Questions on recapping a Seasonic SS-300FS

[everell]

Re: Questions on recapping a Seasonic SS-300FS

Here is a schematic showing ALL of the parts on the add on board

[tj2]

Re: Questions on recapping a Seasonic SS-300FS

Thanks for the schematics and notes! I'll check the SS-300FS to see how closely it matches the SS-250FS. The SS-350FS does claim to have APFC.

[everell]

Re: Questions on recapping a Seasonic SS-300FS

I have been working with my SeaSonic psu tonight. Now I can't get it to fail. The only thing failing is a 6.4 gig Western Digital hard drive (mfg date 1998). Will play with it some more later.

[gonzo0815]

Re: Questions on recapping a Seasonic SS-300FS

I think the SS300FS should be a fine and reliable psu apart from caps.
I have used the ss300FS and especially the SS400FS in most AMD K7 / K8 builds.
The 5v sb is AFAIR a topswitcher circuit, pretty safe and solid IMHO. Not a board killer, even with bulging caps.
Have recently checked one of my K8 builds with an SS400FS (i upgraded the HDD from 40gb to 1TB as the user needed more space) and replaced the last few capacitors, i had not replaced right from the start.
The positive with this psu is, that there are not that much smaller capacitors at all, so i replaced every capacitor in it with FC, FM and LXY.



I know, that most of the SS400FS do have a blown zener diode in it, but i assume that this is from a mistake during production or development and is already fixed at the solder side.

[tj2]

Re: Questions on recapping a Seasonic SS-300FS

gonzo0815, in general, how does one distinguish between a TOPSwitch circuit and the two transistor 5 Vsb circuit by looking at the components? (I'm a noob to PSU design and appreciate any education on the topic I can get.) The SS-300FS does have two transistors next to each other, as pointed out by Toasty. Even if this supply does have a TOPSwitch, I assume that the Everell mod would be more reliable yet. Is that correct?

[Toasty]

Re: Questions on recapping a Seasonic SS-300FS

Lookup TOPSwitch on Google or search for: TOP242 First hit (comet.bg) datasheet and look it over.

The TOPSwitch does what Everell's does and more in one package. Apple used them in the later iMac PSU's and I have not seen a failure in 5vsb where one was used. A few small external components and it works a peach!

Can't speak as to reliability of Everell's mod. It does work from what has been shown. Time will tell...

Toast

[tj2]

Re: Questions on recapping a Seasonic SS-300FS

After learning what to look for, I had to go look at the PSU to see what was there. I didn't see any TOP2xx labeled devices, but the larger transistor appears to be a K3067. So, although I won't know for sure until I pull the board and trace the circuit, it appears that the SS-300FS does have the two transistor 5 Vsb circuit, not a TOPSwitch. Bummer.

[everell]

Re: Questions on recapping a Seasonic SS-300FS

I worked on one psu that had a TOP222. They have an aluminum cap going to the control pin - for frequency or timing. The cap had gone HI ESR, but the 5vsb simply stopped and went to zero. Somewhat of a "critical" cap but does not go overvoltage when failing.

There are several pwm circuits out there for the 5vsb. I have found a few that went to zero when problems developed - but I have not seen any go over volt like the typical two transistor circuits do. Thats why I like them - they save the mother board from destruction.

The TOP switchers are the hardest to identify. The TOP chip looks just like a power transistor screwed to the heat sink. Then you can fine a small TO92 style transistor nearby which is used for startup. The only way to tell is to read the "fine print", that is, read the part number on the chips and transistors.

[tj2]

Re: Questions on recapping a Seasonic SS-300FS

Things get less busy at work during the holidays and I have caps and the DM311 and diodes, etc, on the way. I'm going to start working on the board in the next week or so and I should understand the SS-300FS better then. Of course, I can't see all the "fine print" on all of the three-terminal devices attached to the heat sinks, so one of them could be a TOPSwitch, but I bet not. I'm betting that the SS-300FS is similar to the SS-250FS and will be mod-able with an identical, or nearly identical, DM311 circuit to the one on the SS-250FS.

It sounds like the DM311 5Vsb circuit might be better than one using a TOPSwitch since the DM311 doesn't seem to be designed to dissipate as much heat as a TOPSwitch.

[gonzo0815]

Re: Questions on recapping a Seasonic SS-300FS

Well, i have a SS400FS on my bench, may be i check what kind of 5v Sb circuit they have.
Apart from that, topswitch circuit is a good design, IMHO no need for mods.
The topswitch in to220 is designed for higher power output, thus it comes in a package with better heat dissipation. This is obviously better then a small foot print package.
You can by them in any package, so in reality the DM311 is another form of topswitcher device, just another mfk.

[everell]

Re: Questions on recapping a Seasonic SS-300FS

Hi Gonzo - let me know if that SeaSonic of yours has a TopSwitch 5vsb circuit. I have never seen one in a SeaSonic - but that doesn't really mean much.

I found my first TopSwitch pwm chip in a Enhance EHP-0735 (350 watt). At first I thought it was a two transistor circuit, but when checking a data sheet for TOP222 found it to be pwm chip - and an interesting one! I thought about modifying a psu by inserting a TopSwitch where the power transistor is installed. But......pin connections are such that I would have to do a lot of cutting out circuit traces and rewiring. Also, I wanted to do some esr testing. So I built a "breadboard" of the circuit that is in the Enhance EHP-0735. Drawing and photo attached.

