Re: Trying to understand 30pin simm memory modules capacity, please join if you can help.

Posted on 2021-05-18, 09:09

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I already dug up data sheets to support that claim, see https://www.vogons.org/viewtopic.php?p=940479#p940479 I have that datasheet. I also have the datasheet for MB814400A which is 4Mx1 and has 1024 refresh cycles. So first, my bad, I was so focused on the row size that I didn't consider that …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-18, 00:20

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Yes, except now you have a wrong file (or no file) loaded since it's full of FF, the last byte should've been 00.

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Re: MFM 5.25 floppy with 5ali61

Posted on 2021-05-18, 00:16

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

720k setting should work, but the problem is with media. You need QD floppies to have realiable write to them and 5.25" QDs are rare. It might just work with DD if these are good quality, but I'm not sure about longevity and error rates. And BTW all such flopies will have to be properly demagnetized …

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Re: Trying to understand 30pin simm memory modules capacity, please join if you can help.

Posted on 2021-05-18, 00:01

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Indeed. x4 chips (used on 3-chip SIMMs) typically need one more address bit for RAS-only refresh than x1 chips. x1 chips often ignore the highest address bit for RAS-only refresh, so boards not driving the highest address bit during refresh can work with 9-chip modules, but fail with 3-chip modules …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-17, 23:47

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Basically I highlighted in red the last 00 i see, so i wanna change that to 5d? (i notice on the "output " side that adds in a bracket like ]) Er, how is it the last 00 if there are way more after it? Did you mean first? And anyway that's not the place. The last one, as in the very last byte of the …

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Re: Trying to understand 30pin simm memory modules capacity, please join if you can help.

Posted on 2021-05-17, 18:56

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Be very wary about these SIMMs. I have a set of 4 MB SIMMs like that, consisting of 3 chips of 4M x 4 each, so there are actually 12 bits to choose from. There are 0 Ohm SMD "jumpers" to choose 3 of the 4 bits of each chip, so the module uses 9 of the 12 bits present in the chips. Perhaps it's …

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Re: MFM 5.25 floppy with 5ali61

Posted on 2021-05-17, 18:44

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

The 1015F MOD VI is QD drive - not very useful with PCs. All the cons and none of the pros. It's a nice drive, not doubt, I like these old things myself, but it's just not for PCs. It is 96tpi so has narrow head and can do 80 tracks, but that means not being able to properly erase/write to typical …

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Re: HWiNFO support of vintage hardware

Posted on 2021-05-17, 12:31

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I have a feature request for HWiNFO for DOS - the decompression/decryption of the data structures is very slow when the program is run from a floppy drive. I could play around with DOS buffers and read-ahead but preferably it should work better on a clean boot system as well.

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-17, 08:56

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Most software for programmers have built-in hex viewer with a simple editing mode, that should be enough to change the last byte. If not, get yourself a copy of HxD hex editor, it's simple and small enough.

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Re: FIC 386SC - upgrades and testing

Posted on 2021-05-17, 08:49

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

All SXL(C) parts have clock doublers. The SXL-40 can work at 40MHz or 2x20MHz - obviously the 40 is better because of faster bus though. You can still use it in older 16MHz system and enable clock doubler to get 32MHz for example - and that's where they shine. It's not all that much faster then 1KiB …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-17, 00:06

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

So the VGA BIOS looks OK - I mean it's a bit weird that it's header says it's only 24KiB long, but the checksum does match that entire area, so it's unlikely be a coincidence. Now the mobo BIOS doesn't pass the checksum test, but possibly it's not calculated the usual way. I'd have to disassemble it …

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Re: Have a Zenith 386 16Mhz Desktop computer and want to see if...

Posted on 2021-05-16, 23:41

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

You need the CPU swapped to something 33MHz rated to make sure it works at all, but then the actual frequency at which it'll run is decided by the mobo clock. Which sometimes can be replaced if it's a crystal generator in 4-pin metal package (and I would assume it is for this mobo). But here's the …

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Re: FIC 386SC - upgrades and testing

Posted on 2021-05-16, 23:31

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Ok, playing around with memory sticks now - swapped out my 4x 4MB 60ns 'known working' set and fitted the 8x 70ns 1MB parts that came with the board. It's not happy at 0ws any more due to the slower parts, but at 1ws it runs fine, the memory throughput is ~1MB/sec faster (some sort of interleaving …

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Re: FIC 386SC - upgrades and testing

Posted on 2021-05-16, 15:05

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I always test without memory managers, not even HIMEM loaded - although that one shouldn't really matter. But then again Landmark has some issues every now and then on CPUs faster than 386DX and I noticed having HIMEM.SYS loaded actually helps it to hang/report garbage less. Difference in loading …

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Re: FIC 386SC - upgrades and testing

Posted on 2021-05-15, 23:51

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Your 3DBench results are a bit better but in general on par with mine (Trident TVGA8900D with 1M of VRAM, that gives me 32-bit internal bus, and 0WS jumper is also present) and I'm not overclocking ISA bus. The Landmark results though are a not that impressive. For 386DX-40 and CX-83D87-40 I get 70 …

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Re: 486 - Brief sign of life upon power up

Posted on 2021-05-14, 14:32

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Ah nuts. This board's covered in tantalums. Usually it's just the +12V line that shorts out, sometimes also the -12V one. You'd have to be unlucky to get any other shorts, but it's not impossible. Get an ohm meter and test all the power inputs to the mobo vs ground, anything below 1 ohm is very …

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Re: Tandy 4825 sx Wont Post - Suspect Bios from codes. Anyway to make a new one?

Posted on 2021-05-14, 10:05

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Don't use the programmer software checksums, you don't know what and how they calculate. Maybe it's 16-bit or not even a checksum but CRC. Just write your own script to calculate that. Or post the mobo BIOS image here. As for VGA BIOS, just like any other BIOS extension it has to follow specific …

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Re: IBM EGA Adapter Repair Advice Needed

Posted on 2021-05-13, 17:19

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Ah, thanks, I must have been told that at some point but had forgotten. Just had a quick reread, so is the pull-up via current flowing through the Base-Emitter diode of the input transistor, whereas for FETs there's no current (other than gate capacitance) through the gate? In short, yes. A longer …

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Re: IBM EGA Adapter Repair Advice Needed

Posted on 2021-05-13, 12:36

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I was taught that leaving inputs disconnected could lead to them floating around the switching voltage, leading to large currents flowing and overheating. That's true, and a good practice in general, but it applies mostly to FET technology (so anything MOS). TTL chips are based on bipolar …

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Re: IBM EGA Adapter Repair Advice Needed

Posted on 2021-05-13, 09:50

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

It would be silly to create HW with just the things you thought of during early design phase, only to later find out there's issues you can't resolve without another HW revision or nice features that can't be implemented because you didn't add one more simple signal. EGA CRTC is pretty programmable, …

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