Conservatively modding a JPN Model1 Megadrive (VA4)

[TheShadowRunner]

Hey all,
I would like to mod a Japanese model1 Megadrive VA4 by doing the least amount of changes to the system (and none to the shell).
Ie, I would like to re-use the Din8 output and also keep the front headphone jack in working order (even if signal to noise ratio is pretty bad on this one).

For Audio I found an official mod by Akinori Nishiyama (WORKS NISHI), that can be seen here:



On this page, a user does this mod by replacing:



- the "+5V" on Pin4 of the Din8 by the "Left audio" channel.
- the "Mono sound" on Pin1 of the Din8 by "Right audio" channel
Now my question is the following: I see many solutions for MD audio called "Mega Amp", a project by FirebrandX, etc..
Is this "official" method by WORKS NISHI flawed in any way? If not, why isn't it the prefered method for restoring Stereo on model 1s?
I'm mainly concerned about the sound volume level after doing this mod. If it's on par with the original Mono volume level on the Din8 it'll be fine enough for me.

----------------------------------------------------------------------------------------------------------------------------------

For Video of course my goal is clean RGB, for it to work on both my BVM and XRGB Mini, hopefully without jailbars.
First I got an official Euro Sega RGB cable (R.V.B adaptor model 3085) and applied the mod from this french page to make it compatible with my JPN MD (which in a nutshell involves replacing the SYNC signal by the CVBS signal on input).




Then I realised it was completely silly because I DO want to use CSYNC rather than CVBS, since it apparently removes (most of) the jailbars.
And so I stumbled upon a mystery: Pin7 of the Din8 is supposed to carry SYNC on Japanese MDs but apparently Sega screwed up and connected Pin7 to "CSync in" (pin10 of the CXA1145) instead of "Csync out" (pin11 of the CXA1145).
And by checking my VA4 it certainly seems true, pin11 seems connected to nothing..
However it seems that this isn't a real issue?
Would anyone know if on JPN VA4 the SYNC signal coming out from Din8 is usable at all?
As is, meaning with "Sync in" wired instead of "Sync out" on Din8 Pin7 because of Sega's mistake, does the Sync line also need a 220uF cap + 75ohm resistor to work properly?

Apparently also the Model 3085 mod from that french page isn't even necessary, as another user proposes to keep using the SYNC signal on input but to remove resitor R19 for proper SYNC on NTSC systems.
If so, I would just restore the SYNC trace that I cut on my modded Model 3085, remove the R19 resistor (and possibly add a 220uF cap + 75ohm resistor instead) and call it a day?
Thanks for any input, thoughts, etc.. ^^

[hellbelly]

From watching the weekly videos (weekly roundup and supporter q&a) on RetroRGB.com over the last few months, I believe that there is a decent RGB bypass for the MD, the model 1’s have had mixed success from it but I think that it is close to being resolved now.

That might be your best bet for video, I don’t know about using the official cable with the bypass mod though - I imagine someone will say get a new cable from Retro Gaming Cables or Retro Access depending your yours or their preferences/opinion.

I love the model 1 Japanese MD, great looks!

[TheShadowRunner]

From watching the weekly videos (weekly roundup and supporter q&a) on RetroRGB.com over the last few months, I believe that there is a decent RGB bypass for the MD, the model 1’s have had mixed success from it but I think that it is close to being resolved now.

That might be your best bet for video, I don’t know about using the official cable with the bypass mod though - I imagine someone will say get a new cable from Retro Gaming Cables or Retro Access depending your yours or their preferences/opinion.

I love the model 1 Japanese MD, great looks!

Thanks for your input, I'm not interested in a full RGB bypass, I think it's unnecessary when we have everything on board already (again I'm aiming for the less amount of modding necessary).
But I think you were the one who found out about the sync-in/sync-out oddity.
To go further on this subject, would you remember if Pin10 of the CXA (sync in) connected to Pin7 of the Din8 (the original but apparently flawed design by Sega) was totally unusable?
Retro Access seem to say that it was actually working for her...?
So I wonder if you actually tried to add the "220uF cap + 75ohm resistor" to it (unmodified pin7 of the Din8) before you resorted to using Pin11 (sync out) of the CXA?
And yeah JPN MD looks the best ;)

[nmalinoski]

I would like to mod a Japanese model1 Megadrive VA4 by doing the least amount of changes to the system (and none to the shell).
Ie, I would like to re-use the Din8 output and also keep the front headphone jack in working order (even if signal to noise ratio is pretty bad on this one).
...
On this page, a user does this mod by replacing:
...
- the "+5V" on Pin4 of the Din8 by the "Left audio" channel.
- the "Mono sound" on Pin1 of the Din8 by "Right audio" channel

If I'm following this correctly, this stereo "restoration" mod changes the pinout of the existing 8-pin DIN?

