Am I a Monster?

for bbc micro/electron hardware, peripherals & programming issues (NOT emulators!)
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Hopper
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Am I a Monster?

Post by Hopper » Fri Mar 01, 2019 10:16 pm

So.

The last couple of Beebs I've worked on, I've removed the TV modulator and BNC output and plugged the case holes, One part of me says, yeah its rubbish no one is ever going to use this crap again, however another part says destroying the machines originality.... what say ye?

The main reason for binning the modulator is to run a cable aft for a 2nd processor (watch the pcb screw!) then mounting the Pi down there, close to the vent.

Mike
Last edited by Hopper on Fri Mar 01, 2019 10:41 pm, edited 2 times in total.

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Re: Am I a Monster?

Post by 1024MAK » Fri Mar 01, 2019 10:31 pm

But, but, but! The composite video output on the BNC connector is useful.

Mark

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Re: Am I a Monster?

Post by Hopper » Fri Mar 01, 2019 10:38 pm

For what? even if it was semi useful for something, its the most awkward connector in the beeb from a maintenance point of view.

Mike

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Re: Am I a Monster?

Post by KenLowe » Fri Mar 01, 2019 10:46 pm

Hopper wrote:
Fri Mar 01, 2019 10:16 pm
The main reason for binning the modulator is to run a cable aft for a 2nd processor (watch the pcb screw!) then mounting the Pi down there, close to the vent.
...but why not just mount the PI (Zero/ ZeroW) underneath the Beeb, straight into the 2nd processor slot (ok, via a kjell level shifter first).

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Re: Am I a Monster?

Post by Hopper » Fri Mar 01, 2019 10:56 pm

Why? because I have space in the case because I binned the UHF modulator.

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Re: Am I a Monster?

Post by flibble » Fri Mar 01, 2019 10:58 pm

Hopper wrote:
Fri Mar 01, 2019 10:38 pm
For what? even if it was semi useful for something, its the most awkward connector in the beeb from a maintenance point of view.
Erm, capacitor on the magic transistor legs to turn the composite into colour.

Then a BNC to phono connector on the back, and colour composite into pretty much any TV built in the last 30 years.

It's by far the simplest way to connect a beeb to a currently available display.
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Re: Am I a Monster?

Post by IanS » Fri Mar 01, 2019 11:03 pm

flibble wrote:
Fri Mar 01, 2019 10:58 pm
Then a BNC to phono connector on the back, and colour composite into pretty much any TV built in the last 30 years.
I not seen it done on a beeb, but it's not uncommon for the guts of the modulator in an atom to be removed and wire the phono connector as a composite output. Then you wouldn't need the adapter. (Hmmm, I wonder if you could put a few bits in the modulator case and make one output with colour and one without)

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Re: Am I a Monster?

Post by Hopper » Fri Mar 01, 2019 11:14 pm

flibble wrote:
Fri Mar 01, 2019 10:58 pm
Hopper wrote:
Fri Mar 01, 2019 10:38 pm
For what? even if it was semi useful for something, its the most awkward connector in the beeb from a maintenance point of view.
Erm, capacitor on the magic transistor legs to turn the composite into colour.

Then a BNC to phono connector on the back, and colour composite into pretty much any TV built in the last 30 years.

It's by far the simplest way to connect a beeb to a currently available display.

index.jpg
Yes, but on the otherside of the plastic bulkhead, the BNC is soldered onto the PCB.... but tied to the case, so to pull the board you need to desolder that rubbish.

Mike
Last edited by danielj on Sat Mar 02, 2019 4:22 pm, edited 2 times in total.

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Re: Am I a Monster?

Post by johnkenyon » Sat Mar 02, 2019 12:23 am

I replaced the BNC connector on one of my Beebs with a chassis phono socket. BNC connectors are reserved for test gear and 10base2 as far as I'm concerned. Unhappy memories of numerous broken composite video cables at school, and spending half your lunchtime trying to get a working picture...

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Re: Am I a Monster?

