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Reparing an old DEC Rainbow PC100

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brendan_orr:
Thank you all again.

I'll probably wait then until I get all the components put back in place until I attempt to fire this thing up.  I found a 119mmx38mm AC fan at Jameco (Part #  2125931) for only ~$14.  I've got other things to get as well and will probably shelve the electrical side for about a week.  Although I did have a slight concern.  I slid the mainboard out to see what extension boards were installed.  I saw the RX50, a winchester interface, and a memory module with one other spot open for presumably another memory module.  I did see a little corrosion on a screw near the front that held the plastic runner on the bottom of the board.  But what worried me the most was what looked like a peeling/cracked green laquer on the top side:
Luckily, the traces I probed were all ok.

In the mean time I'll clean the yellowed plastic as much as I can and pop the floppys into an old IBM compatible to see the state of the floppies.  I think I remember there was software that allowed for translation between DEC's format and IBM's

Rasz:

--- Quote from: edpalmer42 on November 18, 2015, 05:59:18 pm ---60W and 100W 115VAC bulbs.  They go from 17 to 220 ohms and 10 to 130 ohms from cold to hot.

--- End quote ---

and 10 ohm at 12V is what?

tec5c:
That crack just looks like some type of formal coating that has split. Doesn't look like the actual PCB is damaged, so should be okay?

SpidersWeb:
My two cents, from a kiwi collector point of view, not a museum curator or EE point of view [so it's what I'd do, rather than best practice] and it's not specific to the Rainbow 100. I'm the type of guy who just plugs it in and runs away.

- paper filter caps, if present and dry, lots of smoke will come out and it will be hilarious, I've had them blow on UNIX systems and taken the time to shutdown the OS correctly before powering the unit down. My wife makes a  ??? face and life goes on.

- load - most power supplies I've seen will have internal resistors that are suitable loads, I've never had any computer power supply become damaged from not having a load, although I respect with some designs it could be possible (I just haven't come across it)

- if load is needed - I use the motherboard. I've found the protection circuits in most of these big 80's supplies to be very reliable. The only exception I've had to this is small mini supplies - like the Commodore 64 which like to go 18V and blow up your favourite DRAM. [Reminder: this is me being me, you can use resistors or light bulbs if you want to do this properly]

- check the resistance on the mothebroard lines before powering up, there is nothing to be gained from testing the overcurrent function.

When you power it up, given it's age, it's also quite likely the hard drive is starting to lose it's original factory format, so if it has errors on startup be aware that you may need to perform a low level format on the media (it doesn't mean the drive is toast). As long as it doesn't sound like it's ripping itself apart and spins up to speed - you're usually golden.

With floppy disks, rotate the centre donut, and shine a light off the surface - if you see any spots, do not put it in a drive. You can buy new sealed media. I'd also recommend not using a valuable disk the first time you try the drive - if the heads are dirty, it'll tear up the disk.

Not sure if that's useful or not, but thought I'd share just in case.

brendan_orr:


Well, she lives!

Off the bat there is a Message 8 - Drive A error after boot-up and a Message 27 - Memory Board error appearing additionally after running a self test.  I'll muck around with those later.  The whole thing is a bit noisier than I remember it, but then again I did replace the fan (with one that has a little over twice the airflow)

Thank you all for your input and help.  I'm glad it was actually something trivial and not anything too involved.  I was actually fearing the worse seeing that I think it was out in a outdoor storage facility for a while.

Edit:  It makes a very nice console for my Dell PowerConnect 3024:

I have to say that smooth scroll is quite buttery smooth!  I need to open up the monitor to fix the margins

Removing the memory module drops the availbable memory down to 127k.  Thankfully the RAM ICs themselves are socketed and populated with MB8264 and HM50256 modules so I may be able to get away with replacing those.  Can't seem to boot to the hard drive, it was probably used only for storage.  I'll mess with that after I can figure out what's wrong with the floppy drive(s).  For now I will bask in its amber glow as a terminal.

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