Repairing TMNT bootleg - SYNC wtf?

[K0NAM1]

Hi,

I have a TMNT board, its a bootleg but it has all the customs so I'm guessing the schematic won't be that far off.

My first hurdle... I'm getting erratic SYNC (I can hear SYNC with my logic probe) on my OSSC (NO SYNC flashes on/off), it won't lock and so no picture, fine, OK, so I enable the TEST MODE DIP switch and the SYNC dies (flatline sound with the logic probe, NO SYNC on the OSSC display), wtf?

Why would SYNC disappear in test mode?

Thanks.
Richard

 

[ekorz]

If it’s a bootleg does it have a test mode for sure? With that particular dip? Maybe the program roms are corrupt and can’t get into test mode, so it hangs and drops the signal. Are the other video signals still present in test mode? Does it play blind out of test mode (i.e. you have audio and controls)?

Does it sync to a crt? Even if it’s erratic that’s worth checking. Also I don’t know what test mode would do for you... if sync is present while the attract mode is running, why not just let that run while you troubleshoot?

 

[K0NAM1]

thanks @ekorz

I'm hearing a lot of activity on the RGB lines in test mode.