Troubleshoot No Video - Magnavox Odyssey 2

[wasedadoc]

Your reading of the schematic is incorrect.

IC5 pin 27 is sound coming out of the sound generator and into the RF modulator.  IC5 also generates the separate parts of the video signal namely red, green, blue, sync and blanking.  Those are fed into IC1 which forms the composite video signal and outputs it from pin 5 into the RF modulator IC6.

D2 and L4 determine the frequency of the 4.5 MHz oscillator.  D2 is a varicap diode.  The sound input via R49, R40 and C35  varies the capacitance of the diode and hence frequency modulates the sound carrier.  That is added to the composite video signal on pin 2 of IC6.  The combined sound and vision then amplitude modulates another oscillator within IC6.  Frequency of that one is around 60 MHz, determined by L6 and capacitors C17, C18 and C32.  The switch around C32 changes the frequency between CH3 and CH4.

The part of IC6 that does the 60 MHz oscillator and modulates it must be working otherwise you would never have got sound through your original chain of console plus two converter boxes to HDMI.  Check that the pin 2 of IC6 is getting more or less the same video signal that you got on pin 5 of IC1.

[Wil_Bloodworth]

So... video signal is coming out of IC1 pin 5 and is making it all the way to IC 6 pin 2.  I believe there is signal coming out of IC 6 pin 4 but it is not making it to the RF output.  I'm unable to test any of the capacitors between IC 6 pin 4 and the RF output unless I desolder them. 

Any tips on figuring out where to troubleshoot next or do I just need to start desoldering stuff?

Thank you,

- Wil

[wasedadoc]

So... video signal is coming out of IC1 pin 5 and is making it all the way to IC 6 pin 2.  I believe there is signal coming out of IC 6 pin 4 but it is not making it to the RF output.  I'm unable to test any of the capacitors between IC 6 pin 4 and the RF output unless I desolder them. 

Any tips on figuring out where to troubleshoot next or do I just need to start desoldering stuff?

Thank you,

- Wil

I'm not totally convinced there is anything wrong with the console itself.  The RF signal coming out of pin IC6 pin 4 will be very small and very difficult for your scope to trigger on.  Easy to appear as just noise.

If you really did get sound as stated in your first post then the output from IC6 is definitely getting to the output socket.  The audio FMed 4.5 MHz and the composite video are combined inside IC6 before that mix is applied as a single input to the 60 MHz amplitude modulator.

I'm wondering if your TVs just don't like the video signal that the console generates.  Those old consoles only generated an approximation to the pukka NTSC standard.  TVs of the era when that console was designed were much more tolerant of deviations from the strict standard.  For example, your console probably generates non- standard non-interlaced video which the upscaler in your Samsungs may not be able to deal with.

The only way to conclusively prove that the console is working OK is to see it working with at least one TV.  Do you have access to, even temporarily, an older TV?

Update:  I just realised you can test the console's output.  Hook it up to the coax to 3 phono output box that you have.  Look at the video output (yellow socket?) with your scope.  Do you see the same waveform shape as when you looked at pin 5 of IC1?

[Wil_Bloodworth]

Well, after resoldering a couple of connections and changing some cords... voila!

Thank you Wasedadoc!  The first thing she said after seeing it working was, "Drop your pants!".  LOL



- Wil