Help about atx psu

Thread Starter

Dzoro

Joined Feb 1, 2019
190
So i got riotoro onyx750 watt psu for cheap,i pluged it and it had 5vsb and the ps-on voltage so i conected the green wire with one of the black and the psu isnt starting but you can hear ticking noise that is tryng to start but it shutsdown every 0.3 seconds so i opened the psu i pluged it in again and mesure the big caps on the input and because it has active pfc on the caps it should have around 360 to 400 volts when is on and around 320 volts when in standby but in stanby it has around 260 volts wich is strange and when i turn it on the pfc doesnt start and the ticking noise continues so i unpluged it and discharged the caps i removed the power mosfets.One for the pfc and two mosfets for the switching of the main transformer and one of the two mosfets of the main transformer switchnig was shorted so i replaced all 3 of them with the same power mosfets i cheked the choke is good i cheked the diode for the output its also good so i powerd it up through a 100watt lightbulb in some case it short again and the lightbulb turned on for a sec when the inrush current is charging the caps and then turned off like it shoud and when i try to start it wit a jumper wire from green to black,still the same ticking sound happend so i unpluged it and because its a high efficiency psu 80+ bronze it had synhronus rectifiers,it had 2 mosfets in series on both sides of the output transformer they all mesured good but i still replaced them all and still the same ticking sound happens when i turn it on and one strange thing is that the 5vsb is not 5v its 4.2v and i dont know if that can make the thing turn on and shut down multiple times a second. I have repaired many 80+ power supplies but this one is so anoying so i had last one hope to ask here if some of you had the same problem and if you know how i can fix it
Thanks
Dzoro
 

Thread Starter

Dzoro

Joined Feb 1, 2019
190
Did you load the +5V rail? A few ATX power supplies need this load (0.5A or so) on start up.
No i didn't but i will try that so 5v devided by 0.5 A is 10 so a 10ohm ressistor should be good but i don't think its going to start eather because the 5v and the 3.3v rails are going through a buck converter but i will try that as well
 

Reloadron

Joined Jan 15, 2015
5,934
No i didn't but i will try that so 5v devided by 0.5 A is 10 so a 10ohm ressistor should be good but i don't think its going to start eather because the 5v and the 3.3v rails are going through a buck converter but i will try that as well
Keep in mind along with the popular 10 Ohm load they typically use a 5 or 10 Watt resistor even though you are only dissipating 2.5 watts. I would also try it without any other loads like the buck converter you mention.

Ron
 

Thread Starter

Dzoro

Joined Feb 1, 2019
190
Keep in mind along with the popular 10 Ohm load they typically use a 5 or 10 Watt resistor even though you are only dissipating 2.5 watts. I would also try it without any other loads like the buck converter you mention.

Ron
Without loads its not working
 

Reloadron

Joined Jan 15, 2015
5,934
Without loads its not working
That is why it was suggested to place a load on the 5.0 Volt output. Many but not all ATX form factor PSUs require a load on the 5.0 volt bus because they regulate off that bus. Therefore a load is placed on the 5.0 volt bus. Really early versions used a 3.3 volt bus sense but newer stuff regulates on the 5.0 volt bus.

Ron
 

Thread Starter

Dzoro

Joined Feb 1, 2019
190
I
That is why it was suggested to place a load on the 5.0 Volt output. Many but not all ATX form factor PSUs require a load on the 5.0 volt bus because they regulate off that bus. Therefore a load is placed on the 5.0 volt bus. Really early versions used a 3.3 volt bus sense but newer stuff regulates on the 5.0 volt bus.

Ron
I will try that and give you feedback but i only have 1 watt ressistors of 10 ohms i don't know if woud last very long
 

Thread Starter

Dzoro

Joined Feb 1, 2019
190
I placed 10 ohm ressistor on the 5 volt rail and still the same ticking is starting and i put my ear close the the bottom of the pcb and the ticking noise is coming from the chip
The chip is cm6901x
 

Reloadron

Joined Jan 15, 2015
5,934
Normally when an ATX form factor makes a ticking noise it is the voltage regulator. The PSU tries to start and can't be it a load it doesn't like or something else. The PSU tries to start and can't so it just repeats over and over again.
If i place them in series it will add up the ressistance
Yes it will and you will just burn up anything less than a 10 ohm minimum 5 watt resistor. Unless the PSU sees what it expects it will just cycle (click) over and over again at a set interval. Again, some ATX form factor PSUs need a load and some don't. The load is normally on the 5 volt bus. There are endless little tutorials out there on how to use an ATX PSU as a bench PSU. Anyway the ticking is just the PSU trying to start and failing for any number of reasons.

