P170HM3 Screen Backlight

Hi all,

I have a P170hm3 that recently developed issues with the screen (vertical corruption). I replaced the screen with a new one and powered up the laptop assuming all would be well. Unfortunately I seem to have managed to make things worse now the backlight no longer works. I can see the lcd part of the screen is working by shining a bright light on the screen so it is just the backlight. I have confirmed that the issue is not the screen by attaching the old screen - the backlight no longer works on that one either.

Any suggestions about where to look next? I've sent off for a repair quote but I expect it will be pretty expensive so if there is anything I can look at first it will be worth trying.

Thanks in advance,

David

 

Most likely cause is a partially defective lcd cable. Some of its ~30 wires may have broken, this would also explain the vertical corruption on the old screen (which could be fine, after all). It happens; opening/closing the lid causes wear, especially near the hinges. Try running the lcd with the cable exposed and push/compress it gently along its entire length; sometimes that force-connects the broken wire.

Alternative is a selectively defective 5V supply on the motherboard. This is highly unlikely, mind, cable's the most usual suspect.

 

When the corruption originally occurred I assumed that the cable was at fault. I could get the corruption to go by pressing lightly on the cable. The repair centre told me that it wouldn't be the cable and wanted £300 to replace the screen. That seemed like a lot to me so I found a new screen for £60 and replaced it myself. However, I am not sure how to diagnose this new issue. Pressing on the cable doesn't seem to make any difference and I cannot find a replacement cable for this laptop/screen combo (I believe its an eDP cable rather than the more common lvds).

Is there any way to test whether it is a defective cable vs motherboard?

 

Technically; yes. Advisable; not so much. Tested an lvds system using a multimeter; could verify the proper 0.5mm pins were functioning, though accidentally made a tiny short while doing so (arc, smoke etc. ). No damage, but it's not something you want to risk.

And that 'repair centre' is to avoid like the plague then, like certain garages. If pressing the cable fixed the problem, then ... hth can they claim it's the lcd ???! Other than to rip off their customers, that is ...

Anyway, that settles it; new cable. Look up the lcd models on Panelook, that'll tell you which interface it is. For reference; the original P170HM came with an AUO B173HW01 V5, which is a 40-pin/2-channel/6-bit LVDS (a very common type). Look up both, please; might be interested in buying one of the two (presuming they're both fine, of course).

 

Have you tried hooking up an external monitor to see if it could be the video card.

 

Thanks for the suggestions.

The panel is this one - http://www.panelook.com/LP173WF2-TPB1_LG Display_17.3_LCM_overview_14168.html

I can't find a suitable replacement cable anywhere

Once (if) I have the backlight up and running again I will confirm if the original panel is any good.

I have checked with an external monitor and all is good - I can even see the new panel is displaying the desktop if I hold it at a very slight angle to a bright light source so I know it isn't the gfx card at least

 

Of course, you had it right the first time; defective backlight (for whatever reason).

And right, didn't get where the "3" was coming from. Saw the 1080p and it said "4-lane", which is ridiculous ... unless it's 3D. Understandably difficult to find 4-lane eDP cables; only used with 3D or 4k panels. RJTech has one though; Video cable for P1xxHM. Your reseller should be able to offer the same for $25.

 

Ask Eurocom for a 50-pin eDP cable for that screen

 

David - send me a pm and I'll get a cable sorted out for you. Assuming that you are in the UK (quoting £ prices) then no offence to Eurocom but it'll be cheaper and easier to get one from the UK than Canada

 

ah you're right I didn't even notice that. But good of you to step up!

 

Just in case that switching the 'back-light ON/OFF by pressing the cable' caused the responsible chip to blow:

http://forum.notebookreview.com/thr...10-owners-lounge.655833/page-550#post-9853867

For my own system I first bought a new screen, then a new cable and ended up having to replace this chip on the mobo to get the back-light working again.

 

Thank you everyone for your help with this so far.

XMG - I am in the uk and I would like to pm you but I am not able to start a conversation. have sent you a pm.

