Re: UM8663AF and UM8663BF are interchangeable?

Posted on Yesterday, 17:55

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Can these chips be used interchangeably? The UM8663AF comes from the Shuttle HOT-433 motherboard The UM8663BF comes from the GA-5486al rev.2c motherboard I would like to test the UM8663BF on the Shuttle HOT-433. If I remember correctly what I saw when I reverse engineered BIOSes, the A and B chip …

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Re: Another turbo display puzzle

Posted on Yesterday, 17:46

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

What tool can give me a good approximation of Mhz when turbo is on vs off? Tools like speedsys, NSSI, or Norton SI can measure clock speed. The result might be surprising, because most early 486 mainboard do not change processor clock at all in deturbo mode, but instead disable memory caches to …

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Re: PS/2 keyboard woes

Posted on Yesterday, 15:06

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Ah, I see. So as long as the PSU +5V line is fine, the power delivery should also be fine.. I suppose I could find whichever choke is on the +5V line (they might all be, I think?) and mess around with different values but I really don't see the point to be honest. It works fine with any AT keyboard …

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Re: PS/2 keyboard woes

Posted on Yesterday, 13:56

by

by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Turned out it was motherboard's fault (btw. it was QDI Titanium IB+), it had transistor to controll voltage on AT keyboard (and I guess PS/2 mouse port) pins and it was faulty. Without anything connected it held at 5V, but when keyboard was connected it was sub 4V. And when you actually started to …

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Re: PS/2 keyboard woes

Posted on Yesterday, 13:09

by

by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

- There are ps/2 keyboards that can work with XT adapters because, although they natively use ps/2 protocol, they can detect and communicate on XT protocol never seen one able to switch automagically People claim that at least early series of the IBM Model M keyboard that came with a DIN-plug cable …

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Re: 486 motherboard reset signal issue

Posted on Yesterday, 08:50

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

It would be too great if it started working after broken trace fix. Now it is reseting but still no numbers on the POST analizer Sounds like more bad traces. Right next to pin 76 carrying the active high ISA reset signal, the 82C602 has pin 75, carrying an active low reset signal that is meant for …

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Re: Why DOS4GW games lead to higher system requirements + slower performance on 386sx

Posted on 2022-08-17, 22:48

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

DOS4GW most likely isn't the cause of the performance issue, but just a piece in the puzzle. Performance in protected mode and in real mode is not significantly different. You lose some performance when you run with paging enabled (EMM386 does it, for example), but unless EMM386 is already loaded, …

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Re: MCGA hardware issues on IBM PS/2 model 30 8086

Posted on 2022-08-17, 22:38

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Since the floppy drive is dead, also the HDD, I have to install an xtide like in order to run software tests. I made a thread about fixing one of the PS/2 floppy drives, turned out I re-discovered that the electrolytics go bad in those drives. See https://www.vogons.org/viewtopic.php?f=46&t=78462 .

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Re: MCGA hardware issues on IBM PS/2 model 30 8086

Posted on 2022-08-17, 22:25

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The fact that characters show repeating data and there is a fault detectable by software (video memory test?) makes me think that the problem is with the video memory address bus (A3 line?) Good idea. Font handling on the MCGA is quite special, though. The processor copies the font data from the …

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Re: 320x240 16bit color mode with WD90C31

Posted on 2022-08-17, 20:26

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by mkarcher

in Marvin \ Video

in Marvin \ Video

It's slow on 640*480 mode, 320*240 would be 4 times faster I expect, since video is a serious bottleneck here, combined with pentium3. If your goal is not about creating an exotic P3 build with the ISA card as primary feature, you should seriously consider using any PCI graphics card instead. The …

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Re: 386/486 Combi Motherboard - Black Screen and Blown Tantalum Capacitor

Posted on 2022-08-17, 20:19

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Currently, I feel like there are no real "cheap" working graphics cards on ebay. Yes, a quick check suggests the cheapest is £30 GBP for a non-VLB card. And they all seem to be the same seller. Based on your currency, I checked ebay UK. I saw a realtek ISA graphics card for £20 + shipping. That's …

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Re: 386/486 Combi Motherboard - Black Screen and Blown Tantalum Capacitor

Posted on 2022-08-17, 08:30

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I don't have another ISA VGA card lying around, so I suppose my only option is to purchase a cheap 'working' one from eBay. Currently, I feel like there are no real "cheap" working graphics cards on ebay. I remember times where you could pick cards based on a TVGA8900B or a OAK OTI-067 chip for …

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Re: PS/2 keyboard woes

Posted on 2022-08-16, 15:07

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

My guess is that the Diamond keyboards fail to work because the power supply isn't good enough. Very unlikely as I'm using a brand new oversized Corsair 550W ATX PSU for this machine. I'm sorry. I meant the power arriving at the keyboard. I didn't mean to imply the PSU itself is bad, but instead …

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Re: PS/2 keyboard woes

Posted on 2022-08-16, 11:31

by

by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hi, I just put together a new Socket 7 Pentium MMX machine that has an AT-style keyboard connector. When I connect an old AT keyboard to it, it naturally works fine. I bought a few PS/2 keyboards from eBay that I'm trying to use via a PS/2 -> DIN adapter because that AT keyboard is a bit worn out. …

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Re: 386/486 Combi Motherboard - Black Screen and Blown Tantalum Capacitor

Posted on 2022-08-16, 11:25

by

by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

[..,] a tantalum capacitor blew up (my eyes were a safe distance away thankfully). I'm using a 10 year old (approx) ATX 250W power supply. I haven't — although probably should have — tested with a mustimeter first. I have a Cirrus Logic GD5428 in the VLB slot. I bought it untested, so it could be …

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Re: 486 motherboard reset signal issue

Posted on 2022-08-16, 11:13

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

If I am not mistaken such motherboard use PowerGood signal for reset. So I have check and PG signal is 4,7V and it's going to OPTI 82C895 pin labeled PowerGood. I was trying to trace from where reset signal comes to ISA slot but I cannot find anything. Do You have any ideas or suggestions how to …

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Re: Already programmed OTP EPROM?

Posted on 2022-08-15, 22:10

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by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

quicknick wrote on 2022-08-15, 21:37: Seems to be a EEPROM, though: You are definitely right. Sorry for the misinformation.

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Re: Already programmed OTP EPROM?

Posted on 2022-08-15, 21:07

by

by mkarcher

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Don't bother with OTPs, better look for pin compatible EEPROMs, such as Winbond W27E512 or SST 27SF512. I ordered some W27C512P but they come from China and I'm still waiting for them. Mind the difference: W27 C 512P is an ERPOM, hopefully not OTP. SSTV2 recommended W27 E 512, which is an early …

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Re: Max colors from WD90C31

Posted on 2022-08-15, 17:11

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by mkarcher

in Marvin \ Video

in Marvin \ Video

That appears correct. Nothing I ever found could display over 256 colors. I believe the datasheet for the video controller even stated something like "up to 256 colors". Using a suitable RAMDAC, you can program the video controller to output 640x200 at 256 colors, and have the RAMDAC take the two …

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Re: DOS32AWE - DOS/4G compatible DOS Extender with Sound Blaster AWEUTIL MIDI synthesizer support for Protected mode,V

Posted on 2022-08-14, 17:33

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by mkarcher

in Marvin \ Sound

in Marvin \ Sound

I am not impressed by your reversing skills. You don't need to be impressed. Anyway, here is a repository with usable source code: https://github.com/karcherm/dos32awe I know some people are annoyed that recent versions of DOS32AWE refuse to work with EMM386. The code enabling this behaviour is …

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