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Double Dragon bottleg no music


telonio

Question

I have this DD bootleg. Picture it's fine with sound effects but no music at all in the startup screen or in game. Although sound effects are not very loud even I turn the sound pot. The pcb is connected to my standart jamma supergun with a scart cable. I read that DD needs -5 but supergun provides -5 so I guess that may not be the case. Any help would be much appreciated.

 

 

 

http://i66.tinypic.com/2qinqtj.jpg

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backyarder test usually you can test if the amp is working by turning up the volume pot and putting your finger across (bridging) all solder pads of amp on solder side of the pcb.

if it makes a humming noise the amp should be okay if your able to adjust volume of humming then volume pot is okay

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Looks like someone has worked on the sound area of this board before. the YM's and 5205's are socketed.

It could be one of several things.

The main parts on the sound bus are...

ROM (27256 masked rom)

RAM (2016 on your board)

YM2151

YM3012

M5205

3x op amps (silk screening on your board says 8727. I believe they're 458's?)

Caps

 

The caps surrounding the main amp in the top corner of the board won't be the cause of the missing music. They may cause the sound to be low though.

I would start with the 4x 10uf caps standing in a row, as the outputs from 2 of the op amps feed through these first before going to the main amp. Unlikely to be the cause as unless they're dead, you would still get some soft sound if they weren't 100%

Next I would replace the op amps. Those (and caps) are the most common causes of low/missing/distorted sound.

It could also be the YM2151. Yours is socketed so it's been replaced before, as is the YM3012.

You could also check connections of the ROM socket (27256 under the YM2151). I would also check the connections of the previous work. I've had a lot of boards where previous repairers have lifted pads, broken traces etc.

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Thanks all for the help. I connect the DD pcb directly with an arcade power supply and a scart cable and suprisingly I can hear music and sound effects. I think it's strange, because with this supergun and my Tetris pcb I don't have any issues with music.
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