The 'out of range' message is likely being generated by the external monitor ~ by the sound of it, the video output is behaving badly and my guess is that's also impacting the builtin display as well. What's the exact model of the machine?

Since its a very old LCD it might actually run at weird refresh. Old laptops had a switch selecting between external display and LCD and you couldnt use both at the same time.

giantclam wrote on 2024-01-31, 08:36:

The 'out of range' message is likely being generated by the external monitor ~ by the sound of it, the video output is behaving badly and my guess is that's also impacting the builtin display as well. What's the exact model of the machine?

but 4/5 times I was able to see the bios on the external monitor and it looked good. furthermore, in the notebook monitor you can see the writing of the bios entries if you look at it from the right angle, the monitor does not always show the same image that I photographed. the model is the BN200

rasz_pl wrote on 2024-01-31, 08:42:

Since its a very old LCD it might actually run at weird refresh. Old laptops had a switch selecting between external display and LCD and you couldnt use both at the same time.

There is no physical switch nor the classic "F6" type key which together with the "fn" key enables particular functions silk-screened on the keyboard. there is no indicator on how to enable the external monitor, there is only the VGA port on the back.

Display is this one 800x600 active matrix, i whis to find one one ebay

use oscilloscope/logic analyzer on vga sync lines to measure what is being output

rasz_pl wrote on 2024-01-31, 20:44:

use oscilloscope/logic analyzer on vga sync lines to measure what is being output

I cant, i not have an oscilloscope and i not use it since 1998...

buy $5 "CY7C68013A-56 EZ-USB FX2LP USB2.0 Develope Board Module" (yes there is a typo, thats how Chinese call it), use with https://sigrok.org/wiki/PulseView
https://community.infineon.com/t5/Knowledge-B … iew/ta-p/252866
https://www.instructables.com/FX2LP-CY7C68013 … Logic-Analyzer/
good up to 14MHz minimum, and you only need something to measure under 100KHz range.

Apparently it uses OPTi 92C178 for VGA and supports standard VESA modes (https://github.com/rwos/notejet)....so yes, you should see BIOS with external display...

.....but what I noticed in your pic....

...capacitor C2 .... that style of cap, from that era of production, are known to fail....as in leak, go high ESR and low capacitance... might pay to check that angle.

Also, does it boot to external display, with the builtin LCD disconnected? (considering failure of LCD dragging sync lines low)

rasz_pl wrote on 2024-01-31, 21:21:

buy $5 "CY7C68013A-56 EZ-USB FX2LP USB2.0 Develope Board Module" (yes there is a typo, thats how Chinese call it), use with http […]
Show full quote

buy $5 "CY7C68013A-56 EZ-USB FX2LP USB2.0 Develope Board Module" (yes there is a typo, thats how Chinese call it), use with https://sigrok.org/wiki/PulseView
https://community.infineon.com/t5/Knowledge-B … iew/ta-p/252866
https://www.instructables.com/FX2LP-CY7C68013 … Logic-Analyzer/
good up to 14MHz minimum, and you only need something to measure under 100KHz range.

That is not even close to sufficient for checking stuff like the pixel clock.

kingcake wrote on 2024-02-01, 01:00:

rasz_pl wrote on 2024-01-31, 21:21:

buy $5 "CY7C68013A-56 EZ-USB FX2LP USB2.0 Develope Board Module" (yes there is a typo, thats how Chinese call it), use with http […]
Show full quote

buy $5 "CY7C68013A-56 EZ-USB FX2LP USB2.0 Develope Board Module" (yes there is a typo, thats how Chinese call it), use with https://sigrok.org/wiki/PulseView
https://community.infineon.com/t5/Knowledge-B … iew/ta-p/252866
https://www.instructables.com/FX2LP-CY7C68013 … Logic-Analyzer/
good up to 14MHz minimum, and you only need something to measure under 100KHz range.

That is not even close to sufficient for checking stuff like the pixel clock.

There is no pixel clock on VGA connector. CRTs dont have pixels.

rasz_pl wrote on 2024-02-01, 01:05:

kingcake wrote on 2024-02-01, 01:00:

rasz_pl wrote on 2024-01-31, 21:21:

buy $5 "CY7C68013A-56 EZ-USB FX2LP USB2.0 Develope Board Module" (yes there is a typo, thats how Chinese call it), use with http […]
Show full quote

buy $5 "CY7C68013A-56 EZ-USB FX2LP USB2.0 Develope Board Module" (yes there is a typo, thats how Chinese call it), use with https://sigrok.org/wiki/PulseView
https://community.infineon.com/t5/Knowledge-B … iew/ta-p/252866
https://www.instructables.com/FX2LP-CY7C68013 … Logic-Analyzer/
good up to 14MHz minimum, and you only need something to measure under 100KHz range.

