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#1
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Pinout for Compaq Presario 425 modding
I'd like to install a new modern motherboard in a Compaq Presario 425 just for kicks and run Ubuntu. Anyway, the motherboard sort of slides into a socket which connects it to the integrated crt monitor. Any ideas on how I could get the schematic or just figure out those "pins" (It is a one-piece computer so the motherboard lacks normal pins etc.) -- Grendal |
#2
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Pinout for Compaq Presario 425 modding
On Fri, 18 May 2007 04:49:27 +0100, Grendal
put finger to keyboard and composed: I'd like to install a new modern motherboard in a Compaq Presario 425 just for kicks and run Ubuntu. Anyway, the motherboard sort of slides into a socket which connects it to the integrated crt monitor. Any ideas on how I could get the schematic or just figure out those "pins" (It is a one-piece computer so the motherboard lacks normal pins etc.) The 3 RGB signals should be terminated by 75 ohm resistors inside the monitor. A DMM should be able to find these. The H & V sync signals would probably best be seen on an oscilloscope, or maybe a frequency counter, or you may find a printed legend inside the monitor. Another way to determine the pinout is to identify the graphics chip and consult its datasheet. Still another way is to find the monitor's vertical output chip and work backwards toward the connector. This site ... http://home.worldonline.dk/finth/adapters.html .... states that the Presario 425 uses Cirrus Logic's CL-GD5420 graphics chip. Here is the datasheet for the "CL-GD542x True Color VGA Family": http://www.datasheetarchive.com/data...rticle=1162723 See page 12. Pins 68 and 69 are VSYNC and HSYNC, and 77/76/75 are the RGB pins. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#3
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Pinout for Compaq Presario 425 modding
Thanks for all that info. It turned out that beneath a glob of glue (or something now crystalline) I have found markings : r,g,and b in pairs - so 6 wires are now identified. Also I see an H and V - so those are identified. Then there is a large Black wire soldered like a ground wire. So the only remaining unidentified wires are a brown and a white wire (no markings) which were just above the H and the V wires. I think the monitor is SVGA. I will go consult all your data and post more info. My idea is to solder these to a 15 pin video plug so that this monitor will henceforth be connected to a 1.2 ghz motherboard. Hope that will work. Any guesses on what the remaining two wires must be? (This is my first ever look at monitor wiring). Thanks again. -- Grendal |
#4
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Pinout for Compaq Presario 425 modding
On Sun, 20 May 2007 18:25:53 +0100, Grendal
put finger to keyboard and composed: Thanks for all that info. It turned out that beneath a glob of glue (or something now crystalline) I have found markings : r,g,and b in pairs - so 6 wires are now identified. Also I see an H and V - so those are identified. Then there is a large Black wire soldered like a ground wire. So the only remaining unidentified wires are a brown and a white wire (no markings) which were just above the H and the V wires. I think the monitor is SVGA. I will go consult all your data and post more info. My idea is to solder these to a 15 pin video plug so that this monitor will henceforth be connected to a 1.2 ghz motherboard. Hope that will work. Any guesses on what the remaining two wires must be? (This is my first ever look at monitor wiring). Thanks again. One could be digital ground, while the others could be Monitor ID bits. See http://pinouts.ru/Video/VGA15_pinout.shtml The ID pins are either grounded at the monitor end, or not connected. I'm not sure if these ID bits are actually used. I say this because my old 486 box has a CL-GD5428 chip which determines the monitor type by sensing the 75 ohm terminations on the RGB pins. If one of these terminations is missing, as recently happened to me (open circuit inductor), then the CL chip thinks that that the monitor is a monochrome VGA type. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#5
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Pinout for Compaq Presario 425 modding
So far I have hooked up just four wires, the horizonal, the vert and the green pair. I was surprised I get this much. I guess my one concern about the unknown wires is that I don't want to blow out something. But maybe that is not really likely? I don't have a scope so I may just need to go with trial-and-error. The last one, (and maybe the middle image), I guess, is "graphics mode" and needs a bit more info to work. '[image: http://img.photobucket.com/albums/v241/pixhopwow/th_DSC04970.jpg]' (http://img.photobucket.com/albums/v2...w/DSC04970.jpg) '[image: http://img.photobucket.com/albums/v241/pixhopwow/th_DSC04973.jpg]' (http://img.photobucket.com/albums/v2...w/DSC04973.jpg) '[image: http://img.photobucket.com/albums/v241/pixhopwow/th_DSC04974.jpg]' (http://img.photobucket.com/albums/v2...w/DSC04974.jpg) -- Grendal |
