Search found 281 matches

by Kazzie
Wed Nov 14, 2018 7:03 pm
Forum: hardware
Topic: Need help with BBC just picked up please
Replies: 75
Views: 1186

Re: Need help with BBC just picked up please

Thanks for those. It may seem like a lot of work poking about, but we're getting a better idea of what's working and what's not in your Beeb. ic 39 pin 9 1H,2H,3H pin 10 1H,2H,3H pin 11 1H,2H,3H pin 12 1H,2H,3H pin 13 1H,2P,3H pin 14 1H,2P,3H pin15 1H,2H,3H --That's behaving reasonably. Inputs of pi...
by Kazzie
Wed Nov 14, 2018 4:25 pm
Forum: hardware
Topic: Need help with BBC just picked up please
Replies: 75
Views: 1186

Re: Need help with BBC just picked up please

Having had a thought (and corrected an error in my previous post), I see the following issues: There appears to be some (separate) chip failures in both the /RAS and /CAS generation There's no sign of the 8MHz clock signal on IC31 pin 11 /VIDPROC is fixed high We've looked at the generation of the /...
by Kazzie
Wed Nov 14, 2018 2:04 pm
Forum: acorn atom and system
Topic: Acorn System 2/3 Refurb
Replies: 14
Views: 465

Re: Acorn System 2/3 Refurb

Just scanning them would be a good start: others here could help out with the OCR (and checking) work. I note that your screen reads "Oracle Microsystems COS" . I was under the impression that Acorn had written their own OS for the System 2. Are you able to elaborate? I'd also be interested to hear ...
by Kazzie
Wed Nov 14, 2018 12:17 pm
Forum: hardware
Topic: Searching File Not Found ?
Replies: 11
Views: 230

Re: Searching File Not Found ?

I can't help on how to open up the keyswitches, but personally I'd be confident in putting a (small) dab of grease on the shaft.
by Kazzie
Wed Nov 14, 2018 10:48 am
Forum: hardware
Topic: Need help with BBC just picked up please
Replies: 75
Views: 1186

Re: Need help with BBC just picked up please

Thanks for the measurements. I note that almost all of these are the same across all three readings. ic33 pin 11 1L,2L,3L pin12 1L,2L,3L pin 13 1L,2L,3L --This is expected behaviour for an OR gate (output on pin 13). Appears fine. ic26 pin 12 1L,2L,3L pin 13 1L,2L,3L --This is unexpected behaviour f...
by Kazzie
Tue Nov 13, 2018 7:49 pm
Forum: acorn atom and system
Topic: System Cassette Interface
Replies: 6
Views: 183

Re: System Cassette Interface

I hadn't realised that you were unable to read cassettes you'd previously recorded. That's some significant chip-to-chip variation you had there! I've still got to get around to building the cassette interface for my System 1 replica, but having seen your experience I think I'll prototype it on a br...
by Kazzie
Tue Nov 13, 2018 7:44 pm
Forum: for sale / freebies
Topic: Worth Taking a Look At
Replies: 2694
Views: 229485

Re: Worth Taking a Look At

A bit of an oddity:

https://www.ebay.co.uk/itm/Power-Supply ... SwdUJb5Zqm

Looks like an Acorn Atom Disc Pack's power supply (no floppy drive or controller card) converted for some other purposes.
by Kazzie
Tue Nov 13, 2018 4:46 pm
Forum: hardware
Topic: Searching File Not Found ?
Replies: 11
Views: 230

Re: Searching File Not Found ?

BeebMan2018 wrote:
Tue Nov 13, 2018 4:32 pm
Nope, I wasn't. I am now though :) SOLVED

Doh.

Nobody told me. 0_0

Thanks Mark.
So rather than a keyboard problem, unfortunately it's literally PEBKAC. #-o
by Kazzie
Tue Nov 13, 2018 4:27 pm
Forum: hardware
Topic: Electron Keyboard - Key Switches and the Aluminium Plate ?
Replies: 9
Views: 196

Re: Electron Keyboard - Key Switches and the Aluminium Plate ?

