Search found 611 matches

by Kazzie
Thu Apr 18, 2019 9:52 am
Forum: hardware
Topic: Logo ROM playing up. Needs replacing?
Replies: 7
Views: 123

Re: Logo ROM playing up. Needs replacing?

Other than the number of chips used, what differences are there between the implementations of Logo? There is a fairly comprehensive article in Acorn User issue 34 (May 1985) comparing the different implementations. Perfect, thanks. This leaves me wondering which version of Logo it was that Gwynedd...
by Kazzie
Thu Apr 18, 2019 9:18 am
Forum: hardware
Topic: How did the Beeb use the /SO pin when selecting ROMs?
Replies: 4
Views: 70

How did the Beeb use the /SO pin when selecting ROMs?

In the (undated) circuit diagram submitted to 8bs by Chris Richardson, there are two diodes (D4 and D5) leading from outputs QC and QD of ROM selection latch IC76 to the 6502's Set Overflow (/SO) pin (pin 38. romsel-so.png As I read things, that means that if the software were to request a ROM other...
by Kazzie
Wed Apr 17, 2019 9:43 pm
Forum: general
Topic: Bit of fun - One change only
Replies: 79
Views: 2397

Re: Bit of fun - One change only

For the original BBC B: Perhaps it would have made more sense for 1) the tube connector to be internal: making 2nd processors cheaper by not requiring a cheese box case with own PSU 2) bring the lines for extra sideways ram/rom to be brought out on an IDC connector(PCB male 'socket') in its place: ...
by Kazzie
Wed Apr 17, 2019 9:25 pm
Forum: hardware
Topic: Colured text all modes (Yellow)
Replies: 4
Views: 121

Re: Colured text all modes (Yellow)

That makes things a little easier. (Do you have any test equipment to help you measure what's going on in your Beeb (multimeter, oscilloscope, etc)?) Firstly, are you happy that your cable is in good condition? A continuity test from pin 3 of the RGB connector to the relevant pin on the other end wo...
by Kazzie
Wed Apr 17, 2019 8:59 pm
Forum: hardware
Topic: Another BBC B Needs Fixing.
Replies: 1
Views: 67

Re: Another BBC B Needs Fixing.

Given that everything works with S25 south, I'd expect it's still a RAM issue. You could have had two faulty RAM chips: one blatantly so, and another with a more subtle fault (e.g. writing to address X also overwrites address Y) that isn't being picked up by a write/read memory test. Could you post ...
by Kazzie
Wed Apr 17, 2019 7:22 pm
Forum: hardware
Topic: Colured text all modes (Yellow)
Replies: 4
Views: 121

Re: Colured text all modes (Yellow)

With additive colours (red, green blue), red plus green would give you yellow. Or to put it another way, the absence of blue would turn things yellow.

What video output are you using: RGB, Composite or UHF?
by Kazzie
Wed Apr 17, 2019 7:16 pm
Forum: hardware
Topic: Logo ROM playing up. Needs replacing?
Replies: 7
Views: 123

Re: Logo ROM playing up. Needs replacing?

That looks more like Acornsoft Logo which was supplied on two ROMs. The behaviour you are seeing is what happens when ROM 1 is missing or corrupted. Hm... I presumed it was Logotron. :roll: And, come to think of it, there is one unidentified ROM chip on the expansion board (which isn't reported by ...
by Kazzie
Wed Apr 17, 2019 12:49 pm
Forum: hardware
Topic: Logo ROM playing up. Needs replacing?
Replies: 7
Views: 123

Logo ROM playing up. Needs replacing?

The (original) Logotron Logo ROM in my Beeb is playing up. Typing *LOGO doesn't bring up the Logo interface any more. Instead I get: >*LOGO LOGO 2 _ The Beeb has switched language successfully, as when I press break I'm greeted with: BBC Computer Acorn DFS LOGO 2 Bad command_ A Ctrl-break switches b...
by Kazzie
Wed Apr 17, 2019 6:33 am
Forum: hardware
Topic: Last Gasp for the 8271
Replies: 11
Views: 289

Re: Last Gasp for the 8271

I'll be wanting an 8271 for my System clone, and would be happy to join in with a bulk order.

(I had planned on fitting a 1770 to my Beeb and cascading the 8271, but the Vine Replay that it's fitted with is 8271-only.)
by Kazzie
Mon Apr 15, 2019 5:16 am
Forum: acorn atom and system
Topic: Using PC Floppy Drives ?
Replies: 6
Views: 183

Re: Using PC Floppy Drives ?

