BBC Model B+ video problem...

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Remklep
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BBC Model B+ video problem...

Post by Remklep » Mon Dec 23, 2019 7:57 pm

I recently purchased some upgrades for my model B+.
1) A Gotek floppy emulator
2) A TurboMMC
3) RGB to Scart cable form my LCD Television (older model Sony 32" from 2005)
4) Retroclinic Pi Tube

Everything works fine, the RGB to Scart cable is great, the picture is clear and sharp on my 32" Sony.
However, whenever I start a game with the Retroclinic Pi Tube connected (ie. Tube Elite) the screen starts rolling/tearing horizontally.

Does anyone have any idea what to do about this?

Thanks.
BBC Model B+ 64K, 128K Memory Mod, RetroClinic External PiDirect with Raspberry Pi 3B.
BBC Master 128, RetroClinic Internal PiDirect with Raspberry Zero, TurboSPI MMC, RobC's VideoNuLa, Gotek Floppy Emulator.

RobC
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Re: BBC Model B+ video problem...

Post by RobC » Mon Dec 23, 2019 10:00 pm

Is it only a problem with Elite or does it happen as soon as you turn on the machine with the Pi connected?

Also, does it happen in every mode?

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1024MAK
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Re: BBC Model B+ video problem...

Post by 1024MAK » Mon Dec 23, 2019 10:05 pm

How is the Pi powered?

Mark

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rmbrowngr
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Re: BBC Model B+ video problem...

Post by rmbrowngr » Tue Dec 24, 2019 6:56 pm

I have a similar setup and the enhanced Elite works just fine. When I get some time I’ll post some pictures of the setup and running the enhanced Elite.
Richard B
Acorn Electrons issue 4 and 6, MRB, Plus 1, AP6, AP5, Pegasus 400, BeebSCSI, Gotek, Raspberry Pi, GoSDC MBE.
BBC B+ 64K (128K upgraded) with Duel OS, Raspberry Pi and Gotek.

Remklep
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Re: BBC Model B+ video problem...

Post by Remklep » Thu Jan 02, 2020 12:13 pm

Hi all, thanks for the replies.

RobC - Whenever I switch modes there is some tearing/rolling for about a second, then the screen stabilizes.
This also happens without the PiTube .
Looks like the LCD TV is trying to match frequency?

1024MAK - the PiTube is powered by the TUBE connector.
BBC Model B+ 64K, 128K Memory Mod, RetroClinic External PiDirect with Raspberry Pi 3B.
BBC Master 128, RetroClinic Internal PiDirect with Raspberry Zero, TurboSPI MMC, RobC's VideoNuLa, Gotek Floppy Emulator.

Remklep
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Re: BBC Model B+ video problem...

Post by Remklep » Thu Jan 02, 2020 12:17 pm

As a test I removed the RGB-Scart cable and hooked my BBC up to the TV via the UHF out, no more tearing/rolling.
But now the quality of the graphics is awful.
BBC Model B+ 64K, 128K Memory Mod, RetroClinic External PiDirect with Raspberry Pi 3B.
BBC Master 128, RetroClinic Internal PiDirect with Raspberry Zero, TurboSPI MMC, RobC's VideoNuLa, Gotek Floppy Emulator.

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tricky
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Re: BBC Model B+ video problem...

Post by tricky » Thu Jan 02, 2020 12:53 pm

Where did you get the scart cable?
There are varying qualities and even more variety in the resistor used for sync.
Can you test with composite? Usually a yellow connector on the TV.
PS has anyone ever checked how "valid" elite's crtc setup is?

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rmbrowngr
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Re: BBC Model B+ video problem...

Post by rmbrowngr » Thu Jan 02, 2020 1:07 pm

I picked up a Scart cable on eBay and it had the wrong resistor for sync 220 instead of 270. Lovely scrolling effect. Didn’t bother to return as I had another working cable. When I next pass an Electrical component store I’ll pickup a replacement resistor.

For the correct wiring check out this page. http://mdfs.net/Info/Comp/BBC/Monitor/BBCtoTV.htm

Bought my working cable from https://rover.ebay.com/rover/0/0/0?mpr ... 1294538937
Richard B
Acorn Electrons issue 4 and 6, MRB, Plus 1, AP6, AP5, Pegasus 400, BeebSCSI, Gotek, Raspberry Pi, GoSDC MBE.
BBC B+ 64K (128K upgraded) with Duel OS, Raspberry Pi and Gotek.

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Re: BBC Model B+ video problem...

Post by rmbrowngr » Thu Jan 02, 2020 5:06 pm

2nd Processor Elite on B+, Gotek, Raspberry PI 2nd Processor and Sony Trinitron TV. As promised earlier in this thread.

