Vintage Computing & Consoles BBC Micro; Teletext Adapter, Winter Project

@jayceebee Pretty sure they're the bootstrap components for the output stage of the TDA1170. Only fault we ever had on my parents' Salora set was that cap failing.

Frame output IC's where a common failure on these packages. The latter  Tab mounted frame output ICs where a lot more robust but suffered dry joints. I think this was caused by the IC getting warm, legs expanding and contracting with use over time there being a circular crack appearing in the soldered joint then turning into a full dry joint. These smaller frame IC's where working hard as as already said the bootstrap capacitor and output coupling capacitor going low would lead to failure. There is a 10uF in there two. Practice for me would be change the IC and three associated capacitors and check the supply decoupling electrolytic usually coming off the line output stage as in this case. This will be the TDA1170S.

The tube on mine is a Mitsubishi 370GUB22-TC01. These monitors were made over a longish time period for a monitor so changes where introduced but I've not had a problem Most of these I have serviced over time had the transformer/tripler combination, yours looks to be the same as mine.  

Forgot to mention, you will be looking for a BBC Master next. The ROM sockets can be paged on some sockets. The Masters ROM in 1Mbyte so contains many 128k ROMS in the single ROM, have I got my bits and bytes correct there? The Master has sideways RAM to. The plug in ROM sockets can be handy to.

I'm working my way through this board, and I'm now at the TDA1170, has anyone figured out, I'm sure you have, how the hell you desolder the heat-sink from the chip wings. I've got a Metcal, so heat should not be a problem, but it's like the proverbial .... to a blanket!

OK, you have to wait an absolute age, goes against my instinct to not overheat an ic.

One happy bunny. 😎 

The clarity of these monitors is astounding, I can now see what all the fuss is about, and a bargain to boot!

Well true to bloody form.... that lasted all of 10-mins now I have no lock. I could get paranoid when others seem to breeze along.

So I move it back to the bench from its display area..... Really!

I swear I heard it say

"To the last, I will grapple with thee... from Hell's heart, I stab at thee! For hate's sake, I spit my last breath at thee!".

Edit:

The real craziness is, I move it back to the display area, no lock, move it back to bench lock, and so on. WTF!

OK, found the culprit, it would appear the TTL socket on the back of the monitor is temperamental, it does not like having the plug removed and reinserted. If I leave that end well alone and just move the cable at the Beeb end, it's happy. I'll have to look at the socket, but tomorrow, I just want to soak test it for a while now.

Bloomin things that are sent to try you! me!

It is easy to put the connector in one pin out.

Sorry Adrian, I'm being a thick old Hector Crusty, that sentence makes no sense to me. The connector from the BEEB is RGB/TTL six pin.

The location grove in the socket will take a pin if you are not looking at what you are doing, seen it done a few times.

Today I've found out my Microvitech monitor is not an 1431MS, but a 1451-MS4. The clues were there, on the board and on the badge, I then checked with the BBC Micro forum and the knowledgable folk there confirmed it.

What does this mean? Slightly better resolution.

1431 & 1432 resolution of 452(H)x585(V), DOT PITCH 0.64mm

1451 resolution of 652(H)x585(V), DOT PITCH 0.43mm

edit:

The highest resolution ones are the 1441 & 1442 both with a resolution of 895(H)x585(V), DOT PITCH
0.31mm

the others:-

MODEL 2030 Resolution of 505(H)x585(V) elements, 80 characters on 6 dot, wide matrix, DOT PITCH
0.8mm

MODEL 2040 Resolution of 940(H)x705(V), DOT PITCH 0.47mm

p.s.

I've also found out Microvitech are still in business, but no longer in the manufacture of CRT. They even used to offer a repair service up until around 2013, a service they have now also ceased.

http://www.microvitec.co.uk/index.html

Today I've had a go at programming a ROM for my model B, on my T43 programmer. A whole raft of ROMs are available for download, 598+ I've found thus far. This covers all manner of software from Word processors to languages, to utilities and everything in between.

