ONN 100012588 Has fluctuating Voltage on PSU 12v

[Davi.p]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

... i finish my post.. so the first thing is to replace u302, maybe also optoc. , if no joy replace secondary side capacitors..

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

... i finish my post.. so the first thing is to replace u302, maybe also optoc. , if no joy replace secondary side capacitors..

i would like to test these components and understand the circuit around them if possible before just replacing stuff. i would like to know for sure which component is wrong and why!

that said, if i do have to replace these. i may need some help finding the replacement. i type EA1 into digikey and i get nowhere!
edit: typing AZ431-A is getting me somewhere

also here is a pic of the optocoupler and its datasheet

[R_J]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

The optocoupler is in the correct way. see the pin 1 dot on the ic, it matches the pin1 of the board (cutoff corner)
Pin 1&2 are the led and are on the secondary side of the power supply, pins 3&4 are on the primary (HOT) side and are the photo transistor.
If you are carefull you can check the voltage ACROSS pins 3 & 4 and see if they change when the PSON changes

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

The optocoupler is in the correct way. see the pin 1 dot on the ic, it matches the pin1 of the board (cutoff corner)
Pin 1&2 are the led and are on the secondary side of the power supply, pins 3&4 are on the primary (HOT) side and are the photo transistor.
If you are carefull you can check the voltage ACROSS pins 3 & 4 and see if they change when the PSON changes

but the datasheet shows that the dot is on pin 3 .... ???? also i dont see any cut off corner? edit: oh on the top silkscreen there is a cutoff corner that matches where the dot is on the IC...but according to the datasheet that dot is on pin 3!

[R_J]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

but the datasheet shows that the dot is on pin 3 .... ???? also i dont see any cut off corner?

If you look ath the top of the board, there is a black rectangle around the optocoupler and one of the corners is not like the others

Does it look like it has been replaced (fresh solder) It seems the Secos brand BL817 and the BL817S have different pinouts.
Here is a different manufacture datasheet for the BL817

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

That datasheet seems to be marked wrong, Check a datasheet of the sharp PC817. If you look ath the top of the board, there is a black rectangle around the optocoupler and one of the corners is not like the others

Can you recheck the number on the optocoupler, Does it look like it has been replaced (fresh solder) It seems the BL817 and the BL817S have different pinouts.

Thank you for taking time with me. I will look closer and see if I do have the wrong datasheet

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

Does it look like it has been replaced (fresh solder) It seems the Secos brand BL817 and the BL817S have different pinouts.
Here is a different manufacture datasheet for the BL817

it doesnt look like it has been replaced. it definitely is a BL817C not an S.
after looking at both datasheets i have no idea how i am supposed to logically decide which pinout is correct without testing the optocoupler itself to find out. is this just how it is sometimes?

am i just supposed to know by the placement of the components around the EA1 that it has to be driving the LED side of the opto so therefore i choose the datasheet that lines up with that pinout? and that noticing the side of the opto that connects to U101 (main switching IC?) must be the feedback, so therefore has to be phototransistor side... i guess i see it now. i will hook up some clip leads to pin 3 and 4 and see whats there before and after PSON.

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

ok heres what i got. red voltage is by itself. blue voltage is with 5v supplied to PSON and to BK. ~ denotes fluctuation. it definitely does change when PSON is applied.

[Davi.p]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

Optocoupler and 431 are two elements of the feedback, it's a bit long to explain, now im using cellular to write and it's hard, under light load like in stby, the feedback is less important, by turning on the set the tension seats and the main board returns in standby, then repeats cycle

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

are there any other tests i can do to surely find the problem or am i at the point now where i should just go ahead and replace these components? i am looking at scrap boards that i have and it seems the 817 opto is pretty common...could take from another board....i imagine if i look hard enough ill find a EA1 but that component is so small...maybe better to buy new than try to get one off another board without damage.
to actually test an opto beyond a simple "pass/fail" i would think i would have to use a function generator and an osciloscope and have a very good understanding of what the output waveform should look like with a given input... dont have those tools yet but i get the idea!

[Davi.p]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

optocoupler is a cheap piece that can be robbed from cheper boards, anyway no need for those equipements, only a small 1,2v battery/generator applied to led side and an ohm meter on the transistor side, no 1,2v - high resistance, yes 1,2v - low resistance.. the most delicate of two is the 431..

