Replacing a transistor, your thoughts?

[Morsus]

Okay, hello everyone! My printer power supply stopped working. After checking the voltages they were not as expected. Checked all of the caps and they were all fine. Then after some searching I stumbled upon this video. This is the exact same board with exact same problem. The thing is that the video is on Russian and I can't understand a thing. But I see I could remove the transistor and place a jumper instead of it and replace one of the smd cap with whatever that element is. After using google translate on comments one of the comments said (maybe) that I could use a 2.6k ohm resistor instead of jumper on the transistor and it would be ok. Your thoughts on this fix? Would this work? Would it be dangerous? Thank you.

[Andrew F. Ali]

Re: Replacing a transistor, your thoughts?

For me the manufacturers designed a circuit to work their product. I would not do any modifications like remove a component and replace it with a bypass. The circuit must have been working before, I would NOT do any thing like that I would try to troubleshoot and repair the circuit keeping it original.

[cpt.charlie]

Re: Replacing a transistor, your thoughts?

It could be a TL431 adjustable voltage reference, very common in low cost power supplies.

[redwire]

Re: Replacing a transistor, your thoughts?

No money was saved in that youtube video lol - the guy shorts out transistor Q5, pulls R26A and then adds a 10k trimpot and manually adjusts for 30.6 and 10VDC outputs. A bit of a hack.

OP it helps to have a model # or something if you want to fix this decently.

Is this a power supply brick? Didn't see an opto-coupler for feedback.

[Morsus]

Re: Replacing a transistor, your thoughts?

First of all thank you all for replying.

For me the manufacturers designed a circuit to work their product. I would not do any modifications like remove a component and replace it with a bypass. The circuit must have been working before, I would NOT do any thing like that I would try to troubleshoot and repair the circuit keeping it original.

I understand this but I am not really sure where to find the same transistor as the original one.

OP it helps to have a model # or something if you want to fix this decently.

Model # of what exactly?
Transistor has only NX (or XN) written on it. And the board is ps-a186.

[Morsus]

Re: Replacing a transistor, your thoughts?

Alright, I got a bunch of random boards with all kinds of transistors physically similar to this one but the markings are totally different. I wanted to find a good enough substitute for it. But the thing is I can't even find the schematics for this one as I said Its written "NX" on it (if you rotate it so one pin is on top and two on the bottom). (Image 1)

Googleing got me these two manuals on identifying the smd transistors:
https://cdn.badcaps-static.com/pdfs/...66be3d5a35.pdf
http://www.s-manuals.com/smd/nx

In the first one I would have to believe that its actually written "XN" since "NX" is nowhere on the list.
On image 2 you can see that I marked an XN witch is a Zeener diode. And on the rest of the pictures you can see that NX is nowhere to be found.

And if you check the second link you can see that there is smd code "NX" but there isn't a package like the one I got.

I am running in circles here :S

[redwire]

Re: Replacing a transistor, your thoughts?

I couldn't find a schematic or service manual for this Canon printer power supply.

You would have to draw a partial schematic (hint: post good pics of both sides on the PCB) to figure it out.
Have you checked Q5 with a multimeter?

SMD marking codes are a guessing game, because so many possibilities. It might be a N-ch MOSFET:
http://chip.tomsk.ru/chip/chipdoc.ns...3001&count=500
http://toshiba.semicon-storage.com/a...SSM3K36FS.html

[Morsus]

Re: Replacing a transistor, your thoughts?

Have you checked Q5 with a multimeter?

Just did. Here is what I got. Since we can't still figure out what element is it i will name the pins A,B and C (A - stand alone pin, B and C two pins on the other side).
From the connector pin:
1 - A = 2,5V
2 - A = 2,5V
3 - A = 5V
3 - B/C = 7,6V
4 - A = 2,5V
5 - A = 7,7V
5 - B/C = 10,4V

Here are the images too.

[redwire]

Re: Replacing a transistor, your thoughts?

Morsus, I will draw it out, maybe need a few pics of the transformer some parts seem to be under it.

[Morsus]

Re: Replacing a transistor, your thoughts?

That will surely help, still I cant identify the broken transistor.

[redwire]

Re: Replacing a transistor, your thoughts?

OK I drew up a schematic for the Canon PS-A186 power supply low voltage side. Your voltages look fine for power-down mode.

This is what I figure:
Q5's purpose is to take the printer power supply out of energy-saving mode. I would say Q5 is a vanilla NPN transistor acting as a switch.
Q5=off, PSU in energy saving mode, outputs some low voltages ~1/3 normal.
Q5=on, PSU seems to full output +32VDC and +24VDC. In the Russian youtube video, he shorts Q5 C-E to get this. Then he puts a trim pot and fiddles with the voltages.

If your printer CPU is not turning on Q5 (voltage at CN2 pin1) then the printer would not power up. So Q5 might be OK.

I am just guessing because I don't know the printer, or all component values exactly.

[budm]

Re: Replacing a transistor, your thoughts?

OK I drew up a schematic for the Canon PS-A186 power supply low voltage side. Your voltages look fine for power-down mode.

This is what I figure:
Q5's purpose is to take the printer power supply out of energy-saving mode. I would say Q5 is a vanilla NPN transistor acting as a switch.
Q5=off, PSU in energy saving mode, outputs some low voltages ~1/3 normal.
Q5=on, PSU seems to full output +32VDC and +24VDC. In the Russian youtube video, he shorts Q5 C-E to get this. Then he puts a trim pot and fiddles with the voltages.

If your printer CPU is not turning on Q5 (voltage at CN2 pin1) then the printer would not power up. So Q5 might be OK.

I am just guessing because I don't know the printer, or all component values exactly.

The circuit topology looks about right, that Q5 alter the Vref TL431. So he needs to find out if there is DCV command signal coming from the printer to turn on Q5 or not. Good job drawing up the diagram.

[Morsus]

Re: Replacing a transistor, your thoughts?

Okay folks, after all of the holidays and being busy with more important stuff I finally got some spare time to mess with the printer. I got the printer too now. It's Cannon iP4300. It just wont react when powered on (no led, no reaction).
After opening the Printer, I found two boards. One for the buttons and one witch probably controls everything.
Since I got problems with internet connection atm I am uploading images to imgur, sry about this.
http://imgur.com/a/8zqG7

What kind of DCV signal do I need to fully start the power board?

[Morsus]

Re: Replacing a transistor, your thoughts?

Do you think a simple cap replacement on that logic board could fix the problem?

[Morsus]

Re: Replacing a transistor, your thoughts?

I disconnected the logic board and tried to find any short circuits but everything seems fine, I checked the caps too and they are all almost perfect (+-10%). Can someone help me figure this out? Here are the pictures of the board, can you tell me if there is some kind of fuse on that board that I can check?
Thank you.