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Old 11-22-2019, 06:35 PM   #21
momaka
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Default Re: Hipro D2537F3H - Teapo output capacitor replacemnt

Quote:
Originally Posted by socketa View Post
Looks like the top of it has suffered from some heating, and subsequent decay
The designer must have desiginated the resistor there for some reason - what are the consequences of removing it and not replacing it at all?
It's there so that if you run the PSU with no load at all on the 12V rail and some (but not full) load on the 5V rail, the PSU won't loose regulation.

So it does have a purpose indeed.

However, typically having just one fan in the PC will put enough minimum load on there to keep the 12V rail happy. Thus, in most cases, the minimum load resistor will not be needed.

I myself don't like to completely remove them, and usually replace them with whatever resistors I have on hand that will work in the circuit. For 12V rail, typically anywhere from 270 to 1000 Ohms is good enough as a minimum load. But removing them completely, at least from my personal experiments and that of a few others I've seen on BCN, usually will NOT cause an issue, either. Nevertheless, I bought a pack of 100 SMD 1-KOhm 1/5W resistors off of Digikey for something like a $1, so I used these on the 12V rail of PSUs quite a bit (typically 2-4 in parallel for a total resistance of 500 to 250 Ohms as a load.)

Quote:
Originally Posted by socketa View Post
The 5V rail resistance to ground is 206 ohms, (and the 3.3V rail resistance is 520 ohms, and 12V is 209 ohms)
No need to worry about those then.
Again, tyically I worry only if the 5V rail is showing 6 to 30-ish Ohms resistance (suggesting less than a 47-Ohm resistor is used), and less than 10 Ohms on the 3.3V rail.

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Originally Posted by socketa View Post
So what's that larger 27 ohm resistor, that's on the other side of the torodial coil, for? One side is connecetd to ground and the other side goes through the brown ceramic cap that is next to it, and then goes underneath the large torodial coil base? Looks like that could do with being replaced.
Yup, that's why I asked for the extra pictures. Looking at it, it might be an RC snubber network on the 12V rail (or some other rail). Can't quite tell, but that one I probably wouldn't replace with any other random value and only use the same resistance. See what the non-ground side of that resistor connects to (use your multimeter on lowest resistance setting to find out.) And also see what the other side of the ceramic cap (that is not connected to the resistor) goes to.

That aside, if the resistor is not showing open-circuit, you don't have to replace it. Just make sure it is not shorting to something metal, as the material/layers under the insulating coating are usually conductive.

Or if you want piece of mind, you can replace it. But in that case, since the coating appears tripped, then maybe use a higher power resistor, as that will run cooler and will be less likely to "blister" over time.
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Old 11-23-2019, 03:50 PM   #22
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Default Re: Hipro D2537F3H - Teapo output capacitor replacemnt

Cool. Appreciated, is the additional info.
So, joining the dots... is the reason why the first cap on the 3.3V gets cooked because a too low load resistance (at least on this particular PSU) on the 12V rail somewhat throws out the overall regulation (because the 3.3V is tapped off of the 12V supply?), and subsequently the 3.3V cap is worked harder, or even subjected to excessive ripple?

This sounds like design fault - should've the designer known about this, or is it more of a hindsight thing?
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Old 11-26-2019, 08:23 PM   #23
momaka
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Default Re: Hipro D2537F3H - Teapo output capacitor replacemnt

Quote:
Originally Posted by socketa View Post
So, joining the dots... is the reason why the first cap on the 3.3V gets cooked because a too low load resistance (at least on this particular PSU) on the 12V rail somewhat throws out the overall regulation (because the 3.3V is tapped off of the 12V supply?), and subsequently the 3.3V cap is worked harder, or even subjected to excessive ripple?
No, that's not exactly the reason why.

Rather, on the 300W and 350W version of the PSU, the load resistor for the 12V rail is located next to the toroid coil and the first 3.3V cap. Because of the low resistance of this load resistor on the 12V rail, a lot of heat is produced by it, and that cooks the first 3.3V cap over time.

As for your PSU, I don't see any caps near the 220-Ohm resistor on the 12V rail, and it's overall max dissipation shouldn't exceed about 0.7 Watts, even with a high 12V rail of 12.3V+.

Quote:
Originally Posted by socketa View Post
(was suspicious of 520 ohms on 3.3V rail, and just realized that makes a difference which way the test leads are, so black to ground = 285 ohms. Is there some diode being added to that when the meter leads are swapped? )
Well, yes, when you swap the leads on your multimeter (red to ground and black on the positive side), you'll be essentially reading across the rectifiers - at least on the 5V and 12V rails. 3.3V rail will be different with these HiPro PSUs, as they typically derive the 3.3V rail from a MOSFET or pair of MOSFETs from a rail similar to the 5V rail.
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