SSL 9K PSU Problem

[The Frizzle]

Hi!

I'm currently building a unit with four standard SSL 9k chanels(not the 500 series, the original one).
To get the 15V and the 18V, I builded two PSUs.
The 15V one with LM7815 and LM7915 regulators and the 18V one with the LM7818 and LM7918 as in the original BOM.
Now the 15V PSU is working fine, every rail delivers the voltage it should.
But when i add the 18V one in series, the fuse blows. I have a 315mA slow blowing fuse. It does not blow right away, it takes like 3-5 Sekonds.
At first, I replaced all the regulators with ones from a different shop, but that had no effect, same problem.
I'm still learning my way with electronics, currently i don't know how to debug that PSU.
Would be great if someone could point out what to look for. Do i have a shortage somewhere? Is there a specific method to find the problem?
What puzzles me, is that the 18V PSU is exactly the same as the 15V PSU, except one bridge rectifier is a different model and  the regulators are different ones as mentioned above.
I added a shitty quality webcam photo of the PSU, sorry no better camera around.
Please help me

Fred

 

[bruno2000]

I don't know what you mean by "in series".  Maybe if you could post a drawing of what you have, we could help you better.  If the fuse blows when you connect the 18V rails, it seems the fault would be in the 9K board, not the power supply.  Just a guess.
Best,
Bruno2000

 

[MikeClev]

Those heatsinks aren't touching each other or any other metal are they?

 

[The Frizzle]

Thanks for your replies.

@ Bruno2000
I did a drawing how I connected both PSUs to the toroid. Maybe i did this wrong?
The 9k boards are not connected yet, I don't want to risk them
I'm just testing with nothing connected. I turn it on, get no voltage reading at all and after 5sekonds the fuse blows.
So it must be either my wiring or a problem with the PSU?

@MikeClev
The heatsinks are not touching each other. At first i put the regulators on the case which made a nice shortage, so when i put them directly on the PSU, i was very cautious that the heatsinks did not touch anything.
Additionally i tested them, they are not conductive. The shortage was on the 15V board tho, so this did not destroy the 18v board.

 

[bruno2000]

Correct me if I'm wrong:
If you have just the +/- 15V supply connected, everything is OK, and you get +/- 15VDC from the outputs.
If you add the +/- 18V supply, the fuse blows after 5-10 seconds.
Have you tried just connecting the 18V supply to the transformer, and leaving the 15V supply board out?
Have you checked the bridge rectifier in the 18V supply?
Are you sure all of the filter caps are good and in correctly in the 18V supply (check for polarity)?
I'll check back in a bit.
Best,
Bruno2000

 

[The Frizzle]

If you have just the +/- 15V supply connected, everything is OK, and you get +/- 15VDC from the outputs.

Thats right

If you add the +/- 18V supply, the fuse blows after 5-10 seconds.

Thats right, too

Have you tried just connecting the 18V supply to the transformer, and leaving the 15V supply board out?

I didn't try that before, but i did now.
Guess what.. it's working! I get +18V, -18V and 44,5V.
So my wiring is bad?
But its a relief that it's working, thanks Bruno! If everything else fails, i can still do that three diode trick which lowers the 18V to 15
Do you know how to wire both PSUs to the toroid? Since i got two now, would be nice if both worked.

 

[bruno2000]

If you have just the +/- 15V supply connected, everything is OK, and you get +/- 15VDC from the outputs.

Thats right

If you add the +/- 18V supply, the fuse blows after 5-10 seconds.

Thats right, too

Have you tried just connecting the 18V supply to the transformer, and leaving the 15V supply board out?

I didn't try that before, but i did now.
Guess what.. it's working! I get +18V, -18V and 44,5V.
So my wiring is bad?
But its a relief that it's working, thanks Bruno! If everything else fails, i can still do that three diode trick which lowers the 18V to 15
Do you know how to wire both PSUs to the toroid? Since i got two now, would be nice if both worked.

Try wiring the 2 PS boards in parallel.  Left terminal of EACH board together, center terminal together, and right terminal together.  See if that works.
Best,
Bruno2000

 

[The Frizzle]

Your the man Bruno!
I was so ready to give this up but now it works!!  ;D
Thanks man! I owe you one.

 

[bruno2000]

Great!  Glad you fixed it.  I think you'll really like those 9K's.
Best,
Bruno2000

 

[signalflow]

Or you could set the whole thing up to run +-15V and not worry about the diode trick or a second supply.

my 2cents

-Casey