Repairing a Music Store Professional GO! SUB 18A - Page 1
Forum section: electronics / repair

author: darox
author_rank: Newbie
timestamp: February 27, 2025, 10:01:44 pm
content: Hello everyone,I'm working on repairing a Music Store Professional GO! SUB 18A bass subwoofer, and I need some help troubleshooting an issue with the power amplifier board. The board uses an IR2153 driver and originally had two SLW20N50C MOSFETs. Unfortunately, these MOSFETs burned out. I replaced them with two TK20J60W MOSFETs; however, these also failed almost immediately.Here are some details:SLW20N50C (original):Rated for 500 VTypical RDS(ON): 0.21 ΩContinuous Drain Current: 20 A at 25°C (13 A at 100°C)Pulsed Drain Current: 80 AAvalanche Energy (Single-Pulse): 1110 mJGate Threshold Voltage: approximately 2.0–4.0 VTK20J60W (replacement):Typical RDS(ON): 0.13 ΩRated for 600 VContinuous Drain Current: up to 20 A at 25°CPulsed Drain Current: 80 AAvalanche Energy (Single-Pulse): 200 mJGate Threshold Voltage: approximately 2.7–3.7 VI've checked the board after removing the burned MOSFETs, and there's no short circuit present on the PCB.My questions:Has anyone used the TK20J60W in similar mains-powered amplifier designs?Could the differences in dynamic behavior (e.g., switching transients, avalanche robustness, gate charge characteristics) between the TK20J60W and the original SLW20N50C be causing the TK20J60W to fail under the conditions present on this board?Could issues with the IR2153's gate drive—such as insufficient dead time or an improperly tuned snubber network—be exacerbating the problem with the TK20J60W?I've ordered the following SMD components to change them all based on the board markings, and I'd appreciate confirmation that these are the correct parts for the IR2153 circuit:• WH – A surface-mount Zener diode. According to SMD marking databases, “WH” typically corresponds to a BZT52C12 series diode (≈12 V Zener) used for clamping the IR2153 VCC.• 2L – A transistor marked “2L,” which is generally identified as the MMBT5401. This device is rated for around 150 V, which fits the higher voltage requirements on this board.• 24 – A transistor with the “24” marking. This is commonly associated with the DTC114EU3 series digital transistor, which matches the typical 50 V rating seen on other similar parts.• HF – A high-frequency transistor. The marking “HF” usually refers to a C1815 in a SOT‑23 package. Since the C1815 is not available, I've ordered an alternative (e.g., the MMBT3904 in SOT‑23) that should meet the frequency and switching requirements.• T4 – A fast-switching diode, typically from the 1N4148 family in an SOT‑23 package, marked as “T4.”Any insights, suggestions, or similar experiences would be greatly appreciated!Thanks in advance for your help

author: MathWizard
author_rank: Super Contributor
timestamp: March 04, 2025, 10:55:43 pm
content: Any luck with new parts ? So was it driving a load when it failed w/ new FET's ?So far most all the SMPS's I've fixed, have had fairly easy to find, component failures, like a cap, or diode, BJT, broken winding...And of the ones that partially worked when testing, the controller IC's were good enough, to shut down, when there was a serious issue.So if I was happy enough to power it up, I'd check a bunch of stuff w/o the mosfets soldered in. In some design's, that might mean there's hardly any power anywhere. For some PCB's, I'd remove them and apply my own power, and test them out.But then I'd put in some cheap HV mosfets, and have a bunch of scope probes ready to go and watch what happens on startup.And very important, I'd use a current limiting lightbulb in series with the device, if possible. IDK how much idle power such a thing would use, but if it's not too much, then it should eventually startup. It depends on the controller IC's too. But if the PSU starts pulling a lot of current, the lightbulb would light up, and use a lot of the power and voltage that otherwise, could fry those mosfets again.You can also try an auto-transformer, it's like an adjustable AC voltage divider, so you can slowly turn up the AC power, and see where stuff starts turning on, and then going wrong at some point.A typical computer PSU might be pretty similar, with 12V at 50 or 80, or 100A ratings. A lot of the times when I was repairing computer PSU's, I did have them in series with a 100W lightbulb. But they were just idling, if I tried to run any amount of load, the series bulb would start robbing all the power/voltage, and the PSU would just reset.

author: Harry_22
author_rank: Frequent Contributor
timestamp: March 08, 2025, 03:37:06 am
content: Hi!Could you attach photos of both PCB sides.