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DEC Rainbow Home or Repair Needed (SE ENGLAND)

S

sysmgr

Member
Joined
Oct 24, 2013
Messages
30
Location
SE UK
The good news (for someone) is that I have two DEC RAINBOW 100B machines both with pedestal stands, graphics cards, and hard disk interfaces. Unfortunately they now both have the same PSU related problem, something on the input side has shorted out. I'd just finished backing everything up to my laptop and was just taking some pictures of the machine running when it went phut...

I know that I do not have the knowledge or skills to fix this problem, I can board shuffle but fault finding at the component level is way beyond my abilities. At the same time I can't bring myself to just put these two wonderful machines that I have used on and off for years in a skip, but I'm also no longer able to store then indefinably in the hope that I might come across a spare PSU at some point in the future.

Ideally I'd like to get one of them running again, but failing that I'd like all the bits to go to a good home (mono CRT, colour CRT, keyboard, graphics cards, floppy disks, hard disk, RAM board, printers, pedestal stands etc)

If you are in SE ENGLAND and can either provide a good home for the accessories or can help repair one of the PSUs I'd like to hear from you.

Thanks

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Almost certainly the input filter capacitors gone short. If you can see something silver with "RIFA" written on the top (and a crack down it) You owe me a pint.
Just snip them out & you'll probably be good to go. Replace them with the equivalent 0.1uF class "X" capacitor & you won't disturb the neighbours radio either.
I have some that'll work 99% of the time if neccessary.
 
I think I have a slightly different assembly as the mains input is incorporated into a single large silver component. Removing an turing it over confirms that it is a mains filter (photograph attached ). The good news is that this exposes the input fuse on the PSU board which looks intact.

PSU_2.jpg
 
As long as the current rating is higher for the new component (which the Farnell one is - 6A verses 2A at 240V) you should be fine.

When you said "it went phut" in post #1 what did you actually mean? If the line filter had gone short circuit then the fuse in the plugtop should have blown. Did this happen? If not, it is unlikely to be the line filter going short circuit. If the fuse plugtop fuse didn't blow - but the line filter went open circuit - then this would account for the lack of working; in which case replacing the line filter should restore operation again.

Do you have access to a multimeter? If so, you could test the line filter to see if it is actually the culprit.

Dave
 
When the filter failed it blew all three fuses all the way back to the MCB, which tripped, so that was a reasonable surge - hence the phut!

Having removed the filter I can see that what I assume to be the input fuse on the PSU PCB is intact so I'm reasonably sure that the problem is 'just' that the filter has shorted, I hope that there won't be any collatteral damage to the PSU itself.
 
good luck, and put a ceramic HRC fuse in instead of what I presume was a glass one. Glass ones don't stop a dead short, the metal can vapourise & either form a path or cause an arc. The sand in the HRC ones breaks up the metal deposition process & can save a bit of damage.
I power stuff up first time with a lightbulb in series with the mains. that way the shorted power supply becomes a light switch rather than a small bomb!
 
Hi All;
I suspect that some of the same rules apply here, as have on my Old Radios..
Any Power cap and possibly others, Must be replaced, before applying Power to the Radio, or in this case the Computer.. Or else it could cause a meltdown, depending on whether its a short or an open..
THANK YOU Marty
 
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