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HELP - Blast city speaker issue

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coll83

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Good day all!
I have a mint blast city always been great, im in the process of refurbing a 2nd machine as I love the hobby.
I tried the 2nd PSU in the refurb and it blew the glass fuse. I replaced and checked the internals and all seemed good.
I plugged 2nd psu into my mint cab and the voltages checked great but then I got the smell.. turned it all off, nothing was plugged in bar the speakers.
Its some how killed my speakers and when I put the oem PSU in no sound.
Ive tested volatge on the power cab side (where it plugs into the speaker boxes) and im getting -24.5V / 24.5V.

Any ideas what I may have done here please?
 
There is a resistor that is commonly cooked in the power supply. I’m not sure if you can end up with no sound but it definitely affects the audio.

From Grok:
The common resistor that fails in the Sega Blast City power supply, specifically in the Model 3 sound amplifier (SEGA #838-12796), causing sound issues such as no JAMMA audio or buzzing, is the R1 resistor. This is a 10 ohm resistor located on the amplifier board, often positioned vertically near two small capacitors on the connector side. Replacing this resistor has been reported to resolve issues where mono JAMMA audio is inaudible or replaced by a buzzing sound, while stereo audio via RCA connectors typically remains unaffected.

And an A-P post to help you:

Chron

Thread 'Sega Blast City no JAMMA sound buzzing fix'

I was having issues with mono Jamma no sound/buzzing but if i hooked up sound via the RCA connectors i had no issues. Obviously i also wanted mono sound to work for my jamma pcb's.

@Hatsune Mike made a thread about his issues last year and it really helped me out. Orginal thread Sega Model 3 (Blast, NVS4000, etc) no JAMMA sound / buzzing fix

I replaced vertical R1 resistor on my amp (10 Ohm) and my issues went away. When I pulled the old resistor i thought it checked good but replaced anyways and it definitely solved my problems.

Thanks and good luck to whoever needs this...
  • Like
 
Ziggy Cheetos Dust said:
There is a resistor that is commonly cooked in the power supply. I’m not sure if you can end up with no sound but it definitely affects the audio.

From Grok:
The common resistor that fails in the Sega Blast City power supply, specifically in the Model 3 sound amplifier (SEGA #838-12796), causing sound issues such as no JAMMA audio or buzzing, is the R1 resistor. This is a 10 ohm resistor located on the amplifier board, often positioned vertically near two small capacitors on the connector side. Replacing this resistor has been reported to resolve issues where mono JAMMA audio is inaudible or replaced by a buzzing sound, while stereo audio via RCA connectors typically remains unaffected.

And an A-P post to help you:

Chron

Thread 'Sega Blast City no JAMMA sound buzzing fix'

I was having issues with mono Jamma no sound/buzzing but if i hooked up sound via the RCA connectors i had no issues. Obviously i also wanted mono sound to work for my jamma pcb's.

@Hatsune Mike made a thread about his issues last year and it really helped me out. Orginal thread Sega Model 3 (Blast, NVS4000, etc) no JAMMA sound / buzzing fix

I replaced vertical R1 resistor on my amp (10 Ohm) and my issues went away. When I pulled the old resistor i thought it checked good but replaced anyways and it definitely solved my problems.

Thanks and good luck to whoever needs this...
  • Like
Click to expand...

Thanks for that, I think there something more sinister at play, possibly the sound amp is nailed. Blew both my speakers and when I tested the line it was pushing 24V.
 
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