So effectively "quad" density was a marketing term where as single, double and high actually describe the density of the data on the disk. Yeah, I should have made sure to includes some "air quotes" there... :oops: If you have a little time, you can read all the Beeb-relevant info and facts behind ...
by Kazzie
Sun Apr 14, 2019 6:38 pm
Forum: acorn atom and system
Topic: Using PC Floppy Drives ?
Replies: 6
Views: 183

Re: Using PC Floppy Drives ?

I've just noticed something else that will cause issues, the GFR version of the Teac FD55 is a 1.2MB, High Density floppy drive. (80-track drives outside the PC world are Quad Density, 40-track are Single/Double Density.) HD 5 1/4" floppies rotate at a different speed to DD and QD ones, 360rpm inste...
by Kazzie
Sun Apr 14, 2019 5:49 pm
Forum: acorn atom and system
Topic: Using PC Floppy Drives ?
Replies: 6
Views: 183

Re: Using PC Floppy Drives ?

Is the Teac just set up as an 80-track only drive, or have you got something double-stepping it when you want to read 40-track discs? If not, it's quite reasonable for the Teac to only read files from track 0 on a 40-track floppy, as it's the only track that's in the same physical place for both typ...
by Kazzie
Sun Apr 14, 2019 5:30 pm
Forum: hardware
Topic: The sound of BBC graphics!
Replies: 12
Views: 387

Re: The sound of BBC graphics!

Apparently the CPC464 made different noises depending on how busy the CPU was.
by Kazzie
Sun Apr 14, 2019 7:27 am
Forum: acorn atom and system
Topic: Faulty um233 rf modulator
Replies: 9
Views: 150

Re: Faulty um233 rf modulator

Nicely done.

If all you have is a hammer... :D
by Kazzie
Sun Apr 14, 2019 7:25 am
Forum: introduce yourself
Topic: Long time Acorn user
Replies: 14
Views: 190

Re: Long time Acorn user

Hello Sparky. With regards to you Atom's Olivetti drive, I have three Olivetti FD-501 floppy drives (as used with early BBC Micros) in a full spectrum of functionality (perfect, works after a brief warm-up, and faulty) , so I may be able to help with diagnosing yours. Feel free to start a thread in ...
by Kazzie
Sat Apr 13, 2019 3:54 pm
Forum: hardware
Topic: Microvitec Cub 653 Monitor (Type 1456 Li2)
Replies: 15
Views: 397

Re: Microvitec Cub 653 Monitor (Type 1456 Li2)

I can't quite make out the markings on the IC in your photo. Hi Kazzie! Attached is a slightly better photo of the adaptor board's IC. Its a ROM. In addition, a 78L05 voltage regulator and a bunch of resistors, a transistor and diodes are on the board. That's clever. I'd guess it's using the ROM as...
by Kazzie
Fri Apr 12, 2019 8:54 pm
Forum: hardware
Topic: BBC B+ fault
Replies: 12
Views: 202

Re: BBC B+ fault

Edit: A video of the Test ROM footage could let us help interpret what it's trying to say. I did do a video but it is 250MB in size. Also, the variant flickering of the monitor versus the fone camera is not good. I could upload to a website if you think it will help. Ah the curse of the rolling shu...
by Kazzie
Fri Apr 12, 2019 8:44 pm
Forum: hardware
Topic: Save my Elk...
Replies: 22
Views: 442

Re: Save my Elk...

When I built my own replica of an Acorn System 1, I built a physical NOP generator based on the one linked to by 1024MAK earlier, rather than program a ROM. If the data bus is permanently populated with the value EA, then at reset the CPU will ask for the contents of the reset vector, be told it's &...
by Kazzie
Fri Apr 12, 2019 8:30 pm
Forum: hardware
Topic: Microvitec Cub 653 Monitor (Type 1456 Li2)
Replies: 15
Views: 397

Re: Microvitec Cub 653 Monitor (Type 1456 Li2)

My CM8833 monitor has a separate board for the very job of converting TTL (5V) RGB values and 0.7V RGB, which was apparently an optional extra. My board uses two ICs (a 74ls368 and a 74ls05) along with a few transistors and passive components. I can't quite make out the markings on the IC in your ph...
by Kazzie
Fri Apr 12, 2019 8:19 pm
Forum: hardware
Topic: BBC B+ fault
Replies: 12
Views: 202

Re: BBC B+ fault

I'm sure we can get some sense out of it for you. Firstly (with all the B+-related posts recently I've got them all mixed up in my head) are we talking about a 64k or a 128k model? Random exclamation marks are a good indicator of where the fault may be. Working from a table of ASCII values (which is...
by Kazzie
Fri Apr 12, 2019 8:06 pm
Forum: hardware
Topic: my beeb just pegged it :(
Replies: 26
Views: 607

