The needs of the one, outway the needs of the many...

Myrddin

Some of you have probably seen the Megadrive overclocking mod I did for o1s1n some time ago, see here. Well it seems after some weeks of use the MD has developed a fault with its sound processing.

O1s1n described the sound output as having gone distinctly 8-bit, or chiptunes like. After a fair bit of trawling, a lot of people have suggested that the capacitors used by Sega at the time were not of the highest quality, and by now a lot of the caps have dried up/failed, thus causing sound/gfx glitches. It has also been reported, although rarer, that the sound amp in the MD has failed causing the above affects.

So I met up with o1s1n yesterday and brought the sick MD home, along with a donor MD that Monkeyfudge had given him. The donor MD was a newer variant, & not the non-tmss "High Definition Graphics" model that the o/c mod was done on. I stripped down both units, & inspected for obvious signs of the fault. Not seeing any, I decided I'd swap the audio circuit caps over from the donor and see what happened.

The audio amp in the overclocked Megadrive:



Another audio amp, although after research I learned this is the headphone socket amp. I therefore disregarded this:



The o/c'd MD with its audio circuit caps removed:



Donor caps fitted to the overclocked MD:



After fitting the donor caps, the problem persisted. 8-bit sounds was all that was being output, so it had to be the amp. Very unlikely for an IC to fail like this, and after doing some research, it seems the MD's CPU (Z80) has direct access to the Yamaha sound processor, so it could be a case of changine clock speeds/power variations are putting undue stress on certain components. I went ahead anyway & pulled the amp from the already fatally wounded donor unit.

In war, there are always casualties:



The donor amp now installed:



Immediately the sound was back to normal again after changing the amp. It's a bizarre one, but the only conclusion I can make is that there are SO many variations of Megadrive motherboards, & certain ones take to overclocking better than others. For o1s1n, I would suggest you use this Megadrive only to play the games where overclocking is beneficial, & use a standard unit for games that arn't affected by slowdown issues. This was at least you will save wear & tear on the amp. Although it COULD have been just a faulty amp and now this won't suffer the same fate - who knows

o1s1n

Wtf, I only dropped that out to you yesterday you lunatic!

Interesting development regarding the Z80 being linked to that amp. To be honest I was going farely ape **** using the overclock due to the novelty. So it would make sense that it resulted in the audio amp failing if they're linked.

Fingers crossed it wasn't that though and the amp just failed due to something else.

Thanks anyway man, I'd be lost without you and thanks again Monkeyfudge for the Megadrive. You brought my overclocked one back to life. I'll give it an honourable burial. (viking maybe?)

Myrddin

o1s1n wrote: »

Wtf, I only dropped that out to you yesterday you lunatic!

Interesting development regarding the Z80 being linked to that amp. To be honest I was going farely ape **** using the overclock due to the novelty. So it would make sense that it resulted in the audio amp failing if they're linked.

Fingers crossed it wasn't that though and the amp just failed due to something else.

Thanks anyway man, I'd be lost without you and thanks again Monkeyfudge for the Megadrive. You brought my overclocked one back to life. I'll give it an honourable burial. (viking maybe?)

Not a problem

If you wanted to hone your soldering skills, I've left the original cpas in a zip lock bag alongside the old amp - you could use the mobo to practice soldering the caps back into place. Then scour the web for a Yamaha YM2612 IC, solder it in & you have a working MD again. Alternatively do something nuts with the case & swap the innards of a working MD into it. Or indeed bury it, with a 3-button joypad & an RF cable

o1s1n

Great idea! I'll see if I can get the board working again. Soldering caps on it something I need to be able to do.

Tempted to make a Megadrive toaster with the case. Although I doubt it could stand the heat!

TouchingVirus

Don't let it die just because it's missing a few caps & an obsolete IC

Make it live again o1s1n *sniff*

Retr0gamer

'Wise from your Gwave!'