Recently revived a BBC Model B

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errors301
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Recently revived a BBC Model B

Post by errors301 »

https://twitter.com/paulcerrington/stat ... 1997200393

Full write up of repairs above. Huge help from the stardot forums. Any questions, feel free to ask! if you spot an error / fix / could have done differently please let me know! happy to hear from you :)
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flaxcottage
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Re: Recently revived a BBC Model B

Post by flaxcottage »

Nice fix. Well done! =D>
- John

Check out the Educational Software Archive at www.flaxcottage.com
Coeus
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Re: Recently revived a BBC Model B

Post by Coeus »

Welcome to the forum and congratulations on getting your machine going again. I was looking at one of those pictures, thinking when did MMFS start using lower case, then I noticed the BBC Computer was affected too. Then it dawned on me that this was the memory fault - there is a single bit difference between an upper and lower case character in ASCII.

You also wrote:
JST Connector This was used so i did not have to desolder the RF wires to remove the mainboard in future. Though i still have to unscrew it to get the board out.
I had my board out today and didn't need to unscrew the connector. After desoldering those wires, removing the screws and the PSU wires, I pushed fingers in the DIN socket holes at the back to push the whole circuit board forward slightly. Then the back of the board will lift and clear the centre pin of that BNC socket. Obviously you can't life the front (south) of the board immediately as you need to get the expansion connections clear of the case and pushing the board forward has pushed them further into those holes, but it still comes out quite easily.
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DutchAcorn
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Re: Recently revived a BBC Model B

Post by DutchAcorn »

Nice fix! You mention that you used white vinigar to clean the pcb. Vinigar is an acid, it’s better to use IPA.

Vinigar is often used to clean a pcb that had battery leakage because the acid in the vinigar neutralises the battery alkali. But in that case it is also wise to clear away remaining vinigar afterwards with demineralised water or IPA.
Paul
errors301
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Re: Recently revived a BBC Model B

Post by errors301 »

Coeus wrote:
Tue Apr 06, 2021 1:31 am
Welcome to the forum and congratulations on getting your machine going again. I was looking at one of those pictures, thinking when did MMFS start using lower case, then I noticed the BBC Computer was affected too. Then it dawned on me that this was the memory fault - there is a single bit difference between an upper and lower case character in ASCII.

You also wrote:
JST Connector This was used so i did not have to desolder the RF wires to remove the mainboard in future. Though i still have to unscrew it to get the board out.
I had my board out today and didn't need to unscrew the connector. After desoldering those wires, removing the screws and the PSU wires, I pushed fingers in the DIN socket holes at the back to push the whole circuit board forward slightly. Then the back of the board will lift and clear the centre pin of that BNC socket. Obviously you can't life the front (south) of the board immediately as you need to get the expansion connections clear of the case and pushing the board forward has pushed them further into those holes, but it still comes out quite easily.
Yes, i think i was really lucky the only thing wrong with it was one chip and all the information to fix it was here. I have also noticed there is no ram on ebay any more maybe the old stocks are running low now. Hopefully more listings in future. I couldnt find a compatibility list, but somewhere found user specify working chips and the part numbers.

I think the JST makes sense. Maybe ive been too careful trying not to damage the ports or bend the board. It should be a long time before its removed again!
errors301
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Re: Recently revived a BBC Model B

Post by errors301 »

DutchAcorn wrote:
Tue Apr 06, 2021 6:20 am
Nice fix! You mention that you used white vinigar to clean the pcb. Vinigar is an acid, it’s better to use IPA.

Vinigar is often used to clean a pcb that had battery leakage because the acid in the vinigar neutralises the battery alkali. But in that case it is also wise to clear away remaining vinigar afterwards with demineralised water or IPA.
Riiight! Thanks you for this Ill do a correction. Ive got an A3010 which appeared to have had a battery leak i cleaned the area in the same way (its working but has some issues). I assumed vinegar would evaporate completely, does it leave a residue to be concerned about ?
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tricky
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Re: Recently revived a BBC Model B

Post by tricky »

Coeus wrote:
Tue Apr 06, 2021 1:31 am
Welcome to the forum and congratulations on getting your machine going again. I was looking at one of those pictures, thinking when did MMFS start using lower case, then I noticed the BBC Computer was affected too. Then it dawned on me that this was the memory fault - there is a single bit difference between an upper and lower case character in ASCII.

You also wrote:
JST Connector This was used so i did not have to desolder the RF wires to remove the mainboard in future. Though i still have to unscrew it to get the board out.
I had my board out today and didn't need to unscrew the connector. After desoldering those wires, removing the screws and the PSU wires, I pushed fingers in the DIN socket holes at the back to push the whole circuit board forward slightly. Then the back of the board will lift and clear the centre pin of that BNC socket. Obviously you can't life the front (south) of the board immediately as you need to get the expansion connections clear of the case and pushing the board forward has pushed them further into those holes, but it still comes out quite easily.
If you really want, you can take the board out like that with the wires still soldered, although then they are still attached.
I've been tempted to put a push connector on the wire connected to the centre to make reming the board easier, but I don't think that any of my boards have needed to be out twice so haven't bothered.
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