Post by tricky » Sat Mar 02, 2019 3:10 am

It did sseem a little strange to not make the BNC removable without a soldering iron, but they do have long enough leads that you can lift the board out, albeit still attached on one corner.
I often use composite "on the bench" as my smaller displays only have composite.
If the rf hole was smaller, I would consider using it to mount an audio jack, but not just repurpose it as I want it to mute the internal speaker.

PS to answer your question, yes, a bit of one. :lol:
Last edited by tricky on Sat Mar 02, 2019 3:12 am, edited 1 time in total.

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Re: Am I a Monster?

Post by geraldholdsworth » Sat Mar 02, 2019 9:40 am

It's your machine to do with as you please.

I have often thought of removing the Composite video BNC and replacing it with an S-Video socket.

Agree with you about the modulator.
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Re: Am I a Monster?

Post by RobC » Sat Mar 02, 2019 10:07 am

I'm with you on this :)

The composite leads are left unconnected on most of my Beebs so that I can easily remove the PCB.

I hardly ever use the UHF output but haven't removed the modulator (yet!). I do have the Pi co-pro fitted at the back of the case attached to the right hand side but it's a tight fit.

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Re: Am I a Monster?

Post by 1024MAK » Sat Mar 02, 2019 10:31 am

Hopper wrote:
Fri Mar 01, 2019 10:38 pm
For what? even if it was semi useful for something, its the most awkward connector in the beeb from a maintenance point of view.

Mike
For me, it’s useful when any of the following occur...
  • when I can’t find one of my SCART leads (have three, but can’t ever find a ‘spare’ one when I want it!)
  • I want to run more Beebs and Elks simultaneously than I have SCART leads for. I have various displays/TVs/monitors.
  • For monochrome displays/monitors the most suitable video connection is the BNC composite. I typically use a Phono/RCA to BNC adaptor.
Apologies if you are aware of the following. But I thought it worthwhile including it for anyone else reading this thread.
It should be noted that with the composite video output, the standard output is monochrome picture in all modes (but a good sharp picture for the 80 column modes). But with a small change, the colour signal can be added. The resulting colour output then works for all modes, but due to the limitations of a colour composite signal, the 80 column modes are no longer useful if you are working with text.

At the end of the day, what you do to your machines is entirely up to you. The removal of the modulator and the BNC connector is minor compared to the changes some users did to their machines in the past. Like one machine I obtained, which has on the top of the case a ZX Spectrum+ PSU, a mains switch, a fan and another opening for a vent!!!

Mark

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Re: Am I a Monster?

Post by 1024MAK » Sat Mar 02, 2019 12:42 pm

Oh yeah, and to remove the main board from the case (which is not a very common activity for most people) it is just one wire to desolder (from the centre pin of the BNC connector). If you can’t handle that, why would you be taking the main board out if not to solder/desolder something?

Mark

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Re: Am I a Monster?

Post by Richard Russell » Sat Mar 02, 2019 2:31 pm

1024MAK wrote:
Sat Mar 02, 2019 10:31 am
due to the limitations of a colour composite signal, the 80 column modes are no longer useful if you are working with text.
This is misleading. The reason that enabling 'chrominance' on the BNC composite-video output degrades the 80-column modes has nothing to do with the "limitations of a colour composite signal" (after all there is no chrominance in the case of the default white-on-black palette!) but arises because of Acorn's poor analogue circuit design.

The chrominance could (and should) have been added in such a way that the luminance component was not affected, typically by summing the two signals at a 'virtual earth' point. In that case enabling chrominance would have had no effect on the quality of 80-column black-and-white text (I am ignoring here the possibility that the presence of the colour burst might result in cross-colour on some monitors).

Unfortunately Acorn used a very crude technique of capacitively coupling the chrominance at a point where there is a significant circuit impedance, so not only does the capacitor add chrominance it also removes high-frequency luminance! It is this, unnecessary, attenuation of the high-frequency luminance components that degrades the quality - in all modes but most noticeably in the 80-column modes.

