HP Forum Archive 16

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[Off Topic] DEC Rainbow Problem Message #1 Posted by Mike T. on 3 Oct 2006, 7:04 p.m. My apologies to anyone who is offended but I'm stuck and have rather run out of ideas for now... The title is a bit of a give away - it isn't just old HP handhelds that interest me, I have some old DEC kit as well. However in my defence I can only say that I have a suspicion that I'm not the only one with an interest in these machines reading this forum. The problem is that my old ('84) DEC Rainbow has died ... or rather it probably hasn't. So as I've very little practical experience in electrical repairs I thought I'd better have a good think about the problem before I go off opening things up and poking around. When I finished using my DEC Rainbow last Saturday night I switched it off - but forgot to turn it off at the mains as well as I normally do. Unfortunately some time during the night something shorted out in the Rainbow and tripped the circuit breaker on the ring main. This is a pity as although it has been in storage for a couple of years under my stairs I now have enough space to set it up again and I'd been using it on and off for a couple of months without any problems. Since it was switched off at the time the problem happened I don't think I'm looking for a fault on the low voltage side of the power supply, which is a good thing as this means that the system itself is probably undamaged. The bad news is that this means the problem most likely to be on the high voltage side, so I need to be very cautious. My best guess so far is that there is some kind of filter across the mains input (before the switch) and that the capacitor in that has shorted, but it could be anything! The question is what and where do I look first? I'd really, really like to avoid damaging the processor boards, memory, or disks as I'm reasonably sure they are still working... Thanks in advance for any help. Mike T.

Re: [Off Topic] DEC Rainbow Problem Message #2 Posted by Thomas Radtke on 4 Oct 2006, 3:37 a.m., in response to message #1 by Mike T. Quote: My best guess so far is that there is some kind of filter across the mains input (before the switch) and that the capacitor in that has shorted, but it could be anything! If it is the capacitor, you should have smelled it the other day and a fuse should have blown.

Re: [Off Topic] DEC Rainbow Problem Message #3 Posted by Tony Duell on 4 Oct 2006, 8:04 a.m., in response to message #1 by Mike T. If you contact me by e-mail, I might be able to help. I've got 'bow schematics, for example... If it trips the breaker as soon as you plug it in (with the front switch turned off), then it's a short very early on in the PSU. There is a mains filter, for example.

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