Openai/691fd47a-4338-8002-8886-35bc70dbf9b5

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gpt-5-1

User: why did this power supply board burn and smoke

why did this power supply board burn and smoke

Assistant: From the condition of the board in your photo, the most likely causes of burn + smoke come from common failures in smal…

From the condition of the board in your photo, the most likely causes of burn + smoke come from common failures in small SMPS (switch-mode power supply) boards. Here’s what I can see and what typically happens:

✅ 1. Most likely failure: Primary-side capacitor or MOV failure

On the top-left, the blue disk components (MOV surge suppressors) and the yellow “safety capacitor” look aged. If a MOV is overstressed by a power surge, it can short → pull huge current → burn and smoke.

Clues on your board:

• Blue MOVs look slightly darkened.
• Area near the AC input looks heat-stressed.

✅ 2. Transformer insulation breakdown

Your main SMPS transformer (center) shows brown stains / melted varnish. This means:

• Internal winding overheated
• Insulation melted
• Transformer began to arc internally → smoke

This is a VERY common failure when:

• The switching MOSFET shorted
• The controller IC ran full-power
• A primary capacitor dried up and caused voltage spikes

✅ 3. Shorted rectifier diode or switching transistor

On the hot side (right side of board), the large heatsink-mounted switching transistor or rectifier could have shorted.

A shorted transistor → huge current → burns the transformer and primary resistor.

You can see some darkened PCB around the hot-side components.

✅ 4. Electrolytic capacitor failure (common cause)

The SAMXON capacitor on the right side is a brand known for failures. If this capacitor went bad (ESR increases), ripple increases → MOSFET overheats → transformer overheats → smoke.

Even if it’s not visibly bulged, it may be internally failed.

✅ 5. Glue turning conductive

The yellow/brown glue around coils often becomes conductive and corrosive when old.

Your board clearly has old glue around the:

• output coil
• transformer
• capacitors

When conductive glue bridges traces → short circuit → smoke.

📌 Which component looks burned?

From the image, the transformer is the most obviously heat-damaged component, showing brown leakage/stains. This means something upstream (MOSFET, capacitor, or feedback circuit) caused an overload.

🚨 Final conclusion

Your power supply board likely burned due to a primary-side failure, most likely:

1. Bad capacitor → unstable switching → MOSFET short → transformer overheated
2. MOV surge suppressor failure
3. Conductive glue causing a short

Once the MOSFET or transformer shorts, massive current flows—causing smoke.

If you want, I can: 🔧 Identify suspect components one-by-one 🔧 Guide you on what to test with a multimeter 🔧 Tell you whether this board is repairable or should be replaced

Just send a close-up picture of the burnt area or underside.