HDMI out not working at all, unless i use a HDMI > DVI cable on a DVI monitor - Page 1
Forum section: electronics / repair

author: malow
author_rank: Newbie
timestamp: December 14, 2018, 03:02:24 am
content: I have a Mini PC (Intel Celeron NUC), it has HDMI output. I use on a Projector to play videos in a school.last week, i got no image at all on the projector with HDMI. (not even bios/boot screen, so its NOT a driver/windows issue - the boot image appeared before this problem) tested projector with a notebook, projector is fine. tried another HDMI cables with the MiniPC, no image at all. tried MiniPC with a LCD TV, also no image at all.at home, tried with a HDMI > VGA converter, (to keep testing the HDMI port) also did not work at all (this converter worked previously with this MiniPC). reseted bios, checked contacts (pins are fine). nada.so i thought, "the HDMI output is gone". but no. if i connect it with a HDMI cable and a HDMI to DVI adapter on a DVI monitor, BAM, works fine. resolutions/monitor is detected, everything fine.i thought something different with DVI/HDMI may be the cause, so i tested the 5V and HotPlug pins on the HDMI, they show 5v as they should.so... my question... what can cause this this?um clueless.. i asked in other forums, and got no response... you guys are my last hope...

author: wraper
author_rank: Unknown
timestamp: December 14, 2018, 03:30:08 am
content: I would first check if monitor detection does actually work. Say run teamviewer to see what happens on another computer. If monitor is not detected, check DDC lines and hotplug.QuoteWhen monitor is disconnected, hotplug should be low.If monitor is detected but there is no image, it could be that one differential output is partially blown up. Sometimes it may somewhat keep working. DVI input of particular monitor may be more tolerant to this. In such case attach DVI adapter and measure resistance to GND on 8 pins I marked on the picture (mirrored on male connector). I would suggesting setting 20+ MOhm range on multimeter. All resistances should be about the same.EDIT: I made an error as it was late night here, I marked wrong data pins. Those are for link 2 which are not used in converter. I was intending to say measuring link 1 pins which are on the left side (1, 2, 9, 10, 17, 18). Though it does not matter as you already found faulty clock pin pin.

author: Armadillo
author_rank: Super Contributor
timestamp: December 14, 2018, 08:05:13 am
content: What you are facing is a interfacing problem not a picture quality problem example the monitor is not being recognized.Some monitors have such kinds of problems of "initiating" a startup comm.Try this sequence;Turn power off everything.Hook up HDMI cable to your monitor.Turn on power to the monitor.then after;ThenPower up your PC.

author: malow
author_rank: Newbie
timestamp: December 14, 2018, 10:35:39 pm
content: @Armadilloi tried every combination possible, and before this problem, it worked in any combination, plugin before power up, after, re-plugin it, during a full year. etc. it not like some notebooks that need to be connected before power up for it to show up as a "secondary monitor".@wraperi tested with my multimeter (it only goes to 2M) and got nothing on the data pins<>ground, BUT i got a 0 ohm between pin 3 and pin 23 which i believe should not be there, don't know if is something with the HDMI > DVI adapter or something else. but i believe now i need to remove the motherboard (trying not to damage it) and test the pins on the motherboard and try to find the problem there.thanks guys for the help so far!

author: wraper
author_rank: Unknown
timestamp: December 14, 2018, 11:03:00 pm
content: Quote from: malow on December 14, 2018, 10:35:39 pmThat means half of clock differential pair is dead. My worst suspicion turned out to be true. Most likely damaged when hot plugging HDMI. Most likely TMDS level shift IC is damaged on the motherboard (output transistor shorted inside IC). Dunno about your particular NUC version but some used Asmedia ASM1442K IC. Here is example picture, marked red.

author: Armadillo
author_rank: Super Contributor
timestamp: December 15, 2018, 02:16:07 am
content: Quote from: malow on December 14, 2018, 03:02:24 amA DVI adapter will not be bring a damaged chip back to life. I think is the way the measurement was done. Would you think so?

author: malow
author_rank: Newbie
timestamp: December 15, 2018, 02:23:38 am
content: this is the mobo (best images i could find):

author: wraper
author_rank: Unknown
timestamp: December 15, 2018, 02:26:53 am
content: Quote from: malow on December 15, 2018, 02:23:38 amWhich version of NUC is it? IC should be on the bottom, somewhere around HDMI connector.

author: malow
author_rank: Newbie
timestamp: December 15, 2018, 02:28:10 am
content: its a "no-brand" Bay Trail Intel Celeron Quad Core N2920

author: wraper
author_rank: Unknown
timestamp: December 15, 2018, 02:31:02 am
content: Quote from: malow on December 15, 2018, 02:28:10 amThen it's not NUC.

author: wraper
author_rank: Unknown
timestamp: December 15, 2018, 02:33:22 am
content: Anyway, do you have hot air station? Without it's not possible to replace faulty IC. EDIT: but for TVS soldering iron is enough.

author: wraper
author_rank: Unknown
timestamp: December 15, 2018, 02:42:43 am
content: Apparently there are 4 dual TVS diodes under HDMI connector. If you are lucky, one of them is faulty and IC remains intact. If you find one which has one of the side pins shorted to center pin, you can simply desolder it and check resistance again. If resistance is fine, then you could attach monitor and check again. If everything is fine, it would be the best to replace TVS but it will work without it. Just those pins no longer would have protection.

author: Armadillo
author_rank: Super Contributor
timestamp: December 15, 2018, 02:48:00 am
content: I suspect its a HDMI bad/loose connector as DVI adapter brings the connection back to life, example Bad GND connection etc.Worth to check it first before you attempt anything drastic.

author: wraper
author_rank: Unknown
timestamp: December 15, 2018, 03:03:12 am
content: Quote from: Armadillo on December 15, 2018, 02:48:00 amDid you read the post with measurement results? One of the clock pins is shorted to GND. And I can say you from my experience that sometimes it may still keep working with some monitors.

author: malow
author_rank: Newbie
timestamp: December 15, 2018, 04:12:12 am
content: thanks again guys, i will test all connections and traces on the hdmi path to make sure there's no bad connection/short/etc, then test those ic's toodidn't know that those where TVS (new knowledge to me). got so much to learn yeti do not have hot air station, just soldering iron. but have a good vision and steady hands

author: coromonadalix
author_rank: Super Contributor
timestamp: December 15, 2018, 01:50:19 pm
content: And please when you do connect an hdmi, power it off before doing so.I personally toasted an mdmi android box in the past while powered on, and connected it to an computer monitor, the monitor survived.Normally you should put the external ground shield and touch the shell first in an slight angle to discharge any voltage potential if there is one, and enter the plug completly.You could be surprised of the differential voltages sometimes present between 2 pieces of equipment.