BBC Micro B Repair Help

[LambdaMikel]

Trying to fix a BBC Micro B which I got for cheap. I already replaced / socketed the 16 KB RAM, but it still shows garbage... I believe the RAM is OK.  All the connections are as they should be. Also, the "big chips" (IC1, IC2, IC3, ...) which are socketed are all ok, swapped and tested with another working BBC Micro B. So, the problem must be with one of the little LS support chips or related. An idea, anybody? One strange thing is - it seems the previous owner did some fixes to the motherboard. There is a white little jumpercable on the back. No idea what purpose it serves. The other yellow cable is from my RAM socketing messups. So, it seems, it is not the RAM nor the CRT controller nor the ULAs.

Maybe @Bryce has an idea?

PS S25 is in "south" position  (-> 16 KB) And that's the bank that I replaced / socketed. RAMs are NOS.

[Chinnery]

I can't help you here, but over on Amibay, admin "the corfoit" knows one heck of a lot about the beeb if you're struggling for info.

[LambdaMikel]

Thanks @Chinnery , I found this board where the Acorn community seems to live:

https://stardot.org.uk/forums/index.php

[chinnyhill10]

Thanks @Chinnery , I found this board where the Acorn community seems to live:

https://stardot.org.uk/forums/index.php

Stardot guys are lovely. Have been a huge help with the Youtube channel. 2 of them fixed me up with a new ROM and a load of games for review without me even asking. All just turned up!


They are certainly the best place to ask.

[LambdaMikel]

Indeed, a wonderful community and board! Extremely knowledable and friendly and helpful.  With their help, I have most of the Beeb working again. The second bank of 16 KB mem still has a bug though, but 16 K mode is working perfectly. 

The CPC 464 is really quite simple in comparision to the Beeb... the Beeb is an amazing computer I must say. One of my PSU's emitted the magic white smoke with a sizzle - caps burned out. But that was to be expected sooner or later. I still have a cap replacement kit.

[LambdaMikel]

In case somebody faces a similar problem - in my case, the 16 KB lower RAM was actually OK.(But the upper 16 KB seems to have a problem - the machine does not boot in 32 KB mode, gives a constant beeb on power up - that RAM bank still needs to be fixed).
In 16 K mode, the problem was *mainly* caused by some (non-visibly) broken resistors R98 - R101, AND a broken trace between the address decoders IC8- IC12. Took a while to diagnose. Lots of continuity tests with the multimeter and the schematics...

[pelrun]

gives a constant beeb on power up


constant beeb


beeb

I would have thought the problem was that the Beeb *wasn't* giving a constant Beeb!

[LambdaMikel]

 

[LambdaMikel]

Just curious - anybody besides @Bryce has a Beeb here?
I am wondering how "disjoint" these communities are... I would assume that Speccy users also have a CPC also have a Beeb. But maybe not  Well, maybe the question really is - if you grew up pin the 80is in the UK, there was no way around the Speccy or the Beeb, or was there? Maybe the CPC was not soo prominent though in comparison.

[chinnyhill10]

Just curious - anybody besides @Bryce has a Beeb here?
I am wondering how "disjoint" these communities are... I would assume that Speccy users also have a CPC also have a Beeb. But maybe not  Well, maybe the question really is - if you grew up pin the 80is in the UK, there was no way around the Speccy or the Beeb, or was there? Maybe the CPC was not soo prominent though in comparison.

I do and it wasn't a purchase for the channel (unlike say my MSX machines). I rescued my BBC Master from going into a skip in 1995. Although it wasn't much use to me until the era where the MMC cards were introduced.

[arnoldemu]

Just curious - anybody besides @Bryce has a Beeb here?
I am wondering how "disjoint" these communities are... I would assume that Speccy users also have a CPC also have a Beeb. But maybe not  Well, maybe the question really is - if you grew up pin the 80is in the UK, there was no way around the Speccy or the Beeb, or was there? Maybe the CPC was not soo prominent though in comparison.

My father still has our family beeb. I'm not sure if it runs anymore.

I got a cpc so I could have my own computer and didn't go back to the beeb.

