I have a Sam Coupé and the last time I turn it on, i noticed a smell of components overheating. After opening the power supply I came to the conclusion that is the resistance R1 (50ºc with IR thermometer).

I took the power supply to two technicians who measured the values in the components and the final output. Both said that everything was fine and that the resistance in question was made to warm up. However I'm worried about the situation because I had never noticed this smell before.

Is this heating really normal?

Can someone with a Sam confirm?

Thanks for the help.

Power Supply

  • 6
    50C isn't particularly hot for a 4 Watt resistor. It looks pretty much like this one farnell.com/datasheets/… which will handle the full power up to 70C, and has a maximum temperature rating of 350C, not 50C!
    – alephzero
    Commented Feb 15, 2019 at 21:33
  • 1
    I used my childhood Sam virtually every day for probably several years but have no recollection of a smell from the PSU.
    – Tommy
    Commented Feb 15, 2019 at 23:43
  • Hi, thanks to both of you. Today i give it a try. I turned on the Sam and used it for about 2 hours, apparently without problems. The PSU continues to smell to hot components. I also noticed that the diode D4 (the first one over the R1 resistor) also heats up a lot (about 60 ° C). The resistance reached 50ºC but was always close to that value. Commented Feb 16, 2019 at 18:30

2 Answers 2


50 ºC is nothing for a 4 W power resistor, so the 'overheating' smell was probably coming from something else.

As this power supply has a single-sided pcb (tracks on the bottom side only) I would examine all the joints and resolder any that look cracked or burnt. You might also consider testing the electrolytic capacitors for ESR and capacitance value, or just replace them anyway as a precaution.

  • I would agree with that completely. Given the very low cost of a handful of easy to find capacitors and a few minutes work ( may as well change that resistor too while you are there ) it would be very worthwhile for peace of mind knowing you are not relying on near 30 year old components in an item that deals with mains voltage and needs to be at its best. Incidentally the smell may of just come from a bit of dust or such that was sat on that resistor and got heated up.
    – AndyF
    Commented Jan 14, 2020 at 21:21

The "overheating" smell might emerge from the dust accreted on the heating components, if the device was off for a long time. So you could try to clean the dust off the PCB and components to get rid of the smell.

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