Turning on my B+ 64k (upgraded to 128k)
IMG_3262.jpg
2nd Processor enabled
IMG_3267.jpg
IMG_3268.jpg
Elite disk image selected
IMG_3263.jpg
Selecting the version of Elite
IMG_3264.jpg
Elite running
IMG_3269.jpg
Richard B
Acorn Electrons issue 4 and 6, MRB, Plus 1, AP6, AP5, Pegasus 400, BeebSCSI, Gotek, Raspberry Pi, GoSDC MBE.
BBC B+ 64K (128K upgraded) with Duel OS, Raspberry Pi and Gotek.

Remklep
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Re: BBC Model B+ video problem...

Post by Remklep » Thu Jan 02, 2020 10:42 pm

rmbrowngr wrote:
Thu Jan 02, 2020 1:07 pm
I picked up a Scart cable on eBay and it had the wrong resistor for sync 220 instead of 270. Lovely scrolling effect. Didn’t bother to return as I had another working cable. When I next pass an Electrical component store I’ll pickup a replacement resistor.

For the correct wiring check out this page. http://mdfs.net/Info/Comp/BBC/Monitor/BBCtoTV.htm

Bought my working cable from https://rover.ebay.com/rover/0/0/0?mpr ... 1294538937
I'll open up my cable and check the resistor.
Easy to change it out if it's wrong.

Thanks for the tip.
BBC Model B+ 64K, 128K Memory Mod, RetroClinic External PiDirect with Raspberry Pi 3B.
BBC Master 128, RetroClinic Internal PiDirect with Raspberry Zero, TurboSPI MMC, RobC's VideoNuLa, Gotek Floppy Emulator.

Remklep
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Re: BBC Model B+ video problem...

Post by Remklep » Thu Jan 02, 2020 10:45 pm

On my RGB-Scart cable the following is printed:
www.retrocomputershack.com
BBC Micro/Master/Electron RGB Scart Lead v3.0 - GSYNC

So I assumed it was the correct one.
BBC Model B+ 64K, 128K Memory Mod, RetroClinic External PiDirect with Raspberry Pi 3B.
BBC Master 128, RetroClinic Internal PiDirect with Raspberry Zero, TurboSPI MMC, RobC's VideoNuLa, Gotek Floppy Emulator.

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Re: BBC Model B+ video problem...

Post by Remklep » Thu Jan 02, 2020 10:49 pm

Just openend up the scart connector and found no resistors.
So I took out my Fluke 175 and measured the resistance of the leads.
The resistances are correct, 270 Ohms on pin 20 and 220 Ohms on pins 7,11,15 and 16.
However there is one discrepancy, according to Fig. 4 in the above url from rmbrowngr, there should be an unresisted lead on pin 8, there is none on mine.
BBC Model B+ 64K, 128K Memory Mod, RetroClinic External PiDirect with Raspberry Pi 3B.
BBC Master 128, RetroClinic Internal PiDirect with Raspberry Zero, TurboSPI MMC, RobC's VideoNuLa, Gotek Floppy Emulator.

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Re: BBC Model B+ video problem...

Post by rmbrowngr » Fri Jan 03, 2020 7:29 am

The cable I have that doesn’t work, doesn’t have pin 8 wired also. Reading I’m not sure it’s actually needed. It appears to have two functions, one to switch the tv to look at the RGB signal AUX\AV, and the other, the picture aspect dependent on the voltage level. It also depends what is available on your TV.
Richard B
Acorn Electrons issue 4 and 6, MRB, Plus 1, AP6, AP5, Pegasus 400, BeebSCSI, Gotek, Raspberry Pi, GoSDC MBE.
BBC B+ 64K (128K upgraded) with Duel OS, Raspberry Pi and Gotek.

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tricky
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Re: BBC Model B+ video problem...

Post by tricky » Fri Jan 03, 2020 2:05 pm

As long as the TV has selected RGB 4:3 you don't need it and as it is usually 5v, technically it is asking for 16:9!

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1024MAK
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Re: BBC Model B+ video problem...

Post by 1024MAK » Fri Jan 03, 2020 3:49 pm

rmbrowngr wrote:
Thu Jan 02, 2020 1:07 pm
I picked up a Scart cable on eBay and it had the wrong resistor for sync 220 instead of 270. Lovely scrolling effect. Didn’t bother to return as I had another working cable. When I next pass an Electrical component store I’ll pickup a replacement resistor.