[everell]

Re: Questions on recapping a Seasonic SS-300FS

The reason I wanted to do ESR testing on the TOP-Switch TOP222 is because it looked like it had a "critical cap" like the two transistor design. Take a look at my drawing comparing the two transistor circuit to the TOP222.

The two transistor drawing shows only SOME of the basic components (taken from Bestec ATX-250 12E) and the TOP222 drawing shows SOME of the basic components (taken from the Enhance EHP-0735).

The critical cap in the two transistor circuit is C1. By inserting a resistor in series with this capacitor to simulate esr, you can see a definite increase in the 5vsb rail voltage - upwards to 17 volts or so. The capacitor in the TOP222 circuit which looks like it should be a critical capacitor is C4. I used resistor values of 6 ohms, 12 ohms, 25 ohms, 50 ohms, 100 ohms, and 150 ohms to simulate ESR. With each resistance value tried, the 5vsb stayed locked at 5.00 volts. Next, I simulated an open capacitor by removing the capacitor from the circuit. The 5vsb went up to 5.26 volts.

Next, I tried all of these resistor values as ESR in series with the capacitor C5 at the control pin. The circuit powered up and worked, locked at 5.00 volts. Only when I went to a 200 ohm resistor did it refuse to start.

In conclusion, the location of the C4 capacitor in the TOP222 looks like a "critical cap" which would cause problems with aging and esr, but test results showed otherwise. I could make the circuit stop, but I could not make it go overvoltage like the two transistor circuits do.

I still prefer the DM311 circuit, but I have nothing bad to say about the TOPswitch series of pwm chips for 5vsb circuits, and would not replace it as I would a two transistor circuit.

[i4004]

Re: Questions on recapping a Seasonic SS-300FS

between dm311 and topswitch (for a 5vstby mod) i would pick the one that requires less external components...
i would think reliability and durability(and preotection form 5v going too high) is about the same, ie pretty good.

>I thought about modifying a psu by inserting a TopSwitch where the power transistor is installed. But......pin connections are such that I would have to do a lot of cutting out circuit traces and rewiring.

doesn't need to be connected there at all...i mean your dm311 addons are not pin compatible either...
<wink>

interesting experiment there with breadboard...keep us up to speed about the progress there...ie how much esr shuts it down....
btw. did you do the same test with dm311?

edit/ ough, that was fast...glad to see you proved topswitch is safe too...

[everell]

Re: Questions on recapping a Seasonic SS-300FS

Good evening i4004 - or at least it is evening here!

I did not do any esr testing on the DM311 circuit because it doesn't have a capacitor in the feedback circuit. Take a look at the schematic I posted earlier. The feedback hooks directly to the collector of the optocoupler and the emitter of the optocoupler goes to common (AC ground). The only aluminum electrolytic capacitor in the DM311 circuit is the filter for VCC. As regards VCC, it either works or doesn't. I have thought about using a tantalum capacitor in this location, but have not tried yet.

As for the TOP222, I was concerned that it might have the critical cap problem like the two transistor circuits. So far, that is not the case.

[i4004]

Re: Questions on recapping a Seasonic SS-300FS

it's morning here, and at -6 or -7°c, so cold that my dish motor was stuck, untill wd40 came to its help.

>I did not do any esr testing on the DM311 circuit because it doesn't have a capacitor in the feedback circuit.

excellent.
excuse my ignorance, i should of payed closer attention and have the 311 datasheet by now.
but the fortrons i buy already have it in, so....heh..you get the point.
<wink>

oh yeah, excellent job, once again, in exposing the +5vstby secrets to us all!
i would be doing the same thing if it wasn't for these damn nice fortrons that are not that expensive at all.
you keep up the good work, it's very interesting.

[everell]

Re: Questions on recapping a Seasonic SS-300FS

I decided to add one more feature to the DM311 5vsb mod on my SeaSonic. A home made heat sink.

Here is how you do it. Eat one can of Libby's corn for supper. Instead of throwing away the can, use the can opener to remove the bottom of the can. Using tin cutters, cut across side of can from top to bottom. You now have lots of heat sink material. Just cut a piece to the shape you want. Then solder it to the pins that need the heat sink. The tin in the tin can takes solder nicely.

[Shocker]

Re: Questions on recapping a Seasonic SS-300FS

The tin in the tin can takes solder nicely.

I thought they weren't made of tin anymore.

Regarding the circuit, why are there three 330k resistors in series??? Why not just a single 1M resistor???

[tom66]

Re: Questions on recapping a Seasonic SS-300FS

Probably a combination of break-down voltage and power dissipation limits.

[budm]

Re: Questions on recapping a Seasonic SS-300FS

Break down voltage is one of the reason. When I do breakdown test for US product, we use 1250V, and up to 3000v for Export. Typical breakdown voltage for the resistor is about 250~500V.

[everell]

Re: Questions on recapping a Seasonic SS-300FS

tom66 and budm are correct. It was done because these resistors are speced for 200 volts max. By using three resistors with about 320 volts across them, each resistor is well within spec. I have seen psu circuits that use one resistor for startup, usually one meg in value. Over the years I have seen many resistors in the megohm value that were open, some of which was probably caused by overvoltage.

If a manufacturer wants to save money and use only one resistor, I don't think the engineer is worried about using only one resistor since he doesn't have to pay the repair bill....................

I still think my tin can heat sink is a classic. I put a red circle around the heat sink to clarify what was done. It may not be 100% tin, but it does take solder.