BBC Micro Smoking...

[tom66]

This BBC Micro worked for a while, but then started smoking... was still working during the smoking but was quickly turned off.

Opened it up to find it uses a switching power supply, probaby single switch flyback. Old technology - Very nice! It has a failed 0.1uF X-cap which has ruptured and most likely the cause of the fault. Machine still works fine, trying to convince user to have the cap replaced...

Despite being more than 30 years old, none of the caps are bulged or failed, apart from this one, which isn't an electrolytic, and might have just died from a line transient. The secondary caps are Nippon Chemicon, the primaries are Marcon.

[retiredcaps]

Re: BBC Micro Smoking...

the primaries are Marcon.

First time I have ever seen "V" vents.

[SIDMX]

Re: BBC Micro Smoking...

First time I have ever seen "V" vents.

First time i've seen either 'V' shaped vents or a BBC micro

maybe this could be helpful :
http://blog.jgc.org/2011/11/back-fro...ly-repair.html

This guy just repaired his bbc micro psu by buying a cap kit that inlcudes C1, C2 and C9, so if such kit exist maybe it will be a good idea to replace those 3 caps, although by the age of that psu better to replace all of them.

[Krankshaft]

Re: BBC Micro Smoking...

Looks like the X across the line cap puked it's metal guts out.

Be sure to replace both of them. Check the link above the image of the instructions tell you the value of the X caps replace the startup cap listed as well. Just for curiosity does the X cap look like it has any UL markings on it? Modern X caps are required to have the approval laboratories stamped on them UL, TUV, etc.

The PSU will be fine just replace the X caps or you'll have some nasty interference on the AC line.

Make sure you clean off all of that loose metal when you replace the cap you don't want it sliding somewhere and bridging something.

The last time I saw Marcon caps was in a mid 90s Dell power supply. The real old fashioned ones with an actual external 120V switch that mounted to the case. Nintendo used them in the early Super NES console power supplies too. I've never seen any bad ones.

Seems like they're out of business haven't seen any of their caps in newer equipment.

Just looked at some images of the underside of the PSU. Wow! The traces on that PSU PCB look hand drawn. Looks like the inside of my 80s Tektronix scope. No CAD programs for PCB design back then. Autorouter? You are the autorouter .

[turbozutek]

Re: BBC Micro Smoking...

You simply MUST save that computer - because it's awesome: and living history!!


Chris...

[tom66]

Re: BBC Micro Smoking...

You simply MUST save that computer - because it's awesome: and living history!!


Chris...

Of course! It's so awesome typing in:

10 FOR N=1 TO 10000
20 PRINT N*N
30 NEXT N
RUN

And watching the computer dutifully performing the task with no questions asked.

Putting ancient 5 1/2" floppies and playing games on it is FUN!

It still works, that capacitor has let out its smoke now, and is now safe. Yes I think it is safety rated (non flammable.) I may replace it later, but it's not my computer, so I have to convince the owner it's worth it. It will only cause more conducted line noise. Which may or may not be a problem.

What I find amazing is that this switching power supply outlasts most modern supplies - no problem with bad capacitors!

We've also got a Sinclair ZX-81. That's a lot of fun too.