Why do that, which will require custom cabling and potentially interfere with normal operation with a standard Genesis 1 cable, when you could fit the console with the kind of 9-pin DIN from the Genesis 2/3/32X/Nomad? I'm not sure what'd be involved as far as wiring goes, but that would get you what you want overall--stereo, no shell modifications--and you'd be able to properly use standard, off-the-shelf Genesis-2-compliant cables, including the HD Retrovision YPbPr cables.

[hellbelly]

aha, apologies - didn't see the bit about least amount of modding necessary.

It was a long long time ago that I messed around with my MD, I don't remember 100% - I *think* I didn't try adding 220uF cap + 75ohm resistor to unmodified pin7 of the Din8

Hmm. Now I want a real japanese model 1 again!

[TheShadowRunner]

I would like to mod a Japanese model1 Megadrive VA4 by doing the least amount of changes to the system (and none to the shell).
Ie, I would like to re-use the Din8 output and also keep the front headphone jack in working order (even if signal to noise ratio is pretty bad on this one).
...
On this page, a user does this mod by replacing:
...
- the "+5V" on Pin4 of the Din8 by the "Left audio" channel.
- the "Mono sound" on Pin1 of the Din8 by "Right audio" channel

If I'm following this correctly, this stereo "restoration" mod changes the pinout of the existing 8-pin DIN?

Why do that, which will require custom cabling and potentially interfere with normal operation with a standard Genesis 1 cable, when you could fit the console with the kind of 9-pin DIN from the Genesis 2/3/32X/Nomad? I'm not sure what'd be involved as far as wiring goes, but that would get you what you want overall--stereo, no shell modifications--and you'd be able to properly use standard, off-the-shelf Genesis-2-compliant cables, including the HD Retrovision YPbPr cables.

Yes it does change the pinout, I plan to do the same as the japanese modder, sacrifice +5v I'll never be using.
It's also much easier to rewire 2 pins on the existing DIN8 than reinvent the wheel by switching to a DIN9 imho (which come to think of it might be just impossible to swap on a model 1).
For audio, I just would like confirmation that the "official" mod's volume level matches that of the original Mono output, or at least that it isn't too low.

[TheShadowRunner]

aha, apologies - didn't see the bit about least amount of modding necessary.

It was a long long time ago that I messed around with my MD, I don't remember 100% - I *think* I didn't try adding 220uF cap + 75ohm resistor to unmodified pin7 of the Din8

Hmm. Now I want a real japanese model 1 again!

Roger that. Hmm I wonder if anyone tried.. I think Fudoh also has a JPN M1 VA4 and used CSYNC as-is (Csync in / Pin 10) without modification.

[nmalinoski]

Yes it does change the pinout, I plan to do the same as the japanese modder, sacrifice +5v I'll never be using.
It's also much easier to rewire 2 pins on the existing DIN8 than reinvent the wheel by switching to a DIN9 imho (which come to think of it might be just impossible to swap on a model 1).
For audio, I just would like confirmation that the "official" mod's volume level matches that of the original Mono output, or at least that it isn't too low.

You might be able to get away without desoldering the 8-pin DIN, but you'll still need to snip those two pins to disconnect the old mono and 5V. (Or cut the traces, but that'd be worse.)

And no, I don't think you can directly swap the 9-pin DIN for the 8-pin. There is, of course, that 9th pin, which I mentioned would need to be snipped; and it's possible that the other pins won't line up or won't correspond to the same pins as on the Genesis 2/3/etc.

