Blast City sound problems :(

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Drachenherz
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Blast City sound problems :(

Post by Drachenherz »

My BC is showing problems with the sound.

One moment, the sound is playing just fine, then suddenly it fades off very quickly. It's not an abrupt cutting off of the sound, more like a very quick fading out, in about half a second or less... Usually, the sound came back when I opened and closed the CP, or when I gently hit in the area around the middle of the lower monitor frame, just above the CP. Sometimes it was even enough to just normaly push the buttons while playing, for the sound to come back.

But now, the sound is gone.

What could be wrong with my Blast, and what can I do to explain even further what this could be?

Please help me solve this mistery. I'm longing to play Metal Slug, it's only a third of the experience without sound. :cry:
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system11
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Re: Blast City sound problems :(

Post by system11 »

Tried the obvious yet?

1) Try another PCB.
2) Unplug and plug the PCB back in.
3) Check the speaker wires.

If all that looks ok, if I recall the blast has an amp built into the power supply. It might be failing.
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nem
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Re: Blast City sound problems :(

Post by nem »

Are you sure it's not your MVS motherboard? They're notorious for missing sound. All three motherboards I've had needed to be recapped.
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Drachenherz
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Re: Blast City sound problems :(

Post by Drachenherz »

Okay, I'm pretty sure it's not the MVS-board, I tried a strikers 1945 II pcb which I know has working sound...

And still no sound on the blast. I *think* the cables are okay (haven't checked them too thouroughly, though...)

But I noticed a high pitched humming sound yesterday evening, at the time the sound stopped working. This high pitched sound is still present. At first, I thought it would come from the monitor/the chassis, because it started around the time as I yoko'd the monitor, or shortly thereafter (as there still was sound).

Today, as I looked closer in the Blast, I localized the sound - it is coming from the PSU... I don't know, maybe I'm taking wild guesses now, but it looks like the sound amp in the PSU is blown... Could that be?

I made a vid, you can hear the "humming" sound quite well in it. Guess it looks like I'm fucked without a new PSU?

http://www.youtube.com/watch?v=w05kKEKWzAc
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system11
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Re: Blast City sound problems :(

Post by system11 »

I think it's time to open the power supply and look for obviously leaking caps or blown components.
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Drachenherz
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Re: Blast City sound problems :(

Post by Drachenherz »

system11 wrote:I think it's time to open the power supply and look for obviously leaking caps or blown components.
This. Any special precautions I have to take besides unplugging the PSU? Is there any "residual" current in it, like in the monitor? (sorry for my bad technical english)
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system11
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Re: Blast City sound problems :(

Post by system11 »

Nothing of any consequence. Don't bridge any larger caps - not likely to be dangerous but it might damage something. You're only doing a visual check anyway. Check the underside of the PCB for dry/cracked solder joins.
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oxtsu
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Re: Blast City sound problems :(

Post by oxtsu »

it's not well known, but that amp was used on a few other sega games so it's a bit easier to find by itself. no need to buy the complete Blast City PSU box. sega part # is 838-12796 (sometimes it won't have the sticker with that part # on the amp, in that case you can go by the silkscreened printing on the board : SJ25-0303-01)

http://www.ebay.com/itm/380439769121
http://www.tms-designs.com/theshed/defa ... ockid=2541
http://www.giz10p.co.uk/index.php?_a=vi ... ductId=109
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