Assembly: Voltage Check IC1 Gnd to +12V

tt302 · Post by **tt302** » Mon Oct 22, 2007 3:11 pm

Assembling power supply: Using 9volt battery (9.0 volts checked with multimeter), the voltage check across IC1 GND pin to + 12V pin, gives 8.5 volt (not 9.0 volt). Is this O.K.? Note: All The voltage regulator checks are good at 4.9 Volts.

Thanks

Post by **brentp** » Mon Oct 22, 2007 3:15 pm

That should be fine. You are likely measuring the voltage drop across the diode in the power supply, which is normal.

Regards,

luke6040 · Post by **luke6040** » Sun Jan 27, 2008 6:30 pm

hey i have just started doin my kit and am reading more or less the same differance with a 9v battery.
Just want to double check that this is ok?

Thanks,
Luke.

MartinM · Post by **MartinM** » Sun Jan 27, 2008 10:52 pm

That's perfect - tt302 was also using a 9v battery....

CurlyBen · Post by **CurlyBen** » Fri Feb 01, 2008 3:40 pm

I've just started assembling a Megajolt kit. Bit rusty on the soldering but it came back pretty quickly! I've assembled the power supply components but on testing the IC1 pins are showing 18.5V (supply is 12V). I've not bridged any pins and all the solder joints seem secure - all the 5V points read 4.99 or 5.00V (though I'm not sure my £5 Maplin multimeter is that accurate!). Any ideas on why I've got the 18V? My first thought was a bridge adding 5V in but that would only account for 17.5V.

Post by **brentp** » Fri Feb 01, 2008 4:38 pm

Are you using a wall adapter to power your unit? Some of these units will measure higher than they advertise- especially if they don't have built-in voltage regulation. Try measuring the voltage from the power supply directly. If it equals what you're measuring on IC1 then you should be OK.

You can also test with a 9v battery- the low current capacity of the battery will be more forgiving if you have a build error.

Regards,

CurlyBen · Post by **CurlyBen** » Fri Feb 01, 2008 4:53 pm

Yep I am using a wall supply, but I've tested the output of that and it's 12 and a bit volts. A good 6V under what I'm measuring on the board. Pin 8 to pin 9 shows 18.5V, Pin 8 to the +ve input is about 12V, and to -ve is 0V. Pin 9 to +ve is 18.5V, and to -ve is 0V. Something doesn't add up but I can't figure out what! I'll try and dig out a 9V battery and see what happens with that, unless you have any other ideas?

Post by **brentp** » Fri Feb 01, 2008 5:06 pm

It may be that your wall adapter is outputting unfiltered DC- chopped DC voltage converted from AC. The filtering capacitor of the MJLJ smooths the voltage peaks, which results on a higher voltage reading on your meter.

If you power the unit with an actual 12V battery and you measure 12V where you measured ~18v using the wall adpater, this is likely the cause. If so, then you are 'ok'!

Regards,

CurlyBen · Post by **CurlyBen** » Fri Feb 01, 2008 5:12 pm

Yep just checked using a 9V battery and it comes up right with that. If only I'd paid slightly more attention in my electro systems lectures I might have figured that out myself!
Cheers
Ben