Should that be the case (the pinout not matching), you could very well mount the new socket upside-down--desolder old socket, solder wires for RGBS/CVBS/5V/ground on bottom of PCB, clean/flatten top surface, insulate the AV vias with with a layer of kapton tape, solder inverted 9-pin DIN to anchor points, solder AV wires to pins of new socket. Yeah, it's be more involved, but the result would be just as outwardly-clean, you wouldn't have to snip or cut anything, and, as I said, it would be more compatible with existing cables than modifying the pinout.

[TheShadowRunner]

Yes it does change the pinout, I plan to do the same as the japanese modder, sacrifice +5v I'll never be using.
It's also much easier to rewire 2 pins on the existing DIN8 than reinvent the wheel by switching to a DIN9 imho (which come to think of it might be just impossible to swap on a model 1).
For audio, I just would like confirmation that the "official" mod's volume level matches that of the original Mono output, or at least that it isn't too low.

You might be able to get away without desoldering the 8-pin DIN, but you'll still need to snip those two pins to disconnect the old mono and 5V. (Or cut the traces, but that'd be worse.)

And no, I don't think you can directly swap the 9-pin DIN for the 8-pin. There is, of course, that 9th pin, which I mentioned would need to be snipped; and it's possible that the other pins won't line up or won't correspond to the same pins as on the Genesis 2/3/etc.

Should that be the case (the pinout not matching), you could very well mount the new socket upside-down--desolder old socket, solder wires for RGBS/CVBS/5V/ground on bottom of PCB, clean/flatten top surface, insulate the AV vias with with a layer of kapton tape, solder inverted 9-pin DIN to anchor points, solder AV wires to pins of new socket. Yeah, it's be more involved, but the result would be just as outwardly-clean, you wouldn't have to snip or cut anything, and, as I said, it would be more compatible with existing cables than modifying the pinout.

Thanks for the extended procedure, I'll keep it in my mind should I go the DIN replacement way, although I'd like to avoid it if possible.
Now I hope MD audio gurus (FBX..) can chime in regarding the audio quality / volume level of this "official" mod before I proceed further.

[FBX]

Okay, so what you have going on here is the Japanese mod is simply a variant of the 'Straight tap' Stereo audio mod. And what this is is tapping pins 1 and 8 of the stock op-amp chip. Now in the Japanese diagram, they show the chip orientated with 1 and 8 on the south side. In reality (at least on the Genesis models I've seen), this chip is actually rotated 180 degrees such that pins 1 and 8 are on the north side. I notice the Japanese mod also includes series polarized 4.7uF caps on each line. These are likely just safety caps, and the typical 'straight tap' mod doesn't include these.

With all that said, My own approach would be to leave the 8-pin DIN alone and instead remove the RF Box. Then do the upside-down 9-pin DIN trick where you remove some solder mask on the board where the RF box used to be, and solder the 9-pin DIN upside down to it using the metal housing for grounding it to the motherboard. Then from there, get a 9-pin DIN breakout board from here:

https://oshpark.com/shared_projects/37rGIZ8P

And this gives you freedom to wire each line, whether you want to use stock, RGB bypass, straight-tap stereo audio, or crystal clear audio amp (M1 Mini Mega, Mega Amp, etc.).

It's a reversible mod that you could always put the RF box back in if you wanted to restore the console to a stock appearance. Furthermore, you get the benefit of not needing custom cabling. A simple 9-pin Genesis model 2 cable will work, such as those made by HD Retrovision for component video, or RGB SCART made by Retro-Access.

As for the quality of the straight tap mod, it's barely any better than the headphone output. If you want a real noticed difference in quality, you need to go the next level and bypass the pre-amp and op-amp with a Mega Amp style board. My own version of this is on my web site here with full installation instructions (instead of RCA jacks, you would just hook the lines into the breakout board on the 9-pin DIN):

http://www.firebrandx.com/m1minimegakit.html

[Link83]

Its my understanding that the French Sega SCART cable (Model 3085 "ADAPTEUR R.V.B.") is only intended to be used with French Master System 1/2 and Mega Drive 1 consoles. From what I read the French systems dont have buffered/amplified RGB signals available on the DIN8 port - internally the RGB signals connect directly to the VDP chip and they dont even have any video encoder chips on the motherboard (Sega continued this on all French DIN8 systems, and only changed when they switched to the DIN9 connector with the Mega Drive 2)

The components included in the Sega 3085's box to buffer/amplify the RGB signals on French consoles are definitely not the correct components specified in the video encoder datasheets used in Mega Drive 1's from outside of France, which typically have the DIN8 ports connected to the video encoders RGB output. However what effect this RGB 'double buffering' will have on the video quality (When using the French 3085 SCART cable on a Japanese Mega Drive) I cant say...