Re: my beeb just pegged it :(

Well done! =D> For the other BBC, rather than unsoldering and replacing all the CAS0 RAM, you could find out which specific chip is faulty by either fixing up an inverter on the S25 so that CAS0 and CAS1 are swapped around or burn Tricky’s test rom in an eprom and replace the OS chip with that to d...
by Kazzie
Fri Apr 12, 2019 8:04 pm
Forum: other vintage computer hardware, software and games
Topic: Megastor 8" drive unit
Replies: 66
Views: 1425

Re: Megastor 8" drive unit

And now, for Kazzie, a quick youtoobz video... https://youtu.be/THLTPThV_UU Looking good! Thanks, again for the demonstration. (I seem to have acquired a reputation of being a video addict somehow :? ) As it happens, there may be a physical thank-you on offer too. See the inbound PM... :wink:
by Kazzie
Thu Apr 11, 2019 8:51 pm
Forum: hardware
Topic: Need help with BBC just picked up please
Replies: 170
Views: 4089

Re: Need help with BBC just picked up please

Voltmeter measurements on page 1 gave the following results for IC49 (which is connected to the D lines of all the RAM chips): IC49 pin 2 (D0) 2.15V pin 3 (D1): 2.17V pin 4 (D2): 2.14V pin 5 (D3): 2.19V pin 6 (D4): 2.14V pin 7 (D5): 2.15V pin 8 (D6): 2.10V pin 9 (D7): 0.13V :!: Future readers bewar...
by Kazzie
Thu Apr 11, 2019 8:47 pm
Forum: hardware
Topic: BBC B+ 128K: Fault after warming up.
Replies: 75
Views: 1713

Re: BBC B+ 128K: Fault after warming up.

I think you've just found a mistake of mine on that thread! :oops: The owner of that B+ just listed the voltages for each pin of IC49 originally (in this post ). When I wrote the portion you commented, I was concentrating on the fault on bit 7, probably just glanced at the pins for RD0 and RD7 on th...
by Kazzie
Thu Apr 11, 2019 4:26 pm
Forum: hardware
Topic: BBC Model B with random 0 on screen
Replies: 16
Views: 376

Re: BBC Model B with random 0 on screen

A spot of background information: The Beeb's 6502 processor uses the very bottom of the RAM as zero page registers, and these need to be working for the Beeb to boot. The memory used for the display will at the upper end of the RAM. If 32k is being used, this will be from a different bank* to the z...
by Kazzie
Thu Apr 11, 2019 5:09 am
Forum: hardware
Topic: BBC B+ 128K: Fault after warming up.
Replies: 75
Views: 1713

Re: BBC B+ 128K: Fault after warming up.

Having only two RAM chips will make things quicker! I can read from your photo that they're HM50464 (64k x4) RAM chips, so as they each provide four bits of data width, a pair is enough for an 8-bit system. If you want to work out which chip does which bits, there's a pinout here that will help with...
by Kazzie
Wed Apr 10, 2019 6:46 am
Forum: hardware
Topic: BBC Model B with random 0 on screen
Replies: 16
Views: 376

Re: BBC Model B with random 0 on screen

S21 is used for controlling the Chip Select lines of the OS ROM and option ROM slots. When fitting a ROM expansion board, you'd typically remove one of S21's jumpers and fit two flying leads from the expansion board, so it could tell when the system wanted to access a ROM. The removal of that jumper...
by Kazzie
Wed Apr 10, 2019 5:21 am
Forum: hardware
Topic: Save my Elk...
Replies: 22
Views: 442

Re: Save my Elk...

Though in executing random garbage, the 6502 could execute an illegal opcode and hang. Check if you see any activity on R/W or Sync immediately after powering up, or pressing break.
by Kazzie
Tue Apr 09, 2019 7:58 pm
Forum: hardware
Topic: BBC Model B with random 0 on screen
Replies: 16
Views: 376

Re: BBC Model B with random 0 on screen

Hi, thanks for the picture. With regards to the keyboard, it's often the case that exercising the keys (by pressing them, say, 50 times or so) can clean their contacts and get them working again without any disassembly. Then, as long as the Beeb isn't put in storage for another decade or two, period...
by Kazzie
Tue Apr 09, 2019 5:15 pm
Forum: hardware
Topic: BBC Model B with random 0 on screen
Replies: 16
Views: 376

Re: BBC Model B with random 0 on screen

A picture can often be worth a thousand words (or a video might be useful in some cases too.

Do the additional zeros (or other corruption) only show up as you press a key, or can it happen on its own?

Also, have you tried switching screen mode (e.g. MODE 0) and seeing what happens in that mode?