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I'm trying to find a replacement for this burned out chip, but I'm bit confused which one do I need. Thisi how it looks like:

enter image description here According to this datasheet, there are several HT74 chips in SSOP and TSSOP, but which one do i need? And what does 66K G4 means?

Thank you!

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The ordering information table on page 1 shows two pacakges that have the "HT74" topmark, SSOP "DB" and TSSOP "PW". The "PW" comes in different size tape/reel, but since you'll probably just be buying a single unit from digikey or mouser all you really need is the DB or PW suffix.

TI's "DB" package and their "PW" package are both plastic small-outline with 0.65mm pitch, but the key difference is the width of the body (i.e. the width of the black epoxy encapsulation between the two rows of pins; 5.6mm for DB package; 4.5mm for PW package). It's possible that the PCB footprint might be wide enough to accommodate either package. You need to measure this to determine which package your chip has. The package outline drawings are towards the end of the datasheet. Page 11 is the "DB" package outline drawing, page 18 is the "PW" package outline drawing. Note that these package outlines sometimes support a whole family of similar package styles, so even though the "DB" drawing says 28 pins it really applies to the 14 pin DB package as well.

You can safely ignore the "66KG4CGKT" lot tracking code, there's no way to order a specific lot number. That's just a tracking number that QA can use if there is a problem.

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There are only two that are marked HT74, one is in SSOP and one is in TSSOP.

enter image description here

So you only need to figure out whether it's a DB or PW case (the other variations describe reels vs. tubes etc.)

There is a slight difference in the case size, as you can see from the drawings on the datasheet. 5.6x6.5mm vs. 4.5x5.1mm but the pitch is the same (0.65mm).

The rest of the part markings is a date code.

Looks like it got wet perhaps. There may be more damage to the PCB than the chip.

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    \$\begingroup\$ Yeah I was about to comment on the PCB itself. Looks like its rather done for. \$\endgroup\$ – user103380 Mar 29 '18 at 20:45
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SN74HCT74PW is the PW package (TSSOP) and is the only one that matches that outline with HT74 marking. There are other suffix letters for bulk packages, tape, reel etc.

enter image description here

The other Misc. markings are always below and are for traceability of factory and date code in code letters.

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