Need help with a Megadrive

[frootloop]

Hi all, hope someone can point me in the right direction!

I recently acquired a Megadrive, cosmetically in decent condition. The PSU it came with was for a ZX Spectrum however with the Megadrive power connecter hacked on and taped, rather than the original Megadrive one. I don't have the PSU to hand as I'm writing so I'm not sure to its rated outputs. Also not sure what the power requirements of the Megadrive is.

I hooked the console up via RF to my 3 year old model LCD TV. I plugged in a cart (Road Rash 2) and powered the system up. The power led lights up on the console. I did a channel search on the TV to try and 'tune into' the Megadrive. No luck, didnt pick up anything.

I then put together a cable to tap into the megadrive's composite and audio outputs and hooked that up to the TV. Powered up the Megadrive. Once again the power LED lights on the Megadrive, but no picture / sound on the TV.

Could someone perhaps help me out with how I should approach diagnosing the problem? Your help is much appreciated!

[SubaruBrat]

The US variants used either channel 2 or 3, do you run NTSC, PAL, SECAM? I am sorry but I am not familiar with the standard in SA. Assuming your Sega and TV are the same standard if you manually set the TV to either of the two options you should get a picture. Another suggestion would be to skip the whole RF thing and get a AV cable and go straight into the component video. If the LED is lit that is a decent sign that the unit is working with the power supply but not absolute. My Genesis adapter says 1.2amps @ 10v. What is the rating of the ZX spectrum adapter?

[frootloop]

Hi there,

SA is a PAL country. The Megadrive is a PAL unit and the TV is multi-standard (accepts PAL / NTSC / SECAM). Thanks for the power input details. I'll get the appropriate figures for the ZX Spectrum PSU tonight and post here.

I've tried going composite, I just built a DIN - RCA cable for the composite / mono audio out pins from the Megadrive. I still get no image, but I may have wired the cable incorrectly. I'll double check tonight, or try and pull a signal directly from the video chip traces rather than the DIN port.

Thanks again!

[frootloop]

Had a look at the PSU last night. It looks like the ZX Spectrum power adaptor is rated at 9V 1.4A. Could this be why I'm getting no picture?
I have cheap adjustable wallwart PSU lying about, will try it tonight. I'm not sure if it can supply 1.4A @ 9V though. If not I'll have to buy a new PSU...I'd prefer not to invest in one if its not necessary. Is that my only option in diagnosing the Megadrive?

[frootloop]

Hmm...been doing some research. It looks like there were models that had different power requirements
http://www.retro-games.co.uk/sega/md/megadrive.htm
I'll have to check my Megadrive tonight to see if it needs 1.2A @ 10V or 850ma @ 9V. Hopefully my Megadrive is giving no picture as its a 10V model not getting enough voltage.

[frootloop]

...and I'm confused again.
http://www.assemblergames.com/forums/showthread.php?t=26134

According to the above link, it shouldnt matter whether the PSU is a 9V or 10V, as thats within the tolerance values. Can anyone a bit more clued up tell me if this is true? If that is right, then I'm back to square one - why no picture on my Megadrive.

Would it make sense to start by testing the PSU Voltage / Amperage with a multi-metre? Will it matter that the PSU is not under load while I'm testing?

Apologies for the arb questions - my knowledge of electronics is just enough to get me into trouble :)

[SubaruBrat]

Testing it under load would give more accurate readings. Can you post a pic of the label on your genesis, that should help in tracking down exactly what you have and what you need.

[frootloop]

I took the pic of the back, and apparently I'm a retard ;)
https://picasaweb.google.com/lh/photo/wTAzX9p_P47flPFsNi3TBw?feat=directlink
https://picasaweb.google.com/lh/photo/wTAzX9p_P47flPFsNi3TBw?feat=directlink


The Megadrive is a 1.2A @ 10V model. I tried with a 1A @ 12V psu last night (according to my research up to 15V should be safe, but the console will run much hotter). Still no luck, nothing on the screen. I double checked the AV cable I built for MD, the cable is fine, so I can confirm no image via RF or composite. I'm beginning to think the dude I bought it from sold me a dud.

[SubaruBrat]

A 1amp power supply might not be able to support that and if it does it would run hot. Obviously you need to get a 1.2amp or greater capacity psu. Amperage is dictated by the load, the current rating on the psu is its capacity and a higher capacity is fine. You could use a car battery capable of 500amps @ 12v and that would be fine. So if you find anything 1.2 amp or greater you can use it. If the Genesis does not boot then you likely have a dead one and it is time to find another.