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BBC Master Turbo

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BBC Master Turbo

by SeanKennedy » Sat Feb 27, 2016 11:45 am

Thanks to Ian2U I finally got my hands on a beeb. I haven't used one since the 7th form, and the keyclicks bring back memories of wasted school hours playing Elite.

Anyway - it turned up in a box earlier this week, and I quickly unpacked it with a view to firing it up in my lunch hour to ascertain the state of things.

In hindsight, I should have done this in a workshop, and not the build area near my desk - even better yet, outside!

So yes, as expected (although not by me at the time...) there was the old familiar crackling pop followed by acrid white smoke. A lot of wafting and assuring everyone in the office that there was no cause for alarm, I popped it in the boot, deciding to further investigate at home.

Stripping the beast down to find the faulty caps revealed something I hadn't expected - a daughter board, and only a single ROM. The daughter board indicated it was a 65602 Co-Pro, making this machine a Master Turbo - and the single ROM was a red herring - it was a large one, with multiple images. A quick trip to JayCar the next day for replacement filter caps, and it was all go.

Ian had included a ROM cart, and manual, so now I can easily bridge the gap between the old BBC B and this incarnation.

I wanted to hang it off my Apple //e green screen, owing to my normal test TV setup being shattered in the recent quake, so I swapped the BNC connector for and RCA one, and lo and behold, it sprang to life.

I've now ordered an Arduino SD card board (<$3 from China) and if I can burn my own ROMs, should be able to have SD card images for a lot cheaper than the Apple CFFA option!
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Re: BBC Master Turbo

by Fesh » Sat Feb 27, 2016 11:22 pm

Hey Sean,

Can you recall off hand what caps you grabbed from Jaycar?
I need to do the same with my master 128 before it goes pop/fizzle, but from reading up a bit it seems like the X2 caps listed in the Jaycar catalog of the right rating have the wrong lead pitch, being too narrow to fit
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Re: BBC Master Turbo

by SeanKennedy » Sun Feb 28, 2016 7:31 am

Yeah, lead pitch was bung - had to bend them a little. I checked the catalogue, which indicated that they had quite a few, but in store there were maybe 6 kinds of X2. So I got what I could (left my specs in the car, so I asked the young lady to ensure that I had the right replacements - she took one look at 103 v 0.01uF and handed me the magnifying glass. Too hard.) Bother, I should have taken pics.

The 104 and 103 ones were of comparable physical size, but the leads required 1-2mm dog legging to fit the pitch.
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Re: BBC Master Turbo

by SeanKennedy » Mon Feb 29, 2016 6:48 am

Well, after several pangs of guilt, and dreading the berating I would receive from LizardBoy at work, I swapped the RCA back to the stock standard BNC connector and fitted an adapter instead. I also dug out my old EPROM programmer, and muddled around with a pile of old chips, but only managed to zero them out - couldn't get any uploads to stick. In the end I found a couple of EEPROM 29C256 which I think were ex 3C509 boot ROMs. These flash ROMs did take a couple of BBC images, so I plugged them into the cart, but alas, they did not appear in the list.

I swapped them around to alternate sockets - and one did appear. Upon pulling the chip, I found that pin 27 was bent out (happy accident) leaving the A14 line floating. This from what I can tell is the MSB, and as I was only using the lower half of the ROM, didn't matter. I bent the other one, and that too appeared.

So now the Beeb can run FORTH and FORTRAN. Next step, getting PASCAL into the mix.

Oh - and to find out why the PCB5 programmer won't burn. Might need more power (I had the secondary feed set to 12.5v) which would make sense as it could load data in flash ROM.
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Re: BBC Master Turbo

by Mark0x01 » Tue Mar 08, 2016 7:01 pm

I would suggest avoiding capacitors from Jaycar.
The quality is not very high.

I had a batch bulge after just sitting in a bag for 2 years, and quite a few in power supplies fail within a few months

I'd recommend get quality brands from element14 or rscomponents.
The freight is often free, so cost isn't much more and they will last.

Mark.
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Re: BBC Master Turbo

by SeanKennedy » Tue Mar 29, 2016 7:30 pm

So, after some success with using an old UV eraser at work, I've managed to make several ROM images, but still trying to get multiples on bigger ROMS. I had a dig around this morning, and decided I had enough bits to make an MMBEED SD card reader. Burnt the required ROM onto an 27C256 (SuperMMC) and managed to track down a copy of the MMBEEB.MMC image with 16M of (pretty much) all the old software I remember, subject to the reasonable use provisions that some chaps in the UK seem to have worked out. Strangely none of the links to it worked, but a bit of digging around references to the Stairwaytohell site, and I found what I needed. (Ignore HTML and look at the files!)

Anyway, I used a generic SD card reader for Arduino, made a 20pin molex cable (but only used the first 8 lines) and soldered female jumper connectors on the end. I ended up hot gluing the jumpers onto the SD card board to hold them all in place after a few slipped off. Not pretty, but functional.

The local publican has finally replaced the old 2? Sony Trinotron that was hanging over the patrons heads in a precarious (yet 10000 earthquake proven) fashion. I offered to dispose of it for him. It plays nicely with the Beeb, and with the addition of the old 470pF cap between a couple of transistors on the Master Turbo board, I managed to fire up some old Acornsoft titles in glorious colour.

I really should post some pics...
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Re: BBC Master Turbo

by tezza » Tue Apr 05, 2016 5:14 pm

SeanKennedy wrote:I really should post some pics...

Sounds great! Please do.
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