Re: Strange behavior with MSI 865P Neo and 3COM 3C905CX-TX-NM NIC (P/N 3892B230)

Posted on 2025-01-14, 20:44

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I would assume 3COM cards were more compatible than other brands. Are there any known incompatibilities with this particular card and the Intel 865P chipset? Am I missing something? It's a long shot but try running the NIC configuration program, from DOS, on the PC that it works with. Disable any …

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Re: Commodore 1084S-P1 horizontal fading issue

Posted on 2025-01-14, 19:56

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Well 10k is already 22 times better but if you can find a 220 ohm one it would be better yet :) I recommend not changing any part values in the horizontal deflection, there's just too high risk of causing HOT/flyback damage. Not to mention I do not think changing the 3534 pot would actually affect …

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Re: SCSI Fujitsu MO M2512a problem

Posted on 2025-01-14, 19:14

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Are you sure that kind of drive/media even supports low-level format? It might not, or possibly it requires a different procedure. The obvious things are termination on the drive and the DIP switch settings - make sure these are set for IBM PC and I would set the terminator power to drive only. It …

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Re: Commodore 1084S-P1 horizontal fading issue

Posted on 2025-01-13, 00:01

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

BTW, are there any places I can fit a variable resistor so I can try and tune the vertical / horizontal circuits in a trial and error method, so I can narrow down the issue to a specific circuit I have to investigate further and then get to the root cause? I'll address the other things when I have …

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Re: 386 board dead?

Posted on 2025-01-12, 11:27

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Never underestimate my abilities to do dumb things! :D It could've been the previous owner. I assume the PSU is known good one? Check for any signs of battery corrosion - it looks clean on the photo but depending on how the mobo was oriented most of the damage can be in one of the corners. Other …

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Re: MB468 motherboard (i486) wont start after reset

Posted on 2025-01-08, 00:40

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Do you have a POST card? If so does it show the RESET LED change state when you press the reset button?

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Re: Maj.Jackyl's Computer Lab

Posted on 2025-01-08, 00:39

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Re: Hmmm.... - maybe the cap was dropped there, somehow, during soldering pass? It doesn't look neat enough to be a factory rework...

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Re: Commodore 1084S-P1 horizontal fading issue

Posted on 2025-01-06, 00:55

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I'm thinking about the possibility to return the old flyback. What are the chances it's still in working order? Slim to none considering that you found a low resistance path between pins 3 and 9. Unless I misunderstood the previous posts. This resistance would be connected between +128V from PSU …

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Re: AT Power Supply - Repair / Replacement ?

Posted on 2025-01-05, 16:57

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Currently looking at an older 486 power supply. Despite looking almost as new, it is not working. I have mixed feelings about this PSU. On one hand looks clean, has proper input filtering. On the other they used up more than 2/3 of the space for the primary side and had to cram the secondary into a …

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Re: Commodore 1084S-P1 horizontal fading issue

Posted on 2025-01-05, 16:51

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Here are the measurements I did following your last posts: All of them look good. So good in fact that I would not bother replacing any of it. 2524 (??) = 5.068uF, 800mOhm Huh, so there is a reason why it's so bloody big for 4.7uF. Apparently it does need to be low ESR and tolerate high current …

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Re: Chip-8 halt opcode/event

Posted on 2025-01-03, 18:25

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

One interesting solution that I found is to check PC regularly, and if it points to the same location more than X (5, 10,...) times, it can be considered as an infinite loop state. The problem with this approach is it can be triggered by a long delay loop (say, to show a splash screen) if you …

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Re: Chip-8 halt opcode/event

Posted on 2025-01-03, 17:03

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

So first of all that infinite loop is expected behaviour. It means your emulator is correctly calculating and executing a jump. As for your question, the answer is you don't know. Either you have some metadata about the ROM (that is, the size of the code in that particular ROM) or you detect invalid …

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Re: Commodore 1084S-P1 horizontal fading issue

Posted on 2025-01-01, 12:29

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

All the test I've done and posted screenshots of so far, were with 3550 POT turned all the way to the left. The vertical size with this setting is reasonable, not too high and not too short. When I start turning it clockwise, the pictures starts to fold at the bottom and the picture starts …

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Re: Commodore 1084S-P1 horizontal fading issue

Posted on 2024-12-30, 21:48

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

What do you mean by "pincushion correction"? The 3537 trimmer pot. Basically the left and right sides should be straight. From top to bottom. Any inward or outward curve will make the screen resemble a pillow/pincushion depending on which way it goes, rather than nice rectangle. Top and bottom are …

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Re: Initializing drives/Accessing parameters?

Posted on 2024-12-30, 17:11

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I wonder if that copy of the PCDOS is somehow broken if it makes the tools behave like this? DOS has its own software interrupts as a HAL to read/write physical sectors, but these I think require already formatted media. So I would guess these tools use int 13h natively. Perhaps the kernel modifies …

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Re: Best advice for a custom 5.25 cleaning disk?

Posted on 2024-12-30, 17:05

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

IMHO there is little point in using cleaning floppies, and zero in trying to make one. Just clean the drive with soft brush and quality q-tips soaked in IPA. If the drive is dirty just wiping the head surfaces is not going to clean it properly. Also if you already get loud noises from it then …

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Re: Initializing drives/Accessing parameters?

Posted on 2024-12-29, 15:38

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I do recall there there were some utilities which would trick the system into thinking it had less memory, but I don't know of any "off the top" (it has been years since I looked at this stuff) - any suggestions? I'm not familiar with PC DOS and its tools, is FDISK32 a real-mode program or …

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Re: Initializing drives/Accessing parameters?

Posted on 2024-12-29, 12:57

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Both FDISK32 and FORMAT fail with "Insufficient memory"! Try with less free RAM? Or slower CPU, maybe turning off Turbo or disabling cache can help. Some of these errors are due to program bugs and the message is not really what is causing it. Might just be some weird runtime library bug that is …

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Re: Tantalum capacitor value

Posted on 2024-12-28, 23:58

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

10uF / 16V. Note that polarity on those is marked differently, the positive lead is marked. This one has a + so it's easy to tell but even a dot or a strip, which might look like -, is the positive end. Get it wrong and watch fireworks again. There are no ceramics that go that high except MLCCs and …

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Re: Panasonic FDD 5.25 not recognized

Posted on 2024-12-28, 23:43

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Well i dont have another 5.25 drive. I try in two connectors (as A and B) and the same problem Hm, I wonder if your cable connectors lack the plastic piece that prevents them from being plugged in wrong? Some photos of the cable, connectors and the drive would help. Did you check the LED operation …

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