Repairing a FujitsuSiemens LSL3230T

[wc_robot]

Re: Repairing a FujitsuSiemens LSL3230T

long delay in response, this is kind of a whenever-I-have-10-minutes-to-investigate type of project

The dell monitor my board is from is a Dell 22" E228WFPF Widescreen Monitor.
Just for the hell of it, I took the power brick (it outputs a 12VDC supply into a monitor) from my 10+ year old "FujiPlus" 19" 4:3 lcd... aka, no-name brand ancient thing. I was kind of surprised to find almost the exact same circuit in a different layout... same cap, same transformers, same relay, etc. etc. Although, the primary on both transformers is 4 leads, and the secondary on the FujiPlus powerbrick only has 2 of the 6 pins used in the circuit.

Rtech is correct about the schematic though. There is one FET which has the Drain lead going into one of the two middle pins on the primary. The secondary on the Dell, the 6 pins are soldered in 3 sets of 2: the set in the middle is ground; the set on the left are connected to the two outside pins of one schottkey diode (SRF10-10 - Diode Schottky Diode 100V 10A 3ITO-220AB), which is mounted adjacent to the transformer's secondary on the other side. The set of pins on the right from the transformer's secondary go to the two outside pins of the other schottkey diode (SB10150FCT - 10A HIGH VOLTAGE DUAL SCHOTTKY BARRIER RECTIFIER). It's worth noting that this one (the SB10150FCT) has a bigger heatsink than the FET and the SRF10-10. (On the powerbrick for the fujiplus monitor, they all just use the brick's frame as a heatsink--and I didn't confirm part numbers for that, but likely the same part from a shittier manufacturer).

For the FujiPlus board, the two outer pins of those schottkey diodes are all soldered together, and the two middle pins are soldered together. The 4 outer pins connect to one of the two secondary pins, and the other pin from the secondary goes to ground.

I desoldered the FET and checked it -- works fine. I have not yet checked the schottkey diodes, but I will... I suspect it's the SB1015.... (the one with the bigger heatsink). I also confirmed that the ticking is indeed coming from the transformer. I rolled up a piece of paper into a ~2cm diameter tube and placed one end right up to my ear and the other end right on top of different parts of the circuit, moving around from FET to diodes to caps to the yellow transformer. It's very obvious that it's only coming from the transformer -- but I suspect caused by a shot schottkey (SEE WHAT I DID THERE?!)

I'm too lazy to take a picture right now, but if this doesn't make any sense I will.

It's nice having another circuit working to compare values to

Now I want to buy all those broken LCD monitors on craigslist for $10 and replace the 50 cent part then resell!

[DMCrimson]

Re: Repairing a FujitsuSiemens LSL3230T

I've beem unable to do a thing on this. We moved recently and subsequently filed for divorce... Currently I'm trying to study at TUAS, but not on full power as I have both depression and panic attacks. I just hope I get my own apartment, then I think I can focus on these things better.

[DMCrimson]

Re: Repairing a FujitsuSiemens LSL3230T

Now, are there any suitable replacements for those Schottky's mentioned, SRF10-10 and SRF10-20? Also, that MOSFET, AP2761P-A? Just on the safe side for the future...

[DMCrimson]

Re: Repairing a FujitsuSiemens LSL3230T

Hmm... wc_robot has srf10150 where I have srf10-20. That's weird. Also, I remeasured that 10-20 and it seems shot - dmm shows 0,002V for forward voltage.

[axh174]

Re: Repairing a FujitsuSiemens LSL3230T

Bump!

I'm beginning to wonder if the transformer itself is faulty - it has markings as follows:

SPW-134 A
E140167
LSE-B3 0839F3

clicking/ticking might be due to failing insulation, so if I was to replace it, what are the specs? Search over the net yielded nada.

Any luck on being able to identify this part?

I'm trying to repair a Hannspree HSG1067 LCD Monitor's power supply, which, from some of the surfing I've done, seems to have an identical power supply as the Fujitsu Siemens LSL3230T.

As DMCrimson indicated, a search for "SPW-134" over the net has yielded zero results, except for the reference made here. The markings on my particular transformer are:

SPW-134
SBI 4.2 E156193
FEC 0924 A g

I'm fairly certain this is the cause of my troubles. It doesn't look all that healthy: it makes a rhythmic fizzle-pop (like a charging and shorting sound), and I've checked the rectifier diodes (10-10 and 10-20) and MOSFET switch which appear to be good.

I've done quite a bit of digging around to try and understand what exactly this transformer is, but I've run into a decent amount of confusion. As I understand it, this is a High Frequency transformer utilized in a pulse mode, isolated flyback circuit. But whenever I search on Mouser/Digikey/web, I find that separate categories exist for "Pulse Mode", "Switch Mode", "High Frequency", "Power" and "isolated flyback" transformers.

-Kevin

[axh174]

Re: Repairing a FujitsuSiemens LSL3230T

Oh, another piece of interesting information:

I tried finding the HSG1067 service manual figuring that it would include part numbers. I wasn't able to find it, but in the process I stumbled on the LG Flatron W2234S service manual, which includes a schematic for the power supply that seems to match the HSG1067 very closely from the traces that I've followed, although I admit it's not exact.

