Need Help to identify a blown chip in Skynet FOR-Z12C switching power supply

[analogRF]

I have a Skynet FOR-Z12C power supply that is part of a Rohde & Schwarz SMB100A signal generator.
As you see in the picture IC1 is completely blown and I cannot read the part number.

It is a 7 pin DIP package and pins 2-3-7-8 are connected together (on the back) and go to the negative pin of the big capacitor (120uF,420V)
Pin 5 goes to the positive pin of the big capacitor through the winding of the transformer
Pin 4 seems to be connected to one of the opto couplers in the top right

I think the chip might be from STMicroelectronics but cannot say for sure...

any help is highly appreciated

[BlownUpCapacitor]

Apart from this potentially being the PSU for a terminator, the control chip seems to be something similar to a DK125. Supply an image of the underside please. That will help us figure out the pinout.

[fzabkar]

https://www.datasheetarchive.com/?q=tny

Possibly TNYnnn by Power Integrations.

Example: https://i.ebayimg.com/images/g/a3gAAOSw-e9hLMKv/s-l500.jpg

[analogRF]

Apart from this potentially being the PSU for a terminator, the control chip seems to be something similar to a DK125. Supply an image of the underside please. That will help us figure out the pinout.

here is the back side.
It's a power supply for Rohde Schwarz SMB100A signal gen.
Generates +/-13.25V and +5V and a 5V standby.

[analogRF]

https://www.datasheetarchive.com/?q=tny

Possibly TNYnnn by Power Integrations.

Example: https://i.ebayimg.com/images/g/a3gAAOSw-e9hLMKv/s-l500.jpg

Brilliant 
It has to be a TNY. Upon very close inspection I can see a very little of the "Y" letter still left after "N"
and the little left from the logo also matches exactly 
It is a DIP chip not surface mount but they do have DIP package too.

Now the question is which one is it? I mean what part number could it be?

[analogRF]

most probably it looks like to be one of these in the datasheet below
but which one? 

[analogRF]

the circuit seems to be very similar to those on page 9 of the datasheet I posted above.

which P/N do you recommend?

[analogRF]

it looks like this chip is only responsible for the 5V standby voltage at the output

[fzabkar]

The standby supply is rated for 0.05A at 5V. That's 0.25W. Therefore, ISTM that TNY263 should be OK. I would also check the surrounding components, particularly the snubber diode and the bulk capacitor.

[analogRF]

The standby supply is rated for 0.05A at 5V. That's 0.25W. Therefore, ISTM that TNY263 should be OK. I would also check the surrounding components, particularly the snubber diode and the bulk capacitor.

yes I noticed that on the label but the rectifier on the other side of transformer on this 5VSB line is a bulky 31DQ06 diode and the filter is made up of two 680uF caps with a choke in between
I mean it looks like the 5VSB should be able to deliver a lot more than that. That's why I am puzzled. Looks more like a 10W to me than 0.25W

[analogRF]

The standby supply is rated for 0.05A at 5V. That's 0.25W. Therefore, ISTM that TNY263 should be OK. I would also check the surrounding components, particularly the snubber diode and the bulk capacitor.

on the drain (pin 5) the clamp circuit is made of two series diodes (Cathodes connected together) one is a SMBY26C rectified and the other is a unidirectional beefy TVS diode 1.5KE120A (=1N6297A) and 100 ohm resistor in series with the above diodes. and all of them are ok at least with multimeter diode test.

[Harry_22]

it is TNY268

[analogRF]

it is TNY268

I installed a TNY264 and it is working