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Hello uk whitegoods friends. Can you help me save an old friend from landfill?
I have a 2005 Samsung RS21DCNS which I has had few problems beyond the occasional iced up fan. A couple of weeks back it developed what looked like another round of iced fan (in the fridge compartment) – frozen at the bottom, warm at the top, freezer fine – but on inspection there was no ice blocking the fan. On power on / holding door switch shut, the fan blips on and off 5 times then nothing. Fridge diagnostics then show fridge fan failed.
Step 1 – nice and easy, check supply voltage at motor. It’s 9V vs. 10V in spec, doesn’t seem too bad. Compressor fan on low runs at 8.3V. Also remove the fan from the spindle in case lowish voltage means it’s not meeting speed threshold. Seems unlikely, it’s only trying to tell running versus jammed. But no change in behaviour.
Step 2 – easy, but more expensive. Replace the fan motor with a new one. Unfortunately no change in behaviour. 🙁
Step 3 – more complicated, free. Open up the circuit board box, and check that the motor speed signal is getting to the IC. Connect the (original) motor to a 9v power supply (so it’s running all the time), connect the speed signal up as normal. Probe the fan signal on the main circuit board as per circuit diagram – checked at R725 and IC pin 41. I don’t have a scope, but a multimeter is showing 5v at IC pin 41. I know this is just some sort of time average as it’s a stream of pulses. Looking at the signal from the freezer fan which is working normally (IC pin 40) this is showing 2v. A bit odd. Swap the old motor for the new motor & repeat – the new motor signal is 1.7v. A bit odder.
So, must be the main circuit board. The main IC is receiving the signal but not recognising either the old or the new motor signal as being a valid input / speed. Maybe the IC input 41 has failed, perhaps related to a too-high peak voltage from the old motor? There’s no protection against overvoltage according to the circuit diagram.
Step 4. Deep breath. Buy a new main board, DA41 00185J as per pre-2006 build. 1/10 of the price of a new fridge. Carefully swap it over connect new motor up to regular connections and…
… Nuts. Exactly the same behaviour. Fan blips 5 times, shows fan fail in diagnostics. 🙁What have I missed? Any suggestions gratefully received.
Mike
Mystery solved. Long journey to a simple answer: despite eBay seller’s assertion, new fan motor was not a suitable replacement for the failed one. When I replaced (again) with an OEM motor matching original part number (DREP3020LA, large “7” stencilled on motor) everything was fine, including when I swapped back to the original main board. OEM motor was 3x the price, sadly.
To unscramble what was going on I got hold of a simple oscilloscope to look at the pulse-train representing motor speed. The original motor was outputting only the tiniest of signals even when powered up on the bench – so signal amplifier internal to the motor package had failed. The first replacement motor produced a nice square wave on the bench but once connected to the mainboard the waveform became a squashed sawtooth – clearly not recognisable to the controller. The OEM motor produced a good amplitude square wave before and after connection.
Looking back at the first replacement motor, the seller claimed it replaced both types 12 and 7 and it was a physical and connector match for the original. However evidence suggests maybe different internal electronics for the speed sensor circuit in the 12 versus the 7. My guess is that Samsung changed both the mainboard circuit and the motor with the 2006 revision. No idea why, probably to improve reliability of the speed signal. Creates a big PITA problem though, as it makes main board and motors non-interchangeable, and makes the use of non-OEM motors a bit of a lucky dip.
First replacement motor has gone back for a refund, main board is on eBay as supplier (quite reasonably) doesn’t take PCBs back once they have been fitted, and had been quite clear about that up front.
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