Author Topic: Please help power supply dead 110V to 24vdc 5vdc (Read 4039 times)

administr4tor · « **on:** February 21, 2020, 01:01:29 am »

hello,
this printer power supply is dead,I cant figure out with my limited knowledge that why the lower output part of circuit is not getting any DCV. I have measured voltages across transformer and I found 24v but nothing on the other side of transformer, please have a look at pictures, any help is kindly appreciated. thanks.

Thank you

techie1234 · « **Reply #1 on:** February 21, 2020, 01:11:35 am »

Transformers don't pass DC from one side to the other - only AC. Are you measuring AC on both sides of the transformer?

ArthurDent · « **Reply #2 on:** February 21, 2020, 01:25:16 am »

That is a switching mode power supply (SMPS) and the connections on the primary side of the transformer could have line voltage on them as well as 160VDC to 400VDC (read the voltage rating on the big capacitor) If you don't know what you're doing, poking around can be very dangerous.

TheMG · « **Reply #3 on:** February 21, 2020, 01:35:14 am »

Check the fuse. If fuse is ok, start checking capacitors with a capacitance/ESR meter (most do not need to be taken out of circuit to measure).

Most common cause of a no-output condition on a SMPS if the fuse is intact is one or more bad capacitors especially the smaller ones on the primary side.

Much of the troubleshooting on these things can usually be done without ever applying power, as most SMPS faults are either something shorted (resulting in blown fuse and other components sometimes releasing the magic smoke) and bad capacitors.

Miti · « **Reply #4 on:** February 21, 2020, 02:14:17 am »

Be very careful when repairing a SMPS if you don't know (exactly) what you're doing, you may get hurt badly!

That being said, what's the controller chip U1? Don't measure across the transformer windings with a multimeter, it doesn't make any sense, and definitely don't use the oscilloscope in the primary side.
How old is the power supply? The first thing I would check, beside the fuse, would be the three capacitors on the primary side, above the transformer in the second picture. In particular, the one on the supply pin of the controller.

administr4tor · « **Reply #5 on:** February 21, 2020, 03:10:02 am »

Measuring AC shows on 0 VAC across any two selected pins on yellow transformer. only in DC mode is showing 24VDC as shown in picture.

administr4tor · « **Reply #6 on:** February 21, 2020, 03:11:53 am »

I only check voltages on yellow transformer and i did not touch/attempt to measure the other visible copper wire transformer next to AC input and CAP.

administr4tor · « **Reply #7 on:** February 21, 2020, 03:25:12 am »

hello,
U1 is following chip

Also, i cant find the fuse, where is it?

administr4tor · « **Reply #8 on:** February 21, 2020, 03:29:40 am »

I found following voltages on capacitors please have a look,

RomDump · « **Reply #9 on:** February 21, 2020, 04:26:39 am »

Quote from: administr4tor on February 21, 2020, 03:25:12 am

hello,
U1 is following chip

Also, i cant find the fuse, where is it?

I would be careful messing around fixing SMPS. It may be cheaper just to buy a replacement SMPS for your printer if it is that valuable.

With some googling U1 appears to be FA5501AP, (I have attached the Datasheet). FS1 appears to be the fuse. I would expect more than 24VDC on the primary side of the 150uf Cap.

The datasheet has an example circuit which resembles the first half of your circuit.

kripton2035 · « **Reply #10 on:** February 21, 2020, 07:12:21 am »

repairing methodology for smps.
https://www.repairfaq.org/sam/smpsfaq.htm
as noted above, please be aware that these voltages can kill you !

I also very doubt of only 24V dc on the 150uF 400v capacitor : it should be around 150V DC for a 110v mains supply.

Miti · « **Reply #11 on:** February 21, 2020, 01:52:17 pm »

Quote from: RomDump on February 21, 2020, 04:26:39 am

With some googling U1 appears to be FA5501AP, (I have attached the Datasheet)....
The datasheet has an example circuit which resembles the first half of your circuit.

I doubt, that chip is a PFC controller. The chip is ID13301 apparently but I can't find a datasheet.
The fuse is FS1 and if that is good, start by replacing the three smaller capacitors in the primary, the 100uF first.
If the cap on the supply line of the controller goes bad, the chip can't start.

TheMG · « **Reply #12 on:** February 22, 2020, 03:31:28 am »

The blue component you identified as a "varistor", is in fact a capacitor, it's there for EMC reasons.

