Search found 165 matches

by JannievanZyl
Fri Jan 05, 2018 8:52 pm
Forum: hardware
Topic: A3020 Restoration
Replies: 14
Views: 543

Re: A3020 Restoration

System 1
Before-2a.jpg
System 2
Before-2b.jpg
System 3
Before-2c.jpg
by JannievanZyl
Fri Jan 05, 2018 8:51 pm
Forum: hardware
Topic: A3020 Restoration
Replies: 14
Views: 543

A3020 Restoration

Had these guys in storage for while, literally too scared to open them up as I know how badly they can corrode.

So opened them up and not disappointed (unfortunately). Any advise on best way to remove the battery acid and things to look outfor, will be appreciated.
Before-1.jpg
by JannievanZyl
Fri Jan 05, 2018 6:28 pm
Forum: hardware
Topic: Floppy switch configs
Replies: 41
Views: 1324

Re: Floppy switch configs

Quick update; Resolved the Error 14 on Track 0. I had two drives connected, ID 0 and ID 1 but only the first drive had power. When I disconnect the non-powered drive, I could format the disk. But only as a 40 track. Assume the media is the problem. So now I can format either side with this program. ...
by JannievanZyl
Fri Jan 05, 2018 5:17 pm
Forum: hardware
Topic: Floppy switch configs
Replies: 41
Views: 1324

Re: Floppy switch configs

Right now I'm still trying to find the DFS format commands, etc. I've got DFS 1.2 on one machine and 0.9 on another. The DFS format commands are *FORM40 and *FORM80 and they are on the DFS utilities disk, or you can type in a short BASIC program: REM > FormDFS REM Quick Formatter DIM X% 31,data% 51...
by JannievanZyl
Thu Jan 04, 2018 7:12 pm
Forum: hardware
Topic: Think I'm loosing my (beeb) memory
Replies: 22
Views: 830

Re: Think I'm loosing my (beeb) memory

It uses a PIC micro controller and the initial objective is to have sockets suitable to test common DRAM chips, such as 16k x 1 bit, 16k x 4 bit, 64k x 1 bit and 64k x 4 bit. That would include the very common 4116, the 4816 (used by the Beeb), 4164 and 4464 chips for example. Then, it would be pos...
by JannievanZyl
Thu Jan 04, 2018 8:06 am
Forum: hardware
Topic: Think I'm loosing my (beeb) memory
Replies: 22
Views: 830

Re: Think I'm loosing my (beeb) memory

Well done =D> I'm after faulty DRAM chips so that when I have made my prototype DRAM tester, I have some real life example DRAM chips to test the tester with. Mark Mark, do you have more details on the RAM tester you're working on? Been thinking lately, it might be a a good tool to have. Alternativ...
by JannievanZyl
Tue Jan 02, 2018 6:39 pm
Forum: hardware
Topic: BASIC Disk Format
Replies: 28
Views: 1159

Re: BASIC Disk Format

jgharston wrote:Here's the code from my site, normally at mdfs.net/BBC:
Tx!!
by JannievanZyl
Tue Jan 02, 2018 5:38 pm
Forum: hardware
Topic: Floppy switch configs
Replies: 41
Views: 1324

Re: Floppy switch configs

That's rather a lot of machines... What's the story? Mark As with most of us here, I guess, got my first exposure to computers as a kid. For me it was around 1978 when I got a Compukit UK-101 (still looking for one). It was the golden age of "home computing" when every man and his dog designed and ...
by JannievanZyl
Tue Jan 02, 2018 1:57 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

Just so you know, the 74LS245 in position IC14 is a known cause of what appears to be RAM problems, but your problem at first did not appear to be a typical symptom of a faulty 74LS245....! Anyway, I glad that you have fixed it :D Mark 100%! I read it in a few places as well but, as you say, the wh...
by JannievanZyl
Mon Jan 01, 2018 4:39 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

Glad it is sorted. Thanks for all the help! Mark (retroclinic) is sending me some goodies to add to the systems, so soon I'll be (semi-)literate on these machines. I really enjoy fixing them, you learn a huge amount actually working on them. Next job now is to fix the PSU on a Z80 Torch dual-floppy...
by JannievanZyl
Mon Jan 01, 2018 4:33 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

See, no "pixels"!! :D :D
Capture.JPG
by JannievanZyl
Mon Jan 01, 2018 4:13 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

Thanks for all the super help and support in this thread.

That virtual round is for sure on me!! :D
by JannievanZyl
Mon Jan 01, 2018 4:11 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

OK, found it. One of the '245's. IC14. When I replaced the LS245 with a HC245, it resolved the 'pixel' problem, but the machine became unstable. For example, it would randomly hang and would never complete loading a program from tape. So I took a LS245 from the other machine and now it all seems fin...
by JannievanZyl
Mon Jan 01, 2018 3:24 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

Swapping CAS0/1 still resolves the problem, so it must be something that is also affected by swapping the banks, right?
by JannievanZyl
Mon Jan 01, 2018 3:13 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

OK, the plot thickens. Considerably. Decided, bugger it and socketed and swapped all the RAM in CAS1 out with a second Model B I've got. Not only is the problem still there but it's worse/different. This is just putting it in Mode 1 and leaving it. Capture.JPG The RAM I took out works fine in the ot...
by JannievanZyl
Mon Jan 01, 2018 11:54 am
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

BTW, how can one continue a BASIC program after a Break?
by JannievanZyl
Mon Jan 01, 2018 11:21 am
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

crj wrote: Have you had the mainboard out of the machine and checked there's nothing obviously awful that's happened to the rear side, by the way?
Yup, all looks good. But then dry joints, etc. often do.

