Generic AT-2005B PSU

[pdavid]

I recieved this psu with vented JEE caps and some snapped wires. I powered it up and laughed at the 3.3V rail which was 3.6 high!
It doesn't look that lame so maybe it's worth fixin, I thought. The label claims 400W max output... right.
Replaced the bad caps along with the tiny 330uF primaries and a thin jumperwire to a coil in the transient filtering. I just used parts what was laying around in the table.
The rest looked okay. 13009 transistors on the primary, mbr3045 and mbr2040 for 5 and 3.3V Two F1620c for 12V! What a rare generous setup :p

Powered it up and the 3V rail was still sky high. Adjusted the regulation which helped a little but as soon as I attached some load it climbed back to like 3.5V damn! It doesn't matter if I cut the 3.3 sense wire or play around with the tl431 in the 3V stabilization. Is there a way to solve this somehow?
At least I can learn something and save it for parts.

[Th3_uN1Qu3]

Re: Generic AT-2005B PSU

That's a half decent design there. Will actually do 400W with that transformer and 13009 primaries.

Interesting bit with the 3.3v rail there. The most that 3.3 sense does is INCREASE the voltage, so there's something else wrong. First try replacing the 431, they fail in weird ways.

[c_hegge]

Re: Generic AT-2005B PSU

I tested an identical PSU and it exploded at 400W.

[Wester547]

Re: Generic AT-2005B PSU

That's a half decent design there. Will actually do 400W with that transformer and 13009 primaries.

I thought you needed 820uF/200V primaries to do 400W continuously (or 680uF, without PFC and/or a passive PFC), and it looks like the 330uF's were replaced with 470uF's. 400W max can be achieved with 470uF/560uF (200V) primaries with a good enough transformer (unless you can at a line voltage of 230V)?

[momaka]

Re: Generic AT-2005B PSU

Looks like a Sun Pro (judging by the "TB" marks on the transformers). generally, I really dislike their PSUs, but this one doesn't seem too bad.

From what I can see in the pictures, the 3.3V rail on this PSU uses a saturation coil, not a MOSFET in a linear setup with a 431 shunt (if it was, you wouldn't see that toroid next to the middle transformer).

The only thing I can think of is to put a bigger minimum load on the 3.3V rail. Try a 33 Ohm 1W resistor. If not, try 25 Ohm 1W resistor. If that still doesn't work, take out that coil next to the middle transformer and add a few more turns on it.

[pdavid]

Re: Generic AT-2005B PSU

Thanks everyone!

I'll see about the tl431 and the coil. If it works out then I'll put some decent caps there plus 680uF primaries. Too bad I won't be able to fit 820 caps, since the ones I can get are too tall and sort of block the fan.

[pdavid]

Re: Generic AT-2005B PSU

That's a half decent design there. Will actually do 400W with that transformer and 13009 primaries.

Interesting bit with the 3.3v rail there. The most that 3.3 sense does is INCREASE the voltage, so there's something else wrong. First try replacing the 431, they fail in weird ways.

Replacing the shunt regulator fixed it! I just noticed that it was running kind of hot too. I think Yageo sy caps are good enough for this thing. I'm going to test the unit... hopefully it won't blow up.

[c_hegge]

Re: Generic AT-2005B PSU

This PSU is indeed a "high end" Sun Pro. I wouldn't trust it with more than 350W.

[dmill89]

Re: Generic AT-2005B PSU

This PSU is indeed a "high end" Sun Pro. I wouldn't trust it with more than 350W.

Yep, It is virtually identical to the TM-350 I rebuilt and upgraded a while ago in basic design, with the exception of the overhead 120mm fan, different heatsinks (to accommodate the fan), some input filtering components moved from the AC receptacle to the main PCB (also to accommodate the 120mm fan), and slightly beefier components due to its "50w" higher rating (although neither will do its rated wattage without a few upgrades).

[c_hegge]

Re: Generic AT-2005B PSU

Yah. It looks identical to the older 420W Thermal Master, even down to the heatsink shape and 120mm fan, although the newer thermal masters are Deer/Solytech built.

[pdavid]

Re: Generic AT-2005B PSU

I have sort of tested the psu with a 3Ghz p4 platform and a couple of hdds, fans for a few days. It worked and wasn't hot. Consumption was 1.1A max according to a cheap tester.

Maybe I'll make a virtual load. There is a sale at a local diy shop. I can buy 20-50-100W heatsinked resistors real cheap. Salvage the other stuff like switches and connectors and put it in a box.

[momaka]

Re: Generic AT-2005B PSU

Replacing the shunt regulator fixed it!

I guess I better take note of that.

[pdavid]

Re: Generic AT-2005B PSU

I guess I better take note of that.

Also it gave me an idea to check all the tl431 in that Chieftec 750 unit which I'm still supposed to fix.