Requesting Advice - PSU 5vsb repair

[Fluxcored]

After successfully reviving a Silverstone Strider 650 (Enhance ODM?) by replacing some blown 8mm Teapo caps with Chemi-Con KZHs I am feeling confident to attempt repairing another Silverstone PSU, this one with 5vsb issues. The unit in question functions well enough, until S3 sleep is invoked. It will wake the system from sleep, but the DRAM voltage LED on the Asus 775 motherboard lights up red after the system wakes. Once that LED is red, the system will invariably hang, with no Windows log to diagnose. Not until the PSU is unplugged (capacitors discharged?) will the led light reset and the system function normally... until the next S3 sleep.

I put quite a few hours into researching block diagrams and general principles of switching power supplies, and compared that to what I see on the disassembled board. Included are some high resolution pictures of what I believe is the 5vsb circuitry and in particular some burnt looking trace connecting one of the components.

At this point I am stumped. The blown caps on the first unit were easy enough to diagnose, but I don't know exactly what I am looking at on this second unit. Have I located the probable cause of the problem? Which components might need to be replaced? I am familiar with DigiKey's site.

IMG_8304.JPG - IMG_8309.JPG are of the possibly damaged area. This corner of the board should be part of the 5vsb rail I think?

IMG_8319.JPG, IMG_8324.JPG, IMG_8325.JPG are other shots of the PSU board

Thanks for any help. I certainly would appreciate any advice from the veterans.

[Khron]

Re: Requesting Advice - PSU 5vsb repair

No, that corner of the board contains the active PFC circuitry.

The 5Vsb area is (somewhat) visible in IMG_8319 - the small transformer on the right edge of the main PCB is definitely, and the 8-pin IC is quite likely part of the 5Vsb circuitry. Also, the part in a TO-220 on a "stand-alone" heatsink just "north" of the small transformer is very likely the 5Vsb switching FET.

[Fluxcored]

Re: Requesting Advice - PSU 5vsb repair

Thank you for your insight.

Aside from the burnt looking part(s) in the first few pictures, I can't make out anything visibly wrong. I'm having a hard time finding information on what components are responsible for 5vsb dying.

For reference, the unit is almost identical to this one reviewed here, except it's the Strider ST60F 600W version:

http://www.jonnyguru.com/modules.php...Story4&reid=27

Dang that was reviewed in 2006, I suppose I should be thankful it has lasted 6+ years. It'd be nice to fix it up, of course

[Khron]

Re: Requesting Advice - PSU 5vsb repair

Both the darkening / charring on that yellow ceramic capacitor, and the looks of its solder joint (on the bottom of the board) look like some sort of overheating - for safety's sake, you'll wanna replace that.

Can you read the part numbers of the two components i mentioned in my previous post? And some well-focused photos from that area might help too...

[Fluxcored]

Re: Requesting Advice - PSU 5vsb repair

Here is a picture closer nearer the 5vsb components. I'm also going to take some readings of output voltages to add to the discussion.

[Khron]

Re: Requesting Advice - PSU 5vsb repair

That 8-pin chip is a TL3843 (current-mode controller), and it's using that heatsinked FET as a switching element. The chip's datasheet says it has a UVLO threshold of 16v for turn-on, and 10v for turn-off.

(UVLO = undervoltage lock-out; it needs its Vcc voltage (at pin 7) to go over 16v for it to turn on, and to stay above 10v after that; if the voltage drops below 10v, it turns off, and won't turn back on until Vcc goes above 16v (again) )


As a first step, i'd try to scrape off some of that tan(?) glue that's all over Q8 and the capacitor right next to it. Next, i'd replace at least those 2-3 electrolytics with much more trustworthy 105C rated japanese caps.

Also, you might want to extract and test those two diodes, and perhaps even the FET.

But indeed, some voltage readings WILL help

[Fluxcored]

Re: Requesting Advice - PSU 5vsb repair

forefront left - Sharp optocoupler PC817
forefront right - Texas Instruments TL3843P - Current-Mode PWM Controller
on the heatsink - Power Integrations TOP222YN - Three-terminal Off-line PWM Switch
the caps are Jamicon in this area.

Yes that is the same kind of glue found all over the unit, binding various parts together.

[Fluxcored]

Re: Requesting Advice - PSU 5vsb repair

Voltages looked good with no load. Voltages looked good with PSU back in the case and all internal connections made. One by one I added external peripherals and toggled S3 standby. Eventually the 5vsb dips down to 4.1v - 4.2v during S3 and will set off the motherboards warning LED. 5vsb returns to normal after resume, but the motherboard warning LED is lit and eventually the computer will freeze without warning.

[Fluxcored]

Re: Requesting Advice - PSU 5vsb repair

Thanks again for your help Khron.

[Khron]

Re: Requesting Advice - PSU 5vsb repair

You're welcome

What capacitors are there, on the 5Vsb output? I think i see a fat blue-sleeved Teapo-vented cap in that area. What're the odds that's either some 85c rated part, or some general-purpose 105c? And is that on the 5Vsb or the -12v rail? I'd still replace the small caps in the 5Vsb area, on the primary - at least for peace of mind. When those start to crap out, they can cause all sorts of wacky behaviours.

Replace those, and the caps on the 5Vsb output with some proper japanese ones, and see if it helps things.

[Fluxcored]

Re: Requesting Advice - PSU 5vsb repair

Shots from around the 5vsb output. Idle and under 100% CPU load, this rail measures ~5.05v at the motherboard connector. Depending which devices are enabled and connected, 5vsb drops to between ~4.15v and ~4.45v when in S3 standby.

[everell]

Re: Requesting Advice - PSU 5vsb repair

I am not familiar with "S3 standby mode". Is this a motherboard function? If so, the problem might be with your motherboard rather than with the power supply.

By placing various values of resistors across the 5vsb rail, you can determine how well the 5vsb is working. Other than that, you have to use "ether theory"....ether it works or it doesn't!

[cheapie]

Re: Requesting Advice - PSU 5vsb repair

I am not familiar with "S3 standby mode". Is this a motherboard function? If so, the problem might be with your motherboard rather than with the power supply.

That's standard "Suspend to RAM" standby. I'm wondering if maybe this PSU can't power all of his RAM (it's on +5VSB during standby, most other times it's on +12V (I think)). Try it with less RAM installed.