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Just to close this one off, I didn't get round to trying anything else and have now put it up for sale on eBay with this known fault.

Yep, I can get colour using RF.

Thanks for the extra info

I've now tested with RF and get white text in modes 4 and 7 so moved on to look at the board. There are no obvious signs of dry joints or damaged tracks in those areas so I'll look at swapping the transistors out and go from there.

Thanks for that. I'll give an RF lead a go.

Yes, I have another Master and a few Bs which all work fine with same cable.

I have a BBC Master 128 which is outputting text via RGB in green, from booting. When I first got it, it was fine, then the text output turned to yellow, then green, and has been like that ever since. I don't really know where to start with this one, and can't find any reference to this issue anywhe...

Eventually got round to fixing the PSU in the dodgy B. From this: https://s3-eu-west-1.amazonaws.com/quokkaz/bbc/cashbeeb-blown-cap.jpg To this: https://s3-eu-west-1.amazonaws.com/quokkaz/bbc/cashbeeb-new-caps.jpg I removed the SWR and croc clips and checked that links S20, 21 and 22 were to their d...

Moved the connector back a couple of mm and all's well

Think I've found the problem. Power light comes on if I wiggle the ribbon cable connector

While fixing the floppy drive control on a Master 128, I've found that the keyboard LEDs have failed. Initially just the Caps Lock and Shi f t :oops: Lock but now also the Power LED. When I first bought it, all three worked fine. The Lock keys do do what they are supposed to and the rest of the keyb...

It's been a while but I finally got round swapping ICs to try and fix the floppy problem, after also replacing the 2 broken capacitors, and started with IC4. Removing the old one was proving difficult until I bought a desoldering iron which made short work of it. I found a broken trace underneath (t...

May have to come back to this one a little later:

Off to eBay for a capacitor kit...

steve3000 wrote:Had something similar to this on mine and it turned out to be due to a bad contact/surface corrosion on one of the RAM chips. Solved by simply taking out the chip and putting it back on again... Hope it's that simple on yours.

Thanks, I'll give that a go.

Found this http://www.stardot.org.uk/forums/viewto ... 71&p=12583 and will give the test code a go tommorow.

Hi, It looks like a RAM fault to me. I can't however figure out which IC it may be off the top of my head, and I am out at the moment. Try setting S25 to the south position and see if mode7 clears up... Lee. Thanks Lee. Moved to south I get random red/white blocks, continuous tone and no keyboard. ...

The knob by the keyboard is wired into the speaker so it'll be a crude volume control. Yep, verified that that's what it is. The other switch is connected to a chip with a label saying "Sideways Ram" so it'll be probably be a write enable switch so you can load a rom image into the chip a...

hoglet wrote:If it seems to be accepting commands, try changing to a different screen mode, e.g. MODE 6.

It may be the fault just affects MODE 7.

Dave

MODE 7 didn't make any difference. MODE 9 I get a prompt in some clear space at the top of the screen but then the same kind of corruption lower down.

Just had delivered a Model B I bought on spec for £22 as it sounded as if it might be in working condition. It turns out that it does work, in that it beeps and outputs to a monitor, but the result is odd (see below) and it looks to be crudely modified. https://s3-eu-west-1.amazonaws.com/quokkaz/bbc...

Interesting probe results from IC2 and IC4 with the new board (previous results from original board on the right):
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I've moved the goalposts slightly... I saw another Master on eBay that was being sold as faulty but looked like the motherboard might be OK - it looked in better condition than the one I've got. I bought it and it arrived earlier today. https://s3-eu-west-1.amazonaws.com/quokkaz/bbc/master2-faulty.j...

Not the usual Sinclair kit: https://s3-eu-west-1.amazonaws.com/quokkaz/sinclair/dm2-3.jpg Still had a (dead) PP9 inside: https://s3-eu-west-1.amazonaws.com/quokkaz/sinclair/dm2-2.jpg Soldered in a PP3 connector: https://s3-eu-west-1.amazonaws.com/quokkaz/sinclair/dm2-4.jpg And it works: https://s3-e...

Pin 5 on IC2 and IC4 is where the fault lies, hence IC2 pin 6 is not producing a correct output. Fun part is figuring out which of the two ICs is faulty. Thanks. That's sort of what I'd figured but wasn't sure if the fault was actually in one of these ICs. Is the only way to swap one at a time? The...

This morning I've taken some readings with the logic probe with both drives connected which I've summarised here: https://s3-eu-west-1.amazonaws.com/quokkaz/bbc/probe-results-1.jpg Column B shows the status at startup, then C and D are after doing a *CAT on each drive. Drive 1 works consistently and...

If you disconnect both drives, and disable both DFS and ADFS, it should be safe to poke any test values to &FE24 to test IC2 and IC4 (unless the MOS gets in the way). Otherwise be careful that you don't try to do something silly like activate both drives at once! :mrgreen: Mark I now have a pro...

A Series 3a and the hinge donor 3c:

Edit: but wait... 3c? What's the difference between that and the Series 3? From Wikipedia: "It has a slightly different external appearance to the earlier variants because a redesigned badge is placed centrally on the lid, the lid has fewer undulations, and a port for an infrared connection is...

I've not seen a Psion 3c in the "flesh", so to speak, but does it by any chance have one of those "rubbery" type coverings? If so I've known a few devices with such "grip finishes" where the coating has started to break down and goes very very sticky. One was a Microso...

Received today: an extremely sticky Psion 3c needing a new hinge (for which I have a donor). Can't imagine where it's been - it's like fly paper.

Looks like I'll be investing in some clippage too, thanks.

in your intro with pic of master insides, there is another unknown rom in the bank below WORD, and maybe something else? a *ROMS list may help. If it's a MMC interface (user port) rom, then weird things do happen :shock: Here's the list of ROMs ROM F TERMINAL 01 ROM E View 04 ROM D Acorn ADFS 50 RO...