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Old 07-06-2017, 07:39 PM   #2735
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Post Task TK-930TX 300 Watt power supply

While on the topic of Sirtec, here is another one: a Task TK-930TX 300 Watt power supply. Date code on its label says 0311 (November of 2003?) PCB inside says “02/12/26”. I don’t know if that’s a manufacturing date or PCB revision, but either way, it is quite old PSU.

Two pictures of the case shell:
Note: these pictures were taken after I did a few modifications to the PSU, like the round on the front (I drilled those for extra ventilation).

As far as the case shell quality goes, this PSU uses rather cheap steel. About the same as a $15 gutless wonder. It is not as light as a gutless wonder, though. Nonetheless, there are other signs of cheapness, like the output wires, which are all rated 20 AWG, 300V (but at least they have a UL number on them). Speaking of output wires, this power supply has a 20-pin ATX connector, a 4-pin 12V CPU connector, 5x Molex connectors, 2x Floppy, 1x Auxiliary connector (AT-style), and a 3-pin fan connector (for monitoring the PSU’s fan speed).

Moving onto the label:
Although there are no combined power ratings to be found anywhere, at least the individual current ratings on each rail appear reasonable. UL number on the label is E144195 – same as on that Jeantech JNP-500AP power supply I posted above. Despite looking like a cheap PSU, the UL and other safety marks do not appear to be forged.

Next, a solder-side shot:
The soldering looks pretty decent. Judging by the separation of the traces on the primary side, this PSU probably does indeed have valid certifications.

And now let’s see the guts:
I’m getting mixed emotions here. :\ It doesn’t look bad, but for 300 Watts, it could be a lot better. The primary heatsink is nice and thick, but lacks fins. Meanwhile, the secondary heatsink has fins but is not that thick. Main transformer appears to be size “35”, but I would say it’s a bit on the skinny side. 5VSB is a 2-transistor design *without* a “critical” cap on the primary side, but it has a free-standing IGBT as the switch device. 3.3V rail toroid is nice and big, but the 5V/12V/-12V rail toroid could be bigger. And finally, two of the three input RFI/EMI filter caps are regular metal film instead of X2-class safety-rated. Speaking of caps, all caps inside this PSU are Teapo, except for the two Jenpo on the 3.3V rail (one of which is bulged and leaked badly). At least the PSU has a decent fan: an 80 mm Protechnic Magic MGT8012MS, rated for 0.15A @ 12V.

So let’s have us a detailed breakdown:

PWM controller: SG6105d
-5V rail regulator: L7905

Primary Side
* has male IEC receptacle for monitor cable (remember those? )
* three 1.0 nF safety approved Y2 caps
* one X2-class safety approved cap (0.22 uF, HQX brand, if I remember correctly) + two metal film caps (0.1 and 0.22 uF, again going off top of my head here)
* two CM chokes (one soldered on IEC receptacle)
* PBL405 (4 Amp) bridge rectifier
* two MOVs in parallel with the bulk input filter caps + one SCK057 NTC thermistor
* input wiring: 600 V, 18 AWG
* NO voltage selector switch (PSU has jumper wire for 115V operation)
* primary input filter caps: 2x Teapo LXK, 200 V, 470 uF, 22 x 35 mm (dia. x h.)
* H-bridge transistors: two 13009 NPN BJTs in TO-220 cases
* primary switch: 12N60 IGBT in TO-220 case (rated for 12A continuous at 110°C and 27A at room temp… lol Sirtec, isn’t that a bit overkill? ), 2-transistor design
* size “35” main transformer, and tall size “19” for 5VSB and BJT drive transformers

Secondary Side

3.3V rail:
* mag-amp regulated
* rectifier: SBL3040PT in TO-247 case
* filter caps: 2x Jenpo CE-LE, 6.3 V, 2200 uF, 10 x 30 mm (one bulging
* PI coil: 5-turn, 6 mm core, between the two caps
* Min. Load Resistor: 6.8 Ohm (?), 2 Watts.

5V rail:
* rectifier: SBL3040PT in TO-247 case
* filter caps: 2x Teapo SC, 10 V, 3300 uF, 10 x 30 mm
* PI coil: 5-turn, 6 mm core, between the two caps
* Min. Load Resistor: 100 Ohm 1-Watt and two diodes + 1 Ohm resistor all in series to 3.3V rail

12V rail:
* rectifier: UF1606 (?) in TO-220 case
* filter caps:
- 1x Jenpo CE-LE, 16 V, 100 uF , 5 x 11 mm
- 1x Teapo SH, 16 V, 1000 uF, 10 x 20 mm
* PI coil: 28-turn, 6-7 mm core, between the two caps
* Min. Load Resistor: don’t remember… 270 Ohm (?), 1 or 2-Watt

-12V rail:
* rectifier: two FR302 (3 Amp) diodes
* filter caps: Teapo SC, 25 V, 470 uF, 8 x 20 mm
* PI coil: more than 6 turns (?), 6 mm core before cap
* Min. Load Resistor: don’t remember (output to -5V rail 7905 regulator)

-5V rail:
* rectifier: none – derived from a L7905 linear regulator from -12V rail
* filter caps: Jenpo CE-WH, 25 V, 100 uF, 6.3 x 11 mm on L7905 output
* PI coil: none
* Min. Load Resistor: ??

