Re: 486 cpu voltage regulator measurements

Posted on 2019-02-28, 21:24

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Use this, and note that pin numbering uses XY system: http://ps-2.kev009.com/eprmhtml/eprmx/h12203.htm Maybe I got your explanation wrong but 6th pin in either direction (F1 or A6) from the slanted corner is not VCC. The red dots are VCC, and since 486 doesn't have split I/O and core all of them …

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Re: Dead 486 motherboard help?

Posted on 2019-02-28, 17:28

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I know cleaning this adhesive off wouldn't have anything to do with the operation of the motherboard, but for some reason the next time I tried starting the motherboard, it worked. The first time it started the POST process, but came up with errors and beep codes. I then restarted the motherboard …

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Re: 486 cpu voltage regulator measurements

Posted on 2019-02-28, 14:35

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

But did you try jumper on 2-3? Does it boot then? Clear CMOS jumper only shorts RTC/CMOS chips VCC line to GND, nothing else. Is why it's dangerous to power the board with it in place, the chip will be shorting all it's bus signals to GND since every modern CMOS I/O pin has 2 protection diodes built …

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Re: 486 cpu voltage regulator measurements

Posted on 2019-02-28, 12:34

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Typically the 4-pin battery connector is wired like this: 1 - external battery (+) 2 - internal battery (+) 3 - to RTC/CMOS chip 4 - ground The 1-4 pin can sometimes be in reversed order, always check. This pinout is very common on 386+ mobos, earlier ones might be different, but usually will accept …

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Re: SCSI2SD - Comparison of SCSI SD, CF, and HDD performance

Posted on 2019-02-28, 10:12

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Have you tried formatting an X DHC A2 card as FAT16 or FAT32 and work in systems designed around S DHC ? I have, many times, and it works, but as I've said before there isn't any guarantee. Let me try to put it in points: - The cards can be the same brand and electrically the same, may even be the …

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Re: SCSI2SD - Comparison of SCSI SD, CF, and HDD performance

Posted on 2019-02-27, 23:37

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Well, the "SD: Sandisk, class 2" is actually a bit faster at both random and sequential reads than "SD: Sandisk Ultra, class 4", but sucks at random writes. Shows that if you mostly do reads (like, have a DOS gaming machine and the only writes are saves) a cheap card will do fine. But I'm curious …

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Re: 8BIT ISA SERIAL I/O TO PS2 MOUSE

Posted on 2019-02-27, 14:47

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

That's a great project, I had to hunt down a NOS serial mouse which, being a ball one, is not exatly great by today's standards. Still more comfortable than my first 3-button Genius. But I have to ask, wouldn't it be easier to put a 5V Cortex-M on that PCB, connect it directly to both ISA and PS/2 …

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Re: SCSI2SD - Comparison of SCSI SD, CF, and HDD performance

Posted on 2019-02-27, 12:04

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Thanks for the test. Does Winbench also test write speeds? If so the combined scores you get will be skewed towards the high-end cards. Keep in mind that in typical DOS, and even modern user-oriented PCs (so not servers or workstations) you don't actually do a lot of writes, mostly reads. You might …

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Re: SCSI2SD - Comparison of SCSI SD, CF, and HDD performance

Posted on 2019-02-27, 09:01

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

CF to IDE is easy because a CF card will natively support that interface. So all you need is match the connectors on both sides. Obviously then an adaptor will be cheap and plentiful. Both are, however, pretty much obsolete tech - I don't think anyone is going to bother making a new SCSI to IDE …

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Re: SCSI2SD - Comparison of SCSI SD, CF, and HDD performance

Posted on 2019-02-26, 12:04

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

There are standards, and there are implementations. You'd be surprised how many mutually incompatible implementations there can be if the standard is lacking and has areas open to interpretation... And then there are bugs. Point here is: When it comes to SD cards (especially in SPI mode), no matter …

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Re: SCSI2SD - Comparison of SCSI SD, CF, and HDD performance

Posted on 2019-02-26, 10:18

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Indeed, the speed rating on SD cards (C10, U1, U3, V60, V90, etc..) only guarantees sequential large-block throughput with zero regard for random small-block IO performance. For the latter, you want the new 'Application Performance Class' rating, which appears as "A1" and "A2" on cards. The …

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Re: 486 cpu voltage regulator measurements

Posted on 2019-02-25, 21:24

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

You can replace that TIP127A with a 125 or 126 as well, so long as it's not a *TU version. These are only ~2W rated and will blow pretty much instantly. I'd suggest adding a bent piece of aluminum or copper plate to form a simple radiator - this transistor didn't have it and as you can see didn't …

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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Posted on 2019-02-25, 20:18

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

So you did not find connection from R13 right side to the 4069? Than it's a problem you have to solve now :) The circuit should look something like this, based on the tests so far: https://i.imgur.com/KxG62ev.png However I'm unsure about the first gate used, I guess it's 3-4 but could be a different …

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Re: Some problems I faced today

Posted on 2019-02-25, 17:45

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Without a multimeter you won't be able to do much. I mean a simple testing circuit made of battery+resistor+LED might do in a pinch but these days you can get a cheap multimeter for a few $ in most shops that carry electric goods like switches, sockets, fuses etc. Start with the keyboard socket and …

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Re: Is it safe to remove old CMOS batteries in this "different" way?

Posted on 2019-02-25, 15:16

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I concur, one sneeze with that rotating blade and that mobo is going to to require a lot of repair to work again, if ever. Also if you remove the battery along with the terminals you can put a socket in there (assuming there is enough space) - that would greatly simplify future replacements. Might …

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Re: SCSI2SD - Comparison of SCSI SD, CF, and HDD performance

Posted on 2019-02-25, 13:56

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

IPerforming the benchmark on a faster system might increase speed differences. Also, using different speed SD and CF cards may have some impact. According to Sandisk, the SanDisk Extreme SD card is rated for 90 MB/s, while the 200x CF card is rated for 30 MB/s. The SCSI host controller is limited …

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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Posted on 2019-02-25, 13:30

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by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I am somewhat on the fence with these cheap "osciloscopes". On one hand, it is a scope and works (mostly) within the advertised parameters - you will not get anything better for 30 Euro. And because it's cheap there won't be much of a loss if you break it by accident. On the other hand... it's very …

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Re: 486 cpu voltage regulator measurements

Posted on 2019-02-25, 10:12

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

TIP127A is a PNP power darlington, not your typical linear regulator like for example LM317. Anyway, looking at the photo, from left to right the pins of that transistor should be connected like this: Vreg, output (to 486 socket), +5V That 5V might be connected permanently or through a jumper so …

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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Posted on 2019-02-24, 23:30

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Well corrosion could still be the culprit but I think we should make sure the battery circuit is operating as it should. Personally I dislike desoldering parts from old PCBs like these, they can be very fragile. Trying to remove a chip can easily rip traces or pull vias, especially those already …

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Re: Old KEnitec 286 Plus (suntac) Rescue, will need help.

Posted on 2019-02-24, 19:37

by

by Deunan

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Thanks for checking the POWER GOOD, we can now safely scratch that off the list. So you do get a reaction after bleeding C83? Well then there is no need to wait I think? Just short it by touching the pins with a resistor (anything from 100 ohm to 10k will do) for a second or two and it will be …

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