+-12V Problem

[stryd_one]

According to that schem, the elkos should have the positive terminal at the bottom, you've got them backwards...

http://www.midibox.org/dokuwiki/bipolar_12v_psu Second schem right?

[minya]

maybe he is the responsible person :D  8)

[stryd_one]

damn metalheadz ;)

[minya]

@stryde_one

yes they are ... the - lines of the elkos are below, so the + side should be on the top ... i think that ist ok. all elkos are build the same direction

[minya]

äääähmmm at the bottom ... i thought the strong lines in the scheme were the - of the elkos :D

[stryd_one]

Well I wasn't 100% sure myself so I googled it and...yep, they're backwards ;)

[minya]

waaa thanks that is  a great tip! but  watching at this wikipedia pic it shows that the strong line in schemes is the - of the elko ... also on the prebuild boards of smash tv ... so if you say i should turn all 4 elkos i will do that but i cannot believe  :o

[minya]

ps: the view of the pic of the wireing is turned around! so it's exactly mirrored to the upper view. the - o the elkos show alwas in the direction of the 79 ...

[stryd_one]

Yeh, when I look at the schem and how it should work, I'd say that the - of the elko should be on the bottom, so they aren't backwards...

I dunno man, I give up.

Told you that the bipolar transformer was the way to go ;)

[minya]

:o :D ??? ::) 8)

puh ... so i'm glad that i'm not the only one not having an idea what the problm can be :)

i guess i'll rebuild the hole circuit a third time and then with the rectifier and a dual transformer ... hoping that solves the problem ... but thanks for the try! i was real getting mad about that  :-X

[nILS]

Amazing how this pretty simple circuit tends to mess with people all the time :-) Let's hope your third build will work!

(Maybe someone needs to write a step-by-step 100% foolproof tutorial on that one [not gonna be me]) :D

[minya]

hehe

i hope the rest of the fm construction won't cause such problems for me :O

[stryd_one]

Amazing how this pretty simple circuit tends to mess with people all the time :-)

Who else has tried this design before?

(Maybe someone needs to write a step-by-step 100% foolproof tutorial on that one [not gonna be me]) :D

when it comes to the bipolar transformer, it's hard to go past northernlightx's thread...

[minya]

hehe

it's me again :D

10x 7912 and a few hours later i have built the circuit with two transformers and a rectifier after it .... the problem is still the same the 7912 gives me -17-18V maybe reichelt and hartnagel electronics haven't sold the best ones

+12v does work as in the first ones

i'll check the hole circuit in the next few days and hope it'll be just human missunderstanding  but for today i 'ts  enough  :o ::) 8)

[nILS]

[ x ] got pictures?

[minya]

looking from top the upper one is the 7812 the lower 7912 sry for bad quality of the picture  8) ::) :P

[minya]

can the elko caps be too big with 2200uF for double transformer version and 4400 uF for single transformer version

[Marxon]

Hi all,

 

i digged out this old topic because i had the same problem.

There was -17V on the 7912 output.

Finally it turns out that it was  increasing to -12V on load.

Maybe this info is usefull for somebody else.

 

Marxon