Amstrad MP-3 SCART mod

[sertacarslan]

Hi friends,


Is it possible to mod Amstrad MP-3 modulator for a SCART (RGB & composite) input?
It would be great if i could use CTM644 as my main retro monitor!


Thanks for your response in advance.   

[Bryce]

Hi friends,


Is it possible to mod Amstrad MP-3 modulator for a SCART (RGB & composite) input?
It would be great if i could use CTM644 as my main retro monitor!


Thanks for your response in advance.

The MP3 is a TV receiver, not a modulator.

Bryce.

[sertacarslan]

The MP3 is a TV receiver, not a modulator.

Bryce.

Oh, thanks for clarification Bryce. I am quite unexperienced on Amstrad CPC's yet


Is it possible to add a scart input to use AN5612 and/or LA7520N IC's in MP-3 receiver to process composite signal and get an RGB out?


I guess, rgb is possible but i need composite input especially. Or something else for Commodore 64

[Bryce]

Creating RGB from composite is difficult and the picture quality will be terrible. Unfortunately, connecting a C64 to anything RGB is difficult, the best picture you can get from the C64 is an S-Video signal, but that's not compatible with any CPC monitors.

Bryce.

[sertacarslan]

Creating RGB from composite is difficult and the picture quality will be terrible. Unfortunately, connecting a C64 to anything RGB is difficult, the best picture you can get from the C64 is an S-Video signal, but that's not compatible with any CPC monitors.

Bryce.

Yes, first i recognized is that C64 with RGB is not easy at all.
I found some solutions about converting composite to rgb in internet but these solutions are too beyond of me since i am not experienced on electronic.
I am not searching a crystal clear picture on CTM644, i just want to see something better than RF.


If AN5612 and/or LA7520N does not have ability to process composite signal, then i will have to buy something from aliex..s or i will try to find something else:(


Any suggestion is very welcome

[Bryce]

Yes, first i recognized is that C64 with RGB is not easy at all.
I found some solutions about converting composite to rgb in internet but these solutions are too beyond of me since i am not experienced on electronic.
I am not searching a crystal clear picture on CTM644, i just want to see something better than RF.


If AN5612 and/or LA7520N does not have ability to process composite signal, then i will have to buy something from aliex..s or i will try to find something else:(


Any suggestion is very welcome

Both the AN5612 and LA7520 are signal processing chips to detect and convert signals for CRT TV's / tube drivers. They wouldn't do what you want and they are most likely very difficult to find.

Bryce.

[sertacarslan]

Both the AN5612 and LA7520 are signal processing chips to detect and convert signals for CRT TV's / tube drivers. They wouldn't do what you want and they are most likely very difficult to find.

Bryce.

I have a hope about AN5612. Regarding AN5612 datasheet, there are R, G, B outputs and R-Y, B-Y inputs.


I don't know what these inputs are, but is it possible if they are luma and chroma?













https://datasheetspdf.com/datasheet/AN5612.html

[Bryce]

It's a bit more complicated. You need all three signals Y, R-Y, B-Y to get RGB output. Y is Luminance, but R-Y and B-Y are differential colour signals. These are signals not usually found outside of the internal TV circuit and converting Composite to these signals is just as complicated as converting Composite to RGB.


Bryce.

[sertacarslan]

It's a bit more complicated. You need all three signals Y, R-Y, B-Y to get RGB output. Y is Luminance, but R-Y and B-Y are differential colour signals. These are signals not usually found outside of the internal TV circuit and converting Composite to these signals is just as complicated as converting Composite to RGB.


Bryce.

Thank you Bryce, now i understand i guess. So, AN5612 is a digital video signal processor and it needs to feed by component video signals instead of analog composite.


I am still keen on adding a female SCART connector to my MP-3 receiver and try to forward RGB signals directly to DIN output. Then i will find a Composite2RGB converter and solder composite input to SCART composite pins (15, 17, 20).


Or do you know about any Composite to RGB DIY project?

[Bryce]

I am still keen on adding a female SCART connector to my MP-3 receiver and try to forward RGB signals directly to DIN output. Then i will find a Composite2RGB converter and solder composite input to SCART composite pins (15, 17, 20).

The CPC DIN connector IS more or less SCART RGB. You don't need to do any conversions, you can feed SCART R,G,B,Sync signals directly into the CTM.
Look at the standard CPC to SCART cable: https://www.cpcwiki.eu/index.php/File:Cpc_to_scart.png
Change the gender of each connector and you have a SCART input for your CTM without the MP3 at all.

Bryce.

[sertacarslan]

The CPC DIN connector IS more or less SCART RGB. You don't need to do any conversions, you can feed SCART R,G,B,Sync signals directly into the CTM.
Look at the standard CPC to SCART cable: https://www.cpcwiki.eu/index.php/File:Cpc_to_scart.png
Change the gender of each connector and you have a SCART input for your CTM without the MP3 at all.

Bryce.

You are right. I already soldered a Din8 to Din6 cable to connect my ZX +2 to the monitor before (which i could not success at the end; i added some 150 ohm resistors and diodes but the picture was so dark, then i gave up).
But one of my aim was also to add functionality to my MP-3 receiver which is just lying under the monitor. Besides, if i add a standard SCART input to the receiver, then i will be able to use a simple scart cable to connect any device to the monitor.

[Bryce]

Why did you add diodes and resistors? That would of course make the screen very dark. did you try direct connections?

Bryce.

[RetroCPC]

Is it possible to mod Amstrad MP-3 modulator for a SCART (RGB & composite) input?

