Re: CRT randomly makes popping noise

Posted on 2022-12-21, 06:41

by

by kdr

in Marvin \ Video

in Marvin \ Video

It could just be a bit of dust/moisture from sitting in storage for a long time. I picked up a CRT that was in good working condition, great picture, but had obviously been in storage for a loooooong time. It made a lot of snapping/popping noises when first powered on, but over the next 5-10 hours …

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Re: Some sofware to do fake EGA scanlines?

Posted on 2022-12-01, 06:16

by

by kdr

in Marvin \ Video

in Marvin \ Video

Also, it's just on the edge of possible to coax a standard VGA into producing a 640x600 mode (37.5khz horizontal and 60hz vertical) using the 28mhz dot clock. The horizontal timings are tight but a good CRT can handle it. If you can then output a frame where each of the 200 EGA lines is …

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Re: Some sofware to do fake EGA scanlines?

Posted on 2022-12-01, 06:02

by

by kdr

in Marvin \ Video

in Marvin \ Video

You can disable the double-scanning bit even in modes that enable it by default. That seems to be just what that 'VERDE' program does if you enable the scanlines option. The vertical CRTC parameters have to be set accordingly, and for a full-screen picture you'll end up with a doubled (or nearly so …

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Re: Possible to output 320x200 for EGA games? (re: doublescanned 640x400)

Posted on 2022-10-25, 20:16

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by kdr

in Marvin \ Video

in Marvin \ Video

For 320 pixels at 15.7kHz you would just need 6.3 megapixels per second. A standard VGA card doesn't provide that clock, so either VGATV needs to do some magic, or it will only work with 640-pixel modes. In 256 colour mode the VGA outputs a pixel every other clock, right? So that plus the standard …

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Re: Possible to output 320x200 for EGA games? (re: doublescanned 640x400)

Posted on 2022-10-25, 00:09

by

by kdr

in Marvin \ Video

in Marvin \ Video

What is the reasons running 70hz at all? chipset designers etc? VGA was designed to provide a 640x480 picture at 60hz. The card generated a 525 line frame and this results in a 31.5khz horizontal sync. IBM designed the VGA monitor as a fixed frequency device, so any additional video modes had to …

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Re: Possible to output 320x200 for EGA games? (re: doublescanned 640x400)

Posted on 2022-10-18, 23:01

by

by kdr

in Marvin \ Video

in Marvin \ Video

The EGA mode (640x350) on a VGA monitor is especially interesting, because the VGA card produces a 449 line frame which is exactly the same as the 449 line frame used for the 720x400 text mode, except for different polarity on the sync pins. This triggers a circuit in the VGA monitor that boosts the …

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Re: Getting power to a fan on an old computer... is the sound board an option?

Posted on 2022-10-11, 19:59

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Lots of 12v fans wont run on 5V voltage (they run but need extra push at start). So i have wired my fans between 12V and 5V wires (12v line to fan + wire and 5V to - ) the voltage between them is about 7 V, this way fan is silent and still has enough cooling power on most cases. Oh that's a clever …

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Re: Getting power to a fan on an old computer... is the sound board an option?

Posted on 2022-10-10, 21:13

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I often re-wire the Molex connectors of 12V fans to run them off the 5V rail instead, this makes them run fairly slow and very quiet. If you have a tiny screwdriver and some patience it's possible to slide the pins out of the plastic housing, so you don't even need to crimp or solder anything! (Edit …

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Re: What are some great games for 8088 computers?

Posted on 2022-09-30, 01:09

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by kdr

in DOS

in DOS

Playing Secret of Monkey Island on an 8088 is torture, but there it is on the front of the box. Barely playable was the norm back then, if you think Monkey Island was slow on an 8088 Secret of Monkey Island is quite playable (albeit a tad sluggish) if you've got a Turbo XT. I sure wouldn't want to …

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Re: What ISA cards for an IBM 5150?

