Harnessed SMPS from a printer.

Thread Starter

lubnaan90

Joined Jan 13, 2010
198
Hello Members,
I just harnessed an SMPS (Switching Mode Power Supply) form a printer of mine which was lying useless for ages. The PS (PowerSupply) look in great shape but i just can't get it working properly for some reason. On the casing of the SMPS (see attachment), it says Input: 100-240V 50/60Hz 0.6A and Output: 24vDC 1.2A, the Output of the the board has 3 pins GND, 3V & VO.

Now the fun part, when i supply Mains (AC) to the SMPS & check the output, all i get is 7vDC across GND & VO, I tried applying load across GND & VO, still the same thing, the Output voltage not more then 7vDC. So whats up with the labeling of 24vDC as the output on the SMPS casing?

Any help will be deeply appreciated.
Best Regards.
 

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gerty

Joined Aug 30, 2007
1,267
Switchnode power supplies should always be tested with a load connected... It won't hurt anything, just needs a load to stabilize ..
 

AnalogKid

Joined Aug 1, 2013
8,157
Did you try it in the printer to make sure it worked in its native application?
What are the markings on U1, the control chip on the bottom of the board?
What are the markings on the switch transistor Q1?

ak
 

Thread Starter

lubnaan90

Joined Jan 13, 2010
198
Did you try it in the printer to make sure it worked in its native application?
What are the markings on U1, the control chip on the bottom of the board?
What are the markings on the switch transistor Q1?

ak
In its native place, it worked well. The only reason the printer was wasted because it's firmware was bricked when i tried to make it use a refilled ink cartridge, DAMN CHEAP CANON PRINTERS!!!!
IC1 is DAP08
transistor Q1 is p4nk60zfp
 

bertus

Joined Apr 5, 2008
20,108
Hello,

Do you still have the printer?
Is there some other connection to the printer (there are three pins on the header) ?

Bertus
 

ian field

Joined Oct 27, 2012
6,539
Hello Members,
I just harnessed an SMPS (Switching Mode Power Supply) form a printer of mine which was lying useless for ages. The PS (PowerSupply) look in great shape but i just can't get it working properly for some reason. On the casing of the SMPS (see attachment), it says Input: 100-240V 50/60Hz 0.6A and Output: 24vDC 1.2A, the Output of the the board has 3 pins GND, 3V & VO.

Now the fun part, when i supply Mains (AC) to the SMPS & check the output, all i get is 7vDC across GND & VO, I tried applying load across GND & VO, still the same thing, the Output voltage not more then 7vDC. So whats up with the labeling of 24vDC as the output on the SMPS casing?

Any help will be deeply appreciated.
Best Regards.
Those things can get over excited if you start poking around with DMM prods!

Start by checking the small electrolytic, if you can find a foil type with the same capacitance that will fit in the space, use that. Better yet; MLCC capacitors have impressive capacitance in tiny size - an amazingly low ESR.

The small electrolytic usually smooths the running Vcc for the chip that comes from an extra winding on the primary side, in the simpler blocking oscillator types, it also provides the bias for the photo-transistor in the regulation opto-coupler.

Its worth checking the resistor values - especially the higher resistance ones.
 

Thread Starter

lubnaan90

Joined Jan 13, 2010
198
Hello,

Do you still have the printer?
Is there some other connection to the printer (there are three pins on the header) ?

Bertus
No, i don't have it anymore, i just made a use of the Scanner lamp & threw everything else. As for the connection, i remember very well that across the PS & the main board existed only three wires, no other connection whatsoever.
 

ian field

Joined Oct 27, 2012
6,539
It says 3v on the pcb, you can alter the out put, by changing the feedback resistors to the opto-coupler, it look like uses a Tl431 zener,
There are two outputs, what is the other giving out?
Obviously; first check the TO92 in the corner is a TL431, if it is, trace where its voltage setting resistors go - they should be the 5-band 1% types.

If it senses the 3V rail, take out the top resistor and calculate the value of a new one to sense from the 24V rail.

If including a preset pot - it should go in the lower part of the voltage sensing divider, if the wiper goes intermittent - it'll intermittently turn the wick up till something blows with the pot as the upper resistor.
 

ian field

Joined Oct 27, 2012
6,539
They're surface mount on the track side Ian, R54,55, my bet is the big zener Zd5 across the output capacitor.
If it has a big zener across the output capacitor - its a cheap & cheerful crowbar job.

They fail pretty much short circuit - if it was allowing 7V to turn up, there'd be smoke.

Are you certain about those component numbers? - the resistor next to the connector looks a bit more quality than run of the mill production quantities.
 

AnalogKid

Joined Aug 1, 2013
8,157
The +24 is the main output, straight off the transformer through a diode and a filter cap. The 3VO comes from Q51 (SOT-23 package) through resistor R58 on the top side. Looks like a very low power output, if it is in fact an output. Could be an enable input.

Also, the 7 V reading could be meter confusion if the main filter cap is open. What does it read on an AC scale?

ak
 
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