It should be possible to modify the Amstrad MP-3 (TV) Tuner to convert an external Composite PAL Video signal to an RGB+Sync that will drive the CTM640 / CTM644 monitor.

I don't have a unit to confirm, but looking at the MP-3 Tuner schematic, remove L207 & CF202 (or cut the PCB trace from the output end of L207/CF202 and TP007) and connect the Composite video signal to TP007, and Composite Video Ground to the metal shielded body of the RF tuner module - or any other convenient signal grounding point...

It might be slightly more complicated as Video Buffer transistor Q603 will not really be correctly biased with an AC coupled Composite Video input signal...

I could modify your MP-3 if it does not work out (I'm located in the Czech Rep.)

Maybe lifting (disconnecting) IC201 pin 22, and inputting the Composite video input on TP008 would work better - but again still Q603 is not really correctly biased...

[sertacarslan]

Why did you add diodes and resistors? That would of course make the screen very dark. did you try direct connections?

Bryce.

Good morning Bryce.


I read that ZX Spectrum 128k and +2 (grey version) versions generate three 0-5V TTL level signals for RGB and also generate another 0-5v TTL signal for "bright" shades of colours.
To connect 128k and +2 (grey version) to a RGB source, we need to distribute bright signal onto RGB signals, as far as i understand.


Here is a paragraph of the source;






Full document is here;
https://mts.speccy.cz/doc/128_rgb.pdf




But it does not work on my CTM644, maybe just because of my soldering skill

[sertacarslan]

It should be possible to modify the Amstrad MP-3 (TV) Tuner to convert an external Composite PAL Video signal to an RGB+Sync that will drive the CTM640 / CTM644 monitor.

I don't have a unit to confirm, but looking at the MP-3 Tuner schematic, remove L207 & CF202 (or cut the PCB trace from the output end of L207/CF202 and TP007) and connect the Composite video signal to TP007, and Composite Video Ground to the metal shielded body of the RF tuner module - or any other convenient signal grounding point...

It might be slightly more complicated as Video Buffer transistor Q603 will not really be correctly biased with an AC coupled Composite Video input signal...

I could modify your MP-3 if it does not work out (I'm located in the Czech Rep.)

Maybe lifting (disconnecting) IC201 pin 22, and inputting the Composite video input on TP008 would work better - but again still Q603 is not really correctly biased...

Good morning RetroCPC,


Wow, thank you for detailed explanation I will try to apply this modification asap and i will share the result here.
If i can't successfully mod it, then i would ask your help, thank you once more

[Bryce]

It should be possible to modify the Amstrad MP-3 (TV) Tuner to convert an external Composite PAL Video signal to an RGB+Sync that will drive the CTM640 / CTM644 monitor.

I don't have a unit to confirm, but looking at the MP-3 Tuner schematic, remove L207 & CF202 (or cut the PCB trace from the output end of L207/CF202 and TP007) and connect the Composite video signal to TP007, and Composite Video Ground to the metal shielded body of the RF tuner module - or any other convenient signal grounding point...

It might be slightly more complicated as Video Buffer transistor Q603 will not really be correctly biased with an AC coupled Composite Video input signal...

I could modify your MP-3 if it does not work out (I'm located in the Czech Rep.)

Maybe lifting (disconnecting) IC201 pin 22, and inputting the Composite video input on TP008 would work better - but again still Q603 is not really correctly biased...

And don't expect too much from a composite to RGB conversion, it won't be a crisp, sharp picture no matter what you do.

Bryce.

[RetroCPC]

Good morning RetroCPC,


Wow, thank you for detailed explanation  I will try to apply this modification asap and i will share the result here.
If i can't successfully mod it, then i would ask your help, thank you once more 

I happened to find a MP3 TV tuner in my basement (but I dont have a working Colour Monitor).

I quickly run some simulations, and as expected the Video buffer Q603 needs to be correctly biased - the modification circuit requires a handfull of cheap components that need to be added to the PCB ("Rats nested" above the PCB), the modification is quite simple. If you feel your soldering skills is up to it then I can try and document the modifications:-

75 Ohm Resistor
270 Ohm Resistor
2.7K Resistor
3.9K Resistor

100uF 16V (or greater voltage) Electrolytic  capacitor

Oh, and a RCA Phono socket that can be mounted to the casework for the Composite Video input signal

[sertacarslan]

Good morning RetroCPC,

Thank you so much for your detailed guidence again
My electronic knowledge is a way worse than my soldering skills to be honest. So it would be great if you could also draw a simple schema shows which component would be soldered to where or which path would be cutted etc

I will also need the amperage grades of the resistors (guess my electronic knowlege )

I was planning to use a female SCART input and use composite input pins; 18 and 20 because i will also use direct RGB input together with composite, but it is a good idea that adding another RCA Phono socket would make the tuner more standardized!

Wish you a great week!

I happened to find a MP3 TV tuner in my basement (but I dont have a working Colour Monitor).

I quickly run some simulations, and as expected the Video buffer Q603 needs to be correctly biased - the modification circuit requires a handfull of cheap components that need to be added to the PCB ("Rats nested" above the PCB), the modification is quite simple. If you feel your soldering skills is up to it then I can try and document the modifications:-

75 Ohm Resistor
270 Ohm Resistor
2.7K Resistor
3.9K Resistor

100uF 16V (or greater voltage) Electrolytic  capacitor

Oh, and a RCA Phono socket that can be mounted to the casework for the Composite Video input signal