5VSB rail:
* rectifier: SB240 (?) (2 Amp) Schottky diode
* filter caps:
- 1x Teapo SC, 16 V, 470 uF, 8 x 15 mm (?)
- 1x Teapo SC, 25 V, 330 uF, 8 x 15 mm (?)
* PI coil: 12-turn, 5 mm core, between the two caps
* Min. Load Resistor: 47 Ohm, 2-Watt

I also did some 5VSB tests for this PSU a long time ago, but I don’t know where I put them. I did a recap of the PSU after that, so the tests I have now are with the recapped, modified PSU (which only has a 100 Ohm load resistor on the 5VSB rail)

5VSB tests:
No load: 1.8 Watts, 5.5 VA
5 Watt load: 9.5 Watts, 18.5 VA (a little over 50% efficient)

Speaking of my mods on this PSU, here they are:
Basically, I removed the CM choke on the IEC receptacle, because the wires looked a bit dodgy, and I didn’t want to risk seeing them get torn and cause a short-circuit. The X2-class safety cap also got removed and replaced the 0.22 uF metal film cap. Meanwhile, the 0.22 uF metal film cap replaced the 0.1 uF metal film cap.

Other notable improvements:
• added a heatsink on the 12N60 IGBT. It’s not that big, but definitely bigger than before.
• Recapped 3.3V rail with one Panasonic FM 6.3V, 2200 uF cap and a 10V, 3300 uF Teapo SC from the 5V rail. Then, the 5V rail got a Panasonic FM 6.3V, 2200 uF cap too. On the 5VSB rail, I replaced the 16V 470 uF Teapo SC cap with a Nichicon HC 10 x 13 mm cap (from a Radeon 9700 video card - that’s all I had at the time). The 330 uF cap got booted for a Chemicon KY 6.3V, 1000 uF. And finally, the 12V rail got a 16V, 1200 uF Teapo SM cap in place of the 100 uF Jenpo. Clearly, I thought this was a worthwhile PSU back when I recapped it…more on that in a bit.
• Drilled round ventilation holes on the case’s front.
• Closed top vents with plastic sheet to improve flow
• Changed minimum load resistors: 5VSB received a 100 Ohm, 1 Watt resistor; -12V and 12V rails got 1 KOhms each; 5V rail got 100 Ohms, 1 Watt; 3.3V rail I don’t remember, but it might have been whatever was on the 12V rail before.
• Finally, I opened up the fins on the secondary-side heatsink for better cooling.

So was all of this worth it? The answer is: NOPE.
After testing the PSU in several different computers (both 5V and 12V –heavy ones), I found that the voltage oscillated very badly. In fact, before replacing the 12V rail 100 uF Jenpo cap with the 1200 uF Teapo SM, I first tried a 1200 uF Panasonic FM. On a 12V-heavy PC, I couldn’t even get the PSU to boot the PC – the PSU would squeal and the voltages would vary all over the place. That’s when I tried the Teapo SM cap. The PSU seemed a bit more stable and would boot the PC, but it still squealed a lot. I then tried back the original Jenpo, and things improved only marginally. That’s when I had enough and ditched the PSU in my spare PSU stash for messing with it another day. It’s been sitting like that for a few years now. And TBH, I have acquired better PSUs, so who knows when I will get to this one. I trust even Deer better than this POS – at least Deer will regulate and operate normally when it is rebuilt properly.

So the conclusion is: Sirtec sucks at voltage regulation. Granted the Panasonic FM caps I used may have been too much in terms of low-ESR to cause this, as well as the minimum load resistor swapping… but still, I’ve never had a PSU from any other brand misbehave like this when modded. Heck, I’ve put Nichicon HN and HZ in a Deer that had general purpose CapXon KM caps… and guess what? – It still worked fine and stable.
Attached Images
File Type: jpg Task TK-930TX (12).jpg (85.6 KB, 21 views)
File Type: jpg Task TK-930TX (13).jpg (101.9 KB, 18 views)
File Type: jpg Task TK-930TX (7).jpg (185.0 KB, 22 views)
File Type: jpg Task TK-930TX (8).jpg (773.4 KB, 19 views)
File Type: jpg Task TK-930TX (3).jpg (268.8 KB, 35 views)
File Type: jpg Task TK-930TX (4).jpg (270.6 KB, 23 views)
File Type: jpg Task TK-930TX (5).jpg (219.2 KB, 22 views)
File Type: jpg Task TK-930TX (9).jpg (295.1 KB, 25 views)
File Type: jpg Task TK-930TX (10).jpg (298.7 KB, 18 views)
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