BBC B / Datacentre Fault

for bbc micro/electron hardware, peripherals & programming issues (NOT emulators!)
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robheaton
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BBC B / Datacentre Fault

Postby robheaton » Sun Sep 24, 2017 8:04 am

My BBC B started playing up yesterday whilst I was creating SSD images from floppies.

Initially it started fine, then it was taking 25 mins to create an SSD image.
I gave up yesterday and tried again this morning, the first image was fine, however now the speed has dropped again.

Symptoms are;
1. Machine won't boot when a USB stick is in the Datacentre USB port, just get a single beep, then a flashing cursor
2. Floppy access times are very slow, when performing a *. the disc drive does nothing for 30 seconds or more, then spins into life
3. When executing the command *EXPORT -D0 TEST.SSD I get the message 'Mounting USB, the USB light continuously flashes, then it starts to create the image after several minutes.

Sometimes you just get the message 'Mounting USB' then it drops back to a BASIC prompt with the USB light on solid.
Running the *Export command again, you will get the message 'Command Failed' and running it once again you just get the message 'Channel'

I've tried different USB sticks and a different floppy drive, but the symptoms remain the same.

Has anyone come across this before?
Any help would be greatly appreciated.

Rob.

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flaxcottage
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Re: BBC B / Datacentre Fault

Postby flaxcottage » Sun Sep 24, 2017 8:09 am

Mine does this if there are many files on the USB stick. The effect varies between sticks, ie some sticks are better than others.
- John

Currently running Level 4 Econet with BBC B, BBC B+ 128K, Master 128K, 4Mb A3000, 4Mb A3020, 4Mb A4000, 4Mb A5000 dual FDD; UK101; HP41CX setup; Psion 3a, 3mx and 5mx; Z88; TI-58c, TI-59 and printer, HP-16C programmer's calculator

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1024MAK
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Re: BBC B / Datacentre Fault

Postby 1024MAK » Sun Sep 24, 2017 9:14 am

Very strange.

Have you tested the +5V and the +12V outputs from the Beeb's PSU?

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki‬ - for answers to many questions...

KenLowe
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Re: BBC B / Datacentre Fault

Postby KenLowe » Sun Sep 24, 2017 9:27 am

I had a similar problem - viewtopic.php?f=3&t=12987&p=168065. Turned out that the Datacentre ROM pins were not making proper contact with the ROM socket. I replaced all my ROM sockets with turned pin sockets, and that solved the problem. I think I had installed ROMs with round pin daughter boards (eg spellmaster, GoSDC etc) into the sockets previously, and over a period of time that had damaged the metal spring contacts in the sockets. Might be worth moving the datacentre ROM into a different socket.

markdryan
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Re: BBC B / Datacentre Fault

Postby markdryan » Sun Sep 24, 2017 10:49 am

I did have an issue with my BBC master's internal datacentre a while back. I don't remember the exact details but I do remember that *IMPORT didn't work and some commands seemed to hang. Running *RAMTEST followed by CTRL-BRK fixed the issue for me and it has not re-occurred.

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danielj
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Re: BBC B / Datacentre Fault

Postby danielj » Sun Sep 24, 2017 11:16 am

I really recommend dropping Mark hayesman a note on Facebook or by email. He's very happy to help diagnose and fix problems with hardware he's created!

d.

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jgharston
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Re: BBC B / Datacentre Fault

Postby jgharston » Sun Sep 24, 2017 11:24 am

danielj wrote:I really recommend dropping ...

On reading the first few words I fully expected it to continue: your machine from about one inch onto the desk. Sometimes a quick fix for intermittantly socketed ICs.

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

dominicbeesley
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Re: BBC B / Datacentre Fault

Postby dominicbeesley » Sun Sep 24, 2017 11:34 am

Did you try checkdisk on a PC / Linux /Mac / whatever to check there's not a filesystem corruption?

The datacentre uses a Vinculum / FTDI chip I think. I had loads of problems on one of my homebrew machines trying to get CP/M to work. In the end it turned out that I had a batch of duff USB sticks - or at least ones that the vinc didn't like, they worked ok on my car MP3 though.

