Need Help to identify a blown chip in Skynet FOR-Z12C switching power supply - Page 1
Forum section: electronics / repair

author: analogRF
author_rank: Super Contributor
timestamp: April 11, 2024, 08:18:16 pm
content: 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 transformerPin 4 seems to be connected to one of the opto couplers in the top rightI think the chip might be from STMicroelectronics but cannot say for sure...any help is highly appreciated

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: April 11, 2024, 09:03:47 pm
content: 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.

author: fzabkar
author_rank: Super Contributor
timestamp: April 11, 2024, 09:07:19 pm
content: https://www.datasheetarchive.com/?q=tnyPossibly TNYnnn by Power Integrations.Example:https://i.ebayimg.com/images/g/a3gAAOSw-e9hLMKv/s-l500.jpg

author: analogRF
author_rank: Super Contributor
timestamp: April 11, 2024, 09:39:37 pm
content: Quote from: BlownUpCapacitor on April 11, 2024, 09:03:47 pmhere is the back side.It's a power supply for Rohde Schwarz SMB100A signal gen.Generates +/-13.25V and +5V and a 5V standby.

author: analogRF
author_rank: Super Contributor
timestamp: April 11, 2024, 09:43:55 pm
content: Quote from: fzabkar on April 11, 2024, 09:07:19 pmBrilliantIt 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 exactlyIt 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?

author: analogRF
author_rank: Super Contributor
timestamp: April 11, 2024, 09:50:41 pm
content: most probably it looks like to be one of these in the datasheet belowbut which one?

author: analogRF
author_rank: Super Contributor
timestamp: April 11, 2024, 10:02:25 pm
content: the circuit seems to be very similar to those on page 9 of the datasheet I posted above.which P/N do you recommend?

author: analogRF
author_rank: Super Contributor
timestamp: April 11, 2024, 10:26:11 pm
content: it looks like this chip is only responsible for the 5V standby voltage at the output

author: fzabkar
author_rank: Super Contributor
timestamp: April 11, 2024, 11:27:03 pm
content: 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.

author: analogRF
author_rank: Super Contributor
timestamp: April 12, 2024, 12:19:54 am
content: Quote from: fzabkar on April 11, 2024, 11:27:03 pmyes 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 betweenI 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

author: analogRF
author_rank: Super Contributor
timestamp: April 12, 2024, 12:46:49 am
content: Quote from: fzabkar on April 11, 2024, 11:27:03 pmon 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.

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 21, 2024, 02:01:14 pm
content: it is TNY268

author: analogRF
author_rank: Super Contributor
timestamp: April 21, 2024, 02:24:55 pm
content: Quote from: Harry_22 on April 21, 2024, 02:01:14 pmI installed a TNY264 and it is working