ONN 100012588 Has fluctuating Voltage on PSU 12v

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

are you getting about 400 volts on the main filter cap/s?

I get a swinging voltage on the pfc that goes from 370 to 380. It doesn't seem to change at all when putting 5v to pson, bk, and adj. Also no change when mb plugged in.

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

Then ok, let's suppose both Power boards are faulty, then try replace the optocoupler and the shunt regulator on the under side, it is connected to optoc. and marked 431.. a good replacement for example AS431..

Shouldn't I only replace them if they test bad? I'll check it out.
Edit: I can't find any component marked 351. What picture are you looking at?

[R_J]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

When the power supply is in standby the pfc circuit should be OFF, so the voltage across the main caps (EC102) should only be 160vdc. I suspect something is damaged around the optocoupler, and possibly U302 which is likely the voltage reference ic.

What is the voltage on the PSON pin (or JMP22) without the main board and without the 5v applied from the external power supply?
What is the marking on U302?
What is the number on U101?

Q207 should be the transistor that switches the power supply from standby to on by controlling U302 which controls the optocoupler. and also regulates the feedback to the main switching ic U101

[Davi.p]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

No, wait a minute, i don't have thought that also pfc tension should have fluctuate, this is not ok, i don't know where R J see the component U302, maybe he has the schematic, i told 431 marking on a sot23 because usually when there isn't a to92 ic there isn't a tl431 on the component side, a possible cause of oscillating pfc are the main 450v condensers.. have you got a cap tester? Last i don't understand how a feedback optocoupler can activate the pfc, can you explain better? usually there's a separate opto that controls the pfc switch but here there's only a opto and that must be for feedback i think..

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

what is the voltage on the PSON pin (or JMP22) without the main board and without the 5v applied from the external power supply?
What is the marking on U302?
What is the number on U101?

Voltage on PSON is 0v when I don't connect mb or add my own 5v. It drops to 4.6v actually when I apply the 5v. When the mb is connected, it fluctuates between 1.8 and 2.8v
There's some nasty glue all over the place, making it hard to read markings but i think this is right.
markings on u101:
TEA1716T
CXZ0/6
CXW260
TAD19522
Marking on u302:
EA1

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

No, wait a minute, i don't have thought that also pfc tension should have fluctuate, this is not ok, i don't know where R J see the component U302, maybe he has the schematic, i told 431 marking on a sot23 because usually when there isn't a to92 ic there isn't a tl431 on the component side, a possible cause of oscillating pfc are the main 450v condensers.. have you got a cap tester? Last i don't understand how a feedback optocoupler can activate the pfc, can you explain better? usually there's a separate opto that controls the pfc switch but here there's only a opto and that must be for feedback i think..

All those numbers you throw out there got my head spinning. I do have a cap tester. Cheap assemble yourself kit one from ebay. Should I desolder and test the pfcs? There are 4 of them.

[Davi.p]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

PFC is a circuit not a component, test those 3 bigger caps, also without desoldering, them must read near the sum of 3, 68+68+68 uF.

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

PFC is a circuit not a component, test those 3 bigger caps, also without desoldering, them must read near the sum of 3, 68+68+68 uF.

doesn't PFC stand for Primary Filter Capacitor? or is the C for circuit? oh and yea there are only 3. i dont know why i thought there were four. it must be getting late! according to my tester i see 198uf which is pretty close to 204uf which would be the 68*3

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

here are the voltages i measured around the optocoupler circuit. red voltages are with the PSU by itself, and blue voltages are with the MB attatched and red light blinking.
i notice a fluctuating voltage at the optocoupler when the main is plugged in, but a stable one and much lower when main not connected.
the base of Q207 is 2.4v without MB and 0v with MB ... that seems a bit strange. of course i dont really know what im looking at so maybe thats totally normal!

but it does seem strange to me that there would be so many 0v there. particularly on the anode of u302, which is 0 whether the MB is connected or not.

[Davi.p]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

PFC= power factor correction, anyway 198uF is ok.. is your meter battery ok? i can't find other sources of swinging pfc circuit other than a faulty activating signal that makes on off, i can only suspect that these are boards like newer Samsung that changes the on / stby state with different loads, so then there is probably a faulty 431 chip or a secondary side management ic..

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

PFC= power factor correction, anyway 198uF is ok.. is your meter battery ok? i can't find other sources of swinging pfc circuit other than a faulty activating signal that makes on off, i can only suspect that these are boards like newer Samsung that changes the on / stby state with different loads, so then there is probably a faulty 431 chip or a secondary side management ic..