For the correct wiring check out this page. http://mdfs.net/Info/Comp/BBC/Monitor/BBCtoTV.htm

Bought my working cable from https://rover.ebay.com/rover/0/0/0?mpr ... 1294538937
A 270Ω resistor in place of a 220Ω resistor is not normally a significant difference. The point of the resistor is to drop the TTL voltage level (typically between 4V and 5V) from the computer down to around 0.7V that is suitable for the TV.

Part of the problem with RGB SCART connections is that some modern TVs are a lot less tolerant of the video outputs from 1980s and 1990s computers.

I have a Sharp LCD TV and it will work with every 1980s and 1990s computer that I have tried it with (be it RF/UHF, composite or RGB SCART). I also have an Argos own brand (I forgot the name) 4:3 aspect LCD TV that also works fine with BBC machines via RF/UHF, composite and RGB SCART. But the same cannot be said for the more modern LCD TV in the living room.

Strangely enough, the budget small screen TVs sometimes fair better :?

I have BBC RGB SCART cables from Retro Computer Shack (eBay link) and from cool-novelties (eBay link) and both work fine for me.

You may well get a momentary loss of synchronisation and loss of picture when you change MODE. When the computers video system changes MODE, the CRTC chip has its configuration changed. LCD TVs have to convert the video from analogue to digital, and analyse the data in order to work out what to display. I have found that some take longer when using RGB SCART mode for some reason.

Mark

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Re: BBC Model B+ video problem...

Post by RobC » Fri Jan 03, 2020 4:49 pm

1024MAK wrote:
Fri Jan 03, 2020 3:49 pm
You may well get a momentary loss of synchronisation and loss of picture when you change MODE. When the computers video system changes MODE, the CRTC chip has its configuration changed. LCD TVs have to convert the video from analogue to digital, and analyse the data in order to work out what to display. I have found that some take longer when using RGB SCART mode for some reason.
And Elite switches mode mid-frame every frame...

Do you get the same issue running standard Elite with the TUBE turned off? I think TUBE Elite (and M128 Elite) uses modes 1 & 2 as opposed to modes 4 & 5 on the standard version.

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Re: BBC Model B+ video problem...

Post by rmbrowngr » Fri Jan 03, 2020 4:55 pm

And there are some alternatives connecting your Beeb or Elk to a TV\Monitor e.g. to HDMI:-

RGB to HDMI using a Pi Zero and a small CPLD viewtopic.php?f=3&t=14430&start=660&hil ... spberry+pi
John Kortink's BBC HDMI (BBC2DVI ) viewtopic.php?f=3&t=15417&p=209460&hili ... pi#p209456, http://www.zeridajh.org/hardwre/bbc2dvi/index.htm

Might be worth reading:-
Best display for a BBC? viewtopic.php?f=3&t=18062&p=252833&hili ... pi#p252833
Richard B
Acorn Electrons issue 4 and 6, MRB, Plus 1, AP6, AP5, Pegasus 400, BeebSCSI, Gotek, Raspberry Pi, GoSDC MBE.
BBC B+ 64K (128K upgraded) with Duel OS, Raspberry Pi and Gotek.

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1024MAK
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Re: BBC Model B+ video problem...

Post by 1024MAK » Fri Jan 03, 2020 6:49 pm

rmbrowngr wrote:
Fri Jan 03, 2020 7:29 am
The cable I have that doesn’t work, doesn’t have pin 8 wired also. Reading I’m not sure it’s actually needed. It appears to have two functions, one to switch the tv to look at the RGB signal AUX\AV, and the other, the picture aspect dependent on the voltage level. It also depends what is available on your TV.
SCART pin 8 and pin 16 are (optional) control signals to the TV.

Pin 8 is the “Status & Aspect Ratio up” control signal
The official levels are:
  • 0–2 V → off
  • +5–8 V → on/16:9
  • +9.5–12 V → on/4:3
Pin 16 is the “Blanking signal up
 / RGB-selection voltage up” control signal
The official levels are:
  • 0–0.4 V → composite
  • 1–3 V → RGB
Some TVs (mostly older CRT types) ignore these signals, or only recognise some of the levels/signals.
Some TVs have user controls to override these “automatic” control signals. Either via remote control button(s) or via on-screen menu settings. For example my Sharp TV.
Alas, some modern LCD TVs don’t appear to have any user controls / settings to override the “automatic” control signals :(.

If you are handy with a soldering iron, it is possible to add extra circuits to provide the +9.5–12V to pin 8 and the 1–3V to pin 16. Note that the input impedance for pin 16 is around 75Ω. So that’s 20mA at 1.5V. You can get +12V from the BBC auxiliary power socket. Things are considerably more awkward for Electron users :(.

Mark

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