odd voltages across IC 1

Johnadrianclark · Post by **Johnadrianclark** » Sat May 05, 2007 2:51 pm

am busy assembling board , have just completed power supply , came to check voltage across IC1 only to find this is approx 15 volts with a 9 volt supply , the 5 volt rail appears ok (4.99v) >>>>>>HHHHHelp , I think the only problem can lie with either the voltage regulator or ????the power supply zener. Any answers....all soldered connections appear ok ( ive built many things from kits before so feel pretty proficient with this side of things )
Cheers john

Post by **brentp** » Sat May 05, 2007 3:39 pm

Do you mean the voltages across pin 8 and 9? This should be the same voltage as the input to the voltage regulator (SAFE12V on schematic).

Are you using a 9V battery or a 9V power adapter? Did you measure the voltage coming out of the power adapter?

Double check your power supply voltage on either side of D2. On D2, you should measure the supply voltage opposite the band.
You can measure approximately this same voltage on the band side of D2 and band side of D3. Trace the power supply circuit and make sure you have the right components installed in the correct orientation.

Johnadrianclark · Post by **Johnadrianclark** » Sat May 05, 2007 4:04 pm

Yes across pins 8&9 on yhe board for IC1 , we are using a dc output from a railway train set and set the voltage from this to 9V using a meter . Im sure all the components are in the right way round , my brother is here out of interest in the project he is very experienced at assembly and has checked comonenets to ensure orientation also ....will try 9v batter and report back

Johnadrianclark · Post by **Johnadrianclark** » Sat May 05, 2007 4:06 pm

Yes across pins 8&9 on yhe board for IC1 , we are using a dc output from a railway train set and set the voltage from this to 9V using a meter . Im sure all the components are in the right way round , my brother is here out of interest in the project he is very experienced at assembly and has checked comonenets to ensure orientation also ....will try 9v batter and report back

Johnadrianclark · Post by **Johnadrianclark** » Sat May 05, 2007 4:10 pm

well who would have believed it but by using a 9V battery the voltages are all correct , perhaps you might explain why this happened ?

Post by **brentp** » Sun May 06, 2007 4:40 pm

The transformer you're using outputs unfiltered (chopped) DC voltage. Once it's filtered by the MJLJ's power supply it measures at a higher voltage, since the filter capacitors in the power supply supplies current during the 'troughs' of the chopped DC.

This website should help illustrate the concepts:
http://www.williamson-labs.com/powersupply.htm

Regards,