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AES 3-6 Low Power/Black Screen Issue

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daskrabs

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I have a 3-6 that was showing video fine but no audio. I thought a cap kit was in order. Did a full cap kit from console5, triple checked my work. Went to turn it on, no video or audio. Red LED on the board was not lighting up. Checked the power circuit. LM2576 was showing 9V on input but 1V on output, should be 5V. Checked D2, read bad in circuit. D1 fine. Replaced 2576 and D2. Same result. Checked original D2 out of circuit, reads fine. I'm stumped. Logic dictates I jacked up the cap kit, but nothing looks bad. Good solder joints, all facing correct direction. Any ideas?
 
1V on output suggests to me that you got a short somewhere on the board. If you don't have a thermal camera, while the board is running, use your finger to find what device is getting really hot - that's your failure.
 
Interesting. I don't recall the LM actually getting hot! It's a high eff switching regulator. Check the inputs on it:

- GND to pin 1 (should be around 9V or more)
- GND to pin 2 (should be 5V)

If not 5V, are you able to lift pin 2 and see what you get? If still not 5V, replace the LM.
 
I see a few issues here, and I'll leave it up to you on how you tackle this:

- It sounds like you never solved the power issue. You replaced the LM without actually seeing if it works correctly or cutting down the section of the PCB that's giving you grief (input section bad? output?) lifting the pin would have told you. (e.g. bad AC plug, bad switch, or one of the caps you installed is shorted, etc)
- You didn't mention how you checked the PCB. Did you eye ball it or did you check the entire PCB under magnification? I've fixed too many PCBs where the issue was only visible under a microscope. (e.g. trace corrosion around the game slot where liquid easily gets in and eats the traces)
- You never solved the original issue - no sound. No sound is never capacitors. SNK used quality caps in the AES. From the couple hundred systems I've fixed over the past 2 decades, I've never seen any leaking or failed caps on an AES. Only failed mod jobs.

I would tackle on fixing the 1V issue. That's the easy problem. The audio problem is probably a broken trace you didn't find yet.
 
leonk said:
I see a few issues here, and I'll leave it up to you on how you tackle this:

- It sounds like you never solved the power issue. You replaced the LM without actually seeing if it works correctly or cutting down the section of the PCB that's giving you grief (input section bad? output?) lifting the pin would have told you. (e.g. bad AC plug, bad switch, or one of the caps you installed is shorted, etc)
- You didn't mention how you checked the PCB. Did you eye ball it or did you check the entire PCB under magnification? I've fixed too many PCBs where the issue was only visible under a microscope. (e.g. trace corrosion around the game slot where liquid easily gets in and eats the traces)
- You never solved the original issue - no sound. No sound is never capacitors. SNK used quality caps in the AES. From the couple hundred systems I've fixed over the past 2 decades, I've never seen any leaking or failed caps on an AES. Only failed mod jobs.

I would tackle on fixing the 1V issue. That's the easy problem. The audio problem is probably a broken trace you didn't find yet.
Click to expand...
Appreciate the reply. I have a short on the ground plane somewhere for sure. No idea where though. I decided to send it out for repair.
 
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