Antec SL300S Standby Voltage high.

[jdTech]

1st, I know... just dump it

I have a Antec Smart Power SL300S that the standby voltage is reading ~6.35 unloaded. If I load it the voltage drops to ~5.0V:

10 ohm load output is 5.08V
5 ohm load output is 5.07V
2.5 ohm load output is 5.05V

This unit had bad Fuhjyyu caps on the +3.3, +5.0, and +12.0V rails. It was working in my dad PC until the fan stopped work. When I when to change the fan I noticed the bad caps. It sat in the to do pile until now. After changing the caps and testing I noticed this STANDBY voltage issue.

When I jump the TURN-ON to GND and main supply comes up the the STANDBY drops to ~5.0V.

I don't think this is normal since the label states 0 amps for a min STANDBY load. Also, there is a internal 50 ohm load on the STANDBY rail.

Changing the two 680uF STANDBY filter caps didn't help.

Thanks!
Jim

[c_hegge]

Re: Antec SL300S Standby Voltage high.

There should be a small 22uF 50V in the 5vsb circuit. replace it. It often causes the 5vsb to go too high when it fails. It it's still no good, then it's time for a DM311 mod or a new PSU.

[Toasty]

Re: Antec SL300S Standby Voltage high.

See: https://www.badcaps.net/forum/showthread.php?t=8024

If it's anything like the 350 or 400, replace all the little caps. The mains caps aren't really a problem.

[Longbow]

Re: Antec SL300S Standby Voltage high.

There should be a small 22uF 50V in the 5vsb circuit. replace it. It often causes the 5vsb to go too high when it fails.

That's good know from experience, but I don't see how it relates to the information given by jd. His loaded voltages look just fine. Some supplies cannot be evaluated under a no-load condition. That is why, for example, that you see load clips available from PC Power and other manufacturers. Great photos and tutorial from Toasty on this supply!

[Toasty]

Re: Antec SL300S Standby Voltage high.

The 5vsb should remain in spec whether it is loaded or unloaded. If it's floating high with no load, then something is wrong. c_hegge is correct in that cap replacement, but I do all the little ones too -
1) because I'm there (and don't want to go back, ever!)
2) it's cheap insurance

[PCBONEZ]

Re: Antec SL300S Standby Voltage high.

""it's cheap insurance""
Like tin foil.

[Th3_uN1Qu3]

Re: Antec SL300S Standby Voltage high.

You should also put a 5.1v 1W zener on that rail after you fix it. If it decides to go wonky, the zener will eat up the extra power. If it decides to go REAL wonky, the zener will short and blow up the switching transistor, but at least the motherboard will survive.

[jdTech]

Re: Antec SL300S Standby Voltage high.

Thanks for all the input! Here is an update.

Changing C14 (22uF 50V) lower the STANDBY to ~5.7V. Changing C8 (47uF 25V) did the trick, STANDBY now reads 5.10V.

I'll now change the remaining small caps.

BTW, I did find the the main supply would not turn on until the STANDBY voltage was =< ~5.5V. Also, the STANDBY would start out at ~6.3V and then slowly fall.

I was thinking about the zener across the output myself. Is there a low voltage MOV that would work better or faster?

Thanks again for everyone's help!

Jim

[jdTech]

Re: Antec SL300S Standby Voltage high.

BTW, that 47uF (C8) read about 5nF on my cap tester!

Jim

[Th3_uN1Qu3]

Re: Antec SL300S Standby Voltage high.

I was thinking about the zener across the output myself. Is there a low voltage MOV that would work better or faster?

No, just use a normal 1 watt zener. Best protection there is.

[everell]

Re: Antec SL300S Standby Voltage high.

You should also put a 5.1v 1W zener on that rail after you fix it. If it decides to go wonky, the zener will eat up the extra power. If it decides to go REAL wonky, the zener will short and blow up the switching transistor, but at least the motherboard will survive.

Here is a picture of a Fortron power supply that had the zener diode and failed. The heat sinks and 5vsb transformer have been removed so that you can see how extensive the burn damage is to the pc board. The motherboard may have been saved but the power supply is not very fixable because the burn damage goes all the way thru the pc board. This board went to the junk pile!