Sinclair ZX80 / ZX81 / Z88 Forums

TMAOne wrote: ↑Tue Jan 23, 2018 12:20 pm
How's the board coming Lardo? I'm on pins and needles here,...
Ian

Sorry for ‘going dark’ for a while - been rather busy trying to sell a house and pack and not get REALLY angry with the conveyancing solicitors who it turns out are completely inept.

Any way I just need to connect the switch and battery and I can test! Fingers crossed that will be this week. And that I have not bodged somewhere...

I've moved the posts discussing the direction of current flow to their own new thread: Direction of current flow.

Mark

Well I finished the assembly (finally) but sadly it does not work. I get nada.
I checked the resistance as per the pretest checks and got just over 1000 ohms.
The batteries are fine.
The LED is fine.
I get power to the board when switched on.
When I jumper pins 1 and 11 the LED does not glow.
When trying the tape recorder playback the LED does not glow even when playing a known good tape at a volume I know it loads at.
Argh. It must be a Monday.
Maybe someone else should have been entrusted with the only PCB?

Some photos in case anyone can spot any obvious gaffs?

You may have some connections that need to be checked for good soldering. Use a magnifier to see if they are soldered properly
(no cold soldered joins), check for shorts also with your wires connecting on the board.

You should check continuity between solder points. I don't know if you remembered that there were a couple of broken tracks that were needing to be jumpered. I sent an image showing the places where I knew for sure that the tracks were cracked.

sirmorris wrote: ↑Tue Jan 30, 2018 5:59 pm You should check continuity between solder points. I don't know if you remembered that there were a couple of broken tracks that were needing to be jumpered. I sent an image showing the places where I knew for sure that the tracks were cracked.

You did indeed! I had looked at the board and it looked like they had been sorted and thought no more of it. However... Doubtless when my ham fisted soldering occured I undid some of your fixing. Having done some continuity testing I found this:-

Two dodgy areas.

The lower one is one of your fixes and should be easy to deal with.

The upper one is definitely mine. What is the best way to fix this? Jumper directly from the left hand pin (1) to the dodgy pin (2) or try and attach it closer to home? Note that pin 1 to 3 and 4 is fine.

For short sections of broken / cracked / missing tracks, unless the track is too thin, I normally solder on a cut to length off-cut resistor or diode lead. That is, across the break. Tin the tracks (carefully), tin the wire. Then hold the wire in place with a screwdriver, while heating with your iron.

If the track is too thin, or too fragile, then I use insulated wire to link the two nearest component pads/connections.

Mark

I have fixed the two issues. And although it doesn’t look pretty I now have continuity where I should. Ignore the fact that it looks like my fixes are short circuiting. - they are not as the jumpers are sat above the board.

I have tested every pin for continuity and every pin for shorts and all appears ok.

I am still not getting anything if I jumper pins 1 and 11. I am still getting about 1000 ohms for the resistance test.

What voltage should I get at the board when it is switched on? Assuming that tells us anything?

About +1.5V between gnd & + terminal, about -1.5 between gnd & negative terminal. About 3v between + and -. Elsewhere? Who knows

Have you had a close look and checked for shorts anywhere? I'm a little concerned by the left-most signal wire in the picture above. If signal touches the ground plane then you won't see any signal.

I have checked pretty much every pin for shorts but I will double check the leftmost signal connections thanks.