as described in my fm-threat i built the psu unit today. but i thought it wouldn’t be good to put this question into it
i build scheme 2 of ±12v exactly as told on the page (with 2Diodes and 1x15V transformer), now i’ve got the half part working when i measure 12v+ vs ground the power is ok at 12v, when i measure 12- vs ground there are about5v more, when i change the pinning of the 7912 i/o there is 24v … i don’t understand this, exspecially because the 12+v is exactly the right amount. but now there is something else which confused me completely, when i measure at ac scale, i don’t get zero. Measuring - vs ground is ok, and +vs- is also ok, so it seems as a ac circuit exists át 12v+ … i don’t understand that, i have changed the diodes and the 7912, checked the circuit nearly 10 times and i don’t have an idea what can cause that.
the - of the small elko behind the 7912 is connected to the input of the 7912, and the output of 7912 to the ceramic 100nf and also the - of the big 4700uF elko
i also thought about an 79 pin issue, but also changing input and output does not change much, but the above mentioned volt change at 12v-, the ground pin must be correct!
i made some photos and tried to mark where the circuit is, but i’m not sure if you can recognize all details. it looks real bad because i just changed the diodes on the back quickly and the i/o pnning of 79xx to see if they cause the error
the solderings in the middle rectangle is the 9v transformator
i checked the circuit a few times but i have no idea where the problem could be. so i’ll buy a 2x15v transformer today and build the circuit 1 with 2 tranform :
I once had a 7812 wich gave 15V while measuring, but proper 12V under load…first i thought it might be labeled wrong, because i would not expect such a round voltage from a malfunction…
thank you very much for your replies, that could be the issue i was looking for … so can you tell me if the input or the ouput goes to the 12v- line? so that i wan’t solder it wrong the next time
it is incredible! i rebuilt he hole circuit working excact and not so dirty as in the first one … i changed the 78xx and 79xx, 10 and 100 caps, the diodes and i’ve got exactly the same problem! the 12+ V vs ground is ok, bt the 12v- vs ground gives me about 24v
i gues the 7912 vom reichel are not working … i don’t know what else can be the problem. i used 3 different of them but nothing changed. i took vacation for today, that i can do that and the parts for building the 2 transformer version have not jet arrived :'(
it gave me 17v after i changed the pinning of i/o in 7912 at the first time
“when i measure 12- vs ground there are about5v more, when i change the pinning of the 7912 i/o there is 24v”
after i read the threats i thought i crashed the 7912 when i changed the pinning, because doc told me, that he got also 17v after he wired the 7912 wrong.
now i checked the pinning of the 7912 before carefully and did not rewire it … i have following pinnings at 7912
ground to ground,
input to 12v- output (- of the small elko)
output through the small cap to - of the 4700uF elko
bugfight told: "is the decoupling electrolytic cap backward on the 7912 input?
the + side should go to gnd (which may be confusing) and the - side to the i 7912 input…"
ps: i deleted the first pics, because of thir size, i’m not a fan of big pictures, but i thought you wouldn’t see anything if i make them smaller … i’ll try to mak them more shape and smaller next time
thank you guys for helping myself in this noob problems … so i took my last 7912 which i had laying here without any usage before and switched the i/o as you told me johnybee (as in the drawing but i/o switched)
the consequences are not far away from the issues before
when i measure 12v+ vs ground the power is ok at 12v, when i measure 12- vs ground there are about5v more, when i change the pinning of the 7912 i/o there is 24v … i don’t understand this, exspecially because the 12+v is exactly the right amount. but now there is something else which confused me completely, when i measure at ac scale, i don’t get zero. Measuring - vs ground is ok, and +vs- is also ok, so it seems as a ac circuit exists át 12v+ … i don’t understand that, i have changed the diodes and the 7912, checked the circuit nearly 10 times and i don’t have an idea what can cause that.
