Vdeo issue - beats all I have ever seen

[taylorkh]

I have several Pi 3B and 3B+ computers. I have one monitor with a DVI connector and a HDMI to DVI cable does the job. I have also used HDMI to VGA converters to connect to a couple of older VGA monitors. All work fine using Ubuntu and Raspbian. Yesterday I came across the CentOS 7 with KDE image. I loaded it and have been playing with it using the HDMI to DVI cable and monitor.

This evening I received a couple more of the HDMI to VGA adapters which I had purchased on evilbay. The same sort of generic adapters with a short cable and a block on the end to connect the vga cable which I have been using for years. As a test I connected the CentOS Pi to a monitor with the adapter and VGA cable. NO video. Not even the splash screen, 4 raspberries screen nor the bootup text. I tried a second monitor and vga cable. Same thing. I tried the adapters with an Intel based PC running CentOS 7. Both worked fine.

I booted the Pi to Ubuntu and the new adapters worked fine I took an older adapter which I have had for a year or so. I connected it between the CentOS Pi and a vga monitor. Worked fine! To summarize all my testing:

Pi + CentOS + new adapter = no video
Pi + Ubuntu + new adapter = OK video
Pi + CentOS + old adapter = OK video
different Pi + CentOS + different old adapter + different vga monitor = OK video
different Pi + CentOS + new adapter + different vga monitor = no video
different Pi + Ubuntu + new adapter + different vga monitor = OK video

I have no specifications on the adapters. They have no manufacturer information. Just cheap Chinese generic stuff.

Does anyone had any idea why Ubuntu works and CentOS does not with some adapters?

TIA,

Ken

[W. H. Heydt]

It is moderately likely that the new adapters have different converters in them than the old ones.

What you probably need to do is ask on a CentOS support site, where there will be more expertise on the video drivers in that OS.

On the whole though, quit getting VGA-only monitors. I've found that it's as cheap or cheaper to get monitors with DVI input than it is to get decent HDMI to VGA converters.

[taylorkh]

Thanks W. H. Heydt,

The last VGA monitor I purchased was in 2011. It was an Acer 19" wide screen. It is still working fine on the wife's PC. The monitor on my test bench is a Samsung 17" which I purchased in 2007. Still works great. My other VGA monitor is a 15" Star Tech which I purchased in 2006. I recently dusted it off and stuck a Pi 3B+ to the back of it with Velcro. It is setup with a mouse to control it, 450 albums worth of music on a flash drive and a couple of powered speakers as the jukebox in my workshop.

As to the CentOS drivers... the Pi image is from a SIG effort. I guess I might see if I can track down there forum or mailing list and ask. I sort of got in a panic when the two new adapters seemed not work.

I have been buying (and occasionally selling) stuff on ebay for 21 years. Up until this year I only had TWO less than OK experiences. One was an antique kerosene lantern which was advertised as "unused." It had the stub of a burned wick and was full of soot. The other issue was a set of DVDs which were not what was advertised. When I asked the seller what was going on she became abusive (and got kicked off ebay.) So far this year I have received a bootleg Sandisk SD card, two wristwatch bands in stead of monitor cables - when I finally got the monitor cables they were defective and two different USB hubs which did not work. Perhaps because of the trade disputes China is sending worse stuff than usual.

Off my soapbox now. And thanks again for your reply.

Ken