Help diagnosing a LVPS from a brother laser printer

[coldfusion]

Hi,

This is about a Brother L2350DW laser printer LVPS board that seems to have failed.

I'm trying to figure out what is wrong with this power supply. It has some components that I don't recognize, and others where I am a bit surprised by how they are connected (probably because I'm inexperienced with PSUs).

Pictures of the components I do not recognize are attached, and they are also listed with a question mark on the (very partial, work-in-progress) schematic here:
 https://www.digikey.com/schemeit/project/brother-lvps-e1921f9669284f2aaa1bee22198fe49d

There is also a picture of the board, front/back and front+back overlay. Notice that the front is mirrored for this to work, with L / N , and L1 / N1 marked. The 24V output is pins 1&3 (+) and 2,4,11 (-) on the connector on the oppostie end of the board.

I've tried to look up any other information about this board on forums/youtube, but could not find anything.

So far I've tested the triac, optocoupler, and the main diodes, and they seem fine. The circuit on the output of the diode bridge measures at about 330V (not sure what it is supposed to be). The 24V output measures at only 6V, so that is one obvious issue. Any advice on what to test next would be greatly appreciated.

Major components:

IC11: 2107 / TLP3073F
IC31: MIP0050 / 050S4M04
BD1: Brdige Rectifier with no clear markings
TR1: BTA10-800BW
D101: LT 1B06 / STPR1020CTW | https://www.diodes.com/assets/Datasheets/STPR1020CTW.pdf
Q1: K5A80F

Unidentified:
IC51: 4 pin smd with marking LK31 / 1004-W
T1: Transformer with marking MP-130I (00) / MH-MP16356 DELTA / DCZM 2117 (03) B1
CX1: ? could not read - hidden by coil (See picture)

Other markings on the board:
200V ADP-66BN AAD00DHH001 PR S 230
PWB t=1.6mm
2941107505

[mariush]

IC51 is most likely an optocoupler .... the hints for that are the big spacing between the pins and the big space with no copper under it and near it, it's a clear separation area between primary side (with potential for high voltage) and secondary side where you have low voltage.
Pretty much everything until the blue relay is high voltage, and only filtering and protection (fuses)  and inrush current limiting (the green ntc to the right), the blue Z1 (or whatever) to the left of the fuse, with some kind of fuse or temperature "sensor" tied to it with that heatshrink.

CX2 is your plain standard X2 grade capacitor, used for AC filtering, rarely fails and the psu would work without it.

T1 is probably a custom transformer, not something you can buy retail.

IC11 is a triac driver to turn on and off that triac TR1 on the heatsink.
On the bottom side is the regular power supply stuff .. more filtering and then you have the smps controller on the bottom, and you have the actual mosfets or transistors that do the switching on that center heatsink under the big capacitor with KMG written on it.
Check those, check the zener diode there (ZD36 I think) and check the small capacitors C26 and C25 if the power supply seems to just randomly start or resets from time to time - one of those two capacitors smoothes power to the smps controller.
Also check the diodes on the output (H23 heatsink)

[coldfusion]

Thanks!

I took out ZD36 to test it, since it is sitting in parallel to that 1W resistor (R45, which measures 0.5Ohm, BTW).

ZD36 is marked 5V68 NZ, and measures 0.718V forward drop on my multimeter. When tested with a 7V source and 10K resistor in series, it tested 0.715V forward and 5.00V reverse. That seems ok, right?

I don't have a capacitor tester here, all I could verify about C26 and C25 is that they aren't shorting, that their resistance is slowly increasing when measured, and the voltages across them are less than their rating (11.5V across C26 and 12.9V across C25)

The diodes on the output heatsink (H23) is a D101 (datasheet) They are connected such that they are simply used as two diodes in parallel, rather than as a rectifier as the part states. Multimeter reads 0.45V forward drop on both internal diodes, and OL in reverse. So I'm guessing that one is ok too?

The transistor on the heatsink near the big 400V KMG cap (Q1) is K5A80F and I am not sure if my test of it is sufficient - I only have a multimeter here (I'll have a scope later, but not a transistor tester yet). I just tested that pin2<>pin3 behaves like a diode, and that nothing is shorted. Is that good enough?

What is the next step? Would a scope help here? What is the right way to check the SMPS chip? I can check the stability of the input voltage to check those caps, but I'm not sure that is the issue since the output is so far from where it needs to be (6 instead of 24)

How would you recommend testing the tiny optocoupler(s) (three of them on the board) without a datasheet?

Thanks for your assistance on this!

[m k]

4 pin opto is pretty straight forward, input side is a diode and output side a collector-emitter.
This pictured one seems to be a mains voltage quality control of some sort.

Assumed heater part on the right is a different thing than others.

[inse]

The interesting part is about the two opto couplers (side by side), I imagine one of them is for voltage regulation and the other one possibly to turn off the power supply.
Is there a separate stand-by supply?
The other couplers are for zero crossing detection and phase angle control of the heater (I assume) and not part of the power supply.

[fzabkar]

I see some people suggesting that this may be a similar SMPS controller:

https://web.archive.org/web/20211016055219/industrial.panasonic.com/content/data/SC/ds/ds4/MIP0060MXL_E.pdf

FWIW, here is a MOSFET marked "K5A80E":

https://toshiba.semicon-storage.com/info/TK5A80E_datasheet_en_20151118.pdf?did=30681&prodName=TK5A80E

[inse]

The 24V rail delivers 6V as you mentioned, is this open load or with the printer connected?
If open load, what happens when you put a load on the voltage, is it stable then?
Check with a multimeter (oscilloscope preferred) if there is voltage across the optocoupler LEDs ( left/secondary side) IC52/53.
Is anything getting hot in open load operation?
Is a unusual sound to be heard from the supply like whining or clicking?

[eeprom1]

I have same power supply outputting 6v voltage without load. Printer was not turning on and no sign of life. I ordered replacement PS and shows same 6v on 24v rail.
Did author get his issue sorted out? Someone suggested issue is with Formatter board which I guess is the heart/mainboard of printer.

[ealex]

i've seen similar power supplies that have some sort of "enable" on the output connector.
wothout that the psu would output a stand-by voltage

the bunch of sot23-3 parts around the 2 optocouplers might implement that function

the images in the first post are to blurry to read the labels on the output.

(on a inkjet psu i've tried re-using there was a npn transistor that was shorting a part of the feedback network when the enable signal was present)

[Vulgrim]

@coldfusion and @on
you have solved the problem?

I have the same problem and only measure 6V instead of 24V.
My printer is a Brother DCP-L2530DW
It won't switch on

I've already checked most of the components on the power supply
No short circuit
Fuses - ok
PTC/NTC - ok
Thermal fuse - ok
MOSFET - ok
Optocoupler - ok
Electrolytic capacitors - ok
C10 and c11 - ok (100pF and 470pf / 1000V)
Primär - OK - 320V DC -OK

Unfortunately I don't have a datasheet of the IC MIP0050 and can't make any measurements - ramp voltage, supply voltage etc.

I would be very grateful for tips

[Vulgrim]

My board looks a little different