Electronics > Repair
KRK 10S Subwoofer: RED LED
higgsboson:
Greetings fellow DIY enthusiasts! I find myself knee-deep in a quest to revive my trusty KRK 10S subwoofer, and I'm reaching out to the community for some collective wisdom. Here's the lowdown on my predicament:
1. The Red LED Dilemma:
The indicator LED on the back stubbornly glows red.
No sound output, not even a whisper of clicks or pops.
2. DIY Detective Work:
Visual inspection of the circuit board revealed a bulging capacitor with a 470uF/16V spec.
Decided to replace it, along with its capacitor neighbor sharing the same spec. Seemed like the logical thing to do.
3. Post-Capacitor Swap:
Swapped the capacitors, but the red LED still proudly shines with no change in symptoms.
4. Schematics Surprise:
Got my hands on the schematics from the service manual, and they match the circuit board exactly. Same IDs and everything.
Schematics state that the capacitors in question should be 100uF/35V. Confusion sets in.
5. Factory Spec Confusion:
Original soldering suggests the capacitors were installed at the factory with the 470uF/16V spec.
Scratched my head wondering why the variance in specs.
6. Black Gunk Dilemma:
Aware of the notorious "black gunk/glue" phenomenon in this brand, I carefully scraped away some dried-up sections.
Visual inspection shows the components beneath are in good shape and no conductivity (hey! amateur here!) was detected under the black glue.
RED led still on.
7. Power Checks:
Confirmed +15V and -15V are reaching the AMP PCB, so the power supply seems intact, should I test the +47 and -47? Should I have special precautions there?.
8. Power Checks (continuation):
Confirmed +47V (≃50V) and -47V (≃50V) are reaching the AMP PCB, so the power supply seemed intact. However this time I left it connected for longer and I saw a bit of smoke coming from the AMP board, and then everything turned off.
9. Fuse check after the power checks:
Since the entire circuit shut off, I chcked the fuse and now its blown (it wasn't before).
10. Next Steps:
Seeking advice on the next steps. What could be causing the persistent red LED?
Despite being an electronics amateur, I'm diving into the schematics, but it's proving to be a challenge.
Conclusion:
And there you have it—the current state of my DIY venture with the KRK 10S subwoofer. Now, I'm turning to you, the experienced DIY community, for insights, suggestions, or perhaps a fresh perspective on what my next move should be.
Any thoughts are greatly appreciated as we work together to bring this subwoofer back to its booming glory!
Schematics:
KRK10S_Schematic.pdf (5538.98 kB - downloaded 216 times.)
higgsboson:
Attachments
Vicus:
I bet there is a large DC offset at the output. You can measure it on L1.
higgsboson:
--- Quote from: Vicus on February 10, 2024, 06:52:58 am ---I bet there is a large DC offset at the output. You can measure it on L1.
--- End quote ---
Thanks! How can I measure that? What exactly is this L1?
The problem right now is that everytime I turn it on with the AMP board connected to the power supply, the fuse blows after I hear a slight heating up noise on the amp board.
The fuse does not blow if the AMP pcb is disconnected
beatman:
It looks like output transistor short.Check the Q442 to Q446 all 6 output devices with digital multimeter (DMM) in diode mode.If there is short component check and the big white and surround small resistors with DMM in the ΩΜ mode with one leg unsoldered .Check the small To-92 transistors and diodes with DMM in diode mode.
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