Truepower 2.0 recap and repair

[999999999]

Re: Truepower 2.0 recap and repair

5V Standby is present at the point after the small transformer, where it's output goes through a larger tombstoned diode next to it (immediately to the left of small transformer if the PCB is turned so the small transformer is closest to you, then a capacitor (appears to have one), then inductor and another cap. It won't be 5VDC until that last inductor-cap point in the circuit, which for most purposes (unless the wire is damaged) means if you're expecting 5V you might as well take the 5VSB reading at the ATX connector pin.

[999999999]

Re: Truepower 2.0 recap and repair

thanks for the hasty reply 9s.

I'll probably take your advice on insulating my probes that little bit more. They've taken only superficial damage this time but i think i'll grab another set all the same.

I tried taking readings on both AC and DC settings and got nothing. I was fully expecting to blow the fuse in my meter at the very least. I had the power-on pin shorted and all.

I read what you wrote to mean that you touched the side of a probe you were measuring with, to common or ground. If that's the case the current wasn't flowing through the meter, just the probe tip... and depending on how bad it is you may just need to take some metal polish and get any residue off.

You don't need the PS-On pin shorted to measure the incoming AC at any particular point, at least not if this design is as I expect then you should be able to measure the ~ 340V or so at the cap after the bridge rectifier. If that voltage isn't present then trace backwards.

Beginning to think the input circuit may need a look at. It's pretty simple but i have to de-solder it from the power socket to get a good look at it. The short seemed to only have blown a bit of solder off, it wasn't in immediate vicinity to any sensitive components anyway.

Isn't it annoying when the build them like that, where you can't pull the PCB out without desoldering first? If the wires give you a little slack you might be able to just rotate, flip the PCB up enough to take some continuity/resistance measurements, no need to have the unit powered, don't even have the AC cord plugged in for these readings.

Actually unless the bridge rectifier's leads are cut really short you don't even have to pull the PCB out, instead try measuring resistance bewtween AC hot and both legs in the center of the bridge rectifier, then AC common and both legs in the center of the bridge rectifier. Resistance (from either AC input) should be at least several hundred KOhms, probably 1MOhm or more to one bridge rectifier leg, and close to 0Ohms for one of the AC contacts and maybe a little under 10Ohms for the other one (due to the inline current limiting).

If you don't have nearly 0 Ohms and under 10 Ohms from the AC input to these corresponding points on the AC-input side of the bridge rectifier, then trace back from the bridge rectifier towards the AC socket. There's not a lot that's likely to go bad there, like the fuse and the thermistor, both of which you may also be able to measure while the board is still fully installed in the casing, with the fuse of course being near 0 Ohm across it and the thermistor being under 10 Ohm. Due to the thermistor's thermal expansion when powered, it is not entirely comprehensive to test it when it isn't running but to find it open circuit while off is already an indication of a problem without having to pull the board out yet.

[Kaine]

Re: Truepower 2.0 recap and repair

you can see here where the two probe points contacted the PCB. the tips of both my probes look like abused soldering iron tips I've cleaned them up with some flux and removed the solder that was baked on.

You can see there the ends of the power cable I butchered to run a nice long ~1m length from the input circuitry to the actual PSU PCB, so i don't have to keep the board in the case if i want to do live testing (which i really don't). I'll get stuck back into it tonight i think, first order of business is to replace the solder I've burnt there.

[Brian C]

Re: Truepower 2.0 recap and repair

huh... dealing with AC mains can be very dangerous !
well, Kane... here are some advices from me.

(1) The purple color wire on the 20-pin / 24-pin connector carries standby 5V voltage.


From ur pictures, point (P) is connected to (+) by black color wire on the top side. Point (P) which is the the (+) from bridge rectifier is connected to the transformer winding (Q)(R). Point (R) goes to the Drain of MOSFET (C). The Source of MOSFET (C) connect to (-) via a small resistance (S).
Pls refer to the attached pictures.



Now, could u pls check the resistance of few points (in the absent of AC mains).
(1) Fuse - make sure not blown
(2) Thermistor - should give low resistance reading
(3) Transformer winding (Q)(R) - should read few ohms (not open circuit)
(4) Resistor (S) - Pls check the color code, should be ~1 Ohm (not open circuit)
(5) MOVs - make sure both MOVs are not short-circuit.

To check MOSFET (C), u do not need to remove the transistor. U can use solder wick to clean the solder so that the pin is disconnected from the copper pad. Pls see below pic.


