Sonos Sub main PCB - R37 resistor burnt

Hi Wiskertango,

I also have a SUB2 with a burnt R37. I've sent a PM to both LennyK and Mic Markow on this subject. We need to find a picture of R37 with the markings or someone who has information on the value. On one of the posts the value was given as 810 ohms but I see that the resistor markings on my unit are 2 numbers and one alpha. R72 is marked as 18d. this leads me to believe an alternative marking system is being used where the first 2 digits refer to a value and the letter is the multiplier. This would make R37 either 15K or 150K. I also believe that the SOT23 devicesmarked 2F and Y2 are a 2n2907 and a 12v zener diode. I have to do some more testing to determine if I am correct. Please let me know how you've progressed.

flyorcw 

Just found a video that shows R37 to be a 1K. Unfortunately the video is in German which I do not speak. Still investigating, don't want any magic smoke.

I have the sub mini but fortunately mine still works…

Anyway having seen some images of this fault before and doing electronic repairs for my work i can say with confidence that blown resistor is a consequence not a cause.

You will need to check for a short on that track and work out where the cause is.

Look at the transistors, ics and inductors and caps.

You are looking for-

Diodes - test with diode function on multimeter

Caps- test for shorts (if its a switching powersupply failed caps can cause other components to fail)

Transistors - check for shorts

Ics- look up data sheet and check for shorts across the power rail).

Inductors - check for shorts.

This is a very basic starter guide and is by no means all inclusive, you will also need to remove any shorted component you find and once the short is gone you would then need to try and work out what the circuit does and then only experience would tell you where to look after that, however the above may be enough if its a basic failure involving only a few components.

If its the power supply then a cascading failure is very common with switch mode supplies and even for me with 20 years experience can be a real pain without a schematic.

From what i remember of the previous thread that resistor goes to the transistor (theres one resistor for each transistor so that suggests either its on the collector as a current limiter or its on the base to drop the voltage.

On the base around 10k is common

On the collector sometimes 10ohm 

If one transistor is pnp and one is npn you could be looking at a preamp for audio or the oscillator for a switch mode and other uses.

I think there was a big inductor near that ic so it could be a buck/boost circuit, would need to know what that ic is.

For future reference if you do get it working, switch mode powersupplies such as in these speakers and usb chargers etc...  work capacitors hard at high frequencies and this means they can wear out pretty quick when left switched on 24/7 its always best to switch it off at the plug when its not being used.

If it has 6 years life expectancy powered up constantly it may have 20 if its only used when needed.

I switch all of mine off when im not using them.

Thank you for your comments, you have added several items to my troubleshooting arsenal. This will be one of my most challenging repairs as there are no schematics to go by and the solder mask is very thick making it very difficult to see the traces. I will do more testing before I power on after replacing several resistors, transistors, and other suspect parts. Wish me luck....

I’m not the greatest fan of constantly powering down because power-up is one of the most stressful events in a unit’s life. Not only do the units experience unusually large current surges during power-up, this initiates a full temperature cycle. After a finite number of these cycles the unit will fail. I power-up units when I first need them in a day and keep them powered until the end of day. This has served me well over the decades because I have very few early failures of any device I’ve ever owned.

If you have R37 broken, the best way is to replace the following components.

condensator smd 1210 1uF 100v (C85)

resistance smd 0603 1K ohm 01B (R37)

resistance smd 1206 1 ohm 1R00 (R77)

Transistor 2F SOT-23 0,8A 60V (Q16)

Transistor ZXMP10A13FQ 7P1 (Q10)

Diode B280 13-F (D15)

Check alway D15 diode, most of the time is in short. This short go to broke R77, Q10 and R37.

Good Luck

Thank you

 Waiting for repair confirmation.