I entirely accept that we, at the BBC, should have spotted this at an early stage and insisted on a circuit change (it would have added some complexity but probably only half-a-dozen analogue components costing a negligible amount). I can only offer the excuse that since the composite BNC output was seen primarily as the means of getting the Beeb's output into broadcast (studio) video infrastructure, and since 80-column text was too fine to broadcast anyway, it was not given the attention it deserved.

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Re: Am I a Monster?

Post by Hopper » Sat Mar 02, 2019 2:47 pm

1024MAK wrote:
Sat Mar 02, 2019 12:42 pm
Oh yeah, and to remove the main board from the case (which is not a very common activity for most people) it is just one wire to desolder (from the centre pin of the BNC connector). If you can’t handle that, why would you be taking the main board out if not to solder/desolder something?

Mark
You are completely right! 100%! now that I have desoldered it, why would I go to the trouble of reattaching something I'll never use?

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Re: Am I a Monster?

Post by Hopper » Sat Mar 02, 2019 2:49 pm

1024MAK wrote:
Sat Mar 02, 2019 10:31 am
Hopper wrote:
Fri Mar 01, 2019 10:38 pm
For what? even if it was semi useful for something, its the most awkward connector in the beeb from a maintenance point of view.

Mike
For me, it’s useful when any of the following occur...
  • when I can’t find one of my SCART leads (have three, but can’t ever find a ‘spare’ one when I want it!)
  • I want to run more Beebs and Elks simultaneously than I have SCART leads for. I have various displays/TVs/monitors.
  • For monochrome displays/monitors the most suitable video connection is the BNC composite. I typically use a Phono/RCA to BNC adaptor.
Apologies if you are aware of the following. But I thought it worthwhile including it for anyone else reading this thread.
It should be noted that with the composite video output, the standard output is monochrome picture in all modes (but a good sharp picture for the 80 column modes). But with a small change, the colour signal can be added. The resulting colour output then works for all modes, but due to the limitations of a colour composite signal, the 80 column modes are no longer useful if you are working with text.

At the end of the day, what you do to your machines is entirely up to you. The removal of the modulator and the BNC connector is minor compared to the changes some users did to their machines in the past. Like one machine I obtained, which has on the top of the case a ZX Spectrum+ PSU, a mains switch, a fan and another opening for a vent!!!

Mark
Sounds like your justification for retaining the BNC is your lack of ability to plan ahead and be organized? :-D
Last edited by Hopper on Sat Mar 02, 2019 2:49 pm, edited 1 time in total.

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Re: Am I a Monster?

Post by 1024MAK » Sat Mar 02, 2019 3:35 pm

Richard Russell wrote:
Sat Mar 02, 2019 2:31 pm
1024MAK wrote:
Sat Mar 02, 2019 10:31 am
due to the limitations of a colour composite signal, the 80 column modes are no longer useful if you are working with text.
This is misleading. The reason that enabling 'chrominance' on the BNC composite-video output degrades the 80-column modes has nothing to do with the "limitations of a colour composite signal" (after all there is no chrominance in the case of the default white-on-black palette!) but arises because of Acorn's poor analogue circuit design.

The chrominance could (and should) have been added in such a way that the luminance component was not affected, typically by summing the two signals at a 'virtual earth' point. In that case enabling chrominance would have had no effect on the quality of 80-column black-and-white text (I am ignoring here the possibility that the presence of the colour burst might result in cross-colour on some monitors).

Unfortunately Acorn used a very crude technique of capacitively coupling the chrominance at a point where there is a significant circuit impedance, so not only does the capacitor add chrominance it also removes high-frequency luminance! It is this, unnecessary, attenuation of the high-frequency luminance components that degrades the quality - in all modes but most noticeably in the 80-column modes.

I entirely accept that we, at the BBC, should have spotted this at an early stage and insisted on a circuit change (it would have added some complexity but probably only half-a-dozen analogue components costing a negligible amount). I can only offer the excuse that since the composite BNC output was seen primarily as the means of getting the Beeb's output into broadcast (studio) video infrastructure, and since 80-column text was too fine to broadcast anyway, it was not given the attention it deserved.
Richard, with all due respect, I was trying to keep it at a simple and practical level without going into the technical details of PAL colour encoding or of the specifics of the actual way that the BBC computer circuits generate the signals.

