Model B+ boot problems

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RetroClarence
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Model B+ boot problems

Post by RetroClarence » Tue Jun 30, 2020 9:36 am

Hi all

I'm new here so thanks for allowing me in.

I recently became the proud owner of a Model B+. However, it has a problem. When I switch it on, I get a continuous tone with the cassette motor LED lit. There is no onscreen display and the keyboard is unresponsive.

The machine has a RetroClinic DualOS MOS chip. That was seated fairly securely but I have tried removing it. The pins look in good shape and I've reseated it securely to the board and the same thing is happening.

I believe that this is a familiar problem. Are there any other obvious potential fixes I can try?

Many thanks in advance for the help.

Chris

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egel
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Re: Model B+ boot problems

Post by egel » Tue Jun 30, 2020 9:53 am

Have you checked the keyboard cable? Is it in the right place? Shifted one place gives weird effects.

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marcusjambler
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Re: Model B+ boot problems

Post by marcusjambler » Tue Jun 30, 2020 10:30 am

Hi Retroclarence

Please post some photos of the PCB.
I've had two issues with B+ tone of death. ( Excluding possible keyboard issues )
Dead CPU and faulty RAM.
Both fairly easy to diagnose but would require desoldering and socketing new ICs.
However thats jumping the gun at this stage.

Marcus

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danielj
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Re: Model B+ boot problems

Post by danielj » Tue Jun 30, 2020 10:34 am

I would add in "dead system 6522" to the list fairly near the top!

d.

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flaxcottage
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Re: Model B+ boot problems

Post by flaxcottage » Tue Jun 30, 2020 1:22 pm

Welcome, Chris. :D

I had a similar problem with my B+. It turned out to be faulty RAM. Mark at Retroclinic diagnosed and fixed it and installed the correct DFS too. Later I had a faulty user 6522 VIA. :(

The problem with the B+ is all that solder keeping the chips in place - cheaper in manufacture, more reliable but awful to swap chips out.
- John

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Re: Model B+ boot problems

Post by stephen_usher » Tue Jun 30, 2020 1:39 pm

I've just recently had to swap out yet another of the Hitachi RAM chips in my B+ 128K. I just died whilst in storage in the last couple of months.

I would have struggled to diagnose the issue without an oscilloscope. IMHO it's THE essential tool for retro-computing maintenance, along with a multimeter.

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KenLowe
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Re: Model B+ boot problems

Post by KenLowe » Tue Jun 30, 2020 2:26 pm

RAM issue with me too on my B+. I thought I had posted about it on here, but it was actually discussed on the BBC Micro mailing list:

http://mdfs.net/Archive/BBCMicro/2008/04/19/084952.htm

RetroClarence
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Re: Model B+ boot problems

Post by RetroClarence » Tue Jun 30, 2020 8:23 pm

Thank you for the suggestions and tips so far.

I've attached some photographs of the PCB, does anything jump out?
Attachments
20200630_201200.jpg
20200630_201205.jpg
20200630_201209.jpg
20200630_201216.jpg
20200630_201219.jpg

shakesc
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Re: Model B+ boot problems

Post by shakesc » Tue Jun 30, 2020 8:27 pm

Well the RAM and 6522 are socketed so they have been replaced in the past
BBC B+ 128K

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marcusjambler
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Re: Model B+ boot problems

Post by marcusjambler » Fri Jul 03, 2020 8:21 am

What test gear do you have Chris?

RetroClarence
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Re: Model B+ boot problems

Post by RetroClarence » Mon Jul 06, 2020 8:57 am

Hi Marcus

None unfortunately. I'm going to send it away for diagnosis and, hopefully, repair.

Kazzie
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Re: Model B+ boot problems

Post by Kazzie » Mon Jul 06, 2020 9:53 am

Given that the B+ has so many parts soldered directly to the board, there's relatively little that you can do without proper testing equipment.

Best of luck on the repair. :)
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM, ZIDEFS with 512MB CF card
Acorn System 1 home-made replica

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1024MAK
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Re: Model B+ boot problems

Post by 1024MAK » Mon Jul 06, 2020 10:46 am

Not entirely true. Tricky’s test ROM is useful.

And on this B+ board, various chips including the DRAM chips are in sockets.

The biggest question is, is this a failed repair effort, or has it failed since this work was done?

If the former, then fault finding may be very time consuming even with the right test gear.

Mark

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Re: Model B+ boot problems

Post by Kazzie » Mon Jul 06, 2020 11:29 am

1024MAK wrote:
Mon Jul 06, 2020 10:46 am
Not entirely true. Tricky’s test ROM is useful.
Quite right, I'd forgotten that!
BBC Model B 32k issue 7, Sidewise ROM board with 16K RAM
Archimedes 420/1 upgraded to 4MB RAM, ZIDEFS with 512MB CF card
Acorn System 1 home-made replica

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