Electronics > Repair

Troubleshoot No Video - Magnavox Odyssey 2

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Wil_Bloodworth:
My wife has her original Magnavox Odyssey 2 (service manual:  https://www.digitpress.com/library/techdocs/o2-svc.pdf) from the late 70s and I've been trying to get it to work again... clearly for some points on the home front!

After purchasing an adapter to go from the RF Out (RCA coax) on the console... to a Coax to RCA (Red, White, Yellow) converter box... to a RCA to HDMI box... to a TV.

I've cleaned the console inside and out, fixed a few soldering points on the main board, tested all of the voltages and now everything "seems" fine.  The input voltage is good and the on-board voltage regulator seems to be working well too.

When I turn the console on, I get audio but no video.  The game is responsive and when I touch keys on the keyboard, the console is responding to my input.  So... everything appears to be loading and running fine. BUT... no video is making it to the TV.

How do I troubleshoot this video issue?  I'm going to assume that the converters I purchased work (let's just go with that assumption for now as they're brand new and I don't have any other 'old' devices in the house to test them with).

The Channel 3/4 module seems to be working fine and I'm getting voltage from the main board to that daughter board... but I don't know how to test the output.  Can I test this somehow with my scope (without a logic analyzer)?

I can post photos of anything you like upon request.

Thank you!

- Wil

wasedadoc:
Do you really need those two converter boxes?  I haven't heard of a TV with HDMI input but not analogue RCA phono jacks,  yellow composite video, white left audio, red right audio.  And even though the US has now no analogue RF broadcast TV transmissions, modern TVs are essentially "worldwide" designs and tend to still have analogue tuners.

Put your scope on pin 5 of IC1 and you should see the video signal that goes into the RF modulator.

Wil_Bloodworth:

--- Quote from: wasedadoc on November 28, 2023, 12:49:07 am ---Do you really need those two converter boxes?  I haven't heard of a TV with HDMI input but not analogue RCA phono jacks,  yellow composite video, white left audio, red right audio.  And even though the US has now no analogue RF broadcast TV transmissions, modern TVs are essentially "worldwide" designs and tend to still have analogue tuners.

--- End quote ---

Yes. None of our TVs have any inputs other than HDMI.


--- Quote from: wasedadoc on November 28, 2023, 12:49:07 am ---Put your scope on pin 5 of IC1 and you should see the video signal that goes into the RF modulator.

--- End quote ---

Ok. What am I looking for exactly?  What should I expect to see?  I recently purchased the scope and haven't used it for anything other than some voltage measurements.

Thank you,

- Wil

wasedadoc:
You expect to see NTSC video.  Similar to the waveform at https://en.wikipedia.org/wiki/File:Analogue_Video_Signal_PS1.png.  Very approximately 1 volt peak to peak.  The pulses at the bottom will be constant.  The top parts between the pulses will depend on the picture content.  Frequency of the pulses is 15.75 kHz.  Period just under 64us.  Set scope to 10us or 20us per division.

If in doubt post a photo of what your scope does show.

I'd like to know the make and model numbers of your TVs.

Wil_Bloodworth:

--- Quote from: wasedadoc on November 28, 2023, 07:54:10 pm ---You expect to see NTSC video.  Similar to the waveform at https://en.wikipedia.org/wiki/File:Analogue_Video_Signal_PS1.png.  Very approximately 1 volt peak to peak.  The pulses at the bottom will be constant.  The top parts between the pulses will depend on the picture content.  Frequency of the pulses is 15.75 kHz.  Period just under 64us.  Set scope to 10us or 20us per division.

--- End quote ---

Awesome!  I will try that and report back.

These are our TVs:

* Samsung - 50” Class CU7000 Crystal UHD 4K Smart Tizen TV
Samsung - 75" Class 8 Series LED 4K UHD Smart Tizen TV

* - Wil

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