Power Supply problems and power reg questions

[ricardo]

Stop press...  For a 7815 to output more voltage than it's input is not reasonable. Either one of two things is going on,
A) Something externally is dumping current/voltage into that PS output.
B) Your measurement is not reflecting accurately what is going on.  +18V on the unregulated input is marginally low. IIRC the basic 7815 had something like a 3V drop out so 18V is about the minimum to support 15V output, but this does not remotely explain an output higher than the input...  You may have stumbled upon free energy, you can use to make a perpetual motion machine.  8) 8)

Hanfri, please check the pinout for the 7815 on the datasheet.

Then check it meticulously with your PCB.  Draw up your circuit diagram and check each node for DC resistance to each expected component connection.  Check off each node as you do this.

Then check DC resistance between the pins on the 7815 & the rectifier & capacitors on the transformer.

It looks like you have IN & OUT mixed up.  This might have killed both 7815 & 7915.

 

[ruffrecords]

Can you post the PSU schematic just so we can see what we are talking about?

Cheers

Ian

 

[dirtyhanfri]

Hi

First of all; I etched a hand-drawn pcb for a power supply using lm317-337 and it works nicely, now I will start checking the EQ.

I've uploaded the Schematic and the Pcb layout, as I said, they're part of the Neeno pdf document about the SSL9k preamp. I've built a pair of these in the past year with good results, but for some reason this time it didn't work... BTW, this time I wasn't using the +48V section.

The board is a bit canibalised right now, home etched and so many replaced comps, a pair of traces are broken. So I will go with the new psu and give a new try to this when my photosensitive boards arrive in Febraury. It became personal...

Ricardo thanks for the tips. I'm almost sure I was not mixing Vunreg and Vreg pins on the regulators.

Thinking about it today, I realized the only components I didn't replace at all were the 100nF polyester caps (C6, C7, C8 & C9 in the schematic). Maybe the wrong oriented cap (C2) damaged any of the other caps in any way so it made no longer propperly work the psu?

 

[RuudNL]

The copper layout is 'as seen through the PCB'.
If the copper layout seen from the copper side is identical to the picture, the orientation of the regulators is wrong.

 

[dirtyhanfri]

We have a winner...

I have to apologize everybody who answered here.  Really sorry for the lost time.

:-[

 

[CJ]

no need for apology, the Lab is all about tracking down problems and sometimes the problems can be tricky,

and everybody learns new stuff when different problems are solved,

 

[hitchhiker]

Mr J  just gotta say HAPPY NEW YEAR! 

 

[CJ]

Happy New Year!

2013-year of the transformer-  ;D

 

[JohnRoberts]

I am a little disappointed that the 7815 was allowed to beat us.

Circuitry is supposed to be our biotch.

JR

 

[ricardo]

Hanfri, please check the pinout for the 7815 on the datasheet.

Then check it meticulously with your PCB.  Draw up your circuit diagram and check each node for DC resistance to each expected component connection.  Check off each node as you do this.

Then check DC resistance between the pins on the 7815 & the rectifier & capacitors on the transformer.

It looks like you have IN & OUT mixed up.  This might have killed both 7815 & 7915.

I'm gonna claim this would have pinpointed the problem if Hanfri had bothered to do so.  8)

 

[dirtyhanfri]

I'm gonna claim this would have pinpointed the problem if Hanfri had bothered to do so.  8)

Yes, actually you should be the winner  ;D

Well, I learned a few things with this: Some theory about Power supplies, To double check the orientation of the paper when insolating the pcb's, and to think a bit more before posting here

Anyway, have a nice 2013