128K RGB Display problem.

Witbear · December 2013

I have just got my hand on a toast rack, but when powered and connected to the telly the picture jumps horizontally at random intervals.

Could it be that my new Samsung telly can't keep a latch on the signal or is it something that needs replacing at the speccy end?

BTW, have not tried analogue output as I don't have a TV cable.

Any ideas?

-Stacey

schombi · December 2013

Take a look at
http://www.worldofspectrum.org/forums/showthread.php?t=45732
and also at the other thread that is mentioned in there. I could revive my toaster and so did Macc.

joefish · December 2013

Is it a widescreen telly, and is the picture otherwise clear and properly coloured?

If so, it might never work. Even with all the right signals, I have a widescreen LCD telly where an otherwise perfect picture jumps up and down. It's because the Speccy doesn't generate the alternate frames of the PAL signal properly, it just repeats the first frame over and over. Tellies that are trying to capture a pair of PAL frames, combine and rescale them, then display them at a higher rate are easily confused.

1024MAK · December 2013

I presume you are currently using a SCART lead and your TV is in RGB mode?
I have a 42 inch wide screen Samsung TV that does not show a correct picture with an "off the shelf SCART cable".

On another TV (a Sharp AQUOS) I have to use the TV menu/settings to select PAL colour system, other wise on "AUTO" it gets confused resulting in the picture coming and going (on, black screen, on, black screen, most annoying).

So go through your TV's settings.

Next, I suggest that you try another telly.
If you have access to one, try an older CRT (tube) type.

Otherwise try a smaller / cheap LCD telly.

Also if you are still having problems, it is worth while trying the UHF connection.

Mark

Witbear · December 2013

All works well with another telly except for a horizontal rolling stripes spaced half a screen apart that move down the screen. I guess this is where my big telly loses the lock.

Any ideas welcome but not essential.

-Stacey

1024MAK · December 2013

Do you have another PSU?

Some PSU faults can cause problems due to the mains AC waveform "breaking through" to the Spectrum instead of being "smoothed out".

Alternatively if you know someone local who has some test gear (oscilloscope), they could test the PSU at the very least.

It may be that the large electrolytic capacitor in he PSU needs replacing.

Other known video problems are due to smaller electrolytic capacitors on the Spectrum circuit board having come to the end of their lives (they dry out with use and over time).

Mark

Lost · December 2013

1024MAK wrote: »

I presume you are currently using a SCART lead and your TV is in RGB mode?
I have a 42 inch wide screen Samsung TV that does not show a correct picture with an "off the shelf SCART cable"

Mark

Hi I have the same problem with my toaster, perfect picture with random jumps. I'm using an old LCD TV and a scart lead. The toaster worked fine on my CRT but that went by-by a few weeks ago.

I heard on another forum that the scart can be modified to work with an LCD tv but they didn't say how. Just wondered if anyone here has an idea?

1024MAK · December 2013

Yes, it is to do with the voltages required on pin 8 and pin 16.
To ensure a TV switches to RGB input mode, pin 16 must be between 1V and 3V.
Pin 8 should be between 5V and 7V for a widescreen 16:9 aspect ratio signal, or between 9.5V and 12V for normal 4:3 aspect ratio signal. Voltages less than 4.5V may switch off the SCART input.

Things you can try:-

First go through your TV's settings / menus to see if you can manually select external AV mode, RGB mode (NOT composite or S-Video mode), PAL colour (as some TV's in "auto" mode get confused even though we are using RGB). If this is not possible, or does not work...

Open your SCART lead and see if there is a wire connected to pin 16. If there is no wire, connect a red wire to this pin. Next connect a black wire to pin 18. Get a AA size battery holder and connect the black wire to the negative end, and the red wire to the positive end. Fit a Alkaline AA cell. Now see if your Spectrum displays a steady picture.

If this does not work, next we look at pin 8. You will need to obtain a +12V supply from either a separate PSU, or get +12V from the Spectrum's RS232 port pin 6 (if you can find a suitable plug). Disconnect any existing wire, and connect +12V via a 100 ohm resistor (1/4W, 250mW) to pin 8 on the SCART plug. Connect the 0V/ ground/ negative (if using a separate PSU) to pin 14 on the SCART plug.

For more information see Paul's web site here :smile: [when checked, part of Paul's site was down, so use the WayBack Machine ;) ]

Mark

Lost · December 2013

1024MAK wrote: »

Yes, it is to do with the voltages required on pin 8 and pin 16.
To ensure a TV switches to RGB input mode, pin 16 must be between 1V and 3V.
Pin 8 should be between 5V and 7V for a widescreen 16:9 aspect ratio signal, or between 9.5V and 12V for normal 4:3 aspect ratio signal. Voltages less than 4.5V may switch off the SCART input.

Things you can try:-

First go through your TV's settings / menus to see if you can manually select external AV mode, RGB mode (NOT composite or S-Video mode), PAL colour (as some TV's in "auto" mode get confused even though we are using RGB). If this is not possible, or does not work...

Open your SCART lead and see if there is a wire connected to pin 16. If there is no wire, connect a red wire to this pin. Next connect a black wire to pin 18. Get a AA size battery holder and connect the black wire to the negative end, and the red wire to the positive end. Fit a Alkaline AA cell. Now see if your Spectrum displays a steady picture.

If this does not work, next we look at pin 8. You will need to obtain a +12V supply from either a separate PSU, or get +12V from the Spectrum's RS232 port pin 6 (if you can find a suitable plug). Disconnect any existing wire, and connect +12V via a 100 ohm resistor (1/4W, 250mW) to pin 8 on the SCART plug. Connect the 0V/ ground/ negative (if using a separate PSU) to pin 14 on the SCART plug.

For more information see Paul's web site here :smile: [when checked, part of Paul's site was down, so use the WayBack Machine ;) ]

Mark

Thanks Mark, firstly I should say tested this with 2 PSUs and both are the same. Been through all (the sparse) options on the TV and it didn't help. The cable I have has a connection at 16 so didn't wire up an AA to test - should I try this anyway?. Thinking of taking the easy option and wiring an rca type composite cable. I know the picture is not as good as the rgb, but technically its in my comfort zone. Just rigged up a test cable and it looks OK.

Macc · December 2013

Anyone tried old fashioned RF?

Lost · December 2013

The AA battery thing worked like a peach.

Can I do this without the battery?

Cheers :-D

128K RGB Display problem.

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