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Sega Genesis Model 1 - no video - but sound is OK


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Hi guys - was wondering if any of have come across this issue where there isn't any video but there is audio with a Sega Genesis Model 1?


I'll try to be as detailed as possible to avoid the obvious troubleshooting steps:


  • The video via RF or Composite A/V does not seem to work I am getting a black screen when the console is powered on - on a regular tube type TV using the RCA inputs - yellow (video) white (audio)
  • The games DO boot up
  • Audio does work from the headphone jack
  • Audio comes out of the TV speakers
  • I can hear through the audio that the controls ARE working - select menus, fire, jump sounds etc.
  • So I believe we can rule out a cart and/or CPU issue and/or memory issues
  • The same power supply, games and A/V and RF cables WORK in my other model 1 genesis
  • I removed and looked at the PCB, removed the heat sinks - all caps, surface mount resistors seem great - there is a little flux residue around the voltage regs - but nothing looks swollen or burnt.
  • I looked for dry solder joints and just for certainty I re-soldered the A/V Connector and RF modulator
  • I searched the internet and did not find anything specific to my problem - other than threads mentioned cart and pin cleanings and then eventually go unsolved

I know these are not terribly expensive, - it is more principal really - it seems like it may be a simple fix - but I don't know enough about what can go wrong in an IC


I think I exhausted all steps.


If you have experienced this and have some suggestions - thank you.







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Sounds like u have eliminated everything else. It might point towards a malfunctioning video DAC. I would eliminate caps first. A bad cap doesn't always look like a bad cap. What model Genesis 1 do u have. There should be a decoupling cap for the CXA1145, maybe try replacing that first.

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so it seems that the caps are charging and discharging - not sure if it as the correct rates - but I tested each cap with 1K ohms and watched the numbers on the meter charge and then discharge - unless I am doing something wrong. Smaller caps discharged faster than others (seems reasonable) - testing those on mV and large caps on v. At one point after the system ran for a little - the video did come on and then went back off. I think I have invested all the time I am willing to at this point unless I get some new information. Thanks for your efforts.

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One more update - in regards to what I said about the game (video) coming on for a few seconds - seems to only occur with Gunstar Heros - when Gunstar Heroes is in - you can hear the intro screen and all that - and at one point - the screen flashes when it comes to the start menu and the TV comes on and shows the start screen and then flickers off - that is weird - seems like a refresh problem now. Why would the screen come on at that point?


Watch the video of it in action:


happens around 1:17

Edited by mtarallo
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That's interesting. That suggests a sync issue in the video signal which might explain why your Tv won't detect picture, or only show it randomly. I would try and replace the cap on the video line. It's a 220uf cap near the cxa-1145 chip. The schematics show it as C32 but yours might be slightly different.


The resistance test doesn't show whether a cap has gone bad. U need an ESR tester which can be expensive. I just troubleshoot down to the likely cap and replace it.

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  • 1 month later...

UPDATE: I did it! - it works! - more of principal really - as I could have probably got another functioning model 1 for $30 - lol -but just a few bucks in caps and a new IC and some hours here and there troubleshooting - but yes - if you are referring to the Sony CXA1145P IC - that was the final fix for the video problem, possibly did not need to replace the caps - I honestly should have started with that first - but I'm learning!!!








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