In any event, the transformer listed in this service manual is:

XFMR SW DIP ER28 PC40 650uH SPW-100 RoHS
Part #: 426000091000R

I haven't been able to find much on this transformer either. But given the similarities between the power supplies, the SPW-134 also appears to be a 4-pin input of 2 separate windings on the primary, and a 6-pin output of 1 winding with 4 center taps on the secondary. 160V DC in, ~16V and ~5V out.

[budm]

Re: Repairing a FujitsuSiemens LSL3230T

Clicking and ticking can be the sign of the SMPS going into shutdown-startup cycle due to the protection circuit detect the fault, or the startup cap is not functioning. Of all the repair I have done, I never have to replace the power transformer yet, but not saying that it is possible.
Can we see the pictures of your board, both sides?

[axh174]

Re: Repairing a FujitsuSiemens LSL3230T

Hi Budm, thanks for your help.

I've attached images of both the front and back of the power board. The backside of the board is from right after I desoldered the transformer, secondary side rectifying diodes and switching MOSFET for testing (so that's why those solder joints are not present). I also have some images of the transformer by itself that I can upload as well if you'd like to see them.

Any suggestions on what portion of the board/where in the circuitry would be the protection circuit? I'm taking a look at some other power board schematics to get a general feel for how these things are put together, but I haven't fully digested them yet.


A little bit of the history of the board:

The owner of the monitor said that it was working fine, he got up and left the room to bring in some groceries, and when he returned the monitor was dead. The power LED does not light up when the monitor is plugged in, and it is unresponsive to all button presses.

The first thing I noticed was some of the original capacitors were bulging (but no leaks), so I replaced all of them except for the large "reservoir" (startup?) capacitor that helps smooth out the rectified voltage coming from the wall outlet.

After replacing the capacitors, I reflowed a lot of the solder to make sure there were no bad connections and then reassembled the monitor, but there was no change. I then started to troubleshoot a few things: I measured 120 VAC into the diode rectifier bridge, and 160 VDC across the main capacitor. I measured 3.0 VDC heading to the logic board (which seems low, I was expecting 5 VDC), and no voltage heading to the backlight inverters. Both the main line fuse and the fuse for power to the logic board are both intact. I then desoldered the transformer, the secondary side rectifying diodes, and the switching MOSFET for testing. Both rectifying diodes seems to test OK and the MOSFET as well (though I'm going to double check that). I measured the resistance of the Transformer primary and secondary sides and noticed a couple of what I feel are odd things, like discontinuities on the secondary side. But I'll describe that in another post since this one is now getting rather long-winded.

[budm]

Re: Repairing a FujitsuSiemens LSL3230T

OK, the power supply is an always on, meaning that it will run and puts out voltages the minute you apply 120VAC to it without having any other boards connected to it.
So put all the parts back in place and power up the board by itself and see if you do get the voltages at the connector to goes to the main board.

[axh174]

Re: Repairing a FujitsuSiemens LSL3230T

Resoldered all the components back on and here are the results:

Voltage across main capacitor: still 166.7VDC

With logic board attached, I'm measuring 1.67VDC on pins 1 and 2 of the connector.

With logic board disconnected, I'm measuring 3.0VDC on pins 1 and 2 of the connector.

Ground was taken to be one of the heat sinks on the secondary side (same potential as pins 3 and 4 of connector).

Also rechecked the switching MOSTFET. With my meter in diode test mode, applying voltage/charging the gate pin creates a short between source and drain regardless of probe placement on the pins. Discharging the gate pin causes an open between the source and drain IF the positive probe is on the drain and the negative is on the source. If I bias it such that the positive probe is on the source and the negative on the drain, I get a 0.526 voltage drop. Is that normal? Is there a diode of some sort built into this MOSFET? I would have thought you'd not want a path from source to drain with the gate discharged.

[axh174]

Re: Repairing a FujitsuSiemens LSL3230T

So I've been poking around with this board and I'm pretty sure I've narrowed the problem down to one of the two dual-package 60V MOSFET ICs on the Inverter Board/Riser Card (which can be see as the "wall" on the right half of the power board separating the inverters from the transformer.)

The story:

I began a systematic effort to try and test all resistors, diodes, semiconductors, and capacitors on the board. Obviously, testing some components while on the board can be tricky, but many of them can remain on the board and give a reasonable indication of proper function. What I noticed was that on one half of the board I could not use my multimeter's diode tester to induce a charge in the capacitors; I was continually getting shorts across all of them (even the ones I had replaced). Through strategic desoldering of one or two components, I was able to isolate the short and discover it existed on the inverter board/riser card. One of the power pins on this card was shorted to the ground pins. I desoldered the inverter board/card from the power board, and all shorts on the power board disappeared.

Closer inspection of the inverter card/board revealed that one of the ICs on the board, a 9945N 60V N-Channel MOSFET package, had its source, gate and drains all shorted together. I managed to desolder this IC and probe it off-board to confirm it is indeed the source of the short and not the board.

During this whole process, I was also able to confirm that the transformer does put out the required 18V to the inverters and the 5V to the logic board, and that as suggested earlier by budm, an over-voltage condition likely existed that prevented the transformer from performing properly.

So I'm in a position to obtain a new 9945N from Mouser and solder it to the inverter board/card. Though before I do, can anyone offer their insight on how/why one of these ICs would blow? I was told they sometimes just die. But if that's not the case, I'd hate to solder a surface-mount component just to have it die again from whatever killed the original one. Anything I should look for on the inverter board/card or power board to see if something damaged the original IC?

Thanks for the help!