Sega Genesis MK1 Sound issue

Hello Assemblergames.

I'm in the UK and have just acquired a Genesis MK1. The sound output is very quiet compared to my PAL Mega Drive units. There also seems to be some static and interfence but this could just be due to me cranking the volume up. The earphone port also has a strange issue; the volume slider does not make it louder or quieter but instead removes the treble and makes it more muffled. Motherboard looks good. Does anyone have any ideas?

 

That is some very weird behaviour from the volume slider. I would try to look into that first thing. Its quite possibly deffective and might partially ground your audio lines.
More testing is needed but i would focus on the slider. You may have to unsolder it to properly troubleshoot the issue.

 

Is it a VA7 board? That's got a terrible sound circuit. [*EDIT* just saw the pic - surprise, surprise! ]

It is a case of fault-finding in the audio circuit. What kind of video / audio lead are you using, by the way? Is there any difference in sound quality through the headphone socket or the television?

Sometimes, the audio caps do go, so it might be worth checking them.

 

Hey,
What makes the VA7 so bad, and how can I avoid it in future? I have tried it over RGB Scart and composite, both from the multi out. The RF port is cream crackered so I can't rule the multi-out out (heh). When I noticed it was very quiet I just shrugged and thought oh well, I'll use the earphone port with some speakers- hence me discovering the slider issue!

Which caps are the audio caps? All looked intact to me?

 

Recorded a video so you can see the earphone output (well, hear it)
http://youtu.be/LrMUYgD-YU4

 

Caps can be bad and dried even though they look fine from the exterior.
The Va7 has crappy sound, just like most model 2. Compared to earlier model 1 it is distorted and muffled out due to poor amplification design on the circuit.

But that does not explain the symptoms you have.
Could definitely be worth it to change the caps, dont bother changing only a few. Just do a full motherboard recap.
They sell cap kits on http://console5.com/store/

As i said earlier, I would still start by inspecting if the volume slider is not broken. But somehow.. just listened to the clip, man thats weird o_o

 

They redesigned the audio circuitry - IIRC, there were Yamaha chips that were modified into an ASIC. The circuit sucked and you always get background hiss. Avoid it by not buying a VA7

It's possible doing a mod such as the crystal clear audio mod or similar might help. I haven't done it myself, so I can't say what it does/doesn't bypass.

The audio caps, at least on earlier boards, were around the headphone socket - and near the Yamaha chip. They should be in that corner / around the Sega ASIC. You won't always see leaky caps, especially when they're still in-circuit. You'd probably need to remove and test them... by which time, you might as well have replaced them!

Sounds like the unit is a bit of a duffer all over, eh? If the socket turns out to be faulty, I guess you could do a video mod, too. I think that's the first (and probably last) time I won't say it's a complete waste of time! lol

 

I think I'll send it back to the seller. Bit gutted as I'm obviously going to be out of pocket for postage, and he lives abroad! My soldering skills are adequate at best, and I'm not confident that I'd manage to fix it- I'd just knacker it.

Is it possible to identify the VA7 from a model number on the unit? My original Mega Drive back when young was a MD2 so I'm not too fussed over sound quality.. but it won't hurt to keep any eye out.

How certain is it that a cap is at fault?

 

You could always get someone in the UK to take a look at it - I'd be happy to, I'm sure Bad_Ad would, too. It needs proper fault-finding, not guessing. It could be a capacitor, it could be something else.

The VA7 is US only. They don't have HIGH DEFINITION GRAPHICS printed on them (unlike older variants), IIRC.

 

I understand, how much would you charge for your time/possible fixing? I think it will probably just be easier to refund and find a replacement, though