Problems with my "other" baby now...

[Ian Rogers]

I have just uncovered my BBC B computer to make sure everything's sweet...

Turned it on and heard the familiar Beeeeeep Beep! and I was a happy bunny.... I normally run them for a whole day!
Hardly 20 seconds in... Hissssssss Crackle Spurt!!! Tons of white smoke poured out of the beeb....

Pulled it apart and found the smell of burnt bits coming from the PSU...

Couldn't see anything wrong, so I boot our good friend google!!! Common faults with the Beeb PSU is the X2 filter caps become fragile.....

I hope that's all it is.... I have caps coming tomorrow.... Bad week for me... This just buries the hatchet!!

 

[Nigel Goodwin]

Couldn't see anything wrong, so I boot our good friend google!!! Common faults with the Beeb PSU is the X2 filter caps become fragile.....

I hope that's all it is.... I have caps coming tomorrow.... Bad week for me... This just buries the hatchet!!

Try it without the caps, they don't do anything as far as actually operating is concerned.

 

[Ian Rogers]

I'll try it tomorrow Nigel.... The PSU is in bits on my bench..... The 0.1uF X2 cap doesn't look very well, but the page on google said to change both X2 caps and an electrolytic 220uF on on the cool side... So I've all three arriving tomorrow... They specify a decent cap so I've plumped for a 220uF 25V Panasonic low ESR with 6000 hours...

Seems to be what a PSU needs....

 

[Nigel Goodwin]

I'll try it tomorrow Nigel.... The PSU is in bits on my bench..... The 0.1uF X2 cap doesn't look very well, but the page on google said to change both X2 caps and an electrolytic 220uF on on the cool side... So I've all three arriving tomorrow... They specify a decent cap so I've plumped for a 220uF 25V Panasonic low ESR with 6000 hours...

Seems to be what a PSU needs....

To be fair, electrolytic failure is EXTREMELY common - but almost always in switch-mode PSU's, and the BBC of course is linear (it was a BBC requirement that Acorn used a linear PSU).

Not that caps didn't fail in the linear days, but it was FAR less common - although, to be fair again, the massive modern failure rates are mostly due to using cheap, crappy, sub-standard capacitors. A friend of mine downloaded the Capxon datasheet for the caps used in the original Sky HD boxes (made by Thomson) which had MASSIVE failure rates - and he also monitored the temperature inside the case of a running box - applying that temperature to the datasheet gave an estimated life of just under 12 months

However, when Sky released the boxes the first comment I made was "why Thomson?" - as every single box they had made prior to that date used the same known sub-standard capacitors, and thus had known massive failure rates.

 

[Ian Rogers]

I never even though about caps being troublesome... But since I have been here and learned about ESR and the effects it can have..

Apparently this cap delays the switching on and lets out a shrill whistle.. Then on power down it seems to sigh of relief.... Mine doesn't but I'm not pulling it apart again.. I should be okay with a Panasonic shouldn't I??

 

[Nigel Goodwin]

I never even though about caps being troublesome... But since I have been here and learned about ESR and the effects it can have..

Apparently this cap delays the switching on and lets out a shrill whistle.. Then on power down it seems to sigh of relief.... Mine doesn't but I'm not pulling it apart again.. I should be okay with a Panasonic shouldn't I??

I always stock Panasonic and Rubycon caps at work, both excellent makes.

Probably 90% of domestic electronics repair work in the last 20 years has been down to high ESR electrolytics, an ESR meter is an absolute essential (more so than a multimeter in many cases).

 

[Ian Rogers]

All fixed.... The tatung monitor won't start up but it looks like the BBC B is good to go... I need to find some books on DFS so I can see what I have...

Nigel Goodwin.... I'm having issues with my spectrum 128k.... If its okay with you, I'll add you to a conversation I'm having with Spec....