BBC Model B No2. Will it live again!

Any 8bit repairs, images, cool things, upgrades etc.
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rubber_jonnie
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Re: BBC Model B No2. Will it live again!

Post by rubber_jonnie »

Tomswork wrote: Wed Jun 02, 2021 5:22 pm @rubber_jonnie

Congratulations

Tom
Thanks! Once I'm in the new place, the Mac Classic is next in the queue 😁
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: BBC Model B No2. Will it live again!

Post by rubber_jonnie »

stephen_usher wrote: Wed Jun 02, 2021 5:32 pm Yay! :yay: :dualthumbup: :yay2: :bravo: :girldance:
Yay indeed! I need to see how it runs now, and if there's anything else wrong.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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rubber_jonnie
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Re: BBC Model B No2. Will it live again!

Post by rubber_jonnie »

PhilC wrote: Wed Jun 02, 2021 5:45 pm :cheer: :cheer: :cheer:
Yeah baby!
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
BennehBoy
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Re: BBC Model B No2. Will it live again!

Post by BennehBoy »

:thumbup: :excited: :thumbup:
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JezC
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Re: BBC Model B No2. Will it live again!

Post by JezC »

@rubber_jonnie It lives!!! :cheers:
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rubber_jonnie
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Re: BBC Model B No2. Will it live again!

Post by rubber_jonnie »

JezC wrote: Wed Jun 02, 2021 10:12 pm @rubber_jonnie It lives!!! :cheers:
Quite right!!

IT_Lives.jpg
IT_Lives.jpg (61.9 KiB) Viewed 2555 times

BTW I ran that little number before you posted :)


And here is the machine re-assembled and looking much tidier than when it arrived:

Nice_N_Tidy.jpg
Nice_N_Tidy.jpg (111.38 KiB) Viewed 2555 times
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: BBC Model B No2. Will it live again!

Post by rubber_jonnie »

So, here's what was wrong with this machine:
  1. Bad keyboard - I managed to get a replacement PCB from somebody off stardot and rebuilt it from the ground up. All keys good, though 4 switches needed 2 days soak in contact cleaner!! The kbd is fantastic I have to say.
  2. Dead CPU - Replaced with a new one.
  3. Bad 16Mhz master clock - One of the caps was dead, so I replaced both caps and the 16Mhz crystal.
  4. A very gnarly short between the 6845 /RESET line (+5v when switched on) and the hsync line from the 6845 to a number of other ICs in the video circuit - track cut and bodge wire used to skirt the dodgy area.
A few other ICs got changed during the troubleshooting procedure, but I think they were probably ok, so I won't count them in. I also replaced sockets and jumpers with new as I went as they were all pretty nasty.

As a little extra I did the colour composite upgrade to both No2 & No3 and it looks great :)

I also fitted the TurboSPI disk emulator to No2 so I could test it out. It's a 2 part kit which has a ROM and an MMC card reader which plugs into the user port. This was a double whammy because it tested the ROM slot and the user port. I might be shopping for a 2nd TurboSPI.....

I even managed to get the joystick port tested as I have a dual analogue stick, though I think that'll be next for a refurb as very dusty and grimy, and no doubt the pots would benefit from a spot of contact cleaner.

No2 is not great cosmetically, the case is very yellow, and the black plastic keyboard surround is pretty grotty. However, it lives, and somebody on stardot is working on getting the surrounds re-made, so it will get one of those when they are available.

I've also got a bus reader/adapter from @cmorley that I'll get built next so I can have a poke around, plus one of his 64K EEPROM kits to play with too.

I want to have a crack at assembly language on the Beeb too, as I have a lot of 6502 machines and a good deal of what I learn will be transferable.

I'd like to say I only used basic tools, and mostly I did, but whilst the Fisher Price oscilloscope did have its uses, as it showed TTL logic nicely, it also showed that you do need to have a minimum spec for looking at frequencies, and it was hopelessly inadequate for what is present in the BBC.

I had been intending to invest in a frequency generator/counter for some time now, especially for when I'm in my new workshop, so I splashed out on one for £66.

Its frequency count function was just what I needed, as it showed all the clocks were correct (16Mhz master clock, 2, 4, 6 & 8Mhz from the video IC) and enabled me to look properly at the vsync & hsync signals coming from the 6845, and that's what got me to the point where I could see that hsync was dead, and from there helped me figure out that it was a short of the hsync feeds.

If you can't afford a scope, then a frequency generator/counter is a reasonable halfway house (Cost half of what my 'scope did).

Having a decent schematic and chip data-sheets was one of the other major reasons I could fix this, along with the service manual and a very specific troubleshooting guide I also found. The basics will get you there, I'm no electronics expert, but I have learned how to read a schematic and understand logic gates. If you can do that it'll take you a long way.

Trouble is, I'm running out of machines to fix! IIRC my last 2 broken machines are a Spectrum and my Mac Classic. Both are in storage, so they will be on the list once I get into my new workshop.

One final thing I learned? Rifa capacitors scare the crap out of you and smell real bad when they enter smoke generation mode!!!

Today has been a good day :)

:girldance: :girldance: :girldance:
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
Tomswork
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Re: BBC Model B No2. Will it live again!

Post by Tomswork »

Rifa capacitor party 🥳 are my favorite stink bomb. You could always run an ad on Facebook for free broken computers. Or my favorite try and fix anything made by bang and Olson

Tom
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Re: BBC Model B No2. Will it live again!

Post by stephen_usher »

RIFA capacitors are merely delayed smoke generators. I don't even call them capacitors any more.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
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rubber_jonnie
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Re: BBC Model B No2. Will it live again!

Post by rubber_jonnie »

@stephen_usher @Tomswork

If I'd known about Rifas back in the day, I'd have saved some so I could have a Rifa party every day :dizzy:
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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