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Hey! Anyone had this issue with Megadrive model1? A friend has a composite cable which works ok with another MD, but this one, runs ok in full colour for a while, but when you heat the console a bit with playing for a few minutes, the colour vanishes and has black and white only. Anyone had this issue before? Any tips what might cause this?
Thanks!
It sounds like a damaged encoder. Replacing it should solve the issue.Quote:
Originally Posted by jpx72
Could also be a problem with the subcarrier frequency on the video encoder.
Video encoder is the CXA1145? Is not that expensive on eBay at all.
Sorry but can you explain how is that sub.frequency fixable? Do you also mean replacing the CXA chip?
I was thinking about voltage regulator. When it's dying, it supplies wrong voltage to the console and causing this effect. Is it plausible?
If one of the voltage regulators was dying, it would cause all kinds of havoc. It's most likely not broken.Quote:
Originally Posted by jpx72
The weakest kind of component in any piece of electronics is the electrolytic capacitors. There's a 100uF cap between the grounded pin 7 (the PAL/NTSC select pin) on the CXA1145 and Vcc. If this cap shorts when getting hot, the pin gets pulled high and the encoding becomes NTSC instead of PAL. There's also a 10uF cap between pin 14 (the reference voltage pin) and GND. If this cap shorts when heating up, the reference voltage gets pulled to GND and the encoder stops functioning.
My best bet would be that your MegaDrive needs a recap :)
Thank you for the awesome answer, that's really what I needed to hear. Ok I will try re-cap-ing the beast and let you know the result!Quote:
Originally Posted by KillerBean2
It took a while but I did a full replacement of all capacitors on board my Sega MD. I also exchanged both the 7805 voltage regulators, just to be sure.
BUT that didn't help. I think now it tooks longer than before recap (about 50 minutes), but after this while, the colours start to pulsate/flash and after a while the colour turns completely black and white again.
We are talking composite output. I tried something new - when I exchange my video cable to a RGB one (without turning the console off), the colour is fine! Putting composite cable back again, colour is gone...
I can upload a video if that helps.
Any of you guys has any idea what might be causing this? Or should I order new CXA1145? :daze:
(I know, I can use the RGB cable, but this is not a solution... I need working composite.)
Could also be as simple as a "dry" joint. They *could cause issues similar to this.
Exactly what I was about to suggest, resolder all the encoder pins and follow the trace to pin 6 and check for any dry joints.Quote:
Originally Posted by omp
Thanks for the suggestions. I tried to resolder the encoder but nothing happened. Traced pin 7 (PAL/NTSC select) but it ended under one of the big chips...
I made a video showing the console after 25mins of running. Room temperature was only 16°C (61°F). During the video, I disconnected the composite cable and insertend RGB cable. Camera is doing some serious flickering (it's a big old CRT TV), but you can still see the difference between the two outputs. After a while I reinserted the composite cable again:
http://youtu.be/zsl7Psm_wJs
I tried to re-heat a couple of joints that seemed dry/suspicious, but nothing helped. I tried three different adapters. Also tried two different composite cables and three CRT TVs. Anybody can help further? :fit:
If not the encoder chip, could the timing crystal be going bad?
I would replace the 1145 just to be sure.
To confirm it is the encoder failing after getting warm, try using a hair dryer, fashion a nozzle of sorts and try and warm up just the encoder (hair dryer won't get hot enough to melt solder). Once warm (but rest of console is cold) try it then.
Thank you all for your great tips and ideas, I have solved this issue today:
First I exchanged the last capacitor that haven't been exchanged and the only one that could have caused issues by changing temperature. It was the small tantalum one by the CXA1145. No luck. Then I resoldered all 68000 pins. Nothing.
I tried to heat up different components of this Sega MD's PCB using a hairdryer, and I found the only component that caused this behavior (loosing colour) was the crystal (xtal "CX0-046" 53.2034MHz). I did a small test, first heat it up until the colour was lost. Then placed an ice-cube on it, the colour returned! (I can make a video if you want to see it in action).
So this mystery is solved, thanks everyone for reading. :fail:
Anybody have a spare crystal or know where to find one? eBay found nothing...
Well done! You may be hard pressed finding that oscillator in the wild new. I remember asking a supplier (that is pretty much all he sells) about the genesis oscillator (as in same rating) & the cost was bloody huge as it would be "custom". I was going to get them to try for region modding as in leave the PAL oscillator in place and then add the new one for 60hz duties.
Actually reading this sparked my memory, had a game gear go bad and replacing the crystal (2 pin) worked.
If cooling the oscillator down brings the color back I wonder if putting a heatsink on it would keep you gaming in color.