Hey,
I just repaired the sound on my Star Castle, just figured I'd post in case anyone else has similar problems. The symptom was no sound. I checked the speaker, it was open (bad), and when I turned the game on, I got 30VDC across the speaker (hmm, wonder why the speaker blew
). I looked at the sound board, and both Q17 and Q18 were dead, and a trace going to Q17 was burnt.
So, I replaced the transistors, fixed the trace, and it was still dead (I was just watching the output with a multimeter rather than trying another speaker, which would just blow). I had 15VDC now, so it was getting better. Looking at the schematics, I saw IC25 (TL081) drives the transistors that were bad, and a quick check with the multimeter showed a short from the output to the VCC-. So, I replaced that, but still no go.
I decided to replace the speaker so I could hear something if it was going to play, but rather than just hook it up and blow the speaker, I added a 470uF cap bipolar cap in series (DC block/high pass crossover at ~40Hz). Why they didn't have this to begin with, I'm not sure. After that, I noticed if I put my finger across the inputs of IC25, I got a hum out of the speaker, which meant I had something good from there on out. So, I grabbed my oscilloscope and started probing the outputs of each stage behind there. I saw IC27 had nothing coming out, but IC26 did, and it was getting to the input of IC27, so I swapped IC27 and it all came together.
Anyway, I hope this helps someone now, or in the future. Thanks to: http://www.outerworldarcade.com/arcade/cinematronics/star_castle_sound.html for a lot of good info as well.
DogP
I just repaired the sound on my Star Castle, just figured I'd post in case anyone else has similar problems. The symptom was no sound. I checked the speaker, it was open (bad), and when I turned the game on, I got 30VDC across the speaker (hmm, wonder why the speaker blew
So, I replaced the transistors, fixed the trace, and it was still dead (I was just watching the output with a multimeter rather than trying another speaker, which would just blow). I had 15VDC now, so it was getting better. Looking at the schematics, I saw IC25 (TL081) drives the transistors that were bad, and a quick check with the multimeter showed a short from the output to the VCC-. So, I replaced that, but still no go.
I decided to replace the speaker so I could hear something if it was going to play, but rather than just hook it up and blow the speaker, I added a 470uF cap bipolar cap in series (DC block/high pass crossover at ~40Hz). Why they didn't have this to begin with, I'm not sure. After that, I noticed if I put my finger across the inputs of IC25, I got a hum out of the speaker, which meant I had something good from there on out. So, I grabbed my oscilloscope and started probing the outputs of each stage behind there. I saw IC27 had nothing coming out, but IC26 did, and it was getting to the input of IC27, so I swapped IC27 and it all came together.
Anyway, I hope this helps someone now, or in the future. Thanks to: http://www.outerworldarcade.com/arcade/cinematronics/star_castle_sound.html for a lot of good info as well.
DogP
