Photocoupler specs... CTR Truly important?

[EEVPiobee]

Hello there... I'm wondering...

I have an LTV817BN opto-coupler that seem to be dead on a circuit board and I'd like to replace it. Now I don't have it on hands, but it happens that I could salvage a 817C from some "New old stock" device that was never used at all but already obsolete...

Now, I've looked at the datasheet: http://pdf1.alldatasheet.com/datasheet-pdf/view/86744/LITEON/LTV817.html

And the MAIN difference from the two is just that:

817B : CTR 130-260 %
817C : CTR 200-400 %

Could one replace the other?

Note: BN is on a TV's inverter power supply, as C is in a general standard power supply

[ConKbot]

I would expect an increase in CTR to not affect it too much as its probably just providing a digital signal for the feedback loop.

If you were going the other way, a reduced CTR could possibly affect it if the design was marginal. In fact, as the LED degrades, you can lose output current, causing the same problems with aging.  What sort of failure do you have that makes you think the opto-coupler?  I'm guessing its not blown up and cratered since you say "seems to be dead"  So LED aging is a possible failure mode. Have you done any testing on the opto?

[EEVPiobee]

Well right until now I don't have any "advanced" way to test it, but, all the 817 optos I've tested on this board act like a diode on both sides with a multimeter and I get decent readings on both sides. (just as if I was reading a normal standard diode)

But still, this 817BN one isn't blown up (destroyed cosmetically), but has an open side, no matter how I read it (polarity)..


When I plug mains power on power board it's on, and send +5v signal for this supply (tv's inverter supply) to turn on, I just get nothing from, or even to the transformer...

I can't really find another faulty part than this little one, and the logic board (that sends +5v) is actually a Samsung factory rebuild to specs...

(Pic included is not the one I have in hands, but the exact same model taken from one eBay's auction..)

[Zero999]

You're replacing it with an opto-isolator with a higher CTR so it should be fine.