iiyama ProLite X486S dead - psu / inverter issue

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Hello guys, sorry to revive an old topic, maybe I should establish a new one. But long story short, I've geared up in terms of equipment and some troubleshooting knowledge.

Gear:
+ 20mhz oscilloscope
+ much better soldering iron
+ good LCR meter

Now using this and some great help on EEVBlog forum, we have finally checked all the
* diodes (good)
* caps (desoldered, checked, good, visually good)
* transistors (not shorted)
* mosfets (not shorted)
* no other obvious shorts / failures

The problem very much seems to be in main driver chip, IC201. Datasheet is posted in IC201.pdf.

Consequence of the problem: there is exactly 13.18V flat line DC on the input of inverter transformers. 13.18V is provided with no load from D902 (12V main diode) - input to the inverter section.

Possible cause of the problem: blown IC201 (mosfet driver). The IC should drive the mosfets with a saw tooth PWM wave from pins 11,12,19 and 20. The problem is, only pin19 shows any reading at all. Pins 11,12 and 20 are completely dead during normal operation (0 volts DC).

In standby, also pin19 has 0 volts, which is expected with backlight off. Main consequence of the problem: backlight does not work, never, at all.

Other measurements at IC201:
pin 1 = 0V
pin 2 = 0V
pin 4 (SST) = 4.63V
pin 5 (VDDA - Supply voltage) = 4.83V
pin 6 (GNDA - Signal ground) -> OK (continuity)
pin 7 (REF - Reference voltage output) = 3.30V
pin 14 (DIM) = 2.03V; 0.60V in standby

As far as I understand it, those measurements should indicate normal driver operation. However as described above, only one of P-mosfet drivers, pin 19, is working. "peak to peak" value of saw tooth wave on working pin19 output is ~4.3V. Other three driver outputs are dead.

Attached is:
* toshiba.pdf - monitor uses almost the same power supply, see page 30 for inverter schematic (applies to mine as well), and page 41 for troubleshooting instructions
* IC201.pdf - datasheet for suspected blown driver chip
* some random pictures - pictures of the board with helpful wiring diagrams for pair of eight mosfets that drive the inverter transformers (4 for each).

Now the question is, did someone ever witness an IC blow up partially like this? If the IC is not blown, what problem could cause only one driver output to work? Is there anything else I can check? I am going to buy CCFL extension connectors so that I can measure the chip with lamps connected, but in the meantime, I'll be glad for any input on the matter.

Thanks and please ignore previous topic messages, this is a fresh start

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

What about this?

http://www.ebay.co.uk/itm/Replacemen...-/230363518011

Would I be able to test my lamps with this?

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Also, T901 is shorted on one side (the "f902" side). I traced the PCB leads and think that shown contacts are not connected by any direct PCB lead. They measure 0 ohms. The other side is always out of range even on 2000K multimeter setting. Also any other pin combination is also always out of range. Maybe this is normal, if not let me know

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

As far as the "faint blue led" problem goes, the LED does not work at all now. Only the orange standby does. The voltage on BLUE led is 2.24V when ON, 0V when Off. Voltage on orange LED is 1.84V when Off (standby), 0V when ON.

Why is this voltage difference present? Is it because the led had burnt out? I don't care about the led, just wondering if it has something to do with the general backlight problem.

Thanks

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

So guys, after a long research & parts availability checking I have replaced AP2761I-A with STP12NM50FP, and also of course replaced fuse F901. The monitor now "works", so it works like before - no backlight at all. I have also found & resoldered another two dry joints on the board, this time on the far side (the F902 side of the circiut) of T901 (big ?transformer?).

What should I check next? The IC901 voltages are correctly measured the last time I did it (before Q903 was shorted).

Thanks!

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

I'll do that, but first I need to get my hands on Q903 (totally shorted). It is not available in any local shops, they said they might have replacements for it but I did not have time to personally go to the mentioned shops recently (too much work & school). I'll try to visit the stores next week, and if I don't find any suitable replacement (or if the replacement will be expensive), I'll order a few pieces off ebay (2$ postage, 2 pieces - 4$, total 6$, approx 4.2€ - fine). I'm also planning to buy a new multimeter capable of testing capacitors and a new soldering gun - thin. I currently only own the standard old-fashioned soldering gun and it is hard to work on electronics with that one

By the way the part number is AP2761I-A and it is a N-CHANNEL ENHANCEMENT MODE POWER MOSFET.

