Repairing old Electronic equipment.

[billwill]

Yesterday I decided to try power up a NEWBRAIN AD computer, which was last powered on in 1987.



After a short while there was a PFFFFT and a lot of magic smoke released from the power supply box (PSU).

They made the box strong in them thar days, the PSU was in a steel case was sealed by pop rivets and the parts inside secured by rivnuts.

Well I drilled those pop-rivets out and found to my surprise that the two main electrolytic smoorhing capacitors looked OK. When I took all the bits out I found that what had blown was a triple (triangle) suppressor capacitor connected straight across the mains electricity input.. Such a component is not essential so I simply cut its wires & removed it and then put the PSU back together and tried it out again. It seems to work fine.

The Newbrain computer itself is not working properly though. It generates a video signal but totally blank and the onboard fluorestent display shows weird characters.. But there's hope yet. I suspect that the Eproms including the character generator eprom have lost their patterns of charges after 27 years in my attic, where summer temperatures can exceed 40 deg C.

[elanfan1]

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[69S4]

Some of the computers I'm still using look like that

I have an old Minolta XM camera from the early 70's that I've not used for about 20yrs - until I tried to get it going again in a fit of nostalgia, and it seems to be suffering from a similar malady. It's fine mechanically but the electronics (such as they were back then) seem to be sulking. Sadly no smoke to give me a clue as it's only 3v.

[billwill]

Some of the computers I'm still using look like that

I have an old Minolta XM camera from the early 70's that I've not used for about 20yrs - until I tried to get it going again in a fit of nostalgia, and it seems to be suffering from a similar malady. It's fine mechanically but the electronics (such as they were back then) seem to be sulking. Sadly no smoke to give me a clue as it's only 3v.

It's usually due to the electrolytic capacitors drying out and one of the techniques for getting old computers to work is to simply go through and replace every electrolytic capacitor with a new one.

I did this to a complex PSU inside a DVD recorder some time ago & that made it work, but it later failed for a different reason.

Maplin sell bags of mixed electrolytic capacitors relatively cheap.

Cameras & mobile phones are rather more tricky as the parts are so small.

[69S4]

Thanks Bill - I guessed (hoped) it might be something like that as nothing looks broken or damaged. I'll eventually get round to taking it to bits and changing the capacitors. Interestingly (to me anyway) I have a Nikon F3 from roughly the same era and it still works perfectly but it's been used regularly whereas the Minolta hasn't. Do the capacitors dry out from non use or is it just somehing that happens with age whether it's used or not?

[john.p.clegg]

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Is that welsh?

John

[billwill]

Thanks Bill - I guessed (hoped) it might be something like that as nothing looks broken or damaged. I'll eventually get round to taking it to bits and changing the capacitors. Interestingly (to me anyway) I have a Nikon F3 from roughly the same era and it still works perfectly but it's been used regularly whereas the Minolta hasn't. Do the capacitors dry out from non use or is it just somehing that happens with age whether it's used or not?

Drying out is an age & ambient temperature sort of thing but they can lose their 'forming' by being unused. Feeding the old capacitors with a restricted DC current (to prevent them overheating & bursting) can reform the capacitative insulating layer, provided that it hasn't actually dried out.

As mentioned the the Heater Topic re Radios, there are numerous suggestions on the Internet as to how to do this:
https://www.google.co.uk/search?num=100 ... dPsO9MFWPo

~~~~~
As far as I can see for the old style 'linear' power supplies (not modern switch-mode PSU) the simplest way of ensuring that the main capacitors in the PSU are reformed would be to find the wire from the recifiers to the capacitors, and cut it to temporarily insert a 30K (or so) 2 to 5 watt resistor. Then disconnect the outputs of the PSU and then run the modified PSU for say 24 hours. Stand it on concrete or metal in a well ventilated place just in case a capacitor blows. Finally check that the capacitors are holding their charge before removing the inserted resistor and trying out the whole equipment.

BEWARE a capacitor must be discharged by shorting a fairly low value resistor accross it, before you fiddle about soldering or connecting things to them. In the case of higher voltages such as valve equipment or switch-mode power supplies the electric shock from a charged capacitor can be LETHAL.

[reb53]

I suspect that the Eproms including the character generator eprom have lost their patterns of charges after 27 years in my attic, where summer temperatures can exceed 40 deg C.

Their name escapes me for the moment but what are those itty bitty particles that zip right thru the Earth ?
Scientists have giant tanks, of what is essentially dry cleaning fluid, at the bottom of mine shafts and have them equipped with sensors to pick these particles up.
I seem to remember that they are the particles that will alter the state of 1 bit in a memory array if they hit the right spot.
Mind you, the chance of it happening within the space of a year is 1 in a million.
However, when you have millions of them.......

Cheers,
Ralph.

[Elanconvert]

Their name escapes me for the moment but what are those itty bitty particles that zip right thru the Earth ?
Scientists have giant tanks, of what is essentially dry cleaning fluid, at the bottom of mine shafts and have them equipped with sensors to pick these particles up.
Cheers,
Ralph.

I believe they are called 'neutrinos'....

fred

[reb53]

Thanks Fred,
That's them !

Wonder what they'll do with them when they catch them....

[Elanconvert]

Wonder what they'll do with them when they catch them....

oh that's easy.....stick a tax on them and sell them back to us.....

an experiment has been set up in USA where they are going to fire them at collector through several hundred miles of rock ....

fred

[billwill]

I don't think neutrinos affect electronic equipment, too small, too fast & too light; just like an Elan.

I think it might be Cosmic Rays that you are thinking of.
http://en.wikipedia.org/wiki/Cosmic_ray

~~~~~~~~~~~~~~

Anyway, I am pleased to say that after fixing the PSU as described above and after replacing the two electrolytic capacitors that determine the start-up conditions (with advice from http://www.newbrainemu.eu/ and http://www.8bit-homecomputermuseum.at/r ... brain.html) I am pleased to announce that my Newbrain AD computer serial number 610442/GDS is now working again avter its long hibernation since 1989.


It would appear that its EPROM memories have not been affected by Cosmic Rays, despite the computer being stored in an attic (closer to outer space) and which gets very hot in Summer.