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XT/CGA laptop dissection

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Reply 40 of 100, by bjt

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You may want to replace the 120 ohm resistor on the sync output with something a little larger, I raised the sync output to 1.9v to try to stabilise the picture on my TV. SCART normally expects a sync voltage of around 1v peak to peak.

I wasn't able to get a stable picture in all modes using this adaptor but I think it was partly because my TV doesn't really like 60Hz modes, and partly because the signal from my laptop is slightly off-spec. Even on a real IBM 5153 it displays off-centre (IBM CGA is fine).

You're welcome to have the CGA->SCART adaptor shown earlier in the thread for the price of postage btw, don't need it now I have a CGA monitor.

Reply 41 of 100, by keropi

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^ thanks for the offer bjt, I'll make a quick adapter to test first... I have a nice trinitron that supports both pal/ntsc so I'll see what resutls I get. Composite is really nice on it , I've tested that already 😀
What resistor value you recomment on sync? 470ohms?

I am still interested in the more complex adapter, if it's easy I'd appreciate someone making a quick schematic so I can test things out 😀

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Reply 42 of 100, by matze79

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Another Idea is using a AD724 RGB to NTSC/Pal Encoder Chip 😀

This Circuit combined with the AD724 Circuit.
C=128-VGA-IBM-Colorfix-sch.png

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Reply 43 of 100, by keropi

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^ now this looks interesting but what is JP1? the ntst->pal converter? how can this be adapted to straight scart connection? I see sync is still h+v

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Reply 44 of 100, by StickByDos

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The NTSC/PAL encoder is missing from the schematic, it is just the input stage.
But the brown color fix is present.

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Reply 45 of 100, by keropi

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I am looking at that schematic but I can't say I fully understand it ... so I have some questions 😀

1. In the schematic there is pin7 at the CGA port, it's marked as M. What is it? I see it's marked as "reserved" in pinouts. Then M goes through 74HC244N and gets outputted , but where?
2. Final output is RGB + H + V signals , so it's vga-ready? What exactly gets converted? We take the digital CGA signal, apply the brown fix and make it a VGA signal. Does this mean that when you use a CGA program that does not support composite mode you get an image like a normal cga monitor and when something switched to composite mode then you get the composite image with fixed brown? Can you recreate the CGA's composite signal from the pins of it's DB9 connector?

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💻WTB Amstrad PC7486SLC-33 system

Reply 46 of 100, by StickByDos

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1 Pin 7 in unused on CGA but on MDA/Hercules, it is monochrome output.

2 For a real CGA to VGA, you need a frame doubler, IIRC, CGA modes on VGA card are displayed with each lines repeated twice to accommodate VGA monitor sync rate (CGA 200 lines are turned into VGA 400 lines)

CGA composite relies on NTSC artifacts so you still need RGB to NTSC and NTSC to RGB

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Reply 47 of 100, by keropi

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So what is this schematic? TTL-CGA to 15khz-RGB signals? I don't get it , why apply brown fix to converted TLL output?
What will this schematic accomplish (leaving the ntsc/pal conversions aside) practically , assuming I build it for testing? If I add a sync combiner will it be good to wire this to a scart plug and use with a tv?
Is the composite signal from a CGA generated from the TTL output in the final stage before it goes to the monitor?

Sorry if this sounds stupid but I'm really interested on the subject 😀

🎵Link to buy a PCMIDI mpu
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💻WTB Amstrad PC7486SLC-33 system

Reply 48 of 100, by StickByDos

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I think there is a way to upgrade this laptop to 2.5MB (640kB + 1920kB EMS)
Here is what I found after reading 82C100 data sheets

Still untested

Set JP1A and JP2A to 1-2 (the 2 jumpers between memory banks)
Put 4 514400 in the DIP20 sockets U8-11 with pin 4 and 5 lifted out
Connect JP1A 3 to U8 and U9 pin 4
Connect JP2A 3 to U10 and U11 pin 4
Connect 82C100 pin 88 to U8 U9 U10 U11 pin 5

I don't think the BIOS support this configuration, there is no strings for more than 1MB

Patch the BIOS or make a device driver that is loaded before EMS driver
Swap everything that is loaded in memory, below and above 512k
Set 82C100 register 4Bh bits 3:0 to Fh (this swap memory between 0-512k and 512k-EMS)

Now you can load EMS driver

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Reply 49 of 100, by matze79

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The Schematic is RGB Digital to Analog Signals so you can Input to a GBS 8220 Video Converter Board or AD724 NTSC/PAL Encoder.

http://www.jammaboards.com/arcade_manuals/GBS … D-Converter.pdf

You can even upgrade your laptop to backlight, by adding EL Foil if this is possible (Space avaible etc.).

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Reply 50 of 100, by keropi

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What I don't understand is why FIXBROWN is used for RGB conversion? isn't that used only in composite mode?

🎵Link to buy a PCMIDI mpu
🎧Orpheus soundcard project
💻WTB Amstrad PC7486SLC-33 system

Reply 51 of 100, by matze79

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https://groups.google.com/d/msg/comp.sys.cbm/ … Sg/QGKgBdYwPkYJ

edit: fixed link

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Reply 52 of 100, by keropi

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allright, thanks for the updated schematic and info matze79! 😀
I'll build that and see what it can do 😉

🎵Link to buy a PCMIDI mpu
🎧Orpheus soundcard project
💻WTB Amstrad PC7486SLC-33 system

Reply 53 of 100, by StickByDos

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@matze79
Thanks for the idea, this screen is really dim I usually hold the laptop with the screen almost horizontal
I've just opened the lcd and I found it's an Optrex DMF651

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Reply 54 of 100, by bjt

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2MB ram hack would be cool, let me know if you try it!
I have ordered a PCB for another XTIDE and plan to solder it to the V86P expansion connector. Have you seen a pinout for it anywhere?

Reply 55 of 100, by StickByDos

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I've already got the DRAM chips but I prefer identifying extension connector before I burn my laptop

Here is what I've found so far

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And here is the J1 connector for the HDD daughterboard
8 IRQ5
3 4 32 36 37 40 GND
5 6 35 36 +5V
21 DRQ3
23 /DACK3
34 +12V

For your dead HDD, there is someone on a French forum with a V86P with the same symptom, it seems that it is actually the 12V path inside the daughter board that is broken

I've bought a LWLA1034 logic analyzer to seach further the extension pinout

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Reply 56 of 100, by ciernioo

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Hi Bjt! Thank you very much for your work on the CGA -> SCART adapter. I`ve built it according to your schematic, and it worked perfectly for my CGA + TV:

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This is sooo much fun!

My Z80 computer project http://ciernioo.wordpress.com/

Reply 57 of 100, by bjt

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Looks great and great choice of game. As mentioned before you may want a slightly larger resistor on the sync output if you used my schematic. I bumped the sync voltage a bit for my particular TV.

@StickByDos: Thanks for the partial pinout, will be great if you identify it fully. I've looked everywhere but I can't find a manual for this machine, I suspect the pinout might be in there.

Reply 58 of 100, by matze79

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Any Progress ?

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Co2 - for a endless Summer

Reply 59 of 100, by SquallStrife

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keropi wrote:

What I don't understand is why FIXBROWN is used for RGB conversion? isn't that used only in composite mode?

The "dark yellow to brown" fix is implemented in the monitor with CGA, not on the card. So any adaptor that uses the TTL output needs to implement it as well.

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