Old TTL chips in the junk box - Page 1
Forum section: electronics / general

author: mark-r
author_rank: Contributor
timestamp: October 22, 2015, 08:38:42 pm
content: I was watching the EEVblog about Dave's old clock and when he was looking at the old 4000-series CMOS in his junk box I was reminded of these 74-series TTL chips in my junk box.When I was a lad, pulling TTL chips from surplus computer boards to use in projects, I remember sometimes there was confusion with chips like these that have two 74xx part number on them. Is the top one a 7432? A 7437? Is the bottom one 7424 or 7475?I'm sure most EEVblog forumites can see what's going on...The top one is a 7437 quad 2-input NAND made in the 32nd week of 1974 and the bottom one is a 7475 4-bit latch made in the 24th week of 1974, but when quickly through the parts bin it was so easy to misread 1974 chips!What interesting items have you got in your dusty old parts bins?

author: Len
author_rank: Frequent Contributor
timestamp: October 22, 2015, 09:14:55 pm
content: I was thinking "What a ridiculous numbering scheme" until I thought of modern SMD components that can only fit a 3-character code, if that.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 23, 2015, 01:47:10 am
content: I recall going through the old stock drawers in a prior company's service department; they had germanium power transistors* and there was a CERDIP 7406 from 7404... or maybe it was the other way around, I forget!*They have a lot of materials handling equipment; who needs to buy new ultrasonic cleaners when you can just plop new transistors into the old ones? It seems this was a popular application for germanium transistors (typically in the 10-20A, 30-60V range, "doorknob" and TO-3 packages), probably in the 50s and 60s.Tim

author: calexanian
author_rank: Super Contributor
timestamp: October 23, 2015, 05:08:02 am
content: I have noticed that myself. Usually you can figure it out easily enough.

author: German_EE
author_rank: Super Contributor
timestamp: October 23, 2015, 10:14:19 pm
content: I would be tempted to