Electronics > Repair
Help repairing a switching power supply out of a Pioneer DJ Disc Player
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jmibk:
I have a switching power supply, that isn't working anymore. I'm shure, thats the supply, because i crosschanged it between two cd player units.

Here's the schematic of it (also available in the service manual of the device):

http://audiowerk.at/djm2000_power.pdf

The problem:
The whole unit isn't working, nothing happens (no display, no leds, nothing).
I checked the power supply:
- fuse F1 is ok.
- voltage on primary energy store cap c5 is ok.
- voltage on output is around 7v dc (instead of 12V) on all outputs. It moves 1V up and down on a Fluke 87/V
- there is a very low klicking noise, around 1Hz, i think coming out of the transformer (i had no chance to localize it).

Anyone an idea to get it back working?

I have a multimeter and oscilloscope here at the bench and a camera for pics, if anyone needs more information. I haven't troubleshooted a switching supply before.
mij59:
Prime suspects are C102 and C103, you could measure the ripple voltage, or swap the caps from the other unit.
SeanB:
Picture of top and bottom of board, though the most likely cause is a few capacitors on the secondary that have died, along with one or two small electrolytic capacitors on the primary side as well.
jmibk:
Hi,

1st, i checked the topic https://www.eevblog.com/forum/repair/focusrite-liquid-saffire-repair-help-needed!/, but it doesn't help in that case...

The pics of the board:





Here a few quick measurements:
yellow trace is output CN2: pin 6 to pin 1,2 (gnd)
blue trace is output CN2: pin 5 to pin 1,2 (gnd)

1) voltages, CN2, pin 3 open:


2) voltages, CN2, pin 3 shorted to ground:


3) i tried to capture the power on cycles of the supply. after 1,5secs i powered it on, it takes approx. 9 seconds to reach the final voltage ov 8 volts.


Check out the ripple, the clicking noise is exactly to frequency of that ripple. If I turn power off, the output takes around 1 - 2 minutes to reach 0V. All outputs measured open circuit.

I hope that helps - if not, i can do more measurements...
PA4TIM:
Probably dead caps. What I do in such cases is look up the datasheet of the controller. They write how it should work and the voltages on the pins. Start up sequence/conditions etc.

But in your case just take the scope and measure the ripple voltage or swap the caps first. The jumpy DMM reading probably is caused by that ripple.

When testing, many SMPS need a minimum load to work good.
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