It didn't work anymore!

More comprehensively, I completed the kit, plugged it in and all the LEDs lit up (as far as I could see). Awesome! I thought, so I turned it off, unplugged the power supply (RadioShack 24v, 1A), then went to answer the phone, came back, plugged it all back in again and...nothing.

Checked the solders and while some are are little "chunky", nothing looks to be shorting out.

Also all polarities look good.

Before I re-solder everything can anyone recommend checks with a multimeter or current tester that might isolate a problem? I'm a relative newbie so could easily be missing something very obvious.

Cheers.

First, make sure that your power supply provides a *regulated* 24 V DC. If it does not say regulated on it somewhere, it may be putting out well over 24 V DC-- make sure that there's no significant AC component, and make sure that it's very close to 24 V.

Check to see that there's 24 V DC across two pins of the switch. Then, check the voltages at R115 and R116. One end of R115 should be 24 V above one end of R116. The common point between these two should be at 12 V, halfway between them.

Thanks for the quick response, I'm getting voltage readings from the switch way above 24V and my readings on R115 and R116 don't tally with any number you gave me (they are very low) so I think it's the power supply, I'll replace it with a regulated one. Will I need to replace any components having used an unregulated power supply?

One lesson I've learned for my next build is to use a finer gauge solder, it's much easier to see good solders when there is less "stuff".

BTW are you a current Dr. Who fan? Big show this week...new Doctor!

Many Thanks

Eeeeeek! Exactly what do you mean by "way above 24V?"

Using an unregulated supply puts all of your chips, LEDs, and sensors at risk of destruction by overvoltage and/or overcurrent.

R115/R116 is a strict divide by two, so the common point between them should be at 12 V. If it isn't, there's probably now a short circuit on your board, so it's likely that at least some damage has taken place. You'll need to take things *very* slowly and carefully at this point.

Do you have a way to test the LEDs on board, for example a multimeter with a diode/LED test mode, or a 3V battery?

Across J400 and S400 I get up to 35V, I'll test individual LEDs/components a bit later to see what damage might have been caused.

Thanks for all your help and Happy New Year

At 35 V, you've exceeded the absolute maximum rating of the chips-- they are probably the component that has failed, and you should probably not apply power to the board until you have at least replaced those. If you're lucky, the LEDs are okay, though.

Hi,

The new power supply showed up and the board works very well (lessons learned), there is one glitch however, the LEDs at D402, 404,406,408 have their default (rest) state as on, they react along with the other LEDs but their behaviour is reversed (they are on when all others are off). I imagine I reversed something, do you have any suggestions?


Thanks

Wow-- It's working except for those four LEDs? Thank goodness!

If four LEDs in a set of five are misbehaving, it's usually because the fifth LED in that set is damaged-- replace that fifth LED.

D400, replaced it and the board works perfectly.

Thanks very much.