Sayona Woofer Model SHT-1221BT – No Output From All Channels, But Display Present, Now Repaired.
A client brought me a Sayona woofer (model SHT-1221BT) for repair. His initial complaint was “everything is okay but bass is missing.”
I did a quick test in his present to confirm what he said. On testing, I discovered that there was actually no output from all channels, not just the bass. The client further explained that the woofer had already been to two other technicians but never improved. Normally, I’m cautious with equipment that has been worked on before, but I decided to give it a try.
My first suspect was the pre-amplifier circuit. It normally runs on 9V supply regulated by a 7809 regulator.
On checking, the output of the 7809 was missing. At the input, I only measured less than 3V instead of the expected higher voltage. Tracing backward, I found a series resistor with 17V on one side and less than 3V on the other. This indicated that the resistor had likely increased its resistance value, often caused by a shorted component further ahead.
The immediate suspect in this case is the 7809 regulator. So I replaced both. Applied the power and all outputs came back except the bass. Progress!
Since the bass was still missing, I shifted focus to the bass amplifier stage, which uses two TDA2030 ICs. I replaced both ICs, but still no sound from the bass.
Measuring supply rails revealed that both +20V and –20V rails were missing. Tracing further back, I discovered that two fuses feeding the bass amplifier were open.
After replacing the fuses, the bass came back, but the quality was still unsatisfactory.
On close inspection, I noticed that one of the filter capacitors (rated 4700µF/25V) was slightly swollen. This was affecting the bass’s smoothness. I replaced it with a new 4700µF/35V capacitor.
After the replacement, I powered on the woofer and was pleased with the results. The system produced smooth, powerful, and soothing audio output, restoring full functionality.
Humphrey Kimathi is from Nairobi Kenya and the author of:
1) Lcd-Led Television Repair Guide
2) LCD-LED Television Repair Cases/Tips Volume 02
3) Microwave Oven Repair Made Easy
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Note: You may check out his previous post on LG Home Theater Model DH3140S – Dead on Arrival, Now Repaired
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Albert van Bemmelen
September 7, 2025 at 5:08 pm
Good job Humphrey. Because of both missing +20V and –20V rail voltages the originally now replaced TDA2030 ICs likely were still fine.
But I guess that putting those back to test them again would be too much work. And just keeping them for future repairs saved you a lot of extra time.
Humphrey Kimathi
September 8, 2025 at 1:43 am
Thank you very much for the encouraging feedback. You’re right—the missing ±20V rail voltages were the root cause of the bass stage failure, and the TDA2030 ICs may not have been faulty after all. At that point, since the unit had already been through other technicians, I opted to replace the ICs first for certainty.
I really appreciate your observation—it sharpens my troubleshooting process further for similar cases in the future.
Parasuraman S
September 7, 2025 at 8:09 pm
Many thanks for sharing your expert service work!
Humphrey Kimathi
September 8, 2025 at 1:47 am
Thanks and welcome, sir.
Kevin Davison
September 7, 2025 at 8:37 pm
There's nothing more enjoyable to me than watching good diagnostics. You both diagnosed and documented your steps extremely well, Humphrey. Great job and thank you for sharing it!
Humphrey Kimathi
September 8, 2025 at 1:49 am
Thank you so much for the kind words! I truly appreciate your encouragement—it motivates me to keep improving and sharing more repair experiences.
Joshua Oloo
September 18, 2025 at 6:43 pm
Thanks for sharing the article, precise and informative. Thanks Hump.
Waleed Rishmawi
September 7, 2025 at 9:30 pm
I do not understand the fact that when devices needing repair go to technician making them worse because the customer said only the base was not working’ I find that strange. Thanks for sharing
Humphrey Kimathi
September 8, 2025 at 1:52 am
Thank you for your observation! I also find it unfortunate when equipment gets into a worse state after passing through several hands. In this case, the customer initially reported only the bass missing, but on testing I found that no output was coming from any channel. It’s possible that in earlier attempts some parts were disturbed or damaged, which complicated the fault further.
Mark J
September 8, 2025 at 12:14 am
Humphrey well done on the repair.
Humphrey Kimathi
September 8, 2025 at 1:55 pm
Thank you so much! I truly appreciate the encouragement. Every repair is a learning opportunity, and I’m glad this one was successful.
Imoudu O
September 8, 2025 at 4:12 am
I like the way you explained the diagnosis of the device,I'm still learning how to troubleshoot woofer player,hoping to be good like you some day.Thanks for sharing friend.
Humphrey Kimathi
September 8, 2025 at 1:58 pm
Thank you so much for the kind words, my friend! Troubleshooting is a skill that gets sharper with every case you handle. Just keep practicing, be patient with the process, and always follow the signal and power path step by step. With time, you’ll gain the confidence and experience to handle even the toughest faults. I’m glad my post could be of help, and I look forward to learning and sharing together.
Michael Gallegos
September 8, 2025 at 7:27 am
Good job and good documentation! I’m just wondering if you had a schematic for this unit?
Thanks!
Humphrey Kimathi
September 8, 2025 at 2:00 pm
Thank you very much for the encouragement! Unfortunately, I did not have a schematic for this particular unit. I had to rely on tracing the circuit manually—following the power rails and audio signal path step by step until I located the faults. Having a schematic would definitely have made things faster, but careful observation and systematic testing worked out well in this case.
Muykit
September 8, 2025 at 1:29 pm
I would feel like I was on top of the world if I was only half as good a repairer as you are. Thanks.
Humphrey Kimathi
September 8, 2025 at 2:04 pm
Thank you so much for the kind words! Don’t underestimate yourself—repair skills come with patience, consistent practice, and a willingness to learn from each case. I also started small and kept improving step by step. With dedication, you’ll soon be handling even the toughest repairs confidently. I really appreciate your encouragement, my friend! I will be looking for you at the top.
Nazir
September 8, 2025 at 2:38 pm
GOOD FAULT TRACING kIMATHI
Humphrey Kimathi
September 8, 2025 at 4:08 pm
Thanks and welcome, my friend,
Yogesh Panchal
September 10, 2025 at 4:58 pm
Good Job! Sir
I learnt not to rely on any customer statement on fault of the equipment until you personally experience and never prior commit. i have very bad experience while handling Laptops for repair.where argument is start from "it was working fine before i handed over to you" as laptop repair is Not predictable, any fault can occur any time when troubleshooting because of complicated circuit.
Reversal diagnosis is good method for fault finding which you applied here.
Humphrey Kimathi
September 11, 2025 at 1:23 am
Thank you so much! You’re absolutely right—customer statements can guide us, but nothing replaces doing our own testing. Laptops especially can be unpredictable, and I’ve also seen how new faults may show up during repair. That’s why I fully agree with you—systematic and reverse diagnosis is the best way to get to the real cause.