testing psu safely

[airmailed]

hi there,

i have a c64 psu and some others that i want to check with a multimeter (individual voltages coming from pins), i just wondered if i have to use the positive or negative probe of the meter or if it doesn't matter which probe i use to check the pins?

all the best

adam

[Screaming_Rabbit]

doesn't matter, it just shows you an other polarisation.

Greets, Roger

[airmailed]

thanks Roger,

i need to find out which are positive and negative pins on one psu, will the meter show the opposite polarity if i use the wrong probe? (like will it always show positive if i use the red probe for instance?)

all the best

adam

[illogik]

hi adam,

The C64 PSU has both AC(9V) and DC(5V) power. The AC doesn't have a positive/negative side, so it just measures 9V AC whenever you probe both pins.

The DC has a + and  - side ( "-" is ground here). The ground pin should be the pin in the middle of your plug. Put your black(-) probe there and with the other probe look for a pin where you get 5V. When you reverse the probes it will read -5V.

So if you don't have any clue which pins are which, just look for two pins that measure 5V or -5V--> when it's 5V you got the red probe on the (most) positive pin when it's -5V you got the red probe on the (most) negative pin (ground).

hope this helps, marcel

[airmailed]

thanks marcel i'll try that out..

the other psu is a +5 +12 -12 volts, using a 5 pin midi style connector, it sounds like your advice also applies well here, look for +5 and -5 then use the black probe on the (newly discovered) ground connector to find the +-12v pins

all the best

adam

[illogik]

hi adam,

yeah

just keep in mind that there is no -5V pin, you just read -5V when you put the red(+) probe on the ground pin (0V) and the black(-) probe on the +5V pin.

cheers, marcel

[kokoon]

excuse me but where did you get that combined PSU? that could be ideal for powering a MBFM? 5V DC and +12/-12 AC bipolar?