(6) MOSFET (C) - diode test between Drain and Source. make sure not short circuit, and the built-in protection diode is OK. Check Drain-Gate and Gate-Source as well. Datasheet for 4N60B:

[Per Hansson]

Re: Truepower 2.0 recap and repair

Wow, sorry to go off topic but what desolder braid did you use?

The ones I've tried never do a thing, that's a really clean desolder job!

[999999999]

Re: Truepower 2.0 recap and repair

Wow, sorry to go off topic but what desolder braid did you use?

The ones I've tried never do a thing, that's a really clean desolder job!

See the flux left behind in that picture, if your desoldering braid won't pick up the solder very well, try putting some flux on it first, it can help a lot. If that doesn't help enough you may need a hotter iron or cleaner tip.

[Brian C]

Re: Truepower 2.0 recap and repair

Wow, sorry to go off topic but what desolder braid did you use?

The ones I've tried never do a thing, that's a really clean desolder job!

It is "Solder Wick" from Chemtronics USA (the right most picture).

[Per Hansson]

Re: Truepower 2.0 recap and repair

Ok, thnx, this is the thing I've been trying without much success

Guess I'm just doing it wrong

[Brian C]

Re: Truepower 2.0 recap and repair

Hmm... yours is SOLDER WICK - no clean SD
http://www.chemtronics.com/products/product.asp?id=230

I am using SOLDER WICK - ROSIN SD
http://www.chemtronics.com/products/product.asp?id=233

This one performs much better as it has rosin flux... U can try it out.

[Kaine]

Re: Truepower 2.0 recap and repair

i was having real trouble with solder wick until i bought a slightly bigger tip (2mm chisel from a 1mm needle) which helped a lot. then i bought a better brand wick (goot) which was a big improvement. Finally i added a flux pen to my kit and now i can suck that solder off no problems at all. at 400C i can move solder very quickly without heating up components barely at all (only just warm to the touch). It makes heavy PCB work so much less frustrating.

[PCBONEZ]

Re: Truepower 2.0 recap and repair

Kaine (or anyone)
Were you able to see what this cap is?

[PCBONEZ]

Re: Truepower 2.0 recap and repair

This cap.
Attachment didn't stick last time.

[Kaine]

Re: Truepower 2.0 recap and repair

This cap.
Attachment didn't stick last time.

47uF 35V if i'm reading it correctly. Replaced Koshin with a Rubycon YXF.

In hindsight i should've only replaced the bulged cap and blown diode, then tested the psu instead of going the whole hog before testing. oh well. Serious lack of motivation on this atm.

[Kaine]

Re: Truepower 2.0 recap and repair

(B) is closed circuit on in->out pins, no connection from COM to in or out.
(C) doesn't have continuity between any pins.

Resistor (S) reads as 2.2ohm (too color blind to read the code in place, removed and tested with multi)

Transformer winding QR reads 1.8ohm

Neither MOVs are closed circuit. Here's hoping they aren't polarized, I can't be sure I put them back in the same way I took em out. Had to remove a primary cap to get at the little buggers too.

[PCBONEZ]

Re: Truepower 2.0 recap and repair

Thank you Kaine.
I would have to pull that one just to read it and I prefer to have the parts here before I disassemble anything when I can.

[Kaine]

Re: Truepower 2.0 recap and repair

OK Quick update, (C) is positive VRM L7812CV

Here's a quick diagram I did that illustrates the results of the continuity tests I did. Can someone tell me if this is right? I can't really glean from the datasheet what the results should look like.

[PCBONEZ]

Re: Truepower 2.0 recap and repair

Yes that's right.
It's shown on page 3 of that data sheet you linked to.

[Kaine]

Re: Truepower 2.0 recap and repair

what i'm actually looking for is confirmation that the diode effect between the pins is as i've described. All the other VR modules i've tested are different. Trying to get my hands on another TPII atm so i can compare.

[Brian C]

Re: Truepower 2.0 recap and repair

what i'm actually looking for is confirmation that the diode effect between the pins is as i've described. All the other VR modules i've tested are different. Trying to get my hands on another TPII atm so i can compare.

The diode test as descrided is correct. To confirm the VR, u can apply 25Vdc to INPUT pin and measure the OUTPUT pin. U should get 12V if it is 7812.

[Kaine]

Re: Truepower 2.0 recap and repair

damnit. back to square one -.-