Lightning struck near my house and destroyed a bunch of things I had plugged in, including a treadmill. I swapped parts with another one and identified that it's the lower motor control board that is the problem and on it I see an opto-isolator that had its top literally blown off. Since I have an identical board I know the part has the following label:


I don't know what the CWN1 means.

TL;DR in the above label is the CWN1 important? Is it some sort of CTR rating? Or is it just like a manufacturer ID and I can substitute any PC817 for this one?


  • 1
    \$\begingroup\$ Assuming that the current spike which blew it's top off, didn't jump the gap to the low-voltage side (sometimes it does.) Jellybean part; worth a try. \$\endgroup\$
    – rdtsc
    Commented Nov 29, 2021 at 22:18

2 Answers 2


The part number is always closest to the logo or company name and the CWN1 = factory/date/batch codes.


I recommend the PC817X3NSZ1B or PC817X4NSZ1B replacement.

Then do a diode test on all other parts or use a conservatively limited CC limited lab supply to bring up DC power externally to locate defective parts.

CWN1 C means CTR = 2 to 4 = Ic=/If= 10~20mA / 5 mA = 2 to 4 @ Vce= 5V but as a switch CTR, like hFE, always reduces to << 10% CTR @ Vce(sat) Proof: from datasheet ... Ic/If= 20mA/1mA= 0.05 @ Vce(sat)= 0.1 to 0.2V so at Vce=Vce(sat) @ Ic=1mA CTR= 0.05/2~4= 2.5% to 1.25% Although the new datasheets do not show any distinction for CTR saturated vs different ranks, they do exist and will be around 10% of the max linear CTR for a fixed Vce(sat) max. They just overdrive the LEDs to ensure low Vce(Sat) but you app might not.

W is the factory now made by LITE-ON in China
N1 is the date code for 2001 January

PC817 SHARP still supplies them to Mouser, but they have new part numbers and they are most likely DIP for HV spacing of 5 kV could easily have been compromised by dust and humidity. over this period. No doubt this will cause a cascade of component secondary failures.

The new stock part number uses 3 for X as Rank C Ic= 10 to 20mA PC817X3NSZ1B for DIP which are the only ones in stock at this time.

You could also use 4 as Rank D Ic= 15 to 30 mA both for If= 5mA which is slightly better and also cheaper a few cents perhaps due to high yield and more common, which is also stocked. PC817X4NSZ1B


enter image description here

other misc info

There are a few other Optos rated for 5kVrms but no others at Mouser are ranked as well for CTR, Onsemi= CTR= 1 to 6 , Everlight = 1 to 2, . Sharp makes some only in Japan also which are also good, maybe better quality PC123X5YFZ1B where 5 is Rank N 10 to 20 mA / 5mA similar to Rank C in the other p/n. but is non-stock. Nobody is better than Sharp in these IR optos. Sharp IR LEDs are now licensed to Vishay.

  • \$\begingroup\$ Phenomenal! I wasn't clear on the role of the diode test. I'm familiar with continuity/resistance testing, but not sure in this case how to interpret the voltage drop, and wasn't sure across what should I be testing? Capacitors, resistors, ICs? From the low voltage side to the high voltage side? \$\endgroup\$ Commented Dec 2, 2021 at 22:39

Probably the rank is "C" according to this datasheet

enter image description here

Assuming your "W" is actually a symbol representing the factory location.

As as often true in these cases, a sharp well-cropped photo is much better than an interpretation.

If so, that means that the collector current will be 10 to 20mA with LED current of 5mA, so a CTR of 200-400%.

And the full part number would be PC817x3 where x is X (through-hole), F (wide through-hole), I (gull wing), or P (gull wing tape and reel).

As @Tony points out, you can probably get what you need from Mouser.

  • \$\begingroup\$ What is perhaps more important is the best new part number \$\endgroup\$ Commented Nov 30, 2021 at 0:22

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