First linear PSU troubleshoot help

[snaper]

Hi Guys,

After avoiding the DIY linear PSU topic for years, recently, I've decided to build my first one.

This is the schematic (based on PCBGrinder's VariPSU) :

And this is the board :

Ironed, etched, drilled, soldered.
The transformer is a 2x17V 0.38A toroid.
The wired the transformer and did the first start.

Pros :

- no smoke
- no explosion
- no sparkle or "lightning"
- generally, everything looked fine

Cons :

- I've got only +8,5 and -10,5 Volts
- the transformer gets really really hot in a really short time

What could be the problem? This PSU should drive only a simple, 1 IC based gain stage, nothing more, 0.38A should be more than enough.

 

[pucho812]

how are you  mains wired?

I would confirm you have your transformer correctly wired on the primary side for the correct mains voltage of your country.

 

[JohnRoberts]

Transformer getting hot is not a good sign.

You need to share the voltages at nodes around the circuit.

JR

 

[snaper]

I'm in Hungary so AC in is 220-230 V.
Transformer primary has 2 red leads, one wired to N on the AC plug, the other is wired to L (thru a switch and a fuse)

 

[snaper]

DCs after the KBU are +9.5 and -12.5

Weird...

 

[radardoug]

Well, the first hint is the unequal voltages. Lower voltage means something is drawing current on that side OR faulty diode in the bridge. Look for other things getting hot, that means they are dissipating power.

 

[snaper]

Can I measure somehow the ouput of the transformer?

 

[radardoug]

Measure the a.c voltage where the transformer meets the circuit board. Then DISCONNECT the transformer and measure again. If the voltage is very different then you have a load on there. But you already have measurements of the d.c. that are very different.

 

[snaper]

Measured the transformer out and it is only 6V...
Dang, that is not a good start for a PSU building :S

 

[radardoug]

Did you measure it with no load? What are the Transformer specifications?

 

[snaper]

Yes, still 6V/rail ...

This is transformer :
https://www.hestore.hu/prod_10028816.html

Could it a bad fuse?
The fuse is the only what was not brand new.

 

[snaper]

Tested it with a different, not toroid, but similar trafo, works.
But, I need the other trafo for something else, so I have to force this toroid to work somehow.

 

[snaper]

This is the wiring :

I've joined the two black wires together, before the PSU board.

Another info, what is I think important, is the that I've found the secondary cables a bit weird.
The were not cables, but only 1 single wire, not so thick, around 0.5 diameter.
Is it OK, or I've received a bad transformer?

 

[Evertide]

Measure the transformer .

Resistance - mains high ,  secondary  2 times low ...

Connect mains  -  measure the 2 secondary  ( about 17 volt )

 

[Evertide]

17 volt between the 2 green and also between the 2 black

 

[snaper]

I think I've possibly found the problem, havent checked yet.
I've used extra wire to extend the secondary cables, and I used one cable for the two black wires...so joined them into one wire

 

[JohnRoberts]

Check that 1000uF caps are inserted correct polarity.

JR

 

[snaper]

Checked every component, no luck.
No I'm absolutely confused.

I'm sure, I messed up the wiring, in the secondary side, but can't find any proper info about this Indel trafo, only dimensions and stuf like that.

I have four wires.
2 green, 2 black.

For me, this means that the two greens are the 17V wires.
But now, after checking the trafo again, 1 of the green wires has a thicker orange silicone on it, and one of  the black wires has this silicone as well...

 

[[silent:arts]]

Check your secondaries.
(Disconnected) you should read some low ohms between both green cables, and some low ohms between both black cables.
You should read nothing between any green to any black.
If all this is the case your connection is wrong, corrected it like in attached picture.

 

[home_listening]

I don't see anything on the product website to indicate you should tie the two black wires together. Check the phase of the secondaries (all 4 disconnected) with a scope. If each secondary winding has its own colour then you would need to tie a green and a black together for the CT.