MDFS PSU capacitor polarity

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philb
Posts: 88
Joined: Sat Aug 05, 2017 6:05 pm

MDFS PSU capacitor polarity

Postby philb » Mon Oct 02, 2017 4:19 pm

Could someone with an MDFS do me a favour and post a photo of the PSU circuit showing which way around the electrolytics are fitted?

On my board I have discovered that at least one of the originals was fitted the opposite way round to the markings on the PCB. I assume this is a PCB artwork error but it made me wonder whether the other ones that I have fitted are now correct since, foolishly, I just followed the silkscreen label and didn't make a note of which way they had been oriented originally.

I guess I could go and trace out the connections on the back of the board and figure this out for myself but a photo might be quicker :-)

philb
Posts: 88
Joined: Sat Aug 05, 2017 6:05 pm

Re: MDFS PSU capacitor polarity

Postby philb » Tue Oct 03, 2017 5:41 pm

Nevermind, I traced out the connections and it is indeed just that one capacitor that's wrong on the silkscreen. So now I have a full set of new PSU caps in there. Just need to figure out why the machine won't boot now!

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danielj
Posts: 5119
Joined: Thu Oct 02, 2008 4:51 pm
Location: Manchester

Re: MDFS PSU capacitor polarity

Postby danielj » Tue Oct 03, 2017 5:45 pm

Sorry Phill - can't get at mine at the moment, am flat out with knackered back :(

The most useful thing I did was write a ROM that looped around the copy ROM to memory commands, and flashed the lights on and off. I'll see if I can find the images for you...

d.

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jgharston
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Joined: Thu Sep 24, 2009 11:22 am
Location: Whitby/Sheffield

Re: MDFS PSU capacitor polarity

Postby jgharston » Tue Oct 03, 2017 7:54 pm

Are any of these of any use?

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

philb
Posts: 88
Joined: Sat Aug 05, 2017 6:05 pm

Re: MDFS PSU capacitor polarity

Postby philb » Thu Oct 05, 2017 8:33 pm

jgharston wrote:Are any of these of any use?


I think the full-res versions of those might have been, but the thumbnails (which seem to be all that was available) didn't have enough detail. Thanks anyway though, I got it figured out.


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