VOGONS


First post, by clownwolf

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I have a cracked capacitor which I just noticed. One of the legs is almost torn off the capacitor body.

Looking at the technical reference, page 78, its value a 0.047pF. https://www.minuszerodegrees.net/manuals/IBM_ … 80089_MAR86.pdf

These capacitors seems to be extinct here in the US. There are obscure international sellers that looks to be selling some, but is there anything else I can use? My last resort is to buy a broken 5160 board and harvest it.

Reply 1 of 5, by majestyk

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This is definitely a typo. These capacitors are operating parallel to the 10µF filter capacitors for the supply voltages. This makes sense to improve filtering high frequency noise.
The traces around the 10µF caps alone have a higher capacity than 0.047pF so it´s nonsense.
My guess is they are in fact 0.047µF = 47nF.
Just replace the broken one with ceramic capacitor 47nF 50V.

Reply 2 of 5, by vstrakh

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That's either a typo, or some naming convention.
It can't be 0.047pF, because the parasitic capacitance between the dip socket pins would be like 10 times bigger, and looking where it's placed (power rails) it would make no sense at all.
I think there should be 47nF caps, but that P letter would mean certain package or chemistry type, and not the pico- prefix really.

Also I see not only UF (suggesting it's a microfarads), but also the µF marks. So that P/U is really some conventions that must be listed elsewhere.
As for 47nF, it should be totally ok to replace it with 100nF. Whatever you have in abundance with similar ESR - will do.

Reply 3 of 5, by clownwolf

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Ok I believe you guys that its a typo, and thanks for explaining the reason. Unfortunately my cheap LCR tester is out of battery, I could have removed one of the undamaged capacitors and confirm the capacitance right now.

Now that I am looking at it more, I also see other typos. For example it says 10UF for "C10-C10" capacitors. Looking at my 5160 motherboard, I'm pretty sure it means capacitors "C10-C16" which are tantalum capacitors next to the ISA slots. Because otherwise C11-C16 are not listed listed on that diagram.

Reply 5 of 5, by clownwolf

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I thought the capacitors were unmarked, but after snipping it off I can make out a faded 473. So it is actually .047uF.

Also, 0.047pF doesn't exist after all. So I dont think anyone has ever accidentally replaced their 5160 capacitors with one. I looked at both the sellers of the "0.047pF" capacitors, and they turned out to also be typos.

One of the shops lists .047pF, but looking at the picture and part number, its a .047uF capacitor.
https://richelectronics.co.uk/product/murata- … f-50-pcs-ol0534

The other seller has multiple pF capacitors, .047pF , 0.033pF, etc. However their model datasheet confirms the models are indeed uF, not pF.