffed up the board due to a schematic or routing error.

At this stage I would be suspecting PBPASI (problem between PCB and soldering iron).

Don't be so hard on yourself - this analogue stuff is triii-iii-iii-cky!

Lardo Boffin wrote: ↑Sat Feb 03, 2018 9:04 pm I have a complete second set of parts I’m happy to send on.

Ahh, as you can see, I have some bits. But if you have a surplus, I'd be happy to help take them off your hands. So thank you for your kind offer. I know that I am very unlikely to have any 1.1k ohm resistors, or indeed any 24k ohm resistors and also may not have a suitable 100pF capacitor (not got as far as looking for these). I also have not gone looking to see what battery holders I have.

I'll also be happy to take a look at your board. I have a few "toys" that I can put to work testing it. Then once it is working, I can send it back to you when you are ready.

Err, when your new house is built (not a self build is it?) that is...!
I hope your house adventures turn out well, without too much more in the way of stress. Good luck

And thank you to Charlie as well

Mark