BBC-B iss.4 PSU odd capacitors

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eXne
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BBC-B iss.4 PSU odd capacitors

Post by eXne » Sun Nov 10, 2019 1:45 pm

Folks,

at the moment I'm working on a BBC-C iss. 4.
First point of attention is of course the PSU caps.
This is where I was a bit puzzeled as the PSU is different from the ones I normaly have.
Acorn BBC PSU Iss 4 marked.jpg
C1,C2 and C9 are marked.
Normally you expect the yellowish square ones but now C1 and C2 are oval brown. Apperently in good condition.
C9 is here C20.
Acorn BBC B PSU capacitors.jpg
The question I have: does any saw this PSU before?
Secondly: C9 will be replaced but should I exchange C1 and C2 aswell.
The PSU pn. is 70165602 rev. 09

Thanks
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Acorn BBC PSU iss4 pn.jpg
Acorn BBC + 6502 and Z80 2nd proc and CoPro, Master 128, 512 + 80186. Atom Prophet

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1024MAK
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Re: BBC-B iss.4 PSU odd capacitors

Post by 1024MAK » Sun Nov 10, 2019 5:43 pm

As C1 and C2 are not made by Rifa, you can choose if you wish to replace them or leave them.

The reason that C1 and C2 are normally recommended to be replaced, is because the capacitors used in these positions were made by Rifa and this type are known to self destruct. When they develop cracks, moisture can get in, then at some stage, they will explode, and release smelly smoke.

Other manufacturers used a different type of construction that normally does not self destruct. These will degrade over time, but the chances of exploding and smoking are far less.

Mark

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