IC: P721F. What is this?

[Wouter Minjauw]

I found an IC P721F in the power supply of a computer monitor I'm trying to
repair. It's a 4 pin IC and seems to be one of the few components that
connects the electronics on the primairy side of the tranformer to the
electronics on the secondary side of the tranformer. May I suggest this is
an opto coupler? I tried yahoo and google, but without useable results.

In case there is someone who knows something about power supply's: when I
plug it in, a relay (is this the correct English word?) gives two clicks in
less than a second (I guess a fast on and off) and thats all. Nothing looks
burned, tranformer doesn't have open windings, power MOSFET has 2.4M channel
resistance (I guess OK for a depletion mode MOSFET?) and no burned gate. I
disconnected the power diodes on the secondary side of the tranformer to
find out if there was a shortcut somewhere in the monitor, but with
absolutely no changes, still the same two clicks. Any tips are welcome.

[Jonas Andreasson]

"Wouter Minjauw" <minj...@skynet.be> wrote in message
news:3d319b5c$0$4088$ba62...@news.skynet.be...

http://www.gaw.ru/doc/Toshiba/TLP721.pdf

[John Gill]

Jonas:
That is a partial part number. The whole part number is TLP721F.
It is an opti-isolator for the feedback on the power supply.
I had a Compaq MV540 with a bad one. I replaced it with an "817B" from a
old Gateway monitor and it fixed the problem. What monitor is it from ?
It should check like a diode on the input side with your multimeter on
the diode-check function.
Hope this helps...
John