Two Boards, One Fault

A wine fridge that wouldn't start, two identical power supply boards inside it, and a diagnosis that came down to measuring one against the other.

Plugged in: no display, no fans, nothing cold, just a quiet sizzling behind the control panel. Unplugged: silence.

A CASO WineDuett 12 from 2017, thermoelectric rather than compressor, so behind the back panel there are two Peltier stacks, two fans and two identical switch-mode supplies.

Two of everything, and that is the whole story. With one board you are measuring against a datasheet you don’t have. With two you are asking why this one reads 0.9 and that one 1.5.

The left board. Mains arrives bottom right, at the fuse and the PTC.

The right board. Same label, same layout, same nine years in the same fridge. This is the broken one, and nothing here says so.

The same point on both boards, every time, both numbers written down. Meter is a BEST DT-9205M, where overrange shows as a bare 1.

| Test | Left board | Right board | |—|—|—| | Bulk caps, unpowered | 0.0 V | 0.0 V | | Fuse continuity | beep | beep | | PTC, 200 Ω | ~8-9 Ω | ~8-9 Ω | | D13, diode mode | ~450 | ~450 | | D16 / D17, diode mode | 1 both ways | 1 both ways | | Mains at CN1, live | 230 V | 230 V | | Fan rail, live, fan unplugged | 0.9 V | 1.5 V | | Peltier module, unpowered | 9.1 Ω | 6.8 Ω |

Mains gets in fine on both, the input side is healthy on both, neither board makes the rail its fan needs, and neither Peltier is shorted.

The meter never found it. Ears did. The sizzle is the right board, and its green LED shimmers rather than staying dark: a supply trying to start a few times a second and failing.

Before you open one of these, two things. The bulk caps hold 300+ V for minutes after unplugging. And HPFI trips on current leaking to earth, so it will not save you from a hand-to-hand shock.

Not repaired. No schematic, no board-level replacement worth the price of a used fridge. It went out as WEEE the same evening.