YLP-013 450W capacitor value.

[rattman]

Hi Everyone.
I have a YLP-013 450W power supply, Rev 2.2
and I'm looking for the value of C28. This disc cap
disintegrated When Q7, part #C5027 shorted out
which is connected to the collector of Q7.
Thank you in advance.

[sam_sam_sam]

Re: YLP-013 450W capacitor value.

Please post pictures of this power supply

[rattman]

Re: YLP-013 450W capacitor value.

I apologize, it is a power supply out of a desktop computer.
Here are a few pics of the power supply with heat sink in
and out of the supply board. Pic #3 shows the damage of
Q7, and the location of C28 that was removed. I cleaned
the board up a little to see the locations of the damaged
components. Any help would be appreciated.
Thank you.

[momaka]

Re: YLP-013 450W capacitor value.

Rattman, are you repairing this power supply for fun / as a learning experience, or actually doing the repair for a customer (or yourself)? Reason I ask is because that power supply appears to be a cheapo unit that isn't really worth investing time into, unless you're doing it to learn / for fun.

In any case, that cap (C28) and transistor Q7 are part of the 5VSB circuit on the power supply. Being a cheap PSU, this is a 2-transistor self-oscillating flyback circuit. Q7 is the main switching component and transistor Q4 is its driver. Chances are, Q4 is probably blown too (either short-circuit or open-circuit is possible, since it's a small transistor.) Also worth checking are all the diodes in that circuit. And if you have an ESR + capacitance meter, check the output capacitors of the 5VSB circuit. If not, replace them. There's a good chance those are bad and caused the circuit to go bad.

As for C28, I can't tell you exactly what it is without some pictures of the other side of the PCB. It may be just a small value cap across Q7 Collector-Emitter terminals, or it may be for something else. As for the ceramic disc cap above that - it appears fairly large and is likely part of the RCD snubber network, so I don't think C28 is a snubber cap.

But again, will need pictures of the traces to determine that.

The 5VSB on this PSU being a 2-transistor circuit means it's going to be a fairly simple circuit. However, those 2-transistor circuits are very "particular" about having all parts working. If one part is bad, they tend to blow themselves up again. With that said, when you do any further experiments (after attempting a repair, that is), make sure to use an incandescent light bulb (about 60-100W) in series with the PSU's live input (or just remove the fuse and connect the bulb across that). This will limit the current and save your PSU from blowing more parts, should the 5VSB try to do anything "ballistic" again.

[rattman]

Re: YLP-013 450W capacitor value.

Thank you for the reply momaka.
Trying to save a few bucks by repairing it, but it appears that YUELIN does not want you to repair it as there are no schematics to be found anywhere.
I have an EDS in circuit cap checker that I checked the caps with, they appear to be okay.
I do use the light bulb trick when repairing TV's, but did not think to use it on power supplies which is a good idea, thanks for the heads-up.
When the power supply shorted out the computer was off. It came with a mid tower Power-up computer case I bought online a while back.
I added a few pics showing the bottom of the power board.
Thanks again.

[PeteS in CA]

Re: YLP-013 450W capacitor value.

Judging from the second picture in post #3 of this thread, it looks like the PSU has generic 1KV (DC) caps where safety agency rated Y caps (250VAC or higher, with special construction) should be used. If so, that is a safety issue.

[rattman]

Re: YLP-013 450W capacitor value.

Here are a few more pictures of the power supply with a couple numbers on the top in Pic #8 that might help. If someone has this power supply I would appreciate it if you could look at the C28 disc capacitor and see what the value is on that capacitor. Thank you in advance.

[R_J]

Re: YLP-013 450W capacitor value.

I don't have that ps but maybe this will help?

[rattman]

Re: YLP-013 450W capacitor value.

It does help me quite a bit, thank you R_J.

[momaka]

Re: YLP-013 450W capacitor value.

The diagram that RJ posted looks pretty similar to your PSU. Check the value of the orange ceramic capacitor above C28. If it's 10 nF like on RJ's diagram, then C28 should probably be around 470 pF. Since it blew up on your PSU, check the resistor next to that orange ceramic capacitor for being open-circuit. Basically, C28 is part of the snubber network, so everything must work properly there. Otherwise, those parts and the switching BJT could blow again.

