Identification required please

discuss both original and modern hardware for the bbc micro/electron
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Colday
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Identification required please

Post by Colday » Fri Sep 04, 2020 4:04 pm

Afternoon all.

I acquired a new Beeb today (number 6 (picking up number 7 tomorrow. Sigh, addictive isn't it?) It was advertised as a Model B with box etc.

So, turns up, boxed, with manuals and immaculate apart from a bit of dust.

Boot it up and get a choral boooooo, however it displays the boot screen. I need to do a little more to test it further.

Still, I popped the lid to find this....
IMG_4853.jpg
Now I suspect this is a Model A due to the lack of RAM. (it reports 16k on screen also)

I wasn't aware they socketed the RAM slots though, and also, what's with the edge connectors instead of the 'normal' pin connectors.

Am I correct and is what you see normal for an A?
BBC B's... I now have 6!
I also have 1 boxed with manuals, unmolested model A.
And also an unmolested model B. (but not boxed sadly)
12x floppy drives (only 1x currently works I think)...
Learning to repair and refurb keyboards next! No more sticky keys!

Coeus
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Re: Identification required please

Post by Coeus » Fri Sep 04, 2020 4:29 pm

I think you;re right that it is a model A.

The Model A was a cut-down version specifically to cost less so people who could not afford the B could still have one. RAM was expensive at the time so that was a big part of the saving but connectors also contribute quite a bit to the cost so they have simply been omitted. I haven't checked but I suspect the edge connector fingers are also present on a Model B with the same board revision but are not visible because of the connector mounted there.

Also notice that the user VIA is missing so there would be no point in having the user port or printer connectors anyway.

Finally, I believe is was normal to have sockets for the missing 16K or memory. That enabled people to buy an A initially and then upgrade to 32K once they had more money.

Coeus
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Re: Identification required please

Post by Coeus » Fri Sep 04, 2020 4:31 pm

Also notice that the RS423 and RGB connectors are missing as is the ADC connector and the ADC chip itself.

Colday
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Re: Identification required please

Post by Colday » Fri Sep 04, 2020 4:33 pm

I was surprised to see the sockets, that's for sure, as I thought they would have been omitted for the same reason as RAM, cost saving.

Solder pads would have been way cheaper, but hey ho, business decisions.

Yes, quite a bit missing from it being a 'B'.

Can anyone advise whether what is missing is 'normal' for an A?

And (not that I will) what is the full list to make it a B?
BBC B's... I now have 6!
I also have 1 boxed with manuals, unmolested model A.
And also an unmolested model B. (but not boxed sadly)
12x floppy drives (only 1x currently works I think)...
Learning to repair and refurb keyboards next! No more sticky keys!

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1024MAK
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Re: Identification required please

Post by 1024MAK » Fri Sep 04, 2020 10:24 pm

I concur that it looks like a model A.

The full details of how and what is needed to upgrade to a model B is in the service manual.

Mark

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Diminished
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Re: Identification required please

Post by Diminished » Fri Sep 04, 2020 10:29 pm

Yeah, it looks like our original A, which I no longer have.

Some very early models (including ours) had practically everything socketed, presumably because they were waiting for parts. I guess when they arrived they could just whack everything in the sockets in a few minutes and ship.

On at least one occasion we had faults that were remedied by just pressing the chips down into their sockets.

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flaxcottage
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Re: Identification required please

Post by flaxcottage » Fri Sep 04, 2020 11:40 pm

Yep, that's a model A all right.

Mine was a model A issue 3 board BITD. It was gradually upgraded to the full B specification. The IC sockets helped greatly with that. The first upgrade was an extra 16K RAM along with a printer interface, which needed the printer and user port connectors soldering in and the user VIA adding.

Much later I acquired a Cub monitor and a dual 40T disk drive so that the machine was then upgraded to the full B specification with a 8271 DFS. By that time the upgrade price had dropped considerably. Later it had a Solidisk 32K sideways RAM added and that was ultimately replaced with an ATPL ROM board with 16K sideways RAM.

To have survived as an unmodified model A is quite a rare thing these days. :D
- John

Check out the Educational Software Archive at www.flaxcottage.com

Colday
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Re: Identification required please

Post by Colday » Sun Sep 06, 2020 9:21 am

flaxcottage wrote:
Fri Sep 04, 2020 11:40 pm
Yep, that's a model A all right.

Mine was a model A issue 3 board BITD. It was gradually upgraded to the full B specification. The IC sockets helped greatly with that. The first upgrade was an extra 16K RAM along with a printer interface, which needed the printer and user port connectors soldering in and the user VIA adding.

Much later I acquired a Cub monitor and a dual 40T disk drive so that the machine was then upgraded to the full B specification with a 8271 DFS. By that time the upgrade price had dropped considerably. Later it had a Solidisk 32K sideways RAM added and that was ultimately replaced with an ATPL ROM board with 16K sideways RAM.

To have survived as an unmodified model A is quite a rare thing these days. :D
And the good news is once I have recapped the PSU and got it working correctly (choral boop, no beep, no keyboard, no LED's but Break/reset works) it will get boxed up back in it's original packaging, with it's original manuals and welcome pack and left as an unmodified A.
BBC B's... I now have 6!
I also have 1 boxed with manuals, unmolested model A.
And also an unmolested model B. (but not boxed sadly)
12x floppy drives (only 1x currently works I think)...
Learning to repair and refurb keyboards next! No more sticky keys!

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BigEd
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Re: Identification required please

Post by BigEd » Sun Sep 06, 2020 9:59 am

When you say break/reset works, you mean some text appears on the screen and you get a Basic prompt?

The caps lock and shift lock LEDs are a good sign of life. If they don't work, it's not a happy machine. The initial beep (the second part of boo-beep) is also a very important indicator of health.

Colday
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Re: Identification required please

Post by Colday » Sun Sep 06, 2020 10:26 am

Yes, there is another thread BigEd however, I do get a prompt, I don;t get the Beep of the BooBeep but the Boooo is choral.

None of the LED's light up, no keys on the keyboard work except the Break key which does reset the machine, I've done further testing on the other thread.

viewtopic.php?f=3&t=20418
BBC B's... I now have 6!
I also have 1 boxed with manuals, unmolested model A.
And also an unmolested model B. (but not boxed sadly)
12x floppy drives (only 1x currently works I think)...
Learning to repair and refurb keyboards next! No more sticky keys!

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