Not being overly versed in the intricacies of BBC command line interface, I found a ROM from 1987 which provides a GUI frontend to the BBC.

Once downloaded, it was loaded into the programming frontend, I used an AM27C128 EPROM, but you can also use AT28C256, though you need to do a little config to write the upper block twice.

This worked perfectly, I installed the ROM which to be honest is a PITA, as you have to open the case, remove the keyboard to gain access to the ROM sockets. *A solution to this at the end.

Once installed I checked that I could see the ROM, it was there.

Then it was time to run the ACP, now I have a frontend.

* Back to making this easier to add a ROM, without opening your case each time

The BBC has what is known as the "ashtray", it got this name as often the perforated piece has broken away leaving a hole. This is where you fit an after market ZIF socket. This just extends one of the ROM sockets to the outside, making it easy to swap in/out ROMS. I have one of these now on order and will fit in due course.

Did some 1983 price research for the display, that's some hellish price for 1983.

Probably explains why I didn't know of anyone of my friends, friends of friends or neighbours who had one when they first came out. Let alone adding the coprocessor wedge, or 5.25 floppy drive, hard drive, expansion boards etc, which would have taken well over the 4K equiv. Then, if you add software, Wordwise ROM £39,and games etc.

However, I did know people who had Spectrums & Commodores etc. I did end up with a Commodore PET at home around 1984, but that was through work.

Thames TV provided my BBC Master for computer self training as with all technical staff in about 85/86. The first thing I needed was to add a 5-1/4 inch floppy drive and next a printer. Both where expensive items, especially the drive. You will need to add them to your cost. I think the Master was about £400 but provided free. The cost of the other items was down to the user but exceeded the cost of the Master by quite a bit. After 18 months you where given a questionnaire and dependant on the answers and use you made of the computer you kept it or handed it back. Glad to say I still have mine.

Posted by: @crustytv

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I've also found out Microvitech are still in business, but no longer in the manufacture of CRT. They even used to offer a repair service up until around 2013, a service they have now also ceased.

http://www.microvitec.co.uk/index.html

I visited Microvitec's factory in Bradford in 1991 in order to pick up a BBC micro type monitor to replace one that had failed at a client's site in Lancashire. I recall that the premises were down a side street and appeared to be in an old mill building.

John

@jjl I visited Microvitec for a training course on these monitors in 1989 when working for the local education authority, I can remember Bradford seemed a bit grim and very cold and damp in March. I still have the workshop manual they provided us.

@hurty The Teletext editing terminal arrived safe and sound. 👍 

It's freezing up here and so is the unit, having sat in a north-east hub over the weekend and the back of a van for the best part of today. It will sit in the warm (75F) showroom for a couple of days to acclimatise, before any attempt at power up. Me thinks a big leaning curve is coming up over the winter to learn how to use it and start creating RatFax pages. 😎 

I hadn't realised it has ECONET, very pleased about that.  I'm going to have to add that to my Model B and set up an ECOLan with file server sharing, that'll help shift files around and the Model B will be able to use the Softel's 5.25 drive.

On top of this, I've got a few mods to do on the Model B. I've got a coprocessor (another cheese wedge) for it now, which will improve performance by 50% and add another 32K of RAM. Then I've got the ZIF socket to install and the 15 ROM sideways expansion board, plenty to keep me busy. I had considered the Pi Tube, which would have allowed me to emulate a second 6502, Z80, 286 etc and run things like DRDOS but I decided to stick with the original Acorn co-pro.