While at it, also check the small TO-92 transistor Q4 for short and open-circuit (will need to remove it from the board to check it properly.)

[rattman]

Re: YLP-013 450W capacitor value.

Thank you for the input momaka.
I will check the value of that disc capacitor above C28
to see if its value is 10 nano, & check Q4 to make sure
it is not open or shorted and also that resistor.
I will post the results and let you know what I find.
Again thank you for the info.

[rattman]

Re: YLP-013 450W capacitor value.

I checked the resistor, (R65=100K Ohms) next to/behind capacitor (C27=10 nF), it measures 99.1K ohms.
Since C27 is 10 nF I agree that C28 should be about 0.47 nF 1KV. Checked Q4 for an open/short, measured
okay but has a crack across it so I'm gonna replace it. Ordered the replacement parts and will let you
know how it goes.

[R_J]

Re: YLP-013 450W capacitor value.

Q4 is not likely cracked, it's just how some of the to92's are made (they are made in two parts and fused together)

[momaka]

Re: YLP-013 450W capacitor value.

Q4 is not likely cracked, it's just how some of the to92's are made (they are made in two parts and fused together)

You're probably right. But he might as well replace it now - less chance of bad components remaining that way.

[rattman]

Re: YLP-013 450W capacitor value.

Got my parts in and replaced Q4, Q7, and C28. There are no shorts, checked with a 75 watt light bulb across fuse connection. Installed the fuse jumped the green wire and a black wire, nothing. Even tried with a hard drive hooked up for a load, no go. With the jumper in place checked for 5v and 12v, nothing. I will retrace my steps to see if I missed something.
Q4 has a crack under the part number around the side to the back.
Thanks again for your continued help and input.

[R_J]

Re: YLP-013 450W capacitor value.

That circuit seems to be the standby circuit only, It should work without any jumpers etc. and you should have standby voltage

[momaka]

Re: YLP-013 450W capacitor value.

I agree with R_J here - forget about jumpering the PS_ON signal (Green to ground) for now. First, you must get 5V on the 5VSB pin (purple wire). This should be up as soon as the PSU is plugged in. Without 5VSB, nothing else will work.

If all components check out fine, check the 5VSB transformer's primary windings for open-circuit: that is, the main winding (which should be connected between Q7 collector and +340V tap on the big input caps) and the aux. primary winding (this one should be connected between ground and the 100-Ohm resistor in front of the 5VSB transformer.) If either of these two windings reads open-circuit or high resistance (over 10-20 Ohms, I'd say), the 5VSB traffo may be gone. Also check the source resistor for Q7 (if there is one, as I don't see it) and the 680-KOhm resistor (color code: blue, grey, yellow, gold) next to it. The 680-KOhm resistor is really high resistance, so you need to remove it out of the circuit to check it properly.

[rattman]

Re: YLP-013 450W capacitor value.

Hi momaka. I checked the resistance on the transformer and the resistance readings are less than 1 ohm. The components check okay. Checked the voltage on the purple wire but it is not 5 volts. The voltage goes from about 2.71 volts to 3.04 volts, goes up and down constantly. Thanks again for everyone's help.

[momaka]

Re: YLP-013 450W capacitor value.

Checked the voltage on the purple wire but it is not 5 volts. The voltage goes from about 2.71 volts to 3.04 volts, goes up and down constantly. Thanks again for everyone's help.

Good observation.
That means the 5VSB is actually either trying to start or not regulating properly.
The issue that can cause the former would be an overload from a component somewhere or perhaps bad startup capacitor (which your 2-transistor 5VSB circuit doesn't appear to have) or bad output capacitors. And the latter could be due to either bad optocoupler or bad 431 shunt regulator on the secondary side. So it might help to swap these with known good working ones, just to make sure.

[Bill Sullivan]

Re: YLP-013 450W capacitor value.

I know this is an old post but thought I would answer since I have this board and Rev 2.1 board.
YLP-013 Rev 2.2 c-28 is 221 1kv, c-24 is 103 1 kv