[ApolloBoy]

With all that said, My own approach would be to leave the 8-pin DIN alone and instead remove the RF Box.

The Japanese Mega Drive doesn't have an internal RF modulator.

[TheShadowRunner]

With all that said, My own approach would be to leave the 8-pin DIN alone and instead remove the RF Box.

The Japanese Mega Drive doesn't have an internal RF modulator.

Yes it doesn't! Besides my approach is to leave the shell intact, I don't care about (heavily) modifying the Model 3085 "ADAPTEUR R.V.B." though.

As for the quality of the straight tap mod, it's barely any better than the headphone output. If you want a real noticed difference in quality, you need to go the next level and bypass the pre-amp and op-amp with a Mega Amp style board. My own version of this is on my web site here with full installation instructions (instead of RCA jacks, you would just hook the lines into the breakout board on the 9-pin DIN):

http://www.firebrandx.com/m1minimegakit.html

Hmm barely any better, Ok, but in terms of volume level, would you say it's comparable to the original Mono output?
Then there's this mod (thanks Fudoh / Konsolkongen):



which seems to recreate for the Right channel the same op amp used for the original Mono signal.
Of course it's not on par with the quality delivered by your Mega Amp board, but it seems satisfactory enough... I wonder.

[TheShadowRunner]

Its my understanding that the French Sega SCART cable (Model 3085 "ADAPTEUR R.V.B.") is only intended to be used with French Master System 1/2 and Mega Drive 1 consoles. From what I read the French systems dont have buffered/amplified RGB signals available on the DIN8 port - internally the RGB signals connect directly to the VDP chip and they dont even have any video encoder chips on the motherboard (Sega continued this on all French DIN8 systems, and only changed when they switched to the DIN9 connector with the Mega Drive 2)

The components included in the Sega 3085's box to buffer/amplify the RGB signals on French consoles are definitely not the correct components specified in the video encoder datasheets used in Mega Drive 1's from outside of France, which typically have the DIN8 ports connected to the video encoders RGB output. However what effect this RGB 'double buffering' will have on the video quality (When using the French 3085 SCART cable on a Japanese Mega Drive) I cant say...

Hmm the Model 3085 adaptor is working just fine with my JPN MD, I just modded it the way Segakore instructed by changing the sync signal source from CSYNC to CVBS (which turns out to be silly in terms of video quality, with the jailbars), but this 'double buffering' doesn't seem to bring ill effects.
However, thanks for the info, I will have to remove the components in the Model 3085 to bring it to specs for the JPN MD.
Here's the diagram of what the 3085 does:

Spoiler

The reason for doing the Segakore mod is because what the Model 3085 does for CSYNC only works on the french RGB MD, and not on JPN MD.
But there seem to be a better way : simply removing the R19 resistor.

[Link83]

Hmm the Model 3085 adaptor is working just fine with my JPN MD, I just modded it the way Segakore instructed by changing the sync signal source from CSYNC to CVBS (which turns out to be silly in terms of video quality, with the jailbars), but this 'double buffering' doesn't seem to bring ill effects.
However, thanks for the info, I will have to remove the components in the Model 3085 to bring it to specs for the JPN MD.
Here's the diagram of what the 3085 does:

Spoiler

The reason for doing the Segakore mod is because what the Model 3085 does for CSYNC only works on the french RGB MD, and not on JPN MD.
But there seem to be a better way : simply removing the R19 resistor.

If you are considering altering the 3085 that much, then you may want to consider purchasing a higher quality ready made MD1 SCART cable from Retro Access or RGC instead. The 3085 can still be very useful for the Sega Mark III, which needs the RGB output to be amplified/buffered, or if you are already happy with the picture quality just keep it as it is. It just seems a shame to modify the 3085 into a cable which can still be readily purchased, but obviously the choice is yours.

