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Double Dragon Arcade PCB - YOU do the repair! - Part 3
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- čas přidán 13. 10. 2022
- This is part 3 of our "You do the repair" video series for the Double Dragon pcb. This time we look into the propositions from part 2 which actually ultimately lead to great advancements in the restoration of this classic game. Enjoy!
Please leave your new comments/repair suggestions for Part 4 now!
You can make a simple audio probe to test the output pins of any audio IC's and the output pins of the op amps.
Really enjoyed watching this video 👍😁 When you initially traced the fault to the '244 I thought "yes, that is a prime candidate." In my experience the 74244 buffer/driver is up there with the 7404 hex inverter (which was also a suspect on the schematic) and the 74245 buffer/driver for failure prone chips. Guess what? The culprit was a 74245! It is a bit concerning as I use 74245's a lot in my designs 😯 Well done tracing the multiplexer selection fault. I find it very strange that the schematic uses the bubble notation (inverting the inputs) for the logic gates. It is logically correct but very confusing! As regards the sound section I would first verify that the sound PROM's have not lost their data and then work backwards from the amplifier IC to find where the sound signal first appears. Well done with sorting the video and good luck with the sound 🤞
Love this series! Hope you will do more of them. As for sound, how about the potmeter?
The schematics for this game are really bad :). As suggested, I would use an Audio Probe (but a scope will work too). Start at the Input of the AMP, then start to follow it back. Through the Pot, then to IC97, IC98, back to IC82. I would suspect IC82 since you're not getting any sounds. If you were getting some sounds or garbled sounds I would suspect IC97 or IC98, however it appears to be a single point of failure. You've already proven that the AMP is working or you wouldn't have gotten them hum/noise.
Pins 9 and 10 on the YM3012 are the Audio Out. If you're not getting any Audio on pins 9 or 10 of the YM3012 then I would check pins 2, 4, 5, 6, and 7 for activity. If you have activity, I would suspect bad YM3012. If not, follow it back to IC32 which is a YM2151. Check pins 19, 20,21, and 23 for activity, if none, then Check Clock (24), CS (7), W (5), R (6), and Data Lines (10, 12, 13, 14,, 15, 16, 17, 18).
Follow further back as needed. Lots of possible failures. I would think that bad ROM or bad RAM would give garbled, wrong sounds so might be selection logic, or bad sound chips.
Nice job getting the graphics running 😀 Wonder is it the DAC. All the sounds missing wouldn't point to a single op-amp I'm guessing. I see most of the faulty chips, if not all, were Fujitsu branded again.
I suspect that's probably part of it. The sound CPU is generating something, but it doesn't appear to be getting to the amplifier. There's no samples or FM, so the idea of using a speaker as an audio probe wouldn't be a bad one to see what's actually getting sent out.
So many Fujitsu ICs start by checking those.
The fact that you are getting no FM sound, nor any PCM sound and you have proven the amp is working fine, I would next suspect the RAM for the sound CPU (IC31), followed by the surrounding glue logic.
Don't leave us hanging...............
Sorry... Part 4 is about finished, hang in there!
I'm wondering how would you detect a floating line with an oscilloscope or a multimeter? (on a powerd board)
Suppose you dont have a logic probe.
You could measure voltage, it won't be a clear high or 0. But a logic probe really isn't expensive, I'd just get one!