Can you help to identify an unmarked 14 PDIP part from the 1980's? - Page 1
Forum section: electronics / general

author: deanclaxton
author_rank: Regular Contributor
timestamp: April 01, 2025, 11:45:13 pm
content: I have a mystery part where the markings have been physically removed. It's a 14 PDIP package but with an unusual pinout.It's likely just an AND gate but the +/-12V connections in addition to +5V and GND are odd - especially on the pins where they are connected. I'm keen to find out what the actual part is. I can't find any opamps/comparators with the same pinout either.Pin 1: NCPin 2: NCPin 3: Digital Input (IOSELECT)Pin 4: +5VPin 5: NCPin 6: Digital Input (A7)Pin 7: -12VPin 8: Digital OutputPin 9: NCPin 10: +12VPin 11: GNDPin 12: NCPin 13: NCPin 14: NC

author: amyk
author_rank: Super Contributor
timestamp: April 02, 2025, 12:12:37 am
content: What's it from? What are the signal levels?+/-12V and +5V reminds me of early NMOS/PMOS digital logic using enhancement load.

author: deanclaxton
author_rank: Regular Contributor
timestamp: April 02, 2025, 12:28:58 am
content: Its from an old sound card for an Apple II computer - the digital inputs are connected to 74LS outputs, and the output is connected to a 74LS input.I'm fairly sure its really just a simple logic gate but I'm just very curious about what the device actually is based on the slightly odd pinout (by todays standards at least).

author: deanclaxton
author_rank: Regular Contributor
timestamp: April 02, 2025, 04:28:32 am
content: After trawling though multiple databooks from the 1970's (thanks BitSavers!) this 5477 is the only hit so far but I'm not sure about the W package - mine is a regular width pdip. The +12 and -12V could have been attached to the unused pins to throw off the scent.

author: EEVblog
author_rank: Unknown
timestamp: April 02, 2025, 04:40:37 am
content: Quote from: deanclaxton on April 02, 2025, 12:28:58 amBrand/Model number?I'd be a bit surprised if some vintage computer nut didn't know.

author: deanclaxton
author_rank: Regular Contributor
timestamp: April 02, 2025, 04:58:14 am
content: Thats the thing - they painted over all the ics. I managed to strip back the tops of a few of them, and was able to read the chip numbers and confirm what they were in a tester but this one IC was illegible, and my testers could not detect what it was after de-soldering (auto identify failed on BackBit Chip Tester Pro and Xeltek 6100N).The board is a Super Mockingboard from Capitol Computer Co - a clone of the sweet 16 mockingboard however they used a single 6522 with some additional logic rather than the more common dual 6522 VIA's.I cant find any photos of the card anywhere so it may be relatively rare and what others are out there are likely painted over also.This is making sense though (the latch) so I could be onto a winner.

author: amyk
author_rank: Super Contributor
timestamp: April 02, 2025, 06:26:48 am
content: Quote from: deanclaxton on April 02, 2025, 04:28:32 amThat's a great point; you can check the resistance between those NCs and the other pins to confirm. Depending on how the traces look, they could've been using those NCs just as extra space to route the +/-12 to other chips, and trusting that a future revision of the part won't have them connected to ground or have some other purpose like a factory test mode.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 02, 2025, 09:35:59 am
content: Analogue switches can have multiple voltage power pins

author: deanclaxton
author_rank: Regular Contributor
timestamp: April 03, 2025, 05:08:15 am
content: Buzzed out the chip in diode mode - those pins appear to be disconnected so I suspect they chose the most obscure part on the board, and made it even more obscure by wiring +/- 12V to the unused pins - to throw off any would-be reverse engineers perhaps!

author: deanclaxton
author_rank: Regular Contributor
timestamp: April 05, 2025, 08:16:01 am
content: I requested the 7477 be added to the BackBit Chip Tester Pro and Evie was super responsive in adding it, and sending an updated firmware version for me to test. Yep - it passes all tests as a 74LS77That's one less mystery!