[TheShadowRunner]

If you are considering altering the 3085 that much, then you may want to purchase a higher quality ready made MD1 SCART cable from Retro Access or RGC.

The 3085 can still be very useful for the Sega Mark III, which needs the RGB output to be amplified/buffered. It just seems a shame to change it into a cable which can still be readily purchased.

Well you're right but I have this one on hand already and getting a higher quality cable would still require me to mod it (as I will mod the DIN8 for Stereo), not to mention the cost.
While I don't mind altering the 3085, I will do it conservatively too ^^
Were you able to make sense of the 3085 diagram? Isn't it strange that it's meant for both the Euro MD and Euro Mark III if they don't output the same signals at their DIN8?

[Link83]

Well you're right but I have this one on hand already and getting a higher quality cable would still require me to mod it (as I will mod the DIN8 for Stereo), not to mention the cost.
While I don't mind altering the 3085, I will do it conservatively too ^^
Were you able to make sense of the 3085 diagram? Isn't it strange that it's meant for both the Euro MD and Euro Mark III if they don't output the same signals at their DIN8?

I believe Retro Access offer custom cables on request, so you could request one with a modified pinout? Also you mentioned wanting to keep the front headphone jack in working order, so I wondered if you had considered using a 3.5mm headphone jack splitter?

The Model 3085 is only intended to be used with French Master System 1/2 and Mega Drive 1 systems, not European PAL Sega systems which are different. The French systems were country specific and only designed to be used and sold in France due to SECAM. There is no Euro Sega Mark III as it was only released in Asian regions, it just happens to also be compatible with the 3085 due to having a similar internal setup.

I assume Sega's thought process was that since none of the video encoder chips used in the Master System supported SECAM there was no point in including them inside French systems. Its hard to say why exactly they decided to buffer/amplify the RGB signals externally though, instead of internally on the system motherboard.

In my opinion it would have made much more sense for Sega to continue using video encoder chips on the French systems (Even though they didnt support SECAM) If only to buffer the RGB signals. However Sega's designers obviously felt otherwise, and once the design decision was taken with the first French Master System they had to continue it with the French Master System 2 and Mega Drive 1 to maintain compatibility with the Model 3085 cable, since all three systems use the same DIN8 port.

Please note that i'm not an expert in these matters, I dont live in France and all this info is just what I have picked up from forums posts over the years. If anyone else has further information to add I would love to hear it

[TheShadowRunner]

I believe Retro Access offer custom cables on request, so you could request one with a modified pinout? Also you mentioned wanting to keep the front headphone jack in working order, so I wondered if you had considered using a 3.5mm headphone jack splitter?

For the cable I'll stick with the 3085, saving 40 bucks and time in the process ^^;
I don't think I'll be modifying it too much.
For video: just restore CSYNC as sync source, remove resistor 19 that's doing troubles and fit the 75ohm resistor + 220uF cap in series in there (or is it better to fit them inside the console before the Din8? It shouldn't make any difference, right?)
For audio: switch either the +5v pin or CVBS pin to Right audio channel.
Regarding the headphone jack, the sound it outputs is pretty bad (noisy), and having a cable constantly connected isn't esthetically pleasing either ^^;
I just wish to keep it working for integrity's sake.

The Model 3085 is only intended to be used with French Master System 1/2 and Mega Drive 1 systems, not European PAL Sega systems which are different. The French systems were country specific and only designed to be used and sold in France due to SECAM. There is no Euro Sega Mark III as it was only released in Asian regions, it just happens to also be compatible with the 3085 due to having a similar internal setup.

Oh, got you for the Mark III. I really don't get how Secam makes any difference whatsoever when it comes to RGB, I mean Sync is Sync, there's no such thing as Secam sync..?
I grasp it has a direct impact on CVBS, but this signal isn't even wired on French RGB MD, so what the heck?

In my opinion it would have made much more sense for Sega to continue using video encoder chips on the French systems (Even though they didnt support SECAM) If only to buffer the RGB signals. However Sega's designers obviously felt otherwise, and once the design decision was taken with the first Master System they had to continue it with the Master System 2 and Mega Drive 1 to mainitain compatbility with the Model 3085 cable, since all three systems use the DIN8 port.