PFC = power factor correction
PFC = Primary Filter Capacitor
not confusing at all!!

my meter is fine. tests everything else without problems.
bedtime for now. hopefully i will have some more time to poke around tomorrow.

A BIG THANK YOU TO ALL WHO TRY TO HELP ME UNDERSTAND!

[Davi.p]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

gold.dreams, dreaming mosfets that jumps in the grass..

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

gold.dreams, dreaming mosfets that jumps in the grass..

i dream of electric sheep!

oh but one last thing i noticed before i go... that ANODE of u302 Marked EA1 (pin 3 according to the datasheet) is shorted to ground. that cant be right, can it?
ANODE should be positive, right? and its 0 in both cases, with or without MB...

so i try to read about anode vs cathode and find this very confusing article but at the end it says the anode or cathode can be negative or positive depending on the situation. great! so i still know very little!
https://www.thoughtco.com/how-to-def...cathode-606452

[Davi.p]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

That EA1 appears to be an emule of 431 so it simulates a zener (is a programmable zener) where correctly anode is at GND..
if ref pin rises over 2.5v then it flows current from cathode to anode and then cathode is very low volt.. have you tested the secondary caps? i can also suspect an intermittent short on them, it happens in cheap chinese miniaturized cap brands.. so i'ts better anyway to be replaced.. use only good rated brands like Rubycon, nichicon, panasonic..

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

That EA1 appears to be an emule of 431 so it simulates a zener (is a programmable zener) where correctly anode is at GND..
if ref pin rises over 2.5v then it flows current from cathode to anode and then cathode is very low volt.. have you tested the secondary caps? i can also suspect an intermittent short on them, it happens in cheap chinese miniaturized cap brands.. so i'ts better anyway to be replaced.. use only good rated brands like Rubycon, nichicon, panasonic..

still a lot to learn. zener diodes....they work in reverse bias or something. hard to keep the dyslexia at bay with all this flip flopping around!
which caps do you mean i should test?

[R_J]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

U302 is not a zener, it is a shunt regulator ic, The reference is connected to a resistor divider network, one end is ground, the other end of the divider connects to the +12v output, when the +12v output changes, the reference voltage also changes, this causes the voltage on cathode to also change. This change in voltage will control the 817 optocoupler, which controls U101 pwm duty cycle. This is how the +12 volts gets regulated.
Like I said before, in standby the voltage across the main filter capacitors should only be 160vdc. You may have a defective optocoupler or U302.

When nothing is connected to Cn201 what is the voltage on the +12v line and is it stable? (in picture red=alone) voltages seem stable.

One more voltage to check would be the actual LED voltage between CN301 & CN302, this should be the un-boosted led voltage, likely around 60~80vdc

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

When nothing is connected to Cn201 what is the voltage on the +12v line and is it stable? (in picture red=alone) voltages seem stable.

yes those voltages in that area are stable when nothing is connected, but do fluctuate when MB is connected.
the 12v line always fluctuates whether mb connected or not, but it fluctuates down to lower voltages with the mb connected.

[Davi.p]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

Now, watching better last photos, i see that p.s. board outputs 9,5v when in standby, when AV board sends back ps on command it tells psb to rise the standby voltage to 12v, this doesn't mean for me that activates also the PFC, i don't think primary can sense the state change st.by> full on.

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

U302 is not a zener, it is a shunt regulator ic, The reference is connected to a resistor divider network, one end is ground, the other end of the divider connects to the +12v output, when the +12v output changes, the reference voltage also changes, this causes the voltage on cathode to also change. This change in voltage will control the 817 optocoupler, which controls U101 pwm duty cycle. This is how the +12 volts gets regulated.

so what should i expect to see at the anode of U302? edit: looking at the datasheet it appears when being used as a shunt regulator, the anode is connected to ground so should be 0v as it is.
also i am a little confused here because i thought that the way an optocoupler works is that it is controlled by the LED which shines on the phototransistor.
in the picture those 2 pins of the optocoupler that are closest to the circuitry we are looking at are pins 3 and 4 according to the datasheet, which is the phototransistor side of the optocoupler. how can we control the optocoupler by affecting those pins? shouldnt it have to control the LED to affect operation? i say this with my limited knowledge hoping to be set correct. thank you

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

Like I said before, in standby the voltage across the main filter capacitors should only be 160vdc. You may have a defective optocoupler or U302.

is there any way i can test these components, either in circuit or out of circuit?