I'll climb in with the scope today.
by JannievanZyl
Sun Dec 31, 2017 10:26 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

1024MAK wrote:Yeah, weird!

Meanwhile, try something like this on a MODE 7 screen (remove the CLS commands, help text and maybe the garbage generator).

IMG_6006.JPGIMG_6004.JPG
Mark
Will do!

First watching the fireworks over Table Mountain. :D

Happy New Year from Cape Town!! :mrgreen:
by JannievanZyl
Sun Dec 31, 2017 8:20 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

OK, you might want to sit down for this...... (I'll admit I've had quite a few glasses of red, but I'm sure my code is correct.) What I did was to keep bit-5 high and then cycle all the other bits, basically 1,2,4,8,16 with 32 added every time. With bit-5 constantly high the distortion appears toget...
by JannievanZyl
Sun Dec 31, 2017 7:49 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

A pound sign in mode 7 is a nice smoking gun. If you see a pound sign where you should see a space character, it means you see ASCII 96 instead of ASCII 32. So bit 5 is sometimes stuck high (+64). If you get that in mode 7 with S25 north you are seeing it in the screen memory on a BBC B configurati...
by JannievanZyl
Sun Dec 31, 2017 6:49 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

So, my next test was to write 1 bit at a time to the whole block from &4000 to &7FFF.

But it pretty much point to the same thing. The pixels only appear when Bit-5 is written. Any other bit, no distortion appears.
Capture.JPG
by JannievanZyl
Sun Dec 31, 2017 6:37 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

A pound sign in mode 7 is a nice smoking gun. If you see a pound sign where you should see a space character, it means you see ASCII 96 instead of ASCII 32. So bit 5 is sometimes stuck high (+64). If you get that in mode 7 with S25 north you are seeing it in the screen memory on a BBC B configurati...
by JannievanZyl
Sun Dec 31, 2017 6:36 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

Damn...nearly thought I had this, Wrote a program that will write a single bit to the screen in Mode 1. All 8 bits are given an equal amount of screen space. You can see the output of the program here. Capture.JPG You can see all the 'distortion' happens in the area where Bit 5 was written. So, it m...
by JannievanZyl
Sun Dec 31, 2017 4:04 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

So as you can see, identification of the cause from the symptoms is sometimes not so easy... :-( Mark Indeed :D Still throws me that it's 'red' that seems to trigger the most severe case of pixelitus. I've ordered new RAM from Mark, as I know I'm going to replace something eventually. It's just the...
by JannievanZyl
Sun Dec 31, 2017 2:34 pm
Forum: hardware
Topic: BASIC Disk Format
Replies: 28
Views: 1159

Re: BASIC Disk Format

1024MAK wrote:BeebMaster! Calling BeebMaster!

He must be busy watching TV about the Royal Family again...

Yes, I believe the format program on his site works.

Mark
Tx!
by JannievanZyl
Sun Dec 31, 2017 12:59 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

Any suggestions on what values I could write to the RAM to try and identify a faulty chip? Err, values between zero and 255, so use a FOR - NEXT loop to count from 0 to 255, write the value to screen memory, wait for key press, see the effect, then continue... I'm now first trying to figure out how...
by JannievanZyl
Sun Dec 31, 2017 12:23 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

I'm going to switch the banks again with the inverter and make doubly sure the fault does not appear then.
by JannievanZyl
Sun Dec 31, 2017 12:22 pm
Forum: hardware
Topic: Random pixels on BBC Model B
Replies: 60
Views: 1779

Re: Random pixels on BBC Model B

It starts in Mode 7, which is the teletext mode with one byte per character. Pound signs have character code 0x60 or 01100000 in binary. Thanks! Previously I though the pixels only appeared in the graphics modes but the same problem seems to show in teletext mode as these pound signs. Is the 1K RAM...
by JannievanZyl
Sun Dec 31, 2017 12:13 pm
Forum: hardware
Topic: BASIC Disk Format
Replies: 28
Views: 1159

Re: BASIC Disk Format

Just thought of something..... Can I connect a 5.25" DS, 80-track drive from a BBC Model B (200KB per side, right?) directly to the BBC Master Compact and format a floppy that way? That'll save me typing in a 70 line BASIC program on the Model B? /Added Just noticed the Compact's floppy interface is...
by JannievanZyl
Sun Dec 31, 2017 12:13 pm
Forum: hardware
Topic: Compact e-waste rescue
Replies: 4
Views: 322

Re: Compact e-waste rescue

It is also pretty straightforward (and cheap) to add an SD Card interface to a Master Compact. See this thread: http://www.stardot.org.uk/forums/viewtopic.php?f=3&t=6001 And this one: http://www.stardot.org.uk/forums/viewtopic.php?f=3&t=13586 Dave Thanks Dave, appreciate it! For sure in my future. ...