Re: NuXT - MicroATX Turbo XT Motherboard - 9.55MHz, UMBs, XT-CF, SVGA, HD Floppy, Serial

Posted on 2019-06-12, 05:50

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

BloodyCactus wrote: Id rather see far less noise on the isa bus / power rails. maybe next revision. What do you mean? I haven't taken any readings for this revision. The board has gone to 4 layers with separate GND and VCC layers.

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Re: NuXT - MicroATX Turbo XT Motherboard - 9.55MHz, UMBs, XT-CF, SVGA, HD Floppy, Serial

Posted on 2019-06-12, 01:53

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

There is this PS/2 to XT Keyboard Converter that I build. https://monotech.fwscart.com/PS2_to_XT_Keyboard_Converter/p6083514_19714002.aspx Out of stock until I get around to drilling the enclosures for the next batch. I do plan on a PS/2 to Serial Mouse converter box at some stage, that can …

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Re: NuXT - MicroATX Turbo XT Motherboard - 9.55MHz, UMBs, XT-CF, SVGA, HD Floppy, Serial

Posted on 2019-06-10, 22:58

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I'd love to see you implement a PS/2 to serial mouse converter next. I've heard of some efforts doing that before but I don't know how successful it was. Working on that one myself. I've been writing PS/2 host/device code since Friday. Almost done with the hardware layer, then just need to …

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Re: NuXT - MicroATX Turbo XT Motherboard - 9.55MHz, UMBs, XT-CF, SVGA, HD Floppy, Serial

Posted on 2019-06-07, 00:53

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

That is the most beautiful thing I have ever seen this morning. LOL Somebody with significantly better FPGA skills than me needs to get in there and clone those ICs. What's the story on the BIOS? Was it hand-crafted or ported from some existing hardware? Glad you like! Go to the first link in the …

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Re: NuXT - MicroATX Turbo XT Motherboard - 9.55MHz, UMBs, XT-CF, SVGA, HD Floppy, Serial

Posted on 2019-06-06, 14:17

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

BinaryDemon wrote: Very cool, just curious why did you lay the power connector horizontal? Thanks 😀 And because I like the look of a side-entering ATX connector more. This board is not as wide as MicroATX boards can be, so there is plenty of space in a MicroATX case.

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Re: NuXT - MicroATX Turbo XT Motherboard - 9.55MHz, UMBs, XT-CF, SVGA, HD Floppy, Serial

Posted on 2019-06-06, 13:36

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I love this. Any hope for a 3D printed I/O shield? Glad you like it! I don't have 3D modelling experience, but could give dimensions to someone that does, or they can look at the gerber files. You can get blank metal I/O shields on eBay. Would need laser cutting machinery for those.. or d-sub …

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Compaq Portable RAM Decoder PROM replacement

Posted on 2019-06-06, 13:23

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hello I recently acquired a Compaq Portable, and have finished restoring it to full working order. In the process of doing that, I upgraded the onboard RAM from 256K to 640K. This is an offically supported upgrade by Compaq, but requires a replacement Bipolar PROM for memory decoding (U35 on …

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NuXT - MicroATX Turbo XT Motherboard - 9.55MHz, UMBs, XT-CF, SVGA, HD Floppy, Serial

Posted on 2019-06-06, 13:15

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hello all I've designed a MicroATX XT motherboard based on Sergey Kiselev's Micro 8088 SBC and ISA cards as seen here: http://www.malinov.com/Home/sergeys-projects Can be used as a full featured XT without any cards. https://i.imgur.com/i5K5GBA.jpg https://i.imgur.com/HttqWjP.jpg https://i.imgur.com …

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Re: How do you select replacement capacitors? (For Compaq Portable 2)

Posted on 2019-05-12, 01:52

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hey nztdm. I'm not sure I'm following forum rules or whatever. Just a quick question. I see you're a veteran on SLT/286 psu. Following three burnt capacitors on it, I'm currently on my fourth. For the first time I'm stumbled cause I'm not sure which capacitor it was before it blew beyond …

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Re: How do you select replacement capacitors? (For Compaq Portable 2)

