"POWER PC" ML915 350W power supply

[Th3_uN1Qu3]

Re: "POWER PC" ML915 350W power supply

They likely made the feedback loop so that it keeps normal voltages with those crap parts they put in, so it sits on the high side with good ones. Put an old hard drive and a few fans on it and see what it does with that.

[Newbie2]

Re: "POWER PC" ML915 350W power supply

They likely made the feedback loop so that it keeps normal voltages with those crap parts they put in, so it sits on the high side with good ones. Put an old hard drive and a few fans on it and see what it does with that.

Could the new caps on the +12V and +5V rails that I put in be too high in capacitance?

+12V rail
Original caps: 2 x BH 1000uf 16V 10mm
New caps: 2 x Panasonic FM 2700uf 16V 12.5mm

+5V rail
Original caps: 2 x BH 1000uf 10V 10mm
New caps: 2x Nichicon HE 2700uf 6.3V 10mm

Unfortunately I do not currently have any hard drives laying around that I want to risk damaging. I also don't have any old computers either that I could be fine with frying the motherboard.

[shovenose]

Re: "POWER PC" ML915 350W power supply

a few fans should do the trick...

[Newbie2]

Re: "POWER PC" ML915 350W power supply

Yep, a few fans brings this PSU into acceptable voltages on the +12V and +5V rails.

The +5V rail went to a safe 5.17-5.18V in my tests, and here are the results from the +12V rail:
Two ADDA 92mm fans: 11.72-11.74V
Two ADDA 92mm fans + One Sunon 92mm fan: 11.69V-11.70V
One Vantec Tornado 92mm fan: 11.62-11.64V
Two ADDA 92mm fans + One Sunon 92mm fan + Vantec Tornado 92mm: 11.58-11.59V

These are within ATX specification, however to me those voltages are a bit low seeing how the minimum allowed for ATX spec is 11.40V, and these fans are a very small load. Should I be concerned?

[Th3_uN1Qu3]

Re: "POWER PC" ML915 350W power supply

This power supply is 5v-heavy, so it needs more 5v load for 12v to be stable.

[shovenose]

Re: "POWER PC" ML915 350W power supply

Yep, a few fans brings this PSU into acceptable voltages on the +12V and +5V rails.

The +5V rail went to a safe 5.17-5.18V in my tests, and here are the results from the +12V rail:
Two ADDA 92mm fans: 11.72-11.74V
Two ADDA 92mm fans + One Sunon 92mm fan: 11.69V-11.70V
One Vantec Tornado 92mm fan: 11.62-11.64V
Two ADDA 92mm fans + One Sunon 92mm fan + Vantec Tornado 92mm: 11.58-11.59V

These are within ATX specification, however to me those voltages are a bit low seeing how the minimum allowed for ATX spec is 11.40V, and these fans are a very small load. Should I be concerned?

I would honestly just try it on a real PC. IMO those voltages are fine, given that the 3.3V rail is not being loaded, and a few other factors.

[Scenic]

Re: "POWER PC" ML915 350W power supply

Might help adding some load resistors internally?! From what you posted, it doesn't need to be much of a load if one fan already brings it down to more sane levels.

Just thought that might help. I imagine there could be some sort of spike on the outputs when that PSU is in a system and you apply AC power to it.
Th3_uN1Qu3 might shed some light on this.. I'm not a PSU guru

[Newbie2]

Re: "POWER PC" ML915 350W power supply

I will do more with this PSU tomorrow in terms of testing and post pictures of the upgrade; I'm busy with some work to do at the moment and need to finish that up.

Other than that, I decided not to replace the MOSPEC F16C20C 16A rectifier on the +12V rail with my STTH2002CT 20A rectifier, as I felt the small difference in rating wasn't worth the effort to remove the whole secondary heatsink to replace it. Would the STTH2002CT make any difference compared to the F16C20C in terms of performance and/or reliability?