Hmm wait, doesn't the french MD1 contain an internal video encoder? (CXA1145 like in the other regions?)

[Link83]

Oh, got you for the Mark III. I really don't get how Secam makes any difference whatsoever when it comes to RGB, I mean Sync is Sync, there's no such thing as Secam sync..?
I grasp it has a direct impact on CVBS, but this signal isn't even wired on French RGB MD, so what the heck?

...and thats exactly why Sega's designers likely decided not to include a video encoder in French systems, because RGB is RGB, and since most SECAM TV's didn't support PAL signals why bother to include a video encoder chip for an incompatible standard (PAL) thats not supported by French TV's? Might as well just connect the VDP RGB signals directly to the DIN8 port...

Hmm wait, doesn't the french MD1 contain an internal video encoder? (CXA1145 like in the other regions?)

As far as I have been able to tell from googling the French MD1 (Model 1600-09) doesn't have composite video output, so it would seem likely there isn't any video encoder.

[TheShadowRunner]

As far as I have been able to tell from googling the French MD1 (Model 1600-09) doesn't have composite video output, so it would seem likely there isn't any video encoder.

Hmm while CVBS isn't connected (or even generated?) it seems they do have the video encoder:
https://youtu.be/x64pXFihiK4 @5min40s

[TheShadowRunner]

Ok so while the audio mod components are on their way, I checked the video (CSYNC) mod again.
And there's a mismatch as to how it should be modified before reaching the display.

For most, to bring the Megadrive CSYNC signal to an appropriate level, 2 things are needed:
- a 220 uF cap (up to a 470uF cap)
- a 75 ohm resistor

This has been confirmed to me by many users here + official CXA 1145 datasheet, japanese modders and more.

--

Yet retrorgb is adamant that MD CSYNC requires:
- a 220 uF capacitor
- a 470 ohm resistor

And others seem to agree.

So which is it for the resistor, 75 ohm or 470 ohm...?

(I'm not sure if it makes any difference but this is for a JPN VA4)

[Fudoh]

220uF + 75 ohm is to bring CSYNC up the specs (TTL) and make it work at all.

The higher resistor includes the attenuation needed to use CSYNC as a composite video replacement in Scart RGB environments.

[MKL]

For most, to bring the Megadrive CSYNC signal to an appropriate level, 2 things are needed:
- a 220 uF cap (up to a 470uF cap)
- a 75 ohm resistor

This has been confirmed to me by many users here + official CXA 1145 datasheet,

The CXA1145 on the Mega Drive doesn't output CSYNC. If it did, then you would need 75 ohm + 220uF but it doesn't...

[TheShadowRunner]

220uF + 75 ohm is to bring CSYNC up the specs (TTL) and make it work at all.

The higher resistor includes the attenuation needed to use CSYNC as a composite video replacement in Scart RGB environments.

Alright, that explains it, So with the targets being a BVM and a XRGB Mini, I could get away with only a 75 ohm resistor for the BVM (since it takes TTL directly) but that wouldn't be enough for the Mini, if I get it right?

The CXA1145 on the Mega Drive doesn't output CSYNC. If it did, then you would need 75 ohm + 220uF but it doesn't...

Hmm but it sure does..

[Fudoh]

Alright, that explains it, So with the targets being a BVM and a XRGB Mini, I could get away with only a 75 ohm resistor for the BVM (since it takes TTL directly) but that wouldn't be enough for the Mini, if I get it right?

as long as you don't have any monitor or switch that requires TTL, don't use it. Go with the higher resistor, since it will work fine on both the BVM and the FM.

[TheShadowRunner]

as long as you don't have any monitor or switch that requires TTL, don't use it. Go with the higher resistor, since it will work fine on both the BVM and the FM.

Great, thank you!
As for the R/G/B lines, should I use 220uF + 75 ohm as instructed almost everywhere, or only 47 ohm resistors?
So many sources with different data..

[Fudoh]

the difference in brightness would be minimal. I've always been using 75 ohms as far as I can remember.

[TheShadowRunner]

the difference in brightness would be minimal. I've always been using 75 ohms as far as I can remember.

Thank you again, time to order more parts

[TheShadowRunner]

An update:
The component I'm missing (470 ohm resistor) for the video mod is on the way.
I also received everything for the audio mod and dove in..
Again this is what I aim to replicate:


I decided to do the mod on the bottom of the board, piggybacking the new LM358N "under" the original one.

