high ac current

[whitelabrat]

I'm nearly finished with my amp4, or at least I thought I was. I've got just about everything attached except the six small transistors and LEDs. I haven't jumpered J5 or J10 yet too and I've had successful 9 and 5 volt tests in the past.

My dilemma. There is a lot of current running through the power transformer and I don't get any voltage from the 317's anymore. It would almost seem as there could be a short somewhere.

Any thoughts where I could have gone wrong?

[xenob]

How did you connect the trafo to the board?
(You do not need to connect anything from the trafo secondaries to GND, just AC1 and AC2)

[whitelabrat]

I have GND to the wall, and AC1/AC2 from the transformer. I get a good 20Vac when not connected. When connected to AC1/AC2 the house lights dimmed and the transformer buzzes. Not good!!! I've tried two separate transformers with the same effect. I've also tried without the GND connected.

I only see a few millivolts going over the 9v section. I would guess there is a short somewhere, but all the soldering looks good. Capacitor polarity is correct as well. I even carefully checked the polarity of D1. I'm stumped.

[xenob]

Can you post some pictures of your amp, the trafo and how you connected it?

[whitelabrat]

Here's a photo of the set up.
Workbench test

[whitelabrat]

On the transformer, the red and black go to the 110V at the wall. Not seen is a power switch so I don't touch anything that's energized! The green and yellow are 17Vac to the amp. The red from the amp goes to ground at the wall.

You can also see the red and black leads for the multimeter. I have it arranged to test the 9V output.

To folks reading this BE VERY CAREFUL!!! Do not touch the transformer or anything AC when plugged into the wall. Also use caution around the capacitors if they are charged up.

BTW xenob, I studied in Austria for a semester. Beautiful country!

[xenob]

Your cabling looks correct. Do you also use a fuse- does it blow?
Seems you have a short either at the trafo input section(fuse should blow), or in the 9v/5V section(regulators go in protection and do not put out any voltage).
If its in the 9V/5v section you should keep measuring the voltage while unpowering- it should then go to 5V while the caps are discharging.

To discourage you: one of my amp4s had a problem in the 5V section(amp rev 1.00)- I could not find the problem, so I build an external 5V supply.

Yes Austria is a great country, ecpecially for hiking or swimming- thats what I will do tommorow sunday-no DIYing.

[whitelabrat]

I attached a 1.75A fuse to one of the transformer secondaries. It blew immediately. If there were a short I would expect something to get hot, or burn up on the board, but everything seems good. Could it be the rectifier?

[whitelabrat]

More photos (hi-res)
Amp4 topside

Amp4 topside different angle

Amp4 bottom



The Nichicons are a bit big. I had them so I used them. I don't expect any improvement though. Shoulda got better input caps instead.

[xenob]

I still suspect there is something wrong the way you connect the trafo to the board.

Could you check with a "wall mart" dc power supply (between 15 and 25V) and connect it to the rectifier + and -, this way you can see if the amp 9V/5V section is o.k.