Posted on 2018-10-14, 10:50

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Great work getting that working again, I especially like the ATX test PSU idea. Seeing your diagnostic work encouraged me to have another look at a broken AT power supply I'd been avoiding, which should now be fixed (broken PCB = broken traces), thanks for the inspiration. I hope that the Compaq is …

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Re: How do you select replacement capacitors? (For Compaq Portable 2)

Posted on 2018-10-13, 10:31

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Replaced all 6 10uF tantalums on the video card with multilayer ceramic capacitors. Then it worked, but only in a random XT I have with the composite output. Would just get blinking cursor in the Compaq. I then replaced all 16 10uF tantalums on the motherboard with MLCCs too. Now everything works! …

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Re: How do you select replacement capacitors? (For Compaq Portable 2)

Posted on 2018-10-12, 13:39

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Just make sure not to use low-impedance caps. While this works wonders for your Pentium 3 or higher motherboard, they can change the way the circuit design behaves in your PSU. Rule of thumb for PSU's, especially, vintage is General Purpose, but from a great brand. I'd go ahead and op for long life …

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Re: How do you select replacement capacitors? (For Compaq Portable 2)

Posted on 2018-10-11, 14:09

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

appiah4 wrote: I replace them with the same size caps. AFAIK cap size is irrelevant aside from aesthetics. From my reading, larger caps generally are rated for much higher ripple, and can withstand more power dissipation.

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Re: How do you select replacement capacitors? (For Compaq Portable 2)

Posted on 2018-10-11, 13:59

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I'm not particularly picky, even no-name caps will probably last a decade or more and there is no guarantee that another irreplacable or irrepairable part of the device won't fail by then. If you can invest in and source japanese caps, go for it, but I am ok with buying no-name chinese caps if it …

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How do you select replacement capacitors? (For Compaq Portable 2)

Posted on 2018-10-11, 13:51

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

I have done a few re-caps before with success. I succeeded with the power brick of my Compaq SLT/286 which went up in smoke. I just acquired a Compaq Portable 2, and would like to fix the dead power supply. I notice nothing out of the ordinary, except the 1700uF cap looks a bit dodgy. Replacing just …

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Re: Identify 386 Motherboard; video error with working VGA card

Posted on 2018-09-10, 10:26

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Did you just remove the battery, or did you connect another battery instead? Some motherboards won't boot without a battery. Even systems as new as a 386? Thought that was more an Apple thing.. I discovered a missing pin 4 of an SO-14 IC (U8, bottom left). A DM7406 hex-inverter with open-collector …

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Identify 386 Motherboard; video error with working VGA card

Posted on 2018-09-05, 09:29

by

by nztdm

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

Hello! I have the following 386 board. "VLSI 311 386SX VER 1.0" I can't seem to find out the model, or get it to get past the 1 long, 8 short beep error (seems to relate to video). Am using a known working Trident TVGA9000A card. Have tried in both 16-bit and 8-bit mode (with plastic covering the 16 …

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Re: IBM PS/2 Model 30-286 with massive upgrades and mods (pics!)

Posted on 2018-05-19, 23:01

by

by nztdm

in Marvin \ System Specs

in Marvin \ System Specs

It takes at least two minutes. Unless you have a rare 16-bit memory board, your one is probably much slower.

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Re: IBM PS/2 Model 30-286 with massive upgrades and mods (pics!)

Posted on 2018-05-19, 16:34

by

by nztdm

in Marvin \ System Specs

in Marvin \ System Specs

matze79 wrote: Now add a MakeIt 486 with internal Clock Doubling 😁 I looked for one of those :3 Found one on eBay, brand new unopened. You betcha I couldn't afford it :p

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Re: IBM PS/2 Model 30-286 with massive upgrades and mods (pics!)

Posted on 2018-05-07, 12:12

by

by nztdm

in Marvin \ System Specs

in Marvin \ System Specs

If possible, I recommend upgrading your FPU from a regular 80287 to the 80287XL. Not long ago there were a bunch of them on eBay going for very little money. They run cooler, and internally they are the same as an 80387SX. They also run 1:1 with the CPU rather than 2:3. Interesting! Good to know. …

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