Microelectronics | NEAT-575 Pentium ISA Single Board Computer

Synopsis

Some of the later MS-DOS games require some more power than a humble 80386 processor can handle. Think Doom, Heretic, Duke Nukem 3D, Hexen, Quake, and the like. Also, I wanted to be able to run Windows 98 and play Starcraft. So I searched the Internet and found something suitable to plug into my DIY ISA system backplane. I ended up buying a NEAT-575 Pentium-class ISA single board computer. It was sold as functional, but the electrolytic capacitors were cooked already and the time-keeper had lost its power for good. It also didn't come with a CPU. I installed a Pentium processor running at 133 MHz and used it for a while like that. But I'm having second thoughts about those electrolytic capacitors. They are about to fail at any point in time. Also, I grew tired of manually setting the BIOS options, which are stored in the CMOS memory (or NVRAM as it's called nowadays), every time I use the PC.

Maintenance

So I bought a Dallas time-keeper replacement. The problem was that the old Dallas IC was soldered directly on the PCB. So I carefully removed the old IC and installed a precision IC socket. Now it is very easy to replace the Dallas time-keeper integrated circuit whenever it fails. One difference is that the replacement part has the DS12887+ designation. The old one didn't have the plus (+) suffix. There is a slight difference between them in the way they hold the date format. Apparently, the new one works fine. But I should have paid attention when I did the parts order. When I ran NSSI, it complained about incorrect date and time. However, HWiNFO and Norton Diagnostics said everything is OK. So there might be a bug in the NSSI code. Or it verifies somehow that the date and time do not look as they should. But to my eyes, they're OK.

As for the capacitors, I went for replacements using a solid polymer formulation. These should hold better in time than plain electrolytic capacitors.

I have measured the old ELNA RJH capacitors. They were still within factory specifications. One of them had a slightly higher ESR but nothing to be scared of. Interesting. Considering this board was built in the late '90s, I initially had the impression that these were fake ELNAs. But now I think they are the real deal. But anyway, I have ditched them. Their lifespan is over.

Pictures

Here are some pictures that I took during this operation.

The CPU voltage regulator section is a bit crowded and exposed to high heat sources.

These capacitors are cooked, and the PET sleeve has shrunk.

Removing them is pretty difficult without a good (de)soldering station. The PCB is multi-layer (probably 6-layer) and it sinks a lot of heat.

New parts versus old ones.

All new capacitors are installed.

There are some parts missing on the PCB. Most of them are part of the would-be video circuit. There are revisions of this computer card with VGA.

A final picture of the old components.

This ISA card should be good for at least a decade.


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