SMD CODE

[BMTELEC]

Hi everyone,

There is a SOT-23 and 3 pin component. SMD CODE is C8JZB and tehere is a = sign under J letter.
I searched this SMD CODE from web pages. I think its a RT916A-18GV but I am not sure. Could anybody help to me. AM I right or not?
Thank you.

[gamalot]

Si2318DS

https://www.vishay.com/docs/72322/si2318ds.pdf

[BMTELEC]

Hi Gamalot
Firstly I would like to say "thank you"
I thought as like you before and I ordered si2318ds and soldered it. When I applied power to the system it self-protected and shut down. I asked for this help because I was not sure about it. Could this not be? Please do not misunderstand. When I get a response from you, I will put the second one I have on the card. I am sure the fault is not elsewhere.
Best regards

haldun

[gamalot]

If you have another Si2318DS in your hand, you can clearly see that it is the same model as the original one on the PCB, right?

There must be something else wrong.

If you are still worried, you can take a clear picture of the original one and the one you bought, and many people here will help you identify it.

[fzabkar]

What is U20?

[gamalot]

What is U20?

Should be an oscillator/transformer driver or something like that, R41 should be a current sampling resistor.

[BMTELEC]

Hi
U20 is MAX668EUB.
Thanks

[BMTELEC]

Original part smd code: C8JZB
Ordered part smd code:N48

[gamalot]

Original part smd code: C8JZB
Ordered part smd code:N48

The one you bought with the N48 code should be LN4812LT1G, it should be no problem although it is not the same model as the original one.

[BMTELEC]

Many thanks for your detailed information.

Regards,

[fzabkar]

I ordered si2318ds and soldered it. When I applied power to the system it self-protected and shut down.

I would check the resistance of C20 and C21. These appear to be the positive and negative outputs of the DC-DC converter.

https://datasheets.maximintegrated.com/en/ds/MAX668-MAX669.pdf

[BMTELEC]

Let me check.
I will reply again

Thanks

[BMTELEC]

I would like to additional information.

Problem:  I am measuring -7V in leg of D5. This voltage is expecting voltage and its ok but I am reading +2.0V in the D4. It should be +7V.
C8JZB is warming.
Thanks

[fzabkar]

Problem:  I am measuring -7V in leg of D5. This voltage is expecting voltage and its ok but I am reading +2.0V in the D4. It should be +7V.
C8JZB is warming.

I suspect that these supply rails would be used by the analogue section of the circuit, possibly op amps. I would use your meter's continuity test to determine which ICs are powered from these supplies.

What are the resistances between ground and each of these rails? I would think that in a working circuit they should be similar. I would also confirm that D4 is not leaky.

When the circuit is regulating properly, the FB pin (5) of U20 should be sitting at +1.25V.

[BMTELEC]

You will let you know from the result
Thank you