So whichever way you want to discuss it, the practical result is that when the composite video is as supplied, monochrome, you get a really good sharp video picture. But when the colour component signal is mixed in, text is a lot less clear to read.

Mark

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Re: Am I a Monster?

Post by Lardo Boffin » Sat Mar 02, 2019 5:43 pm

Hopper wrote:
Fri Mar 01, 2019 10:16 pm
So.

The last couple of Beebs I've worked on, I've removed the TV modulator and BNC output and plugged the case holes, One part of me says, yeah its rubbish no one is ever going to use this crap again, however another part says destroying the machines originality.... what say ye?

The main reason for binning the modulator is to run a cable aft for a 2nd processor (watch the pcb screw!) then mounting the Pi down there, close to the vent.

Mike
If you have any spare modulators I could do with a couple. :D
Doesn’t matter whether they work or not so long as the case is intact.
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Re: Am I a Monster?

Post by Coeus » Sat Mar 02, 2019 6:25 pm

Whether you consider it to be sacrilege is a personal thing, I suppose. If something has become rare and you happen to be sitting on one of the last examples then, even if it is legally yours, one might consider himself just being the custodian of it for future generations. I am sure that is the way museum curators feel. I am not sure the BBC micro is quite that rare yet.

On the question of the 2nd processor you remind me that I had a one of the alternate cases that allowed disc drives to be mounted in the same box as the main board by replacing the top part of the case with a different design. To get the floopy cable to the drives without having a loop around the case I bent the cable that came out of the IDC connector that went into the floppy port on the motherboard in the opposite direction from usual so instead of the cable coming down and out under the computer it went up instead into the enclosure. I think it may have been necessary to remove the circuit board screws and move it slightly to do this, but the result was very neat.

The Retroclinic datacentre can be fitted internally - I wonder if that uses the same trick. Could you do the same with the Pi and just stick it to the bottom of the lids with double sided tape (the type with foam in the middle)?
Last edited by Coeus on Sat Mar 02, 2019 6:34 pm, edited 2 times in total.

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Re: Am I a Monster?

Post by paulv » Sat Mar 02, 2019 7:05 pm

Coeus wrote:
Sat Mar 02, 2019 6:25 pm
If something has become rare and you happen to be sitting on one of the last examples then, even if it is legally yours, one might consider himself just being the custodian of it for future generations. I am sure that is the way museum curators feel. I am not sure the BBC micro is quite that rare yet.


There are some items in the wider Acorn ecosystem that are getting that rare though. Whilst the Elk/BBC Micro/Master/Arc/RiscPC aren't rare in themselves, there are peripherals for each machine that are rare.

Some of the Hybrid devices were rare when new, nevermind now, the Arx HD floppy interfaces for the Arc's are rare. Some of the I2c devices for the arc too.

For the things I have which I know are rare, I do tend to think of myself as just a caretaker but whilst I look after them, I don't treat them as museum pieces, IMO they're meant to be used and enjoyed.

I try my best not to damage it break them and I'm repair them if needed but I won't restore them if you see what I mean.

Paul

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Re: Am I a Monster?

Post by richardtoohey » Sat Mar 02, 2019 9:24 pm

Monster:
Monster.jpg
Hopper:
Hopper.jpg
So to answer your question I think you are not a Monster, you are a Hopper. :wink:

Cough. Shuffles off stage left.

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Re: Am I a Monster?

Post by Hopper » Sat Mar 02, 2019 10:10 pm

richardtoohey wrote:
Sat Mar 02, 2019 9:24 pm

So to answer your question I think you are not a Monster, you are a Hopper. :wink:

Cough. Shuffles off stage left.
:-)

If you had seen what I did to dozens of school beebs back in the early 90s involving paper clips and the vent, you'd be in no doubt! knocking in the ashtray was another classroom passtime.
Feel bad about it now, thats why I am ''looking after'' so many beeps now perhaps.

Mike

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