Delta PSU won't power up after recap

[Pentium4]

at work I got a delta psu that wouldn't do anything, no standby, nothing. I opened it to find 3 bulging caps, one of them being the 5VSB cap. after the recap, once plugged in, the green light will light up in the back but it won't start up. I plugged it into our coolmax digital psu tester, and once plugged in the green light turns off in the back. is it being shorted somewhere?

[retiredcaps]

Re: Delta PSU won't power up after recap

Maybe this will give you some ideas? Your PS might be in some protection mode?

https://www.badcaps.net/forum/showthread.php?t=22171

[ben7]

Re: Delta PSU won't power up after recap

Is the 5vsb going to 0v? Did you replace all the caps in the 5vsb circuit?

[Pentium4]

Re: Delta PSU won't power up after recap

I don't have a multimeter right now to check, but yeah I replaced all the caps except one Ltec that I didn't have on hand but it wasn't on the 5VSB I'm pretty sure. The 5VSB seems to be working amazingly. After unplugging it, the light on the back stays lit up for over a minute. Thanks for the link, I'll check that out.

[retiredcaps]

Re: Delta PSU won't power up after recap

After unplugging it, the light on the back stays lit up for over a minute.

I have noticed that many of the ATX power supplies I have worked on, the large filter caps tend to hold their charge for as long as 2-5 minutes. These caps can hold up to 400V DC if you have PFC involved.

I remember not waiting long enough for one PS and I got a bit of a rude surprise. Now I check with a multimeter before I start working on them.

[Pentium4]

Re: Delta PSU won't power up after recap

I have noticed that many of the ATX power supplies I have worked on, the large filter caps tend to hold their charge for as long as 2-5 minutes. These caps can hold up to 400V DC if you have PFC involved.

I remember not waiting long enough for one PS and I got a bit of a rude surprise. Now I check with a multimeter before I start working on them.

Wow, 2-5 minutes is pretty impressive. This one doesn't have PFC but the large filtering cap is a UCC KY series cap, replacing an Ltec LTG series cap. How bad was the shock? I can't imagine it being too bad.

[retiredcaps]

Re: Delta PSU won't power up after recap

How bad was the shock? I can't imagine it being too bad.

Since I was a complete newbie in every respect back in April 2010 to electronics, I had a heathly respect for the large filter cap based on my readings here (particulary thanks to PlainBill using the words lethal, 911, hospital, heart stoppage, etc).

It scared the sh** out of me when it made a big spark.

In my thread that I linked, I expressed how I hate working on the ATX form factor due to its compactness and difficulty in making voltage measurements. When I do measure DC voltage on an ATX PS, I wear safety googles and try to use aligator clips so I don't have to use both hands.

I also use Fluke's touch hold feature to get a reading so I can concentrate on holding the probe steady and not slipping.

[retiredcaps]

Re: Delta PSU won't power up after recap

Wow, 2-5 minutes is pretty impressive.

I worked on a LG 2234s (22 inch lcd). The big filter cap did not discharge overnight (it sat at 165V DC the next morning). I had to manually discharge with a 100k ohm resistor it before working on it.

Good thing I checked the voltage across before I began soldering.

edit: PS, the 100k resistor was pulled from a junk PS board.

[Pentium4]

Re: Delta PSU won't power up after recap

I worked on a LG 2234s (22 inch lcd). The big filter cap did not discharge overnight (it sat at 165V DC the next morning). I had to manually discharge with a 100k ohm resistor it before working on it.

Good thing I checked the voltage across before I began soldering.

edit: PS, the 100k resistor was pulled from a junk PS board.

It had that much charge left after sitting overnight??? No wonder you check them now before you start working on them

[ben7]

Re: Delta PSU won't power up after recap

It had that much charge left after sitting overnight??? No wonder you check them now before you start working on them

Yeah, I always check too - after having a few scares from sparks and bangs, and zaps

[momaka]

Re: Delta PSU won't power up after recap

The 5VSB seems to be working amazingly. After unplugging it, the light on the back stays lit up for over a minute.

Try hooking some sort of resistance on the 5VSB. 0.25 to 1A is usually good enough. I have an incandescent 12V 30W car light bulb for this. After unplugging the power supply, it takes just a few seconds for the large cap to discharge. I can even hear it on most power supplies (they make a high-pitched "whizzzzz" sound). At that point, the primary cap(s) should be at 30V or less. regardless, DO CHECK WITH A MULTIMETER FIRST!

Also, if you load the 5VSB with any decent load (0.25A or more) and you hear high-pitched whining noises, the 5VSB may not be regulating properly. Usually happens when the 5VSB output caps go bad. If you hear this noise, unplug PSU quickly and check the 5VSB output caps. Running the PSU like that can damage it further.

How bad was the shock? I can't imagine it being too bad.

Depends how you receive it. If it goes just across your fingers on one hand, it's not THAT bad. More or less feels like getting stung by a bee for a second. Now if it goes through one hand and out from the other - that could hurt a lot more. In fact, you may uncontrollably pull your hands or fingers - and that's the dangerous part cause you can get cut on something or throw a tool in your face.

I worked on a LG 2234s (22 inch lcd). The big filter cap did not discharge overnight (it sat at 165V DC the next morning). I had to manually discharge with a 100k ohm resistor it before working on it.

I've had that happen with a CRT monitor as well. In my case, the primary cap stayed charged for over a week! No PFC or voltage doubling circuits, so like yours it was sitting just at 165V. Luckily, I decided to check it before I started working. Shorted the terminals with a screwdriver and nearly crapped myself when the sparks flew.

The worst I had was a 450 V 150 uF cap in an LCD TV charged to 380 V. That one I just didn't check since it was a new PSU and I ASSumed it was discharged. Well, it wasn't and I got stung.
Just FYI, a 150 uF cap charged to 320 V is more painful than a 330 uF cap charged to 160 V - packs almost 2x the punch.

[ben7]

Re: Delta PSU won't power up after recap

Haha momaka! I bet there was the smell of burnt flesh in the air after that!

Pentium4 - are any of the output rectifiers shorted?

[momaka]

Re: Delta PSU won't power up after recap

Haha momaka! I bet there was the smell of burnt flesh in the air after that!

Fortunately, no. Not powerful enough.

[tom66]

Re: Delta PSU won't power up after recap

Certain cheap Vestel TVs are well known for keeping the filter cap at ~200V when unplugged due to the lack of any discharge resistor. I also had an Atec TV which due to a fault wasn't drawing much current so the filter cap also stayed charged.