Links to data sheets for easy reference:
ST STTH2002CT: https://cdn.badcaps-static.com/pdfs/...29d9a8155e.pdf
MOSPEC F16C20C: https://cdn.badcaps-static.com/pdfs/...6b56a0265d.pdf

[Th3_uN1Qu3]

Re: "POWER PC" ML915 350W power supply

The STTH2002CT has significantly lower forward voltage which means higher efficiency - less heat.

[Newbie2]

Re: "POWER PC" ML915 350W power supply

The STTH2002CT has significantly lower forward voltage which means higher efficiency - less heat.

That's good enough reason for me to spend the effort on replacing the F16C20C rectifier. Less heat is a plus when the heatsink is wimpy, and especially when the +12V rail is the most demanded from modern PCs.

I'll do the replacement later.

[Newbie2]

Re: "POWER PC" ML915 350W power supply

Here's the results from the rebuild. While I did not do as much to this PSU as I did to my Delta Power 450W, I believe that it is now a bit better than before.

Here's what I did:
1. Replaced the four 3A 1N5408 diodes on the primary side with a "D4KB" 4A 800V bridge rectifier (from dead Bestec ATX-250-12E PSU)
2. Placed L and N wires in proper place along with the thermistor, and installed a fuse from the dead Bestec into the proper fuse location (I won't bother touching the 5A 250VAC fuse already in it on the "J1" position of the PCB)
3. Added transient filtering components (X cap, two Y caps, and coil); X cap and coil came from dead Bestec while Y caps came from dead Enermax EG301P-VE PSU
4. Replaced secondary side capacitors (see capacitor list below)
5. Replaced MOSPEC F16C20C 16A rectifier on +12V rail with STMicroelectronics STTH2002CT 20A rectifier (on advice from Th3_uN1Qu3)
6. Replaced "Legend" 80mm exhaust fan with Dynatron/Dynaeon Top Motor DF1208BC 80mm double ball bearing fan

Capacitor list (original cap -> new cap):
2x BH 1000uf 16V 10mm -> 2x Panasonic FM 2700uf 16V 12.5mm
2x BH 1000uf 16V 8mm -> 2x Panasonic FC 1000uf 16V 10mm
4x BH 1000uf 10V 10mm -> 2x Nichicon HE 2700uf 6.3V 10mm (on +5V rail) and 2x Panasonic FM 1500uf 10V 10mm (on +3.3V rail)
1x BH 470uf 16V 8mm -> 1x Panasonic FC 470uf 35V 10mm

I did not replace the two "KDC" 560uf 200V primary caps, the small caps (less than 470uf), or the two MOSPEC S20C45C rectifiers on the +5V and +3.3V rails as I did not want to invest more in this power supply and to use only what I had available. I feel those parts are not as critical to the reliability and quality of the PSU as the transient filtering stage components, bridge rectifier, secondary caps, +12V rail power rectifier, and new double ball bearing exhaust fan.


Here are the pictures:


The upgraded "POWER PC" 350W PSU.


Overhead picture of the internals, with the upgraded components visible.



The transient filtering stage components on the primary side.


The D4KB 4A 800V bridge rectifier is clearly visible in this picture.


The secondary side power rectifiers, with the new STTH2002CT being the middle one.






Five pictures of the new secondary side output capacitors.

Pictures from my smartphone (not the best quality):

The new STTH2002CT 20A power rectifier on the heatsink (it's the part in the middle).


Secondary side picture of this power supply. (my old oscilloscope is in the blurred background)



My simple "load test" of this PSU after the component upgrades, showing 11.62V on the +12V rail shown when five fans are connected to the PSU. One of the 92mm fans shown is connected to the +5V rail to provide a little load there.


Here are the voltages I measured with my multimeter on my five fan load test of this PSU (shown in the two pictures above) after the rebuild:
+12V = 11.62-11.64V
+5V = 5.10V
+3.3V = 3.29V
+5VSB = 5.01V

When this power supply had the MOSPEC F16C20C 16A power rectifier, the +12V rail went right down to 11.62V-11.64V with my one Vantec Tornado 92mm fan running off it. When I replaced that with the STTH2002CT 20A power rectifier, running that one Tornado 92mm fan on this PSU brought the voltage down to 11.70-11.72V, which is higher than the same load with the F16C20C rectifier.