[00WReX]

Just curious - anybody besides @Bryce has a Beeb here?
I am wondering how "disjoint" these communities are... I would assume that Speccy users also have a CPC also have a Beeb. But maybe not  Well, maybe the question really is - if you grew up pin the 80is in the UK, there was no way around the Speccy or the Beeb, or was there? Maybe the CPC was not soo prominent though in comparison.

I had never seen a BBC until I got my hands on a couple a few years ago.They were ex high school computers (both model B's...well I believe they were upgraded to model B spec).They are not the prettiest ones you'll see but they are fully functional.I really like the BBC and it is nice to 'tinker' with.A really cheap mod is to add an SD card reader along with a ROM (MMC), only costs a couple of dollars.
Cheers,Shane

[LambdaMikel]

The BBC made the archieve available recently

https://hackaday.com/2018/06/30/the-bbc-computer-literacy-project-from-the-1980s-is-yours-to-browse
Recenty I was stuck in / on a long car ride and could listen to "making the most of the micro" (well, audio mostly).
And, of course, "MicroMen" is a must watch too for anybody interested in British micros 

[LambdaMikel]

I had never seen a BBC until I got my hands on a couple a few years ago.

Same here. Wasn't on my radar at all, didn't even now it existed until say 5 years ago. It is a great machine, very versatile and the number of IO connectors - gosh... analog input, GPIOs, support for a second CPU (the tube), network (!), ... really quite fun the machine.

Germany's (were I am from) schools used CBM / Commodore a lot; originally my high school had CBM 3032, CBM 8032, and  these huge double disk drives (3030, 3040). Later, many schools had PC 10 and PC 20. Commodore was quite successful in Germany (Braunschweig-based; actually, the PC 10 / PC 20 were German developments). I wish we would have had BBC Micros though, would have been more fun 
What was used in other countries (besides England?)

[LambdaMikel]

Same here. Wasn't on my radar at all, didn't even now it existed until say 5 years ago. It is a great machine, very versatile and the number of IO connectors - gosh... analog input, GPIOs, support for a second CPU (the tube), network (!), ... really quite fun the machine.

Needless to say, the CPC of course is and always will be my favorite 8bit micro, just in case you were worried 

[chinnyhill10]

My father still has our family beeb. I'm not sure if it runs anymore.

Usually just the PSU caps need replacing.

[keith56]

I was watching the 'Micro Live' series when I had a week off recently, and coupled with what I've heard elsewhere about the functionality of the BBC Micro, it certainly sounds like an interesting machine, and I plan to look at learning some basic development for it in the future.

From what little I know about it, I understand it's graphics ability is more limited than the other 8 bits, and can't really be double-buffered causing flicker, due to the 16/32k memory available on the early systems... I guess that's unavoidable due to the early release date, but it's a pain compared to the 64/128k systems!

The ability to code ASM in basic is really amazing, it's a shame more systems weren't provided with basic assembler functionality back then! (I think the commodore 128 had a built in assembler too)

[Bryce]

The Corfiot is also a member here, on stardot and Amibay (As I am too, and also on WoS)

Bryce.

Gesendet von meinem Motorola DynaTAC 8000x mit Tapatalk

[LambdaMikel]

What"s WoS? World of Sinclair?


Btw, Beeb is fixed 


https://stardot.org.uk/forums/viewtopic.php?f=3&t=15501&start=60

https://stardot.org.uk/forums/download/file.php?id=39702&mode=view

[LambdaMikel]

From what little I know about it, I understand it's graphics ability is more limited than the other 8 bits, and can't really be double-buffered causing flicker, due to the 16/32k memory available on the early systems... I guess that's unavoidable due to the early release date, but it's a pain compared to the 64/128k systems!

That might be true, but its hacking capabilities / hardware tinkering and hands on experimentation potentials were unlike any other machine, it seems. It has GPIO and analog input, EPROMS, etc. In that regard, Rasperry Pi of the 1980s. 

Still today an amazing amount of DIY hardware is still being produced for the machine. Check out the PiTube - simply astonishing!

[LambdaMikel]

Usually just the PSU caps need replacing.

Well, mine (60 $ on Ebay, "untested") was messed up quite a bit. Took about 20 to 30 hours to fix. But yes, PSU also blew up during that fixing. More fixing, and bad smoke