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DEC Rainbow repair thread

VERAULT

VERAULT

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I am continuing this from another thread: https://forum.vcfed.org/index.php?threads/rainbow-100-pickup-where-to-start.1242775/#post-1311409

Thanks to some photos from @tradde I was able to replace the disolved ceramic diodes. I replaced all but the two largest 820UF 250V caps and one 330uf 20v cap (I have those 330uf caps on order as I dont have one with a value anywhere near that low).

IMG_20230421_172713.jpg
IMG_20230421_172648.jpg

So I got my working rainbow out of storage so I can do some comparisons etc. Of course its a different model PSU and mainboard.

The PSU on the faulty unit has a model number of 5015186D while the psu on my working Rainbow has a model of 5015186E1-P4 The faulty psu has a connector that breaks off into molex connectors with 8 pins, while the working psu has a molex cable with 10 pins.
IMG_20230425_140924.jpgIMG_20230425_140933.jpg

Going off the PDF @tradde posted in the last thread: https://forum.vcfed.org/index.php?attachments/psu-pdf.1255668/
I took some measurements
VOLTAGES.jpg
The faulty psu measurements are in blue and the working psu in red for reference. We have 12V.. Almost. Thats a start right?
 

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So onto the motherboad issues. There are glass encased capacitors which have broken off in a couple places.
In one place it seems they forgot to solder one leg on, it was barely making contact resting agains the hole it was meant to be inserted in.
IMG_20230425_153239.jpgIMG_20230425_153306.jpg

IMG_20230425_153128.jpg


So the faulty board and my working rainbow are two different board revisions. Here is the faulty one:
IMG_20230425_154439.jpg

Below is the working board model
IMG_20230425_154428.jpg

I looked for those glass capacitors that are missing on the working board and in the same spots were capacitors with Z5J 337 (see below) . I looked it up and it says these are tantalums, is that right? Waht type of caps should I buy to replace them on the faulty board?
IMG_20230425_161807.jpg



While removing the few socketed chips one crumbled. Most of the legs came off. Its labeled X2212D on both boards (only socketed on the faulty board) Can I find this chip or is that impossible?




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I guess one last thing to note is when taking my working DEC rainbow apart I was please to find it had a color graphics board in it besides the RAM board and RX50 controller. The working board has an 8088 on the mainboard as well.
IMG_20230425_161009.jpg


But this broken DEC rainbow board had a separate card with the 8088 cpu off the mainboard, and from that board the RAMboard was piggybacked onto it. There is also a 40 pin header about the 8088 cpu. Whats that for?
IMG_20230425_161944.jpg
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Thats it for now, Sorry for the onslaught of all the photos.
 
Is it a 100A, 100B, or 100+? Lucky you that the one has the color graphics. I don't believe my Rainbow has the 8080 and I know it does not have color.
 
tradde said:
Is it a 100A, 100B, or 100+? Lucky you that the one has the color graphics. I don't believe my Rainbow has the 8080 and I know it does not have color.
Click to expand...
I thought ALL Dec Rainbows came with an 8088? Both of these did. The faulty machine is a PC-100A my working machine with the color graphics board is a Pc-100B2. They both have a different style front badge as well. Get a photo of that tomorrow.
 
Maybe they do. I don't know much about them. I'd have to pop off all the extra boards to see on the main board. I believe mine is a 100B.
 
Mine is a PC100-A1. Could have sworn it was a B. Shows how good my memory isn't. And you're right it does have an 8080 buried down in there.
 
I think one of the biggest differences was the A originally only supported 256k of RAM. And later was fixed by an expansion board. There are quite a few minor differences. I just searched on DEC Rainbow A vs B.
 
Well I have the X2212D on order. Id love some insight about which replacement caps to get for the mainboard. once I get those parts in I can test the mainboard using the good psu in the interim.
 
index.php
glass cap.jpg

Can these really be tantalums? I see no polarity markings of any kind. And the glass tube ones were the same.
 
Wouldn't a quick look at the traces route on a curiiut diagram confirm the polarity?

Or a ground/earth plane check with a cap as chips yellow multimeter?
 
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Not trying to steal your thread, but this is about my Rainbow 100. Since I already had the lid off the PS I decided to extra the power supply board itself from it's metal box and look it over some more. I did this once before but did not see anything and I am not a power supply expert. I try to avoid them actually as I know they can
be dangerous. Looked again and spotted some schmooze (is that a word) under the 2200uF 35v cap (shown in the pic below). I am trying to determine if this is part
of the 12v circuit and believe it may be. The machine in question would boot and show its "insert disk" on the screen, but the floppy never was read when inserted.
I believe this was due to the 12v line either being not there or low. I tried to check but I did not have a load set up so I think the +12v will not power without a load?
This is something I can replace finally. Maybe get this working again too.
 

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tradde said:
Not trying to steal your thread, but this is about my Rainbow 100. Since I already had the lid off the PS I decided to extra the power supply board itself from it's metal box and look it over some more. I did this once before but did not see anything and I am not a power supply expert. I try to avoid them actually as I know they can
be dangerous. Looked again and spotted some schmooze (is that a word) under the 2200uF 35v cap (shown in the pic below). I am trying to determine if this is part
of the 12v circuit and believe it may be. The machine in question would boot and show its "insert disk" on the screen, but the floppy never was read when inserted.
I believe this was due to the 12v line either being not there or low. I tried to check but I did not have a load set up so I think the +12v will not power without a load?
This is something I can replace finally. Maybe get this working again too.
Click to expand...
That schmooze is suspicious, but I have been fooled before with caps that were glued down and I thought were leaking, but it was glue. That was on an LA50 board. Maybe just your pic, but I would also be concerned about what looks like burned board under that heatsink.
 
Yes, that is a darker area, but there are large areas of this board that are of the same color. So those areas must have gotten quite warm. Another heatsink further over is even a bit darker. I really think this cap is bad as it's the only one of 2200uF in the hand drawn schematic I can see that seems to be part of the +12v rail.
 
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