Problem with HDMI connection in ASUS mobo

June 20, 2011 at 05:19:02
Specs: Windows 7 Professional (32 bit, SP1), AMD Athlon II x2 250, 4GB RAM
Some time ago, I decided to build a budget pc to serve mainly as an HTPC of sorts. The idea was to spend the bare minimum initially and then upgrade the system as I go along. I therefore opted for a mobo that has (what I thought was) decent onboard graphics and HDMI output (ASUS M4A78LT-M) so that I could hook it up directly to my TV (Toshiba Regsa). As I mostly work on my laptop, I don’t have a computer screen (and no real reason to buy one).

Here are the system’s specs:

Mobo: ASUS M4A78LT-M
Processor: AMD Athlon II X2 250 3.0Ghz
CPU cooler: Stock
RAM: 4GB (2 X Crucial DDR3 PC3-10600; 3.25GB usable)
HDD: Western Digital Caviar 500GB
ODD: Pioneer DVR-A18LBK
OS: Windows 7 Professional (32bit, SP1)

From the start the video outputs have been giving me a headache. After putting the system together and working with the VGA connection, I was trying to install Windows XP on the machine, but the screen kept going blank after POST while getting the onscreen message “unsupported video format”. I almost gave up thinking it was a compatibility issue with my TV or that the modo was DOA, but then I tried to install Windows 7 and suddenly everything worked fine. After installing the OS, I updated the bios to the latest version (0802), as well as the graphics drivers for the chipset (AMD 760G) and the HDMI connection came to life. So far so good.

After that the system worked without a hitch for about 5 months.. But then two weeks ago the TV screen suddenly went blue, indicating there was no signal from the HDMI port. I went back to the VGA connection and that way the machine works fine (except for the severely degraded graphics of course).

I’ve tried everything I could think of to bring the HDMI back to life, including:
(1) changing the HDMI cable to a new one
(2) troubleshooting with Windows 7 diagnostic tools (no hardware problems found)
(3) checking all the bios settings thoroughly, and then…
(4) flashing to the latest bios again (ver. 0802, which was already installed)
(5) re-installing the latest driver for the chipset (760G)
(6) clearing the CMOS
(7) re-installing the ATI Catalyst software (which is supposed to control the graphics)
(8) connecting the system just with VGA cable (ok, but degraded resolution), then just with the HDMI cable (nothing at all), then with both (VGA ok, HDMI nothing).
(9) jacking up the resolution from 1280X1024 to 1600X1200 in the hope the system will switch for VGA to HDMI mode (VGA goes blank as expected, but HDMI channel remains blue/unresponsive)
(10) writing to ASUS support (and getting the most inane and annoying response – not worth repeating here.)

All these attempts led to absolutely no result.

As a last resort, I tried re-installing Windows 7, and this is where things get really weird. I don’t know if this is another problem altogether or one that is related to the original problem, but when I try to boot from the Windows installation disk, after POST the screen goes blank and the system hangs. This is happening in VGA! It is as if the moment the system finishes POST and tries to go beyond the Bios, something in the video signal fails. If I take out the installation disk and do a regular boot of Windows from my HDD, everything as it should (except for the HDMI…). I can’t make sense of this.

So now I’m really stuck. I can’t get the HDMI connection to work. I can’t re-install Windows cause the screen goes black after POST when the Windows installation disk is in the optical drive (even in VGA). I can’t afford to buy a new mobo.

The logical conclusion seems to be that this mobo is simply defective, but having the mobo work fine for five months with HDMI, I know it can’t be a compatibility issue. I can’t rid myself of the feeling that it could be made to work again if only I could find the source of the problem. The fact that the screen goes blank and the TV gives the “unsupported video format” message if trying to boot from anything other than the OS which is already installed on my HDD might be a clue as to what goes wrong, but I don't know what to do with it.

Sorry for the long story, but I wanted to save everyone the hassle of suggesting things I’ve already tried.

Any idea or suggestion would be very much appreciated.

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June 20, 2011 at 14:55:39
Borrow a monitior to test with.

Dunno what the state of the hardware is. You'd need to run some diags on it.

Dunno the state of the tv either. Could be going between tv and monitor if you have way to set that or use the special output. I'd start with the computer setting then move back to tv if both support both.

1/3 of highway deaths are caused by drunks. The rest are by people who can't drive any better than a drunk.

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June 20, 2011 at 15:40:48
Jefro hi,

many thanks for responding.

I run dxdiag and it says no problems were found anywhere.

I also looked at the device manager and tried checking with Windows 7's troubleshooting tool but found nothing.

Are there other diagnostic tools you think I should run?

As to borrowing a monitor - this would be difficult as all my friends use laptops. But if I won't find any other solution I'll try to see if I can get one.

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