#6
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Pinout for Compaq Presario 425 modding
On Wed, 30 May 2007 01:15:54 +0100, Grendal
put finger to keyboard and composed: So far I have hooked up just four wires, the horizonal, the vert and the green pair. I was surprised I get this much. I guess my one concern about the unknown wires is that I don't want to blow out something. You really should have a separate digital ground for the sync pulses. As it is now, you are using the green analogue ground for this purpose. But maybe that is not really likely? I don't have a scope so I may just need to go with trial-and-error. The last one, (and maybe the middle image), I guess, is "graphics mode" and needs a bit more info to work. '[image: http://img.photobucket.com/albums/v241/pixhopwow/th_DSC04970.jpg]' (http://img.photobucket.com/albums/v2...w/DSC04970.jpg) '[image: http://img.photobucket.com/albums/v241/pixhopwow/th_DSC04973.jpg]' (http://img.photobucket.com/albums/v2...w/DSC04973.jpg) '[image: http://img.photobucket.com/albums/v241/pixhopwow/th_DSC04974.jpg]' (http://img.photobucket.com/albums/v2...w/DSC04974.jpg) The latter looks like a horizontal sync issue. I'm assuming that you haven't chosen a resolution that drives the monitor outside its allowable H and V limits. If so, then you could be observing the same problem that I had when I attempted to hook up an older monitor to a newer graphics card. The problem in my case was that the newer card couldn't handle the load on the sync signals when their polarity switched from positive to negative, as it does during the change from text to graphics modes. You may need an oscilloscope to see this. In my case the fix was to change a resistor and/or capacitor inside the monitor, as described in the first URL: http://groups.google.com/group/sci.e...e=source&hl=en http://groups.google.com/group/comp....e=source&hl=en - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#7
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Pinout for Compaq Presario 425 modding
Here it is with the blue and red pairs too at 640x480 resolution (That fixed the random mess). I still haven't been able to figure out the other two wires. I read all the info you provided, though comprehension was around 30% ! Also, I am wondering if I can tweak the little pots in the monitor to stretch the image to fill the screen. Or is that not a good idea? '[image: http://img.photobucket.com/albums/v241/pixhopwow/th_DSC04977.jpg]' (http://img.photobucket.com/albums/v2...w/DSC04977.jpg) '[image: http://img.photobucket.com/albums/v241/pixhopwow/th_DSC04981.jpg]' (http://img.photobucket.com/albums/v2...w/DSC04981.jpg) -- Grendal |
#8
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Pinout for Compaq Presario 425 modding
On Fri, 1 Jun 2007 03:37:05 +0100, Grendal
put finger to keyboard and composed: Here it is with the blue and red pairs too at 640x480 resolution (That fixed the random mess). Sorry, it appears that I may have misled you. I thought your "random mess" looked like a horizontal sync problem. I still haven't been able to figure out the other two wires. I read all the info you provided, though comprehension was around 30% ! The horizontal and vertical sync signals can be either positive or negative. I believe that's how the earlier monitors were able to detect the video mode. ___ ___ ___ +5V ___ ___ +5V | | | | |_| ~2V ___| |___ |_| 0V positive negative faulty sync sync sync In my particular case, the sync polarity changed from positive to negative when the graphics card switched from text to graphics mode. Unfortunately the new card was unable to pull the sync signal down to 0V, so that created a "horizontal tearing" issue for me. I resolved this by modifying the monitor's circuitry. Also, I am wondering if I can tweak the little pots in the monitor to stretch the image to fill the screen. Or is that not a good idea? '[image: http://img.photobucket.com/albums/v241/pixhopwow/th_DSC04977.jpg]' (http://img.photobucket.com/albums/v2...w/DSC04977.jpg) '[image: http://img.photobucket.com/albums/v241/pixhopwow/th_DSC04981.jpg]' (http://img.photobucket.com/albums/v2...w/DSC04981.jpg) Tweaking the "vertical size/height" and "horizontal width" should be OK, although be aware that multisync monitors may have more than one height or width setting to accomodate the different H and V frequencies. I wouldn't touch the linearity controls, though. You may want to use circles and a crosshatch in your test pattern if you are making big changes. Be aware that the width is sometimes adjusted by means of a coil with a brittle ferrite slug. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#9
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Pinout for Compaq Presario 425 modding
Ok, Franc, I'll look for that slug. So far this is working out pretty well. The monitor can now run at 600X800 and I am trying to figure out if it can go to a higher resolution or not. Anyway, it looks like it will be a usable Linux box soon. -- Grendal |
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