I wouldn't be surprised if Prema is correct and that chip needs replacing - however, I wouldn't attempt that repair myself so I'll try with a new cable first If I do need to get the chip replaced (or anything else) can anyone recommend a decent repairer? Preferrably in the south west of the uk.

 

Always happy to setp up ;-)

It's possible he's correct, but more cost effective to try the cable first if you want to.

Recommend a repairer you can trust - yes, see pm

 

Got the cable courtesy of XMG today. Unfortunately it didn't fix the backlight.

Do you know if it would be the same chip on my P170HM3? If it is, how would I locate it with a view to replacing it? If I'm feeling really brave and that area of the board is fairly open and easy to access I may attempt the repair - depending on what the repair centre quote me that is!

 

Yes; it's called ' 74LVC08PW1' on the P170HM3 service manual, on the board it will be labelled "U8C". Name's slightly different, but all searches turn up the same spec. sheet. Just to be sure, you can look for the "U8C" on the board; the IC itself is labelled (need good eyesight or magnifying glass).

Spoiler: Clevo P170HM3 - backlight-on-off circuit

However, you first want to verify that this is actually the culprit. Run the system and check pin #22 check pin #8 on the U8C for a signal with a multimeter (pins are much bigger than on the eDP connector, so it's easier).

 

I have explained the issue (and referenced this thread) to a local repairer. They have said it is probably the inverter that has gone and that it will cost £80 to replace. This seems like a reasonable price to me but he has stated that the inverter is a thin pcb located under the screen. I cannot see anything below the screen so I wondered if this is correct? All the other info on this thread points to a component on the motherboard - is this where the inverter is located on my laptop? I have also tried contacting the repairers suggested by XMG but I haven't heard back from them yet.

 

These screens use LEDs and have no inverter. CCFL where phased out on Clevos 5 years ago.

 

True, but it does have a led driver board (that does dc->dc at higher voltage). Old habits die hard, so guess it'll be called ' inverter' for while ... even Clevo still calls it "INV". Anyway, not sure how £80 is feasible; it's pretty much embedded in the panel, so a lot more work than an attach-cable+screw-on inverter replacement.

There's also the bit where the boards of both panels somehow gave up; it's possible, though unlikely (unless the motherboard killed them). Best bet would be to run both panels from another P170HM3 or any other Clevo model that has a 4-lane eDP panel as a factory option (3D or 4k).

Alternative is to power it directly using the corresponding pins on the lcd cable (PLVDD and ground). It needs 5V, so could use 3x 1.5V batteries in series. It's possible that INVBL_ON needs a signal as well (3.3V), if so; use 2x 1.5V for that. Schematic shows the mb connector, lining up the cable's connector accordingly will show which pins you need on the cable.

Spoiler: dry-running a backlight

 

Keep it simple...you already have two working screens and cables now, stop wasting more money.

Just measure DC @ PIN 22 against ground while the system is on, if there is no 3.3v then simply get the 7408 replaced. Had two systems with exact same problem HM and EM generation.

The 7408 Quad 2-input AND Gate chips are just 2$ for 5 peaces...won't get much cheaper than that...

 

Now that I have replaced the screen and cable it does seem very likely that the chip you mention needs replacing but I have no tools or expertise in this sort of thing. I would happily pay someone (a reasonable price) to do it for me but the repair centre recommended by XMG hasn't returned my emails and I don't know who else to trust with this issue.

Is replacing a chip something that I could do given that I have no experience? Removing a chip with a heat gun and soldering a new one sounds like something that could go badly wrong. I would happily test the chip with a multimeter (I'll have to buy one first!) once I can locate it, if I connect the multimeter to pin 8 and pin 7 of the U8C chip would that be correct?

 

Correct. Measure DC voltage at those pins

The chips print is quiet small, the Pins are about a third of a millimeter...
Its not too difficult with a heat-gun and some good flux...best is to order those chips and (it'll take a while) and then take them alongside the disassembled mobo to the shop. Should be a 5 Minute job that way...