I shorted out the power transformer while recasing my dynahi. Help

[sbelyo]

I decided to recase my original dynahi.  I wired the ac inlet, then hooked up the transformer primaries (Avel Lindberg transformer) gray and bown wires went to hot, blue and violet went to neutral.  I got correct voltage on the primaries and secondaries when I threw the power switch.  I mounted the original psu in the case.  This is the board http://gilmore.chem.northwestern.edu/dynahipsbig.bmp 

I connected one pair of secondary wires to AC1 and the other pair to AC2.  The order went 1 to orange, 2 to yellow, 3 to black, 4 to red.  I threw the switch and the fuse blew.  Now the transformer primaries and secondaries are shorted when checked with a meter out of the circuit.  

What mistake did I make?  And did I damage the PSU.  How can I check it?

[johnwmclean]

The transformer is hooked up correctly, based on Avel Lindberg wiring colours. Did the windings or transformer come in contact with the chassis ground? I’ve had a transformer short to the chassis, took out the fuse but didn’t damage anything up stream.

[sbelyo]

Not that I can tell.  But it sure looks like it did.

[sbelyo]

Can I test the rectifier diodes on the circuit with a meter?

[spritzer]

Sure, that's not a problem.  Also isolate all the winding's and check for continuity.  Shorting though the barrier between primary and secondary is no easy task so I'd call it unlikely. 

[sbelyo]

I'd agree...  Both secondaries short to each other and the primary shorts to itself.  The primary does not short to the secondary.  I'm leaning towards the board.

I get a momentary short from -30 to GND and again on +30 to GND on the output.  The meter rings continuity for one second then shuts off.  Is that normal?

[luvdunhill]

I'd agree...  Both secondaries short to each other and the primary shorts to itself.  The primary does not short to the secondary

Define "short" within the largest precision available.

[swt61]

4 minutes ago, luvdunhill said:

Define "short" within the largest precision available.

You might as well just throw up a beacon! But I'll take the high road this time. 

[sbelyo]

For the secondaries if I check for continuity between orange and yellow its positive, if I check for continuity between red and black it's positive.  For the primary the gray and brown wires are twisted together and the violet and blue are twisted together for 115V operation.  If I check for continutiy between them it's positive.

I cant figure out how it got this way.  I'm not sure where to start looking on the board

Edited May 22, 2016 by sbelyo

[luvdunhill]

As opposed to negative ohms? You want to measure resistance.

[sbelyo]

4.8 ohms between the primaries and 1.1 ohm between each of the secondaries

[luvdunhill]

Ok, so what is the definition of a short then? Looks like your transformer and Ohm's Law came out unscathed.

[sbelyo]

oh ok, I had assumed it was shorted because I tested another Avel lindbeg transformer and it doesn't set off the continuity alarm.  I'll put it back in the case and see if it blows a fuse when it's not connected

Edited May 22, 2016 by sbelyo

[sbelyo]

ok, the transformer is good.  its back in the case and does not blow a fuse.  So it's got to be something on the psu board.  How do I test the rectifier diodes with the diode setting on the meter?  What value should I expect?

[spritzer]

Google that!!! 

[sbelyo]

ok, diodes all show 0.368 voltage drop and 0L in reverse.  These appear to be good.  What could be next, the electrolytics?

[luvdunhill]

oh ok, I had assumed it was shorted because I tested another Avel lindbeg transformer and it doesn't set off the continuity alarm

This is why I asked you to define what a short is. It seems you don't know what a short is, from your answer or how to measure one. Anyways, don't use the little beeping thing. Just measure resistance.

[sbelyo]

I got lazy and trusted the beeper.  The transformer is fine and the rectifier diodes seem ok, my measurements on them are above.  What should I check next?

[mwl168]

Did you try check things step by step?

First check the transformer is working properly without connecting to the power supply. Then check the power supply without connecting to the amp boards and see it outputs correct voltages?

[Mister X]

1 hour ago, mwl168 said:

Did you try check things step by step?

Why would you do that when you could waste your time testing the diodes by measuring the resistance!

[sbelyo]

Diodes all show 0.368 voltage drop and 0L in reverse.  These appear to be good.  The transformer checks out ok when not connected to the PSU board.  Fuse blows immediately when powering on with no amp boards connected.  What could be next, the electrolytics?

[Pars]

Check resistance on the inputs of the PS board (both for each winding input 1-2, 3-4) as well as to ground. Shorts (near 0 ohms) would be what you are looking for. Post pictures of the board. You didn't drop something onto the board that could cause a short when you were recasing it? I attached a schematic of the original dynahi PSU in case you don't have one.

Edited May 23, 2016 by Pars

[sbelyo]

Thanks Pars...  I'll check this when I get home.  I didn't drop anything on it that I know of.

[n_maher]

I'd also take the PS board out of the chassis for testing purposes.  Eliminates the chassis as the source of the issue and if something does go arcy-sparky or if you are sending voltage into the chassis or something weird it'd be nice to not inadvertently cook the amp boards.  Make sure you keep a fuse in the loop for all of the testing.

[Pars]

Good advice Nate. I hadn't thought about that, but maybe in recasing it you inadvertently made contact with one of the standoffs or something. Measuring all the inputs to ground should find if that is true or not. Might also ohm them to chassis.