Seasonic S12 (SS-500HT F3) zener

[Behemot]

I got this PSU which is not working, no stand-by voltage.

From quick finger-test the PFC is OK, capacitor was charged. I found blown resistor (white gold gold orange orange, no idea what resistance) on +5 V SB and also zener at Vcc for the ICE2A0565G controller. It says it wants 8,5-21 V in datasheet. I am not able to read the value of the SMD zener. It seems like 8 V but that is too low. What would be the best value? There is chemi-con KY 47 uF/25 V cap on the Vcc.

[Behemot]

Re: Seasonic S12 (SS-500HT F3) zener

I finally found good photo of this PSU (or PSU with this board) and the resistor is indeed like that: orange, orange, gold, gold, white. That seems to be 0R33 +-9%? Wut?

[Behemot]

Re: Seasonic S12 (SS-500HT F3) zener

Anybody has any explanation for the resistor? I will jsut stick some zener in, possibly around 15 V, but the resistor is a mystery…

[Majestyk]

Re: Seasonic S12 (SS-500HT F3) zener

I don´t think there´s a white ring for tolerance.

My suggestion would be
Orange=3
Orange=3
Gold=Multi 0,1
Gold=Tolerance 5%
White=Voltage 900V

It seems to be a MOX (Metal Oxide) resistor that has a special characteristic when disrupting the circuit in case of a short / overload.
It must be replaced by a MOX type again for continued safety.

[Behemot]

Re: Seasonic S12 (SS-500HT F3) zener

So you think 3R3 metal oxide? Seems plausible…

[budm]

Re: Seasonic S12 (SS-500HT F3) zener

I would use 20V 1/2W Zener so the VCC cannot go above the 21V Vmax of the VCC when the power supply first start-up, that IC is probably running at around 16~18VDC or so.
That resistor (3.30 Ohms), is one end connected the main cap + and another end is connected to to one of the leg of the SMPS Tranformer for that ICE IC

[Behemot]

Re: Seasonic S12 (SS-500HT F3) zener

Cool, thanks. But wouldn't be 18-19 V safer?

[Behemot]

Re: Seasonic S12 (SS-500HT F3) zener

With 20V zener and the 3R3 resistor, I got lightbulb fully on and no stand-by voltage. There still seems to be some short or similar problem…I got 2A0565Z here, do you think it's worth replacing? Maybe the PWM controller itself is shorted internally…if both the resistor and zener are blasted…

[budm]

Re: Seasonic S12 (SS-500HT F3) zener

The 3R3 is blown for a reason, so how is that resistor is connected? What is the resistance reading between the Source pin3 and and the Drain pin4/5, Pin 8 Ground and pin 7 VCC of that ICE2 IC?

[Behemot]

Re: Seasonic S12 (SS-500HT F3) zener

Drain to source and Vcc to ground is OK but there is short between source and ground. So either the IC or small TO-92 transistor in there, I detect short between 2 of it's legs as well.

[budm]

Re: Seasonic S12 (SS-500HT F3) zener

Source and Ground resistance will be <1 Ohm for the I sense Resistor circuit, so that is normal. I guess you will have to see what is shorted out that causes the lamp to light up brightly.

[Behemot]

Re: Seasonic S12 (SS-500HT F3) zener

Well, the FET inside does not seem to be shorted, that's for sure.

The resistor connects high voltage from capacitor to one pad of transformer, that is also connected through ceramic capacitor to some diode. I'll check more components in here tomorrow and take some pics probably…

[momaka]

Re: Seasonic S12 (SS-500HT F3) zener

Well, the FET inside does not seem to be shorted, that's for sure.

The FET may not be, but it's driver inside the chip could be. No way to tell, though. My advice would be to just take out that 3.3 Ohm resistor and see if the light bulb lights up and stays lit again. If it does, the problem is elsewhere.

The resistor connects high voltage from capacitor to one pad of transformer, that is also connected through ceramic capacitor to some diode.

The ceramic capacitor and diode are probably for the snubber network - they clamp down high voltage spikes from the transformer's inductive kick-back when the FET turns OFF.

Also, some PFC circuits tend to fool the light bulb trick (or it takes a very long time until the cap charges, and then it goes OFF). Therefore, I suggest you temporarily disable the PFC circuit until you get at least the 5VSB supply running (but also preferably the main PS too). You are on 230 V line, so the lack of PFC won't cause many adverse affects. You can disable the PFC either by removing its MOSFET or by removing the MOSFET's Source resistor (probably another low-Ohm resistor).