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

optocoupler is a cheap piece that can be robbed from cheper boards, anyway no need for those equipements, only a small 1,2v battery/generator applied to led side and an ohm meter on the transistor side, no 1,2v - high resistance, yes 1,2v - low resistance.. the most delicate of two is the 431..

ok that is a good "simple test" that would tell me basically if its working or not...but it could still be "defective" in some subtle way that could only be seen with the osciloscope and function gererator... gotta use what you got. its an easy part to replace either way. its the u302 thats more of a pain. ill get to it soon and report back with more info. thanks!

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

ok i have been doing research and perfecting my "tools" for testing opto isolators easily. i tested a couple other ones i had laying around to get a feel for it before trying it out on the ONN board.

the other ones i found were also 817. i have this breadboard with a power adapter plugin board for it that can make 5v or 3.3v.
i went with the 3.3v and then used 2 resistors totaling 110ohm to drop 2.1v
over the resistor, leaving 1.2v for the LED.

i got the resistor value to use by this process:
according to the datasheet, the LED wants 0.20A and 1.2v
i have 3.3v from the power board so i need to drop 2.1v over the resistor to leave only 1.2v at the LED.
so using ohms law R=V/I = 2.1v/0.20a = 105 ohms but i didnt have a 5 ohm handy and figured 110 would be fine. and it seems it is. i get 1.19v going to the LED on any 817 i test. the two that i tested seemed to work. the resistance on the other end of the optocoupler dropped from infinite to around 40 ohms.

i tested one opto out of circuit, and another in circuit.

i get similar results when i test the one in the ONN PSU. (in circuit)
when the 1.2v is applied, the resistance on the other end of the opto drops to 45 ohms.

i cant find in the datasheet where it tells what ohm value to expect here when the 1.2v is applied...but it seems pretty close to the other ones i tested so i have a hard time suspecting that the optocoupler on this board is the culprit.

could this test be incomplete? is the only true test replacing the component with a brand new one? or is it an indication that we might look elsewhere for the problem?

i still have to figure out a meaningful test of the component U302.

[Davi.p]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

optocoupler is been probably passed by a power surge wihout damage, but 431 is more delicate i think..

[pop70458]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

Did you have any luck?

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

i still have to figure out a meaningful test of the component U302.

but i have been mapping this board out by hand. put quite a few hours into it.
along the way i was checking resistors and looking for shorts and all that. i didnt find anything obvious until i got to R355 which is marked 2R2 so should be 2.2 ohms but instead its 20.3k and on the other power supply board it reads 35k so i think it has failed on both boards...but failed slightly differently with regards to the end resistance value it attained. this circuit is very simple it only has 2 capacitors and a diode in it. the plus side of the diode goes to hot ground (negative leg of PFC). the negative side of the diode goes with 2 capacitors in parallel to the main IC i need to look up this chip. TEA1716T and see what that line does. its pin 6. i put a yellow arrow pointing to R355. its pretty nearby the optocoupler circuit but not connected to it in any way i can see.


from the datasheet pin 6 is SUPIC
input low-voltage and output of internal HV start-up source;
externally connected to auxiliary winding of HBC or to external DC supply

i read it like 10 times and im still not entirely sure what they mean.
HV definitely means High Voltage... but what is HBC?

[R_J]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

The datasheet explains it. HBC is Half-Bridge resonant Converter. It is the drive part of the ic for the main power supply.
Basically the ic has an internal startup cell, it takes the HV in and has a small internal regulator that supplies the initial vcc for the internal circuit and also charges the external cSUPIC capacitor. Once the circuit starts the auxiliary winding of the transformer supplies the vcc run voltage that keeps the cSUPIC capacitor charged to keep the ic operating.

R355 is acting like a fuse for the Auxiliary supply from the transformer, D107, EC103 If this resistor is open, the power supply will try and start then fail and try again.

[R_J]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

You should have a voltage of 20 volts across EC103, if the voltage drops to 13v the ic stops working, If R355 was open, also check R354

[triplefour]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

You should have a voltage of 20 volts across EC103, if the voltage drops to 13v the ic stops working, If R355 was open, also check R354

i get a fluctuating voltage across EC103 which goes between about 14.5v and 18.5v
R355 was not open it just shows as 20.1k when it should be 2.2ohm.
R354 seems in spec. 4701 marking means 4.7k and it reads about 4.6k

[R_J]

Re: ONN 100012588 Has fluctuating Voltage on PSU 12v

Did you replace R355 with a 2.2Ω? or just leave the one that checked 20.1k