Sound problem Chase HQ

fluxgold

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Hi, i just hear the sound and music at a very low rate and all distorted.

I still have changed all marked capacitors and ics at the picture attached. The volume knob behind coin door with that 3 positions is also working.

Any ideas what i could have missed ?

Greets
 

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Not sure if you have followed the schematics, an audio probe can help you diagnose audio issues, use it to test the inputs of the amplifier ICs, if not there, walk the path backwards until you hit the problem. It may not be an analog audio issue, rather a digital problem (ie digital to analog problem). Looks like ic69 YM2610 is involved in that.


Audio section on page 20 of the pdf in the link.

p
 
Ic69 pin 27 ( analog out ) i hear nothing with my new audio probe. At another boards ym2610 i can hear sound on pin 27 …. So the ic69 is damaged ?
 
Sh1 sh2 is only garbage - thx i learned a lot - ic will be changed tomorrow …

Thx also for the audio probe tip 🤓
 
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Then I'd start checking the other pins, especially the control lines and data/address lines, see if you get activity there.
 
here you can hear a small video of the problem . the music and sound fx are all there but lowest lowest volume and crackling/distorted

 
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D0 - d7 all traffic with logic probe … which one are the control lines
Anything with a / next to it. The clock may be harder to diagnose as logic probes may report it stuck (need an oscilloscope to properly verify).

p.
 
If the sound is all there but just quiet/distorted look at the preamps next - the TL074's. You will see these feed IC76 which is a game programmable volume control. So the output of that (pins 3 & 4) would be the next thing. After that it's the power amp.

(Btw, SH1/SH2 probably wasn't garbage - it's the digital output to the DAC :) )
 
Pin 27 is not linked to anything but should give audio out. Have you checked SH1 and SH2?

I bought a signal generator and put a sinus on the 3 pins sh1 sh2 and pin27 and i could hear nothing

With my audio probe with pc speaker amp on the test rig without chase hq pcb i heard my 1 khz sinus very loud … that means the problem is after that ic ?
 
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