Comments on: Sony PVM1454Q Monitor Repaired

By: Parasuraman S

Parasuraman S — Sun, 20 Aug 2017 01:39:57 +0000

Excellent article. Very informative!

Likes(0)Dislikes(0)

By: Parasuraman S

Parasuraman S — Sun, 20 Aug 2017 01:39:32 +0000

No idea, how I missed this article. Excellent informative explanation! (Thanks to Jestine Yong for providing the related links!)

Likes(0)Dislikes(0)

By: Paris Azis

Paris Azis — Mon, 31 Aug 2015 18:30:25 +0000

In reply to Hicham.

Hello Hicham

Thanks for your good words and please excuse the delay to answer you as well.

Best Regards

Likes(0)Dislikes(0)

By: Hicham

Hicham — Sun, 07 Jun 2015 11:43:58 +0000

Thank you Azis,

Your answer was fully usefull, keep up your nice interventions.

Likes(1)Dislikes(0)

By: mahmoud_tajpour

mahmoud_tajpour — Thu, 04 Jun 2015 19:46:36 +0000

hi dear Reza thanks for your best article iam very glad that my compatriot see it here.your truly M-tajpour from iran

Likes(1)Dislikes(0)

By: Robert Calk

Robert Calk — Thu, 04 Jun 2015 17:10:13 +0000

In reply to Paris Azis.

The emitter is Pin 4.

Likes(2)Dislikes(0)

By: reza

reza — Thu, 04 Jun 2015 11:27:20 +0000

In reply to MOHAMMED ALY.

hi mohammed aly
thank u for reading my article
go to this address: (How to test an optocoupler)
http://www.antimath.info/electro/how-to-test-an-optocoupler/
or search in to google.

Likes(0)Dislikes(0)

By: reza

reza — Thu, 04 Jun 2015 11:24:06 +0000

In reply to Paris Azis.

hi Paris Azis
thank u for tell me nice guidance.

Likes(1)Dislikes(0)

By: Yogesh Panchal

Yogesh Panchal — Wed, 03 Jun 2015 16:28:15 +0000

Congratulations! and keep up sharing.

Likes(0)Dislikes(0)

By: Paris Azis

Paris Azis — Wed, 03 Jun 2015 15:22:10 +0000

Hello M.Reza,

Nice and interesting repair!
Anyway, I would like to bring to your attention the following:
The replacement optocoupler you used belongs to the “general purpose” family of optocouplers and this, although I noticed in its data sheet that it can be used in “feedback control” applications, encompasses drawbacks which the PC111 is free of.
In other words, the 4N37 can function perfectly in “on-off” switching of thyristors or triacs isolating the power circuitry from the controlling one.
On the other hand, the PC111 is especially designed for use in controlling the output voltages of S.M.P.Ss.
The most significant characteristic we need from the optocoupler to offer us in this application is that of the stability of the controlled-output voltage. This means that the linearity of the transfer characteristic of the optocoupler has to be as higher as possible, just because of the nature of the application.
Putting it more practically, “equal changes of current intensity through the infrared photodiode of the optocoupler, should result in equal changes in collector current through the phototransistor”. And this is not an easy task for all optocouplers to accomplish!
For example, if we test the stability of the output voltage of this power supply through the entire dynamic range of the input voltage for which the designer guarantees stable operation, it will be questionable if the replacement you used can satisfy this demand. This in turn means that in cases like this one there is always a danger for an unexpected and inexplicable second blow of the same power IC you already replaced, due to an oscillatory response of the new optocoupler to a sudden (or even slow!) change of the input line voltage as it tried to establish stabilization of the output voltage.
I would suggest you therefore to replace once again the optocoupler with the original spare part and in case that you either cannot find it in your domestic market or if you order it and until you install it, please connect a 100pF capacitor across the B-E terminals of the 4N37 (pins 5 and 6) you already installed. This is a simple but nevertheless a drastic countermeasure against any oscillatory tendency, applicable to all “general purpose” optocouplers.
Thank you for sharing this experience.

Best Regards

Likes(4)Dislikes(0)