[selldoor]

Re: iiyama ProLite X486S dead - psu / inverter issue

I'd desolder the DB901 and test it properly

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Desoldered Q903, shorted. No other parts show as shorted on the circuit at this time. Did not desolder anything else at this point. I'm going to replace the transistor. Do you think it's enough or should I desolder something else (like DB901) and test it out?

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Damn that's a really good idea Why couldn't I think of that sooner? Anyway three parts are about to be desoldered today and measured (maybe tomorrow if I'll run out of time). I'll let you know what I find

[selldoor]

Re: iiyama ProLite X486S dead - psu / inverter issue

Those IC901 contacts are so tiny, that it's really hard to control your hand like that ulness your are a surgeon
.

Easy to be wise after the event but you dont always have to use the pins.
It is sometimes easier to follow the trace out to the next component and use that as the test point.

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Thanks that is a nice video. I will desolder the rectifier, main capacitor and main transistor tomorrow and try to test them.

[selldoor]

Re: iiyama ProLite X486S dead - psu / inverter issue

Sorry i dont know but if you remove DB901 you can test it like this
http://www.youtube.com/watch?v=dqkT6hF0O3E

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

well at least Q903 (big transistor near big capacitor) is nicely shorted.
D-G 16ohms
D-S 0ohms
G-S 16ohms

Also main Rubycon capacitor shows 1.5ohms (shorted), but I think it's the transistors fault (same leads and whatnot)

Also DB901 shows shorted on pins 1-4 but again, it's the same PCB leads as the C905 is hooked onto.

From your personal experience, which part is faulty? Is it the transistor? What does blow up most commonly first (other than the fuse)? When I look at it, IC901's pin 8 goes directly to Q903's gate, so when I shorted the pins, bad things could happen

I know many people including me would advise to let it go and throw the monitor in trash, but I like to learn, and even though I've blown it this time, I still hope it is repairable.

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Bought new F901, soldered, plugged in, instant burnout of the same fuse. What could be wrong?

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

While I sort this out, I remember the readings (I was just verifying them when the fuse blew out), so here goes:

CCFLs connected, logic board connected, LCD panel disconnected:

2) What is the DC voltage for pin 3?
standby - 14.95V
monitor on - 16.92V

3) What is the DC voltage for pin 7?
standby - 12.04V
monitor on - 13.36V

4) What is the DC voltage for pin 5?
standby - 1.04V
monitor on - 1.05V

Also, the monitor would randomly turn itself on (from standby) when I measured the chip. Also, I'm pretty sure that the high frequency noise coming from the board is made by IC901 (the one I measured).

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Hello guys, thanks for the help, buf F901 had blown out.. blowing fuses in our entire home on the way out. I guess my hand must have slipped and connected pins 7-8 or 7-6 or something like that, causing an electrical short. Those IC901 contacts are so tiny, that it's really hard to control your hand like that ulness your are a surgeon

I have checked all the 8-leg Q's on the board, they are still OK, nothing else seems to have blown out (only the fuse smells bad & is blown). So give me a little time, I'm going to buy a new fuse right now, should be up & running this evening (in ~5 hours max).

[retiredcaps]

Re: iiyama ProLite X486S dead - psu / inverter issue

CCFLs disconnected, everything else connected:

2) What is the DC voltage for pin 3?
standby - 14.95V
monitor on - 16.92V

3) What is the DC voltage for pin 7?
standby - 12.04V
monitor on - 14.07V

Can you retest with the ccfls connected? Also, measure pin 5.

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

CCFLs disconnected, everything else connected:

2) What is the DC voltage for pin 3?
standby - 14.95V
monitor on - 16.92V

3) What is the DC voltage for pin 7?
standby - 12.04V
monitor on - 14.07V

4) What ohms reading did you get for fuse F902?
0 ohms, 0.5 to be exact

[retiredcaps]

Re: iiyama ProLite X486S dead - psu / inverter issue

Refer to
http://pdf1.alldatasheet.com/datashe...C/SG6841S.html

1) Use pin 1 (GND) for your black probe.

2) What is the DC voltage for pin 3?

3) What is the DC voltage for pin 7?

4) What ohms reading did you get for fuse F902?

[kbs1]

Re: iiyama ProLite X486S dead - psu / inverter issue

Hi, I have tested the mofsets and values were always out of range. I also tried to test things like "S2-G1" just to be sure, always out of range. So they seem good. Previously I have done this test, and the results were the same.

5) the number is
SG6841SZ
KA497280603Q

It is really hard to read, so just in case I got it wrong here is a photo of it (I had no chance to read it using bare eye or using magnifier ;-)