Posted on 2022-09-29, 04:49

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

At this point, I'll be happy if the thing turns on after I recap it. It's actually very rewarding to play around with an IBM PC and its basic CGA graphics. The best part about CGA is that the games are perfectly playable using the composite video output because all you need is a regular television …

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Re: Is it possible to get CGA NTSC Artifact Colors when running an IBM PC in Europe?

Posted on 2022-09-29, 04:20

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by kdr

in Marvin \ Video

in Marvin \ Video

IBM PCs with CGA graphics adapters were able to produce "artifact colors" when running in the NTSC region Even in PAL regions the IBM PC with CGA generates video with NTSC timings (262 lines per frame at 60 frames per second) on both the RGBI (digital) and the composite outputs. On the composite …

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Re: 15kHz why does it matter,what is the fuss about?

Posted on 2022-09-23, 07:48

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

On the PC the big deal is that CGA/EGA games were designed with 15.7khz RGBI monitors in mind: you get 16 fixed colours and the monitor displays 200 scanlines with fairly large black areas between each line. You can play these games on a VGA system, but they are displayed in a double-scanned scheme …

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Re: What ISA cards for an IBM 5150?

Posted on 2022-09-23, 07:41

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by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I'm open to suggestions for the VGA and Audio cards, and would prefer "new" cards to vintage ones to avoid capacitor troubles. What might be a good option for the fifth slot? (My 5150 is configured with 100% IBM expansion cards as a proper "period correct" system, but that's because I have other …

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Re: Bought these (retro) hardware today

Posted on 2022-09-23, 03:23

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Wow thats a really cool find I have never seen this card! I have also been using COPY II PC and it was able to copy all my copy protected disks even without that card. Please let us know if/how it works! Yeah this is easily one of my "top 5" finds from trawling the local markets etc. When I first …

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Re: Debug an 8086 that won't power up

Posted on 2022-09-22, 09:42

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

There are clear signs of bus contention visible on the oscilloscope waveforms. Not necessarily. While CMOS drives 5V for a logic '1', the 74xx series TTL has weak logic '1' levels and can only get the output up to 3.6V-3.8V or so. I can see a lot of 74LS logic on that XT clone's motherboard and the …

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Re: Bought these (retro) hardware today

Posted on 2022-09-22, 03:24

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Went to one of the local recycling centres (which doesn't usually have any retro gear at all) and to my surprise found a box of assorted ISA/PCI/AGP cards for $1 each! Grabbed the best five and left the remainder for the weekend warriors to rummage through.... can't be too greedy heh heh IMG_ …

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Re: Debug an 8086 that won't power up

Posted on 2022-09-21, 21:22

by

by kdr

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

What else can I try? If you ground the IOCHRDY signal (pin A10) on the ISA bus and then power on the machine, the CPU will halt immediately before fetching the first instruction from ROM. This should leave all the data and address lines static and you can then check the various chip selects and bus …

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Re: Did VGA (EGA?) standard lose support for CGA Mode 5h color palette with light red color?

Posted on 2022-09-21, 21:14

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by kdr

in Marvin \ Video

in Marvin \ Video

I wonder if the light red color was more like a bug/unintended artifact, that was a side result of disabling color bursting, rather than an intended effect? It was intentionally designed that way by IBM but left undocumented. (Just like the 16-color 160x100 "graphics" mode.) My theory is that the …

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Re: IBM VGA BIOS initialization

Posted on 2022-09-12, 20:50

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by kdr

in PC Emulation

in PC Emulation

I seem to recall that "Vertical Retrace" (both the status bit and the optional interrupt) is triggered by the scanline counter reaching Vertical Displayed End. The intention must have been to inform the program "okay now you can write to video memory without worrying about screen tearing". …

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Re: What is a genuine PC?

Posted on 2022-09-07, 20:32

by

by kdr

in Milliways

in Milliways

I did not know this! The source I recall reading on the matter (wish I remember what it was) led me to believe that the creation of a clone army was unintentional on IBMs part and more or less resulted from them "rushing it" - ie. the use of off-the-shelf parts was more of a timesaver than a …

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