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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 15th Oct 2011, 1:21 pm   #1
coulson1986
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Default BBC Master trouble!

Hello, I wonder if anyone can help. I have a BBC Master and it is my pride and joy, however I have just turned it on and the usual two tone beep sounded faint and on the screen it diplays "THIS IS NOT A LANGUAGE" and the writing is really large as if it was in MODE 5.

I have turned it on and off again and it still displays the same, it was perfectly okay when I last used it.

If anyone can help I will be truly grateful.
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Old 15th Oct 2011, 2:31 pm   #2
julie_m
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Default Re: BBC Master trouble!

It sounds like a ROM problem. Either not all the pins are making contact, or it's got corrupt Alternatively, it could be a problem with the bank-switching logic. Can't remember if this was "discrete" TTL or a ULA in the Master series.

Does any IC get noticeably hot when it misbehaves?

Even if the ROM is duff, someone with a working machine and the right kit could copy theirs for you.
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Old 15th Oct 2011, 2:35 pm   #3
Andrew2
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Default Re: BBC Master trouble!

I don't know much about the Master, but I do believe it was based on the BBC-B. The first things to check are the supply rails (probably +5v, +12v and -12v) coming out of the PSU. The electrolytics in there must be pretty poorly by now.
This may be a long shot, but I've seen some very odd effects caused by an incomplete reset pulse on start-up. In the BBC-B, there was a cap which generated the start-up reset pulse and as the machine got older it would start to produce an incomplete reset. Results ranged from a screenful of rubbish to a complete no-go.
Incidentally, we've still got our BBC-B which we bought new in 1983 (I think) and it still works! And so does the 100K floppy drive!
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Last edited by Andrew2; 15th Oct 2011 at 2:44 pm.
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Old 15th Oct 2011, 2:38 pm   #4
Dave Moll
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Default Re: BBC Master trouble!

Quote:
Originally Posted by ajs_derby View Post
Even if the ROM is duff, someone with a working machine and the right kit could copy theirs for you.
If the offending ROM is identified (presumably the OS), I may be able to make a copy - assuming that my BBC-based ROM programmer still works, as I haven't used it for years.

Just to clarify - I have a Master from which to copy the ROM, but the programmer runs on a Beeb. Although it would probably also work on a Master, my Master would be out of action with the ROM removed!
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Last edited by Dave Moll; 15th Oct 2011 at 2:41 pm. Reason: clarification
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Old 15th Oct 2011, 4:19 pm   #5
cmjones01
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Default Re: BBC Master trouble!

Could this be as simple as a CMOS RAM problem? I think, on the Master, you can hold down 'R' while switching the machine on to get it back to sensible default settings (Mode 7 screen, BASIC language and so on).

<fx: googles/>Ah yes, look at this:
http://blog.joel.co.uk/?itemid=888

Try those first before delving into the hardware. If the configuration fixes the problem, it's probably just a duff CMOS RAM battery, easily replaced (it's AA cells in the Master).

Chris
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Old 15th Oct 2011, 4:31 pm   #6
coulson1986
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Default Re: BBC Master trouble!

Thankyou for your help, i have fixed it now, i just reconfugured it and it now seems to be working fine

Cheers, for the replies
Marc

Thank you for your help. I have fixed it now, I just reconfigured it and it now seems to be working fine.

Cheers for the replies,
Marc.
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Old 15th Oct 2011, 5:29 pm   #7
8 Tracker
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Default Re: BBC Master trouble!

One good way to tell if the battery is going flat. Set the time on the machine with TIME$= etc. Then power down for a few minutes. When you power up again, if *TIME returns garbage, or the wrong time, it's time to change the battery. For some reason, the real time clock stops functioning long before the settings are lost when the battery is on its' way down.

Don't forget the year will return 1911. Masters are not year 2000 compliant!

Mark.
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