Need help rebuilding "The Best Power" 500W PSU

[Newbie2]

Hello people,

I have recently decided to try to rebuild my "The Best Power" MT-500P 500W power supply so it can be a backup PSU for my Celeron 2.2GHz computer. I started by adding in the input filtering components that were missing on it. When I tried to power up the power supply, the 6.3A 250V fuse in it blew, lighting up the inside of the power supply for a second. I have one other fuse, a 10A 250V fuse that I took out from an old power supply, to replace that one with. But, I don't want to blow the other fuse I have and potentially start a fire.

Here are pictures:

The primary side of this power supply.


The input filtering components that I added in (notice the blown fuse near the X cap, it's black because it blew)


Underside of the primary filtering section (the soldering on the primary caps look bad, they were better when I powered it on, I was trying to find a short somewhere in them)


Could this be a short?

When I added the X cap, the fuse was in its way. I heated up its solder joints to move it slightly outward so the X cap would fit. But looking at the last picture I have, could it be shorting to another component in the power supply?

I won't replace the fuse until I'm absolutely sure what's making the fuse blow.

[370forlife]

Re: Need help rebuilding "The Best Power" 500W PSU

What is that piece of wire or something that looks like it is sticking up out of the pcb near the leg next to the positive leg on the bridge rectifier.


You can try to see if that is a short on the fuse, if it really is suppose to be like that then it just won't power on. Either that or take out the things you put in one by one and see if that fixes it, as one might be bad, if you have that many fuses at least.

[Newbie2]

Re: Need help rebuilding "The Best Power" 500W PSU

The fuse doesn't have a short, those two pads are meant to be connected as the PCB is like that:


Another picture of the underside of the primary input side (I redone the solder joints on the primary caps):


A picture of the X cap:


A picture of the blown fuse:


Also, the place where I put the X cap in, is that even a place for an X cap? On the PCB it had "R1" in the rectangle, but it had "'CX2" next to it which I guess means a place for an X cap.


Willawake's ISO 420W PSU, which has the same PCB layout, I think has an X cap in that location:


Which component I installed could possibly be causing this weird problem?

[momaka]

Re: Need help rebuilding "The Best Power" 500W PSU

Looks like you put the input coil the wrong way. I think it should be rotated 90 degrees (doesn't matter clockwise or counter-clockwise). Let's double check that though...
First, remove the X cap. Then, with the coil in there as is (don't remove it or change its position), set your DMM to resistance and put the probes on the two spots I circled in red in the picture below. Do you get a short (0 Ohms)? If you do, you've put the coil the wrong way.

Now remove the coil, set your DMM to resistance check again, and put the probes on the two spots I circled in yellow. What do you get?
If you get a resistance that is low at first but then begins to climb up and goes high, your power supply most likely hasn't been damaged.
In that case, flip the input coil 90 degrees like I said, and it should be working again.



Also, I recall that the bridge rectifier configuration for that power supply was a bit different that other power supplies I've seen. It looks like you got it right, but can you post another picture of the top side of it just to double-check it.

[Newbie2]

Re: Need help rebuilding "The Best Power" 500W PSU

Looks like you put the input coil the wrong way. I think it should be rotated 90 degrees (doesn't matter clockwise or counter-clockwise). Let's double check that though...
First, remove the X cap. Then, with the coil in there as is (don't remove it or change its position), set your DMM to resistance and put the probes on the two spots I circled in red in the picture below. Do you get a short (0 Ohms)? If you do, you've put the coil the wrong way.

Now remove the coil, set your DMM to resistance check again, and put the probes on the two spots I circled in yellow. What do you get?
If you get a resistance that is low at first but then begins to climb up and goes high, your power supply most likely hasn't been damaged.
In that case, flip the input coil 90 degrees like I said, and it should be working again.



Also, I recall that the bridge rectifier configuration for that power supply was a bit different that other power supplies I've seen. It looks like you got it right, but can you post another picture of the top side of it just to double-check it.

I did the first thing you said and got 1.0-1.1 ohms on the multimeter. I did the second thing you said and got a small but rising resistance.

I flipped the coil 90 degrees and installed the 10A 250V fuse, and the power supply works.

Thanks momaka.

[Newbie2]

Re: Need help rebuilding "The Best Power" 500W PSU

I completed my rebuild on this power supply, all Japanese capacitors on the secondary side (Panasonic, United Chemi-con, and Nichicon) along with all the tiny caps. Primary side capacitors are Nippon Chemi-con (forgot the series) 470uf 200V capacitors.

[ratdude747]

Re: Need help rebuilding "The Best Power" 500W PSU

good job! have fun with it, i dare you.

[Newbie2]

Re: Need help rebuilding "The Best Power" 500W PSU

I just hooked up this power supply to my Celeron 2.2GHz computer, and with Prime95 running at the CPU running at 100% I took voltage readings with a DMM:

+12V = 12.13V
+5V = 5.17V
+3.3V = 3.43V

All three of those voltages are within ATX specification.

The -12V and -5V voltages are (these two readings are from the motherboard):

-12V = -11.53V
-5V = -5.10V

The -12V reading from the motherboard is also within ATX specification.

So far this power supply is working great.

[momaka]

Re: Need help rebuilding "The Best Power" 500W PSU

Nice work!
Looks like you got another decent 200w PSU for basic systems.

The voltages seem a bit higher than usual, but they're still surprisingly good (considering that your system is loading mostly the 12v rail... I would have expected the 12v rail to sag). Definitely not bad for a group regulated PSU.
How's the 5vsb, by the way?

[Newbie2]

Re: Need help rebuilding "The Best Power" 500W PSU

I don't really remember the 5VSB reading from the motherboard, I believe it was 5.11V. All voltage readings from this power supply are normal, within specification. It's certainly not frying the motherboard!

My rebuilt L&C power supply is also good on the +12V rail when powering my Celeron 2.2GHz computer, I just took readings of its +12V rail voltages. At idle the +12V rail of the rebuilt L&C is 12.05V, and at Prime95 100% CPU load the +12V rail of the L&C is at 11.90V. Both these voltages were measured directly from the power supply with a DMM.