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MD Sega Mega Drive VA4 severe issues (audio, freezing)

R0y

New member
Original poster
Jul 30, 2019
1
0
1
Hello guys!

Months ago I bought two MD1s sold as untested. Both of them are VA4 PAL boards, manufactured in 1991, and 1992. The '91 one had buzzy audio, I replaced the caps, easy win. However, the other one...it's behaving exactly like this guy's console:



Tested with a bunch of games:

- Sonic 1 has the same fuzzy, distorted SEEEGAAA voice, everything else works like a charm
- Sonic 2 has no audio at all, sometimes just the beep, like in the video, game works flawlessly otherwise
- Altered Beast cannot boot past the Sega logo screen
- Hyperstone Heist behaves like Sonic 3 in the video; fuzzy, ear-raping buzzing, hissing, bitcrushed sound, seems to work fine beyond that
- Streets of Rage 2 has the same bitcrushed, insanely hurtful buzzing if I play anything from the VOICE test in the menu
- Mega Games 2 Streets of Rage 1 = Streets of Rage 2
- Mega Games 2 Revenge of the Shinobi exhibited the same sample distortion, and then froze 8-10 minutes in, only the (I guess) background layer was visible

I don't really have more PAL games for testing, only the US Bloodlines + JAP Bare Knuckle 3 and I didn't install a region switch (now that I think i'm out of switches..). Maybe I have a JAP Gunstar Heroes that can boot in PAL, dunno. Somebody attempted a repair (untested, yeah) before, I found Chong caps around the headphone amp area. Anyway, the board has no visible damage, I checked it thoroughly, no corroded vias, traces, I even checked for them under the ICs I replaced. I suspected the fault is somewhere around the audio section, but after I replaced multiple chips, I'm clueless, the issues still stand.


What I exactly did to the VA4:


- Cleaned cart slot with isopropyl
- Replaced the two 7805s
- Reflowed the cart slot
- Reflowed the 68k
- All electrolytic caps replaced
- Z80 replaced
- YM2612 replaced
- Sony CXA1034 replaced
- Z80 SRAM replaced

I have a physically broken JAP VA6, all the chips are harvested from that board. Since I'm not that electro-knowledgeable, shotgunning was my best approach. Yesterday I removed the VDP (thinking that the PSG chip is integrated into the VDP, and maybe it's the root of the cause) from the VA6 with hot air, but I figured I'll stop and ask more experienced repair gurus. All the through-hole stuff were removed with a desoldering pump, and at this point, I'll kill myself is the 68k is toast lol...

Thanks for the help,
R0y
 

Capt. 2110

Member
Jul 31, 2019
11
0
1
I'm not 100% positive, but I feel like this might be caused by a 74XX series logic chip being faulty. If you have a logic probe I'd poke around a bit and see if you can find anything off (pins stuck high or low on logic chips) or if you have a multi-meter I'd check the voltages around the board. Even with new regulators other parts can pull the voltage down. I don't think it's the 68000, but if it ends up being that, and it's the (68-pin?) DIP version, I'll give you one I have lying around somewhere.
 

bart_simpson

Well-known member
Registered
Aug 10, 2019
54
8
8
I was going to say where are you based as i would love to have a crack at fixing these :)