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Old 03-15-2012, 12:38 PM   #491
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Default LC-235ATX and LC-B300ATX

Let’s look at some Eastern European L&C samples now – a LC-235ATX (235W) from 2001 and a newer (2003?) LC-B300ATX (300W). These are probably the cheapest of the cheapest you can find from L&C. The B300ATX I got for 7 Euro (or thereabouts) when I was building a PII PC for use in my grandmother’s house. The 235ATX was in use in my cousin’s computer for a few years before he gave me his old computer.
Outside, 1st and 3rd pictures (LC-235ATX on the left, LC-B300ATX on the right), 2nd picture (LC-235ATX on top, LC-B300ATX on bottom).

Let’s start with the LC-235ATX… top side and primary side:
Missing input choke and X cap, 1KV ceramic caps, 1.5A diodes for the bridge rectifier (that’s a bit low, but still okay for 230V line use), average gutless-wonder TO-220 transistors mounted on somewhat whimpy primary heatsink, 33 -sized transformer, KA7500 PWM controller, LM339N quad comparator (for OVP and UVP)
And the underside:
Again, acceptable soldering and no long or untrimmed leads. And the secondary:
3.3V rail: 2x 1000uF 10V Jun Fu WG (before and after PI coil), not sure about rectifier (probably 10A schottky), 4.7(?) Ohm 3W dummy load resistor, and another PI coil instead of a choke!
5V rail: 1x 1000uF Jun Fu WG (after PI coil) and 1x 220uF 10V CapXon KM (before PI coil), B1545 15A schottky rectifier, 47 Ohm 1W dummy load resistor.
12V rail: 1x 1000uF 16V CapXon KM, 6A diodes-on-a-bracket “rectifier” (2x 3A FR diodes), 100 Ohm 2W dummy load resistor.
-5V and -12V rails: 1x each 470uF 16V CapXon KM caps, no PI coils installed, 2x each 1A or 1.5A FR diode rectifiers.
5VSB: 2x 100uF 16V Jun Fu HK (1x before 7805 regulator, 1x after it), 7805 regulator for output, 1.5A FR diode rectifier.

Like the 1999-built Deer, this one uses a 7805 linear regulator in a self-oscillating 5VSB circuit with no feedback as well (again, note the lack of an optocoupler). Hence, why it still works fine after so many years. The fan, a Powerlogic PL80S12M, is wired in series with a 10 Ohm resistor to the 12V rail – it’s been running near full speed all these years without problem (probably explains why none of the caps have gone bad either).

And now the LC-B300ATX - top side and primary, that is:
Looks almost unused, doesn’t it? Well, that’s the PSU I was talking about it post #486. In nearly 3 years of use (about 1 month only of each year), I was forced to change it back to the LC-235ATX after the wires shorted/smoked because I just didn’t trust it anymore. This thing was actually making my (at that time) PII computer restart when I tried to play some 3D games. When I upgraded that computer to a Pentium 3, the PSU would usually make it boot-loop instantaneously 3 times on a cold boot (the CD-ROM would seek 3 times after turning the PC on) and the computer would restart with a very heavy load.
As you can see, for 300W, it’s very gutless. But regardless of the wattage rating, this PSU too has missing input filtering just like the other LC above and same lame 1KV ceramic caps. At least the bridge rectifier is made of 3A diodes. Primary caps are 200V 470uF YC units. Main transformer is 33 –sized instead of 35, 5vsb transformer is tiny, and there are jumpers for just about every coil and choke. Only the heatsinks are not too bad. Note that the position of the primary and the secondary are switched as opposed to a regular PSU – this is what the “B” in the model number signifies.
Next, the bottom side:
Very decent soldering, especially for its price. Only 1 or 2 leads were slightly longer.
Finally, a shot of the components on the secondary side (or lack of, that is):
Yup, not much to talk about here. Each rail has only a single cap and absolutely no PI coils. Explains why my computers were boot-looping. PWM controller is labeled “2003”.
3.3V rail: 1x 2200uF 10V YC cap, no PI coil, 10 A schottky rectifier, 6.9 Ohm 2W dummy load resistor
5V rail: same as 3.3V rail, but it has a 20A schottky and not sure on the load resistor.
12V rail: 1x 2200uF 16V YC cap, no PI coil, 10A FR rectifier, no idea what load resistor.
-5V and -12V rail: 1x each 470uF (?) 16V cap, no PI coils
5VSB: 1x 1000uF(?) 10V Koshin KH cap, 1 or 1.5A FR diode, no PI coil
Fan is a crummy sleeve bearing Rulian Science & Technology RDM8025SA rated at 0.13A. 5VSB circuit is standard 2-transistor affair.
I might rebuild it some day, just so I have a spare PSU for testing computers when I go to my grandmother’s house.
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Last edited by momaka; 03-15-2012 at 12:44 PM..
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