The component you identified as a MOSFET is simply a dual schottky diode in a TO-220 package. Very common to see these in SMPS. It's the secondary rectifier diode (note how the two outer pins are inter-connected, effectively paralleling the two internal diodes).

I think it would be wise to set this repair project aside for a bit and brush up on your electronics knowledge particularly when it comes to SMPS theory of operation and typical design characteristics.

Haenk · « **Reply #13 on:** February 22, 2020, 11:21:28 am »

You did notice, that it has an external on/off function, did you?
Just connecting the PCB to mains will not fire up the PSU - you will have to activate it via that on/off line. (to ground? to 24V? resistor to gound? - You should explore the connector, or maybe someone has an idea).
And as already said - this PSU could easily kill you. Even when it has been disconnected from mains before. Not kidding.

administr4tor · « **Reply #14 on:** February 22, 2020, 06:39:57 pm »

hello, i measured more voltages, please have a look..

viperidae · « **Reply #15 on:** February 22, 2020, 07:14:39 pm »

By the looks of it, you need to do something with the pwr on/off pin to turn the triac on.

timenutgoblin · « **Reply #16 on:** February 23, 2020, 12:57:29 am »

Near the top of the PCB, I can see a green-coloured component glued to the common mode choke. Is that a thermistor? Could it be open circuit or measuring high resistance? The O.P. measured 20Vac at the input of the bridge rectifier which may indicate a fault in the primary side of the PCB.

shakalnokturn · « **Reply #17 on:** February 25, 2020, 10:14:22 am »

You apparently don't know enough to be making live measurements on this, however those who survive learn.

As previously mentioned by Haenk and others, there's a On/Off control, the best would be knowing how this is controlled and testing accordingly.

My bets are on a failure of that part of the PSU rather than the rest.
If you don't know how the On/Off is controlled (via host computer's USB 5V or seperate standby supply in printer?) you can check the supply by shorting A1/A2 power pins on QT1 triac.

If your secondary voltages appear either your lacking the On/Off control voltage, or that portion of the PSU is defective. (QT1, R3 to R7, PC2, R1, R19.)

timenutgoblin · « **Reply #18 on:** February 26, 2020, 07:20:43 am »

There are 2 things that I've learnt about Switch Mode Power Supplies:

1) They usually require an external load to be applied to the output rail(s) for them to operate. This is especially the case with some ATX power supplies found in computers. Some ATX power supplies need to be connected to a HDD for them to operate.

2) They sometimes require an external signal to enable or disable them such as your SMPS.

As shakalnokturn suggested, try shorting the 2 pins of the triac QT1 that he refered to. Doing this should result in the 110Vac being applied to the bridge rectifier.

transistor12 · « **Reply #19 on:** April 07, 2020, 07:29:56 pm »

Need to start externally. At output terminals there written PS_ON , look carefully .

administr4tor · « **Reply #20 on:** May 01, 2020, 03:25:35 am »

Quote from: transistor12 on April 07, 2020, 07:29:56 pm

Need to start externally. At output terminals there written PS_ON , look carefully .

how do i start it externally?

administr4tor · « **Reply #21 on:** May 01, 2020, 03:36:28 am »

aqibi2000 · « **Reply #22 on:** May 01, 2020, 08:01:30 pm »

Ps on/off via a 300’ohm resistor goes to the anode of the optocoupler, therefore this needs to be connected to some form of power source.

If you have like 3.3/5V on PSA THEN this would be the right place to short it to.

asis · « **Reply #23 on:** May 01, 2020, 08:24:59 pm »

Hi.

"If your secondary voltages appear either your lacking the On/Off control voltage, or that portion of the PSU is defective. (QT1, R3 to R7, PC2, R1, R19.)"

Here are all the answers.

If you are not sure of your actions, apply power through a 40-60Watt household incandescent lamp.

http://www.cosmo-ic.com/object/products/KMOC308X.pdf

GT1 triac MAC8NG

Vladimir

asis · « **Reply #24 on:** May 01, 2020, 09:13:40 pm »

More specifically.
You must have somewhere an autonomous power supply that provides current through the emitting diode of an optocoupler.
It can be a USB cable connected to the printer or a built-in functional autonomous source in the form of a ~ 3V battery.
Which printer is that?


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Author Topic: Please help power supply dead 110V to 24vdc 5vdc (Read 4039 times)

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