create new tag
, view all tags
In testing monitors and computers for CFK, I found a number of problems (opportunities) which I describe here with potential solutions.



Testing Procedure and Questions

<as posted to the lvlug mail list (i.e., "quoting" myself)>

I tested some of the CFK monitors recently (and marked each that I tested with the results, at least the max resolution they could achieve -- oops, I should have noted the color depth as well).

I'm testing them by using a machine running Knoppix with a card that can do 1028x764 (that might be at color depth 8), 800x600, and 640 x 480. (I guess I should look for a card that can do 1028x764 at a higher color depth.)

My test procedure is then to basically use + to cycle through those three resolutions and see which ones the monitor displays correctly.

Two Images Side by Side Problem

Anyway, I've found some machines that work fine at 640x480, do not work at all 1024x768, but show two horizontally squished but stable images side by side with a blank space between them at 800x600.

(I've also found others (using a different video card) that repeat the image vertically, with no space -- I attribute that problem to insufficient memory on the video card.)

With respect to monitors that show the two images side by side with a blank space between them, is that a problem that might be fixed with a different mode line?

If so, tell me more -- what / where is the easiest way to learn how to create and install the alternate mode lines. (Well, I guess installing should be straightforward, the big problem is determining the proper values.)

I got responses from Faber Fedor, (pointing to the XFree86-Video-Timings-HOWTO), and fingolfin suggesting I use more modest HorizSync and VertRefresh values.

I read the HOWTO, and although this particular symptom is not mentioned, I suspect playing around with the Mode lines or related things may be educational and potenially worthwhile. The HOWTO mentioned that sometimes during start up, X gets the wrong timings (particularly if other programs are running during the startup of X), potentially resulting in display problems.

Here is some of the relevant information from section 6.3 of the HOWTO:

In order to avoid the clock-probe inaccuracy, you should clip out the clock timings and put them in your Xconfig as the value of the Clocks property --- this suppresses the timing loop and gives X an exact list of the clock values it can try. Using the data from the example above:

Clocks 25 28 40 3 50 77 36 45 0 0 79 31 94 65 75 71

On systems with a highly variable load, this may help you avoid mysterious X startup failures. It's possible for X to come up, get its timings wrong due to system load, and then not be able to find a matching dot clock in its config database --- or find the wrong one!

Inconsistent Operation at 1024x768 Problem

The above may explain why, with some other card/monitor combinations, I sometimes got a display at 1024x768, and sometimes could not (blank screen). (In testing at home, I had one card that consistently achieved 1024x768 if I had my KVM switch set to a different computer (i.e., no monitor, mouse, or keyboard attached), and consistently failed to achieve 1024x768 if the KVM was set to it. Wierd, but maybe this is the explanation?)

Using a Mac Monitor on a PC

<as posted to the lvlug mail list (i.e., "quoting" myself)>

I noticed that many of the Apple monitors use a 15 pin connector (2 rows instead of the PCs 3 rows) -- has anybody ever investigated whether the Apple monitors can be used on a PC with a suitable adapter?

Jeff Wood and Mark responded, both indicating that it was possible with certain monitors, and Mark pointing me to a website that sells an adapter for $15.

quoting Mark:

Yes you can use one of the old Mac monitors (pre 1999?) with the 15 double row connector. It requires an adapter. A quick search found an example here: http://eshop.macsales.com/Catalog_Item.cfm?ID=3747&Item=GRI0262PCM Apple dropped that style connector when the B/W Mac came out. That was the first desktop Mac to use a PC style vga connection. When the B/W Mac came out, Apple included the adapter with computer.

I've already found about 4 of those monitors (I believe) at CFK. I'm not sure $15 apiece for the adapter will be worthwhile — I wonder:

  • Why it costs $15 (is there some "active" circuitry installed, or is it just wire)?
  • What the cheapest source of the adapter is?

BTW, you can look at the picture, but it looks like just a variation of the old "hard" serial 9 to 25 pin converters, which basically are a 9 pin and 25 pin connector (of the appropriate genders) in a plastic or rubber block, and with wiring between the appropriate pins of each connector. In this case, the appropriate connectors are a "PC type HD-15 Male to Mac DB-15 Female". If the internal circuitry is just wire, and I found the "pinouts" it would be fairly cheap and easy to make one for test. (Maybe at some point I'll look for the pinouts of each.)


  • () RandyKramer - 26 Apr 2003
  • If you edit this page: add your name here; move this to the next line; and if you've used a comment marker (your initials in parenthesis), include it before your WikiName.

Page Ratings

Topic revision: r1 - 2003-04-26 - RandyKramer
  • Learn about TWiki  
  • Download TWiki
This site is powered by the TWiki collaboration platform Powered by PerlCopyright 1999-2017 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding WikiLearn? WebBottomBar">Send feedback
See TWiki's New Look