Help Identifying Early 70's Fairchild CPU|ALU|??? - Page 1
Forum section: electronics / general

author: flanneltuba
author_rank: Contributor
timestamp: February 07, 2016, 01:04:57 am
content: Greetings,This is my fist post here so forgive me if it's out of place or too off-topic, but I thought I would put it out anyway, and see if anyone can help me.For 25 or 30 years, I have had in my electronics enigmas bag a vintage Fairchild ceramic 40 pin DIP IC, and have never been able to identify it beyond some guesses based on its production date stamp and manufacturer's logo. My best guess is either a PPS-25, 4-bit microprocessor, or a 3800, an 8 bit arithmetic unit. I am (hopefully!) attaching a photo of the chipIf there are any electronics archeologists out there that might be able to shed some light on this little guy, I would love to know what you think it is—or better yet, what you're sure it is!Here is the picture. Thanks in advance. - Scott

author: free_electron
author_rank: Super Contributor
timestamp: February 08, 2016, 02:44:02 am
content: That's not the fairchild logo but the Ferranti logo. Also, SL is a typical ferranti prefix. Ferranti spat out their semiconductor business which became Plessey . Plessey continued the SL and SP product lines.as for what this thing exactly is ? no clue.

author: flanneltuba
author_rank: Contributor
timestamp: February 08, 2016, 04:04:02 pm
content: Thanks for the reply. I'll do a bit of research on Ferranti. I'm not completely convinced it's not a Fairchild chip though; I've seen other 60's fairchild parts with the same non-italicized, slightly elongated "F" logo. (Example, see the F 702 chip here:http://homepages.nildram.co.uk/~wylie/ICs/monolith.htm#MicronorI) Of course my need to know is purely curiosity and sentimentality based, as I will almost certainly never even apply power to this part let alone find any use for it. I halfway suspect that the number could be internal or pre-production, and may not appear in any historical literature, certainly not any Googlable literature anyway. I have Googled the chip numbers six-ways-to-Sunday, and with the exception of a very oblique potential match to the 3801 part of the bottom number set (which reads 11-33801) whichmaybe/kinda/sortacould be from the 3800 CPU family of the early 70's. A tenuous and optimistic connection at best here though.Anyway, I have always been curious about the Ferranti company, and will spend a few cycles reading up on their history. Perhaps there is a connection here.- Scott

author: rich
author_rank: Frequent Contributor
timestamp: February 08, 2016, 06:40:41 pm
content: I was going to suggest opening the lid and peering in with a microscope, but probably not to be recommended if it has sentimental value. Apart from the date code, nothing pattern matches in my mind, sorry.

author: flanneltuba
author_rank: Contributor
timestamp: February 08, 2016, 06:56:30 pm
content: I had half a mind to do just that—pop the lid off and inspect it. It would at the very least allow me to roughly determine the Vcc and Gnd terminals. I'm just assuming it's bipolar and not MOS based from that age. I also have half a mind to just walk around the pins with my curve tracer and see what I can deduce.It really is just a curiosity though, but I've wasted as much or more time on even less seemingly important pursuits. But isn't that what makes us all tick really, diving into things simply =because= they are unknown, and oh, how we cannot tolerate not knowing! Who cares if they're relevant to daily life or have any material value or use. Meanwhile, other seemingly important projects sit waiting on the shelf or worse, on the bench in mid-surgery. They can wait. This 44 year old chip is currently the most important thing in the universe. Heh heh. Oh, why did I need to accidentally find it in the back of one of my parts drawers...Oh me, oh life.

author: miguelvp
author_rank: Super Contributor
timestamp: February 10, 2016, 05:19:14 am
content: Part of the puzzle but not the solution.I think the OP is right about being a Fairchild chip.Look at the logo for this Fairchild program divider, 16 pin DIP from the end of 1978, just 6 years and a half after the OPs chip:Edit: image source:https://www.surplussales.com/Semiconductors/IC-10.html

author: cpushack
author_rank: Newbie
timestamp: February 02, 2025, 01:00:10 am
content: I am going to necropost as my first post, but I think it is warranted, as mysteries should not be left unsolved.This is a Fairchild 3807, it is the lesser of the 2 keyboard input controllers for the PPS-25 (as the original post guessed). The other was the 3803Both of these chips could be customized as needed, thus the strangish markings.

author: flanneltuba
author_rank: Contributor
timestamp: February 02, 2025, 02:02:14 am
content: Ah ha!The mystery is solved! This IC was given to me when I was probably 12 or thirteen years old. (I'm 61 now. You do the math) It was a treasured little thing throughout my early teen years with an almost mythical aura. I'm somewhat astonished I've managed to keep it all these years, but I suppose this was one of the seed crystals in what would become an addiction familiar to many on this forum, I speak of irrational propensity to collect electronic "stuff" of any and all sorts, but especially the mysterious stuff.Anyway, Thank you, @cpushack for finally restoring this chip's identity!