From all you've done, it seems as though the key switches are operating fine. Is the fault be elsewhere, perhaps? In the lower left corner of the keyboard (under the plastic case), there are four resistors (as well as eleven diodes). These "pull-up" resistors should ensure that the electron reads a ...
by Kazzie
Tue Nov 13, 2018 4:05 pm
Forum: hardware
Topic: Need help with BBC just picked up please
Replies: 75
Views: 1186

Re: Need help with BBC just picked up please

Right, then. Here are some tests to do with the logic probe, looking at the parts of the board that should be generating the /RAS, /CAS and /WE signals for the RAM. Could you give the same kind of report (with break, just after break, several seconds later) for each of the following: For the /RAS: I...
by Kazzie
Tue Nov 13, 2018 3:54 pm
Forum: hardware
Topic: Need help with BBC just picked up please
Replies: 75
Views: 1186

Re: Need help with BBC just picked up please

1 - what happens to a pin when when break key is held down continuously 2 - what happens to a pin immediately as the break key is released 3 - what happens to a pin several seconds after the break key is released pin 3 1,high 2,high 3,high pin 4,all low pin 5 1,Low 2,sometimes high sometimes pulse ...
by Kazzie
Tue Nov 13, 2018 3:18 pm
Forum: acorn atom and system
Topic: System Cassette Interface
Replies: 6
Views: 183

Re: System Cassette Interface

I haven't got a CD4024B to hand at the moment to test this, but looking at the CD4024B datasheet, at 5V I calculate the following propagation delays: Clock to Q5: 580ns typical, 1680ns maximum Clock to Q2: 280ns typical, 690ns maximum Q2 to Q5: 300ns typical, 990ns maximum From the circuit diagram ,...
by Kazzie
Mon Nov 12, 2018 6:18 pm
Forum: hardware
Topic: Searching File Not Found ?
Replies: 11
Views: 230

Re: Searching File Not Found ?

It sounds like a shift "stuck-on" fault. I'd put good money that when you turn caps lock off, you find that you still can't type any lower case letters.
by Kazzie
Mon Nov 12, 2018 8:21 am
Forum: hardware
Topic: BBC B repair help
Replies: 27
Views: 824

Re: BBC B repair help

I know that previous versions of DFS/DNFS (including the one pictured by Mark) interrogate the hardware and disable themselves if it's not detected. (This bit me in the behind with an econet installation where one pin missed the socket.) Are you confident that you've followed all the instructions , ...
by Kazzie
Sun Nov 11, 2018 12:41 pm
Forum: hardware
Topic: Looking for RAM chips Micron 4067-15 or equivalent
Replies: 2
Views: 69

Re: Looking for RAM chips Micron 4067-15 or equivalent

These appear to be matching chips, but rated for 120ns instead of 150ns (no problem):

https://www.silicon-ark.co.uk/mt4067-12 ... technology
by Kazzie
Fri Nov 09, 2018 9:43 am
Forum: hardware
Topic: Help for a WE RAM / ROM board not working
Replies: 45
Views: 449

Re: Help for a WE RAM / ROM board not working

Thanks for the suggestion, I note that some have had success in using the TL866 under Linux (which is my main OS), so that may well find its way on to a shopping list. :)
by Kazzie
Fri Nov 09, 2018 7:37 am
Forum: hardware
Topic: Help for a WE RAM / ROM board not working
Replies: 45
Views: 449

Re: Help for a WE RAM / ROM board not working

IC 18 makes a lot more sense. That means S21E goes to an active-low enable pin on the '138. On the topic of replicating schematics, I know it can be a pain to do: I've tried it on a floppy drive circuit board with a large mix of ICs and discrete components, which was slow work, following tracks by e...
by Kazzie
Fri Nov 09, 2018 5:30 am
Forum: hardware
Topic: Help for a WE RAM / ROM board not working
Replies: 45
Views: 449

Re: Help for a WE RAM / ROM board not working

Now that you've got a scope to hand, it might be interesting to look at what else is happening on IC16. Particular candidates would be pin 7 (output for pins 5/6), pin 1 (select pin 5 or 6) and pin 15 (strobe/enable output). Kazzie, that's the scope output (pins name are corrected now, sorry for pr...
by Kazzie
Thu Nov 08, 2018 7:30 pm
Forum: hardware
Topic: Help for a WE RAM / ROM board not working
Replies: 45
Views: 449

Re: Help for a WE RAM / ROM board not working

So the Beeb is sending plenty of (active low) S21 requests to the board, but the board isn't sending any back. That's in keeping with the behaviour you've described so far. (BTW, is S21E connected to IC16 pin 5 or pin 6? Your last two posts mention both pins.) Now that you've got a scope to hand, it...
by Kazzie
Thu Nov 08, 2018 6:56 pm
Forum: hardware
Topic: Help for a WE RAM / ROM board not working
Replies: 45
Views: 449

Re: Help for a WE RAM / ROM board not working

On the BBC circuit diagram, S21 SE is a logic output (low when Sideways RAM/ROM address is on the bus) and S21 SW is the enable input for IC76. So from the expansion board's perspective, S21E is an input and S21W is an output. Perhaps the output for S21W is generated elsewhere (IC20 perhaps?) but is...
by Kazzie
Thu Nov 08, 2018 4:25 pm
Forum: hardware
Topic: Help for a WE RAM / ROM board not working
Replies: 45
Views: 449

