In message <1090322113.28481.37.camel_at_weka.localdomain>
Jules Richardson <julesrichardsonuk_at_yahoo.co.uk> wrote:
> On Tue, 2004-07-20 at 10:40, Philip Pemberton wrote:
> > Get an oscilloscope and a logic probe out then :)
>
> :-)
> It's looking that way...
You have got a scope, haven't you? If not, I've got one I could let you
borrow (or I could be tempted to part with it in exchange for a small
donation to the "Philpem's Wallet" fund :P )
> Power's getting where it should be and the reset's ok; I haven't checked
> clocks for anything yet though.
Clip the ground clip onto the nearest available ground and take the witch-hat
(if your probe has one) off the probe. Make sure the needle tip is nice and
sharp. Check the signal as near to the chip as you can.
> One thing I have found though - a *lot* of chips in this machine are
> replacements, and the solder quality is total crud.
Ugh. Add "Solder sucker", "Desolder wick" and "RoadRunner wiring pen" to the
"Tools Required" list too. I hope you've got a good soldering iron and a
powerful light (60W or so).
> All the RAM chips and both MC6821's are replacements, and the sockets
> for the LM1889 and MC6847 look to be non-original too, implying that
> those suffered some form of destruction and were replaced. Given solder
> quality, I'm going to check continuity on the address / data lines for
> all the RAM chips and check for shorted tracks too.
Watch out - the tracks to the RAM may be mixed up, i.e. A0 going to A8 and so
forth. Check the schematics, then buzz out the board with a continuity
tester.
> For some reason one of the RAM chips has a 220n decoupling cap, whilst
> the rest are 100n.
Shouldn't make much difference. If it looks like the 220n is a replacement,
swap it for a 100n.
> Be nice to get it working as this is a grey-cased machine with GEC
> labelling, plus I have the box and a boxed floppy drive to go with it...
:)
Speaking of floppy drives, anyone got a spare CBM 1541 or similar drive? It
would save me a few days' work sorting out a disc controller - the uPD765 is
a total PITA, especially the external data separator that I need to sort
out...
Later.
--
Phil. | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
philpem_at_dsl.pipex.com | ViewFinder, 10BaseT Ethernet, 2-slice,
http://www.philpem.dsl.pipex.com/ | 48xCD, ARCINv6c IDE, SCSI
... Divers do it deeper.
Received on Tue Jul 20 2004 - 08:15:36 BST