Date : Mon, 28 Jul 2008 15:28:10 +0100
From : dominic@... (Dominic Beesley)
Subject: BBC B+ Disc Fault
I'd fix the power supply first, especially if the disc drives are powered
from the beeb (via the 4-way connector thing). I've had dodgy capacitors in
a beeb psu cause all manner of weird behaviour.
It sounds like one of the smoothing capacitors has gone bad and now when
there is an above-average current drawn (for instance spinning up the disc
and thinking hard at the same time) the voltage drops and the machine
"browns out".
If a capacitor went bang its usually pretty obvious which one needs
replacing but be careful there could still be high voltages in the PSU even
after disconnecting from the mains and with duff capacitors!
Dom
-----Original Message-----
From: bbc-micro-bounces+dominic=brahms.demon.co.uk@...
[mailto:bbc-micro-bounces+dominic=brahms.demon.co.uk@...] On
Behalf Of Ian Wolstenholme
Sent: 27 July 2008 17:44
To: bbc-micro@...
Subject: Re: [BBC-Micro] BBC B+ Disc Fault
I've tried ADFS 1.30 with much the same results, *ADFS spins the disc for a
couple of seconds and then nothing else happens.
If I do *FADFS and then *MOUNT 0, I get the complete noise cut-out and the
machine crashing as I reported earlier with SHIFT-BREAK under DFS.
Best wishes,
Ian
----- Original Message -----
From: Ian Wolstenholme [mailto:bbcmailinglist@...]
To: bbc-micro@...
Sent: Sun, 27 Jul 2008 15:25:57 +0100
Subject: Re: [BBC-Micro] BBC B+ Disc Fault
A curious thing is happening now, which wasn't happening before the PSU
popped.
I've got DFS 2.22 in at the moment, and SHIFT-BREAK causes the Beeb speaker
to go completely silent, that sort of background buzzing which is always
audible from the Beeb speaker cuts out entirely, and the machine locks up,
not changing the LEDs with caps lock and shift lock. The same thing as
before happens to the disc drive, light on and disc spinning for about 2
seconds and then it stops.
Also pressing Z-BREAK, to go into 8271 emulation mode, does the equivalent
of SHIFT-BREAK, except that there is no drive activity (and the speaker
buzzing carries on). Before the pop, Z-BREAK came straight back into BASIC
as it should do.
Best wishes,
Ian
----- Original Message -----
From: Ian Wolstenholme [mailto:bbcmailinglist@...]
To: bbc-micro@...
Sent: Sun, 27 Jul 2008 15:20:25 +0100
Subject: Re: [BBC-Micro] BBC B+ Disc Fault
The DFS has never worked as long as I have had it, but I think the previous
owner thought it was working, so it may have become damaged in transit.
When I opened it up last night, it had two DFS ROMs, an original Acorn DFS
2.0j in EPROM and DFS 2.22 which I programmed myself. I can't remember if
it came with DFS 2.0j, which doesn't have the SRAM utils, so the Beeb
reports itself as Acorn OS 64K when using this one, which would appear to be
a bit strange since the SRAM on the daughterboard wouldn't be useable
without third party utilities. It's also possible it had no DFS in it and I
put in DFS 2.0j from somewhere else.
Anyway, that's a side issue, I've tried it using each of the DFS ROMs
separately and the same thing happens.
Best wishes,
Ian
----- Original Message -----
From: Mark Haysman [mailto:jumbos.bazzar@...]
To: bbc-micro@...
Sent: Sun, 27 Jul 2008 15:03:32 +0100
Subject: Re: [BBC-Micro] BBC B+ Disc Fault
Hi.
Did it come to you in a non-working condition, or was it working one day,
then all of a sudden stopped? The reason I ask is if it came to you broken,
have you checked things like a bent or pushed in pin in the 34 way
connector? Is there other track damage around the broken VR1?
If it was working and suddenly stopped, check the EPROMs (and any other ICs
in sockets) have not come dislodged - reseat them a few times, and if
possible, verify the DFS rom to ensure it's not started to lose it's
program. Apart from that, it's get the scope out time, unless anyone else
has some suggestions. Myself, along with a few others in here I'm sure would
repair it for you if need be.
Mark.
----- Original Message -----
From: "Ian Wolstenholme" <bbcmailinglist@...>
To: <bbc-micro@...>
Sent: Sunday, July 27, 2008 2:52 PM
Subject: [BBC-Micro] BBC B+ Disc Fault
I have a BBC B+ 128K, complete with the 64K daughterboard and
1770 disc interface but unfortunately, the disc interface doesn't
seem to work.
DFS will attempt to access the disc for about two seconds and then
the drive light goes out and nothing else happens, the Beeb just waits
there and doesn't come back with an error message or anything.
I checked the disc interface against the fitting instructions in the
Service Manual and all the chips and link settings are present and
correct.
The only obvious damage to the motherboard is that variable
resistor VR1, just below the speech sockets, appears to be broken
but I don't think that's related to the disc interface.
It has had a replacement PSU at some point in its life, it is date
coded 8718, well after production of the B+ ended. I wonder if
the PSU blew and could have blown the disc interface chips?
Is there anything obvious I can try or check, such as checking
the disc chips for voltages?
Best wishes,
Ian
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