Hi,

I would really appreciate some expertise here. I am trying to convert an RGBHV signal from a GBS-8220 board modified for GBS control, to composite video. The GBS is outputting a 15Khz signal and I am using the sync combiner circuit described here: https://www.retrorgb.com/building-a-passive-sync-combiner.html. I have previously tested this with the RGB lines on an old RGBS monitor and a Scart TV and it displayed perfectly.

I have followed the example circuit detailed in the datasheet here: https://www.alldatasheet.com/datasheet-pdf/pdf/46644/SONY/CXA1645P.html (PAL version). But the result is no output from the composite pin. Have tested with a oscilloscope and it's a flat line (see screenshot). I have verified the RGB signals and they do register on the oscillioscope - measure around 0.9v with the multimeter on the input pin. Further debugging shows the two vcc pins are both getting 5v, the composite sync signal is around 2.7v. I have a 4.43 MHZ crystal oscillator connected between the SCIN pin (6) and ground. Specifically one of these: https://www.aliexpress.com/item/1005002600232112.html - I think that's the correct setup for PAL.

I have attached photos of everything connected on the breadboard. I appreciate these are not the easiest things to follow but I really don't know how else to show the setup. If anyone has any suggestions please let me know. I'm at a loss as to where to go with this otherwise.

Thanks in advance.

 

A circuit schematic drawing is readable. a photo of a protoboard is a serious challenge.

 

Yes I understand that but the schematic is the one in the datasheet (the link of which I posted). That's what I have built. Except I get no output so I surmised I had done something wrong, hence the photos showing how I connected everything up. I am now lead to believe the crystal oscillator is just a crystal so I have to add some resistors and a 5V supply to it but in any case I would still expect something like a monochrome image or a garbled signal. For convenience I have attached the schematic.

Any help appreciated. Thanks again.

 

A quartz crystal alone will not oscillate.
What you need is a quartz crystal oscillator module.
They look like this:

 

Thanks very much. I have actually ordered some of these but they are really hard to find at 4.34MHZ. I have had to order some of Australia so they will take a little while to arrive. In the meantime I think I should be able to use the crystal with some 22pF resistors and a 1M ohm resistor setup like this. Would appreciate any expertise on here as to whether this will work.

+5V
│
│
( ) 1MΩ (optional)
│
X1 ---┴----||---- GND
22pF
X2 --------||---- GND
22pF

 

You something that looks like this circuit.

 

Hello again. I'm pleased to report some progress with this. The oscillator arrived, as did a replacment IC. It seems it was an issue with the IC. The replacement is giving an output, and I'm getting an image on screen. However it looks rather scrambled. I've attached a screenshot of this. The image is stable (I had missed a ground connection on the sync combiner circuit, but now it's good). I've included the oscilloscope readings for sync, the crystal oscillator and the composite output itself - in that order.

Does anyone recognise what might be going on here and how I can resolve it. For reference the image on the TV should be colour bars - I would hope that is easy enough to see.

Would really appreciate any advice offered. Thanks.