Hi Crusty, glad it got to you in one piece. The Master comes with quiet a bit of software. I has an Econet socket as you have seen but you will need a ROM for that. Two more units shown below which I have done the basic PSU repairs to, and battery back up. The one you received has not had the battery backup mod done and is using Softel's implementation which I assume is a rechargeable NiCad. Its is down to 1 volt so will soon lose it configuration settings, just so you know. The installed Master software ROMS are also shown below 9 to 15 in one mega ROM. there are still 3 X ROM slots available and the Softel software sits in the two pluggable ROM cartage slots. ROMS 0 to 3. The unit will work as a standard Master if you boot it out of the Teletext Editor. There is no CTRL R function as the keys are completely different when booted. As you can see there are many more keys than a normal Master, 110 altogether and that is the major difference between this and a master. The original keyboard decoder has been removed and a new keyboard interface fitted which addresses the new expanded keyboard. This is the main mod that has been carried out by Softel. I have no idea why I saved these?? one maybe for spares for my own Master but other than that I have no idea what I was thinking. These units provided the Teletext Pages for Sky for about the first 10 years,

I await your work and will be watching how you get on with interest.

Back to my Model B project.

The scope of this project was chiefly to have it up and running, with the intent to decoding Teletext pages. That was achieved, along the way I also found myself a Microvitech monitor, which was a fun repair in its own right. I did say in the very first post of this thread......

Posted by: @crustytv

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A BBC micro & boxed Teletext adapter 'Cheese Wedge' complete with manuals and ROM, specifically bought for the Teletext element, but I'm sure I will get side tracked into its other abilities.

That's where I am now.

What's next?

After looking into things further, I found a few modifications worthy of pursuit, which are to follow.

1. A solderless sideways ROM board to expand ROM capabilities.
2. An external ZIF socket for quick ROM testing
3. A second processor
4. Two ROMS to enable the above

To implement items 3 &4, and still be able to run Teletext plus other features, I will need to implement item 1. Item 2 just makes life easier for quick ROM testing or quick access to rarely used ROMS such as word-processing or Disc tool.

Second 6502 Processor

The BBC Model B was always designed with a second processor in mind, I believe it was not added to keep the already high cost (£399) down, so was an option you could purchase later. The second processor gave up to 44K of user memory for the programs in the second processor, and execution speeds were 50% faster. The second 6502 has a further 64K of RAM and interfaces to the beeb via the 'Tube'.

With the second processor fitted things change a little, the 6502 in the main computer now takes on the role of I/O processor, handling keyboard, RS423, text and graphics to the monitor, printer and peripherals such as printers disc drives etc.

The second 6502 runs basic, word processing and user programs. The 'Tube' mentioned above handles the two-way communications between the beeb and the second processor, leaving the second processor to get on with running programs, whilst the main unit handles all input output requests by the second. Boiling it down, you get faster execution and far more user memory.

First thing before powering up is to service, if required, the power supply and check the +5V rail is OK, it was.

ROMS

The two ROMS required for all this to work are DNFS and HiBasic.

DNFS

This is loaded into what is now the I/O processor (the main beeb) upon power up and now form part of the I/O O/S. This ROM also contains the disc filling system and network filing system, so I'm already halfway there for my ECONET, just need the hardware for the Beeb.

HiBasic

This is specifically for use with the second 6502 and contains an extended version of BASIC. Both Basic and HiBasic work on the second processor, but HiBasic will not work on the main beeb if you do not have a second processor. If you have a second processor and only use the stand BASIC ROM, then you lose some of the features of having a second processor, such as access to some memory.

These can be bought or all, and many more are available for download to blow if you have an EPROM programmer. I bought some EPROMS and EEPROMS, downloaded the files and blew my own.

ROM Extension

As I mentioned at the start of this post, first I have to install the sideways ROM extension module before I can install the second processor. This was produced by Watford Electronics. This allows me to increase the sideways ROM capacity from the standard 4 sockets to the full 16 supported by the operating system.

ZIF Socket

The final one is the addition of the ZIF socket, this in my opinion is a must-have. Each time you wish to add a new ROM, you have to open the case up, which can be a pain. This allows for quick access to ROMS you don't need permanently installed and for ROM testing.