Audio problem with MegaFlashRom SCC+ and a Sanyo Wavy-70FD

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By rjp

Master (193)

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14-07-2015, 03:48

BTW, I got some audio problems with my Sanyo Wavy 23, the SCC sound was really low, compared to PSG. We soldered a trimpot, in order to raise up the sound. Now it sounds perfectly. Big smile

But I tried a FM cartdrige too, and the problem remains, it's too low compared to the PSG (and now, the SCC) sound.

I think it's a Sanyo's problem. Sad

By Gustau Pérez-Querol

Resident (61)

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14-07-2015, 20:32

That's interesting. Could you provide us more info about that? Where did you solde the trimpot, any schematics, etc?

By sd_snatcher

Prophet (3454)

sd_snatcher's picture

25-07-2015, 00:08

I just bought a Sanyo PHC-70FD myself and tested its sound. The result was exactly the same as the other Sanyo models: too low sound volume for all external sound cartridges: SCC, SCC+, MegaFlashROM SCC+ and even the Toshiba Music Module.

According to this site, this Sanyo machine indeed has some weird issues related to the SCC sound. Maybe your machine was modded by the previous owner to solve the SCC issue, but the mod isn't good enough for the MegaFlashROM SCC+ (and maybe other sound cartridges).

Try to test your machine with an MSX-Audio cartridge, for example.

By syn

Prophet (2061)

syn's picture

25-07-2015, 00:37

Hmm odd. I dont own a konami scc game at this time to test, but I borrowed nemesis 2 a lot from my friend like 20+ years ago. I don't recall noticing the SCC was too soft. It could have been softer than on my sony, not sure, but it surely was not up to a point that it becomes problematic.

I did test it with philips music module and its very soft indeed but I just brushed it off as the music module being too soft in general (afaik this is a known fact).

I also noticed the PSG drums in Moonblaster sounded very loud compared to internal OPLL.

I am the first owner of my sanyo phc-70FD2. Unless the MSX Centrum in Amsterdam sold it to me with some modification to the sound part,which is very unlikely without me knowing.

By Daemos

Paragon (1951)

Daemos's picture

25-07-2015, 14:35

anyone who likes to do a serious fix on this problem. Try the following: Use a multimeter and see how much resistance there is between the audio pin of the cartridge port and the PSG output of the MSX. If you meassure resistance, most propably some "engineer" combined the audio parts together the very wrong way.

Adding trimpots and resistors is only a half fix and will result in crosstalk and crossover distortion which is not really pleasant to ones ears.

If no schematics are available on the internet one can only figure out what is going on by figuring out the audio stage with a multimeter and scope wire by wire and draw a schematic.

By Gustau Pérez-Querol

Resident (61)

Gustau Pérez-Querol's picture

25-07-2015, 16:55

Daemos wrote:

anyone who likes to do a serious fix on this problem. Try the following: Use a multimeter and see how much resistance there is between the audio pin of the cartridge port and the PSG output of the MSX. If you meassure resistance, most propably some "engineer" combined the audio parts together the very wrong way.
.

Hi @Daemos,

I've searching the schematics with no luck, even in p2p networks. I'll keep searching.

I can do that test (I have a multimeter here around). I have two questions:

  1. About the cartridge audio port, do I take the measure directly from the slot port or do I need to have the MFRSCC+ in the bay (and thus I'd need to wire the pin in the cartridge to take the value).
  2. About the PSG output, is the DIN-8 audio pin?

By Daemos

Paragon (1951)

Daemos's picture

26-07-2015, 00:20

Quote:

About the cartridge audio port, do I take the measure directly from the slot port or do I need to have the MFRSCC+ in the bay (and thus I'd need to wire the pin in the cartridge to take the value).
About the PSG output, is the DIN-8 audio pin?

You will have to meassure from the PSG pin directly of the PSG output. In case there is a MSX engine you will have to meassure from there. No cartridge needs to be inserted and the machine can be left powered off.

If you find a resistance value the culprit is found. If not there is a change the PSG output is buffered with a transistor before the signal is mixed down the wrong way. Then you need to find the transistor and work from there.

By sd_snatcher

Prophet (3454)

sd_snatcher's picture

16-12-2015, 13:05

Daemos wrote:

Schematics. Just get me schematics of that machine and I can figure it out. Photo's are not enough.

Here it is, Daemos! Sorry it took so long. Smile

Belavenuto kindly took the time to reverse engineer the audio circuit of the PHC-70FD and draw the schematics.

I hope it helps to solve this problem.

By Daemos

Paragon (1951)

Daemos's picture

16-12-2015, 13:26

Ill have a look at it. Give me a few days Smile

By Daemos

Paragon (1951)

Daemos's picture

16-12-2015, 13:31

I allready see the problem. Instead of using a summing amplifier the signal is passively mixed down and fed into a non inverter. I will draw some suggestions when I get home.

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