BBC B PSU

for bbc micro/electron hardware, peripherals & programming issues (NOT emulators!)
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jpagen
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BBC B PSU

Post by jpagen » Sun Jan 19, 2020 11:40 am

Hi

Opened up my Model B today to replace the PSU Caps but on opening I noticed one of the screw heads is damaged. I have had this since new (1984) and the PSU has never been opened so it must have left the factory like this. :( I have carefully tried different screwdrivers without success and don't want to make it worse. Any ideas?
Thanks

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1024MAK
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Re: BBC B PSU

Post by 1024MAK » Sun Jan 19, 2020 12:34 pm

Which screw? Can you show us by posting up a photo please.

Mark

jpagen
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Re: BBC B PSU

Post by jpagen » Sun Jan 19, 2020 1:22 pm

Thanks for the reply. One of the 3 screws which holds the circuit board to the metal case
https://ibb.co/WxBZgv1

Thanks for any help.

mr-macrisc
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Re: BBC B PSU

Post by mr-macrisc » Sun Jan 19, 2020 1:29 pm

Good set of needle nose mini vice grips will probs get it started...

Of hacksaw to cut a flat headed screwdriver slot.

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flaxcottage
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Re: BBC B PSU

Post by flaxcottage » Sun Jan 19, 2020 2:36 pm

The head looks as if the correct-sized flat-bladed screwdriver might work here. The screw is secured with locktite and will be stiff to remove. One way could be to tighten first to break the seal and then try unscrewing.

Perhaps an impact driver would work to crack the locktite seal?

A Dremel-type cutting tool could remove the screw head then after the PCB has been removed mole grips would remove the rest of the screw.

A multi-tool type cutter with a metal cutting blade could also do the trick.

Maybe a 50W+ soldering iron could loosen the seal by applying the bit to just the screw head?

Good luck with this. [-o<
- John

Image

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1024MAK
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Re: BBC B PSU

Post by 1024MAK » Sun Jan 19, 2020 2:36 pm

If you can get in at it with pliers, that’s what I would try first. It may be cross-threaded, hence why it was damaged during manufacturing.

If not, the options are:
  • Cut a slot in the head and try to use a slotted screwdriver,
  • File two sides of the screw head off, to create two flats, then use an open spanner 🔧,
  • Not sure how easy this would be, but the final option, is to carefully drill out the screw.
Good luck.

Mark

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1024MAK
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Re: BBC B PSU

Post by 1024MAK » Sun Jan 19, 2020 2:39 pm

flaxcottage wrote:
Sun Jan 19, 2020 2:36 pm
The screw is secured with locktite and will be stiff to remove.
The surface coating of locktite can be chipped off / removed with a small metal pick or small flat-bladed screwdriver.
You could also try various solvent cleaners, as they may soften the locktite.

Mark

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tricky
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Re: BBC B PSU

Post by tricky » Mon Jan 20, 2020 6:29 pm

Last resort I would say drill the head off and live with three screws.

jpagen
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Re: BBC B PSU

Post by jpagen » Mon Jan 20, 2020 10:19 pm

Thanks all for the advice and suggestions.

I found some mini gripping pliers on line which came today. They had mixed reviews but within seconds, the screw was out! :D

I reckon I have not switched the Beeb on since I got my Archimedes in the early 90's, so it will be tense moment after I have replaced the capacitors at the weekend and try the switch.

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