Re: Help for a WE RAM / ROM board not working

And a spot of further conjecture about those remaining ICs: S21 should be forwarded back to the board only when S21in is low, as well as the latched values of D2 and D3. So S21out = S21in + D2L + D3L. That's probably done by the 74ls02 NOR gates (IC20). The other twelve sockets (on the expansion boa...
by Kazzie
Thu Nov 08, 2018 3:49 pm
Forum: hardware
Topic: Help for a WE RAM / ROM board not working
Replies: 45
Views: 449

Re: Help for a WE RAM / ROM board not working

A spot of conjecture of how the "ROMSEL" signal may be generated: A particular ROM is selected by a program by writing to address &FE30 according to the literature, but the BBC's circuit diagram shows that it only looks at the top 12 bits of the address (so it's effectively mapped to &FE3x). The exp...
by Kazzie
Thu Nov 08, 2018 2:01 pm
Forum: hardware
Topic: Help for a WE RAM / ROM board not working
Replies: 45
Views: 449

Re: Help for a WE RAM / ROM board not working

The decoding of the ROM selection latch to provide ROM chip select signals is likely to being done by one or both 74LS138 chips... Mark Good call. (My browser had been loading low-quality versions of the above photos earlier, hence my asking for a photo. How does that Song go? "I can see clearly no...
by Kazzie
Thu Nov 08, 2018 1:20 pm
Forum: hardware
Topic: Help for a WE RAM / ROM board not working
Replies: 45
Views: 449

Re: Help for a WE RAM / ROM board not working

Thank you Kazzle, you explained very well the rom selection logic, and confirmed most of the ideas I made myself. I have already checked E and W expansion board for continuity, and they are ok from connectors to the two ICs on the Watford card. So, I am afraid of one or more 74xx failure, but they ...
by Kazzie
Thu Nov 08, 2018 11:50 am
Forum: hardware
Topic: Need help with BBC just picked up please
Replies: 75
Views: 1186

Re: Need help with BBC just picked up please

hi its in ttl mode and just low lit when i press break hi comes back when i let go So when you let break go, both Hi and Low are lit (for all eight pins on IC49)? In that case that test is inconclusive. After you've had a look at the thread Mark linked (good background reading), you'll need to try ...
by Kazzie
Thu Nov 08, 2018 11:45 am
Forum: hardware
Topic: Help for a WE RAM / ROM board not working
Replies: 45
Views: 449

Re: Help for a WE RAM / ROM board not working

IIRC, The Beeb looks for a Language ROM (such as Basic or Logo) from the highest priority socket downwards, ignoring non-Language ROMS (such as DFS). If it fails to find one at all, that's when the Language? error comes up, as described by Mark. Without an expansion board, that search goes from left...
by Kazzie
Thu Nov 08, 2018 11:11 am
Forum: hardware
Topic: Need help with BBC just picked up please
Replies: 75
Views: 1186

Re: Need help with BBC just picked up please

Odd. Is that with your probe in TTL or Strobe mode? Also, when you say "if i press break just get low lit", is that while you're holding break down, or after you release it? The Break key operates the reset line on the system, so while you hold it down everything is still being reset, and the probe ...
by Kazzie
Thu Nov 08, 2018 9:31 am
Forum: hardware
Topic: Need help with BBC just picked up please
Replies: 75
Views: 1186

Re: Need help with BBC just picked up please

Hi all With the logic probe flashing with me pressing the break key mean the cpu is working fine. Many Thanks Yes. Pin 7 will flash when the CPU fetches an instruction. The CPU is working fine just after it resets, and then it stops running. It probably stops because it received erroneous data, and...
by Kazzie
Wed Nov 07, 2018 5:07 pm
Forum: general
Topic: Beeb Spotting
Replies: 37
Views: 3642

Re: Beeb Spotting

Found in the foyer of Conwy Library: DrRFSo4XQAEghqI.jpg Picture is the organiser's, not mine. My camera had a sulk and didn't keep the photos I'd taken. A local primary school's recently closed for redevelopment, and they were holding an exhibition and gathering ex-pupils' recollections. The organi...
by Kazzie
Wed Nov 07, 2018 2:59 pm
Forum: other vintage computer hardware, software and games
Topic: Dragon 32 or Amstrad CPC 464
Replies: 24
Views: 334

Re: Dragon 32 or Amstrad CPC 464

Another few points: The Dragon32 doesn't make any noise on startup (unlike our Beebs), so a lot of eBay sellers have brought down their old Dragon down from the attic, found they can't get a picture on their modern HD TV (or maybe can't even plug it in) and list them as faulty or untested. There's a...