Ron
 

Thread Starter

Dzoro

Joined Feb 1, 2019
190
Normally when an ATX form factor makes a ticking noise it is the voltage regulator. The PSU tries to start and can't be it a load it doesn't like or something else. The PSU tries to start and can't so it just repeats over and over again.

Yes it will and you will just burn up anything less than a 10 ohm minimum 5 watt resistor. Unless the PSU sees what it expects it will just cycle (click) over and over again at a set interval. Again, some ATX form factor PSUs need a load and some don't. The load is normally on the 5 volt bus. There are endless little tutorials out there on how to use an ATX PSU as a bench PSU. Anyway the ticking is just the PSU trying to start and failing for any number of reasons.

Ron
I know that it has some reasons for why it is failing and cant start but i checked eveithing and i cant find anything and i found 10 ohm 10 watt ressistor and still didnt start.Its strange that the +5v stand by is 4.2 volts and thats the only thing that its not good but i dont know what would decrease the voltage on the 5 volt
 

SamR

Joined Mar 19, 2019
3,410
I don't know how many 10Ω 1W resistors you have but placing them combined into series + parallel units you can maintain a total of 10Ω plus increase the wattage,
 

Reloadron

Joined Jan 15, 2015
5,934
That 5 volt SB is a little low, it should be 5.0 Volts +/- 5.0% or 4.75 to 5.25 volts. Since pulling the 5 volt SB to ground is the PS_On command I am not sure how much a low 5.0 Volt SB matters. Never ran into that before. Is this a known good PSU as I can't come up with a reason it won't start. Pulling the green wire on a 20 or 24 pin connector low should start the PSU and that is about all there is to it.

Ron
 

Thread Starter

Dzoro

Joined Feb 1, 2019
190
That 5 volt SB is a little low, it should be 5.0 Volts +/- 5.0% or 4.75 to 5.25 volts. Since pulling the 5 volt SB to ground is the PS_On command I am not sure how much a low 5.0 Volt SB matters. Never ran into that before. Is this a known good PSU as I can't come up with a reason it won't start. Pulling the green wire on a 20 or 24 pin connector low should start the PSU and that is about all there is to it.

Ron
Yes but the ps on voltage is low too its around 2.4 volts and on other power supplies i have repaired it was around 5 volts sometimes 4.4 4.5 4.7 but around 5 volts and this thing has 2.4 volts and also on the chip cm6901x that the ticking noise is coming from in the datasheet it says that it has internal 7.5 volts on the Vreff pin and when i mesure that pin has around 2 volts and thats strange as well
 

Thread Starter

Dzoro

Joined Feb 1, 2019
190
I don't know how many 10Ω 1W resistors you have but placing them combined into series + parallel units you can maintain a total of 10Ω plus increase the wattage,
In that case yes but you previusly sad just in series but i found 10 watt ressistor so its not a big deal
 

Reloadron

Joined Jan 15, 2015
5,934
Yes but the ps on voltage is low too its around 2.4 volts and on other power supplies i have repaired it was around 5 volts sometimes 4.4 4.5 4.7 but around 5 volts and this thing has 2.4 volts and also on the chip cm6901x that the ticking noise is coming from in the datasheet it says that it has internal 7.5 volts on the Vreff pin and when i mesure that pin has around 2 volts and thats strange as well
With that in mind I would have to guess the PSU has some issues. Generally I just toss them out. You can keep chasing a problem but good luck on that note. Been years since I messed with them but even years ago it was about impossible to find a decent schematic.

Ron
 

Thread Starter

Dzoro

Joined Feb 1, 2019
190
With that in mind I would have to guess the PSU has some issues. Generally I just toss them out. You can keep chasing a problem but good luck on that note. Been years since I messed with them but even years ago it was about impossible to find a decent schematic.

Ron
The manufacturers arent giving their schematics,neather they have service manuals so the last hope was here so i will just use it for parts but thanks for the help i realy apreciate it
Dzoro
 
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