Feel free to comment on my work.

[Newbie2]

Re: "POWER PC" ML915 350W power supply

A before and after post (nothing drastic):

Before:


After:

[Th3_uN1Qu3]

Re: "POWER PC" ML915 350W power supply

Good work. You're right, 5v and 3.3v aren't so critical in new computers anymore. Good job on the recap - that filtering toroid seems to have few turns on it, the larger caps are surely going to help getting more stable output voltage and less ripple.

If you want, you can install a thermal fan circuit too, the circuit is simple and the parts are likely to be found in other scrap PSUs. But if the new fan isn't too noisy, i wouldn't bother.

[Shocker]

Re: "POWER PC" ML915 350W power supply

not a big fan of mospec

Why not???

[c_hegge]

Re: "POWER PC" ML915 350W power supply

Nice improvements. I often run into the sky 550W (like the one I mentioned) with bloated KDC primary caps. I would probably replace them with some good 105*C rated ones.

EDIT: You could also bend the fins of the heat sinks apart a bit more. They won't get much air between the fins as they are now.

[PeteS in CA]

Re: "POWER PC" ML915 350W power supply

One thing to remember about DC fans. That nice number on the label is the average current. If you look at the actual current using a current probe and an oscilloscope, you'll see that the current is pulses that are much higher than the average rating.

[Newbie2]

Re: "POWER PC" ML915 350W power supply

I often run into the sky 550W (like the one I mentioned) with bloated KDC primary caps. I would probably replace them with some good 105*C rated ones.

That makes perfect sense to replace the stock KDC primary capacitors, however for me getting two 560uf 200V caps (that aren't the common snap-in type) would be expensive. United Chemicon 560uf 200V SMG series capacitors go for $4.62 CAD a piece on Digikey.ca, and getting two of those ($9.24 CAD) along with paying for $8.00 shipping and ridiculous 15% sales tax (in my province of Canada) would bring an order total to $19.83 CAD (for about $10 worth of caps!).

I spent a total of $23 CAD on this PSU ($20 + 15% sales tax) and spending another $19.83 on it would bring that to $42.83 CAD total, which I feel isn't worth it. With just over $40 CAD, here I could purchase a decent not-so-gutless power supply, or even a good well-built power supply that's on sale.

I know I spent some serious money rebuilding my Delta Power 450W, however I don't have so much money to waste these days. This POWER PC PSU won't be used much if at all by me, so I just wanted to do whatever I could with it provided the parts I had. I would most definitely replace the KDC primary caps with good replacements if I could, however the cost for me doing so currently isn't justifiable considering the PSU not being actively used right now.

[Scenic]

Re: "POWER PC" ML915 350W power supply

No old/dead PSUs to rip caps out of..?

[Shocker]

Re: "POWER PC" ML915 350W power supply

That makes perfect sense to replace the stock KDC primary capacitors, however for me getting two 560uf 200V caps (that aren't the common snap-in type) would be expensive. United Chemicon 560uf 200V SMG series capacitors go for $4.62 CAD a piece on Digikey.ca, and getting two of those ($9.24 CAD) along with paying for $8.00 shipping and ridiculous 15% sales tax (in my province of Canada) would bring an order total to $19.83 CAD (for about $10 worth of caps!).

Ever thought of enlarging the PCB holes???

[Newbie2]

Re: "POWER PC" ML915 350W power supply

I do have two old PCE-TUR 680uf 200V caps in a dead Enermax EG301P-VE PSU that I have, however I'm afraid that I might damage the solder pads on the POWER PC PSU PCB if I try to enlarge them for radial snap-in caps. I don't know if the PCE-TUR caps would be too good, with that dead Enermax being almost a decade old plus the PCE-TUR brand.