Spoiler

What I did was:
- remove resistor R43 to prevent audio mixing
- solder a wire with a 10k ohm resistor (to replicate R43) going to the op amp (which is exactly similar to the stock one, LM358N by Signetics).
- soldered a 33k resistor between pin 1 and 2 of the op amp
- soldered a 10 uF cap on the exit pin (pin1) of the op amp (positive side towards the audio-out)
- tested continuity / shorts, all good
- finally tested!
It does work, but the sound is too loud, clipping and a bit crackling versus the other channel :(

To troubleshoot the issue, I went to hunt for the volume levels at different places in the audio "stage".
Also I used this for reference:

Spoiler

I hooked my headphone jack to ground and the other wire to different points, here are the results:
---
- Pin 1 (L channel) of CXA1034: volume very low
- Pin 8 (R channel) of CXA1034: volume very low
(both expected results, ok)
---
- Pin 2 of original LM358 (was mono, now L channel): volume marginally higher, still very low
- Pin 2 of mod LM358 (R channel), same as above.
(expected too, mod 10k resistor acts the same way as R42 does for the other channel, so far so good).
---
- to mod 10uF cap (positive side as per schematic, red wire on the image above): bad clipping sound, volume too high, the problem.
- to Pin 8 (audio-in) of the CXA1145 (= C30 positive side), same behavior, volume too high, clipping!
So the original left channel at this point is the same as my modded Right. Unexpected but it shows that up to this point the recreation of R channel is faithful.
---
Then the official way goes from Pin9 (audio out) of the CXA1145 to positive side of C31 (also a 10uF cap) and finally C31 negative side is connected to Din8.
And here it becomes the twilight zone...
- to Pin 9 (audio out) of CXA1145, blue wire on the image above (= C31 positive side): I get no audio / signal, test point is silent, wtf..!?
- to C31 negative side (= Din8 audio pin): I get perfect line-out L channel volume, great sound quality!

So the CXA1145 is clearly doing some magic here, the fact I'm getting no audio signal out of its pin9 (audio out) is extremely strange too!
From the specsheet it says it's "buffer" and then there's another cap C31, that's generating good sound back somehow.

How are modders who used this method (Konsolkongen, Fudoh) not getting (way) above line-out volume and clipping sound out of the piggybacked LM358 when even the original design [before going to CXA1145] exhibits this behavior?
I'm at a loss here.. o_O

[sl1pkn07]

hello

i have done the official mod (the "WORKS NISHI" mod). works like a charm in my VA0 MD JAP. using COMP pin for L audio and MONO pin to R audio. i have modified the DIN8 connector without dissasemble, only unweld the pins 3 and 6, and blend it from interior. then use a stereo cable and weld the wires directly the bend pins. GND welded into the hidden welded holes in the edge of the connector





my problem now is the video. i have two types of output i whant to use right now

1) the 3085 cable
2) the Sega 32X

for the 3085 cable, if disconnect the R19, and route cables/pins for use CSYNC line with the sync circuit in the 3085, without any other video change (have R1 disconnected for stop generating 12v and remap the COMP pin to L audio) i get video. but little missplaced to right). still needed the 75ohm+220uf (10v?) cap in the sync/csync circuit? also, if follow the 3085 schemes. show the R, G, B pines not have any 220uf caps, but only 95ohm (27+68ohm) ressistances (with other components) i need remplace those with 75ohm+220uf caps?

for the 32x just use the original 32x jap patch cables. the din8 to din9 can be dissasembled (the din9 side), so just remaps the pins for use COMP (pin4 in din9) and Mono (pin6 in din9) as R and L respectively. the patch cable din9 to din9 leaves intact.




and also use the European MD2 RGB cable (MK-1637-09), because the same cable JAP. the din9 is not possible remaped because the pin is fixed in the connector. the european ones i can dissasemble (after 2 fffff hours), because the connector have no-populated pins as free holes. so is can "easy" swapped. so. move from pin 5 (comp) to pin 4 (csync)





the Jap unit


so. i need put an 75ohm+220uf cap in the MD2 cable. right?

greetings