Anyway It might be worth backing your stick up to another and try that?

D

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hoglet
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Re: BBC B / Datacentre Fault

Postby hoglet » Sun Sep 24, 2017 12:58 pm

The only problem I've had with Data Centre was because I routed the ribbon cable underneath the BBC circuit board.

After a while (a few years) the ribbon cable got pierced by one of the socket pins.

This caused an intermittent short between the 6845 hsync output and NMI, which manifested in all manner of weird behaviours.

Dave

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robheaton
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Re: BBC B / Datacentre Fault

Postby robheaton » Sun Sep 24, 2017 2:10 pm

I've tried a brand new USB stick and still get the same issue.

Things seem to be getting worse!
Now powering on the machine without a USB stick attached you get a single beep and just a flashing cursor on screen, if you then press break you get the message 'Bad sum'
Pressing CTRL+Break then gives you a blank screen with a flashing cursor, shift+break makes the machine start and load the retroclinic CF-HD welcome screen, pressing escape at this point should break out into BASIC, but just gives you a flashing cursor on a black screen again.

I think this is going to have to be one for Mark @ RetroClinic!

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1024MAK
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Re: BBC B / Datacentre Fault

Postby 1024MAK » Sun Sep 24, 2017 2:22 pm

jgharston wrote:
danielj wrote:I really recommend dropping ...

On reading the first few words I fully expected it to continue: your machine from about one inch onto the desk. Sometimes a quick fix for intermittantly socketed ICs.

It's gone metric. It has to be 25mm... :lol:

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki‬ - for answers to many questions...

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robheaton
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Re: BBC B / Datacentre Fault

Postby robheaton » Sun Sep 24, 2017 2:31 pm

I've managed to get a screen of what seems like random characters now!

Current screen;


%*pTf
F
LW
> o>


It's certainly not well!

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robheaton
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Re: BBC B / Datacentre Fault

Postby robheaton » Sun Sep 24, 2017 3:33 pm

I've spoken to Mark @ RetroClinic, the machine is going in for repair.

Time to switch to a BBC Master whilst it's away...


Thanks for the help everyone!

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robheaton
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Re: BBC B / Datacentre Fault

Postby robheaton » Mon Oct 02, 2017 7:44 pm

Mark @ RetroClinic has worked his magic on my BBC B, here are his findings, I guess they might be useful for someone else on here.

Marks comments below;

1) It had a 65C02 CPU fitted. These can be used, but the board needs modifying and I don't recommend it as the timings for the CMOS CPU are different. I've swapped it out for a standard 6502A

2) You'd fitted a 27C512 into the free socket - this socket is for 2764/27128 only. Fitting a 27C512 leaves one of the address lines floating, which can cause all sorts of intermittent errors.

3) You had a non-release version of RamFS 1.01 fitted? Not sure how you came about that, but I've reprogrammed both CombiROMs with the latest versions of software, which includes RamFS 1.04.



I bought the machine on Amibay last year & the only changes I made were fitting a set of Speech ROMS, which I later removed, I guess the machine had been through a tough time prior to me owning it!

Cheers,
Rob.

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1024MAK
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Re: BBC B / Datacentre Fault

Postby 1024MAK » Mon Oct 02, 2017 9:08 pm

The 'floating' address pin on the 27C512 EPROM sounds like the cause of all the strange symptoms.

The inputs on CMOS chips like the 27C512 are very sensitive, and can be influenced by just about anything electrical nearby. This causes random voltage levels on the pin, and so the EPROM will return data randomly from two different areas of it's memory when the CPU reads it. This can (and does) cause all manor of strange symptoms. Worse, as the humidity also has an affect, the symptoms may not be consistent each day... (yes, you could say it was under the weather...)

Glad that you are now sorted :D

Welcome back to 8 bit Acorn computing :mrgreen:

Mark
For a "Complete BBC Games Archive" visit www.bbcmicro.co.uk NOW!
BeebWiki‬ - for answers to many questions...

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robheaton
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Re: BBC B / Datacentre Fault

Postby robheaton » Tue Oct 03, 2017 8:59 pm

BBC B should arrive back here tomorrow.

Can't wait!!


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