That is not even close to sufficient for checking stuff like the pixel clock.

There is no pixel clock on VGA connector. CRTs dont have pixels.

Along with HSYNC and VSYNC it's a fundamental part of VGA signaling. I'm not sure what you're talking about. Every VGA chipset produces and uses a pixel clock.

rasz_pl wrote on 2024-02-01, 01:05:

kingcake wrote on 2024-02-01, 01:00:

rasz_pl wrote on 2024-01-31, 21:21:

buy $5 "CY7C68013A-56 EZ-USB FX2LP USB2.0 Develope Board Module" (yes there is a typo, thats how Chinese call it), use with http […]
Show full quote

buy $5 "CY7C68013A-56 EZ-USB FX2LP USB2.0 Develope Board Module" (yes there is a typo, thats how Chinese call it), use with https://sigrok.org/wiki/PulseView
https://community.infineon.com/t5/Knowledge-B … iew/ta-p/252866
https://www.instructables.com/FX2LP-CY7C68013 … Logic-Analyzer/
good up to 14MHz minimum, and you only need something to measure under 100KHz range.

That is not even close to sufficient for checking stuff like the pixel clock.

There is no pixel clock on VGA connector. CRTs dont have pixels.

VGA Chipset datasheet from 1990 showing pixel clock waveform. There were purpose built ICs just for generating all the pixel clocks for various modes.

This is internal inside ramdac. There is no pixel clock on the VGA connector. There are no pixels in a CRT monitor. To a monitor there is zero difference between 80x400, 640x400 and 1920x400 signals as long as they use same HV timings. HV timings dont go above ~100KHz unless we go into late workstation territory - something able to max out FW900.

Agree !! On DB15 VGA port there are the H sync and V sync clocks (pins 13 and 14) both which can be checked with a fairly low end oscilloscope....
example of two 800x600 VESA modes 800 x 600 37.9Hkhz 60.0Vhz 40.0PCmhz and 800 x 600 46.9Hkhz 75.0Vhz 49.5PCmhz

I took the computer that I left without being touched for a few days, I physically disconnected what I believe are the cables that go to the integrated LCD, connected the external monitor and immediately the bios appeared. Then with F4 from the bios I performed the reset and there was no longer any way to see anything appear on the external monitor, as if something was discharged when I didn't turn it on for a few days and after showing me the bios on reboot it no longer happened see. I tried both with the buffer battery disconnected and connected but nothing changed

Yeah, I suspect there's bad capacitors inside ... this is the typical weird behaviour you get. That said, and given they way these are built, it wouldn't hurt to disassemble it further, if not only to search for bad caps, then to unplug/clean all the intercard connectors...ie; deoxit or similar. If you can get it booting reliably to external display, and reconnecting LCD results in original fault, the LCD panel itself has some problem.

I tried turning the computer back on after 3 hours and the video signal was visible correctly on the external display. I then changed the setting that you see in the bios photo of two messages above, where it says "LCD" I changed it to "CRT" and actually now it always worked with the output on the external monitor, so I was able to do a little of tests. Even without a backup battery, every time I turned it off (even when I disconnected it from its power supply, despite not having the main battery installed) it always turned on correctly using the external monitor via VGA cable. At this point I replaced the original 500mb hard disk with a 2GB one that I had in the disk drawer and it sees it perfectly, both GB! Not bad for a 486DX4 75Mhz, with 2000 Megabytes I will have much more space than I need, and considering that it already has 16MB of RAM I would say that it is well placed for memory. I then tried Phil's Dosbench of which I attach the screens, you make your own considerations. I wrote that there was also a sound card, well I tried with Doom and it works perfectly with Sound Blaster, both music and SFX work, it's not such a obvious thing to have an SB compatible sound card in a 486 laptop, especially in this one which was dedicated to office work given the integrated printer. The integrated LCD screen, even when the contacts are removed, always appears to be corrupted, so I would say that it is actually faulty, just as the floppy disk drive seems to be faulty... I don't even know whether to disassemble the computer to try to clean it... in the end I would never use it, I installed the drivers and it sees the ZIP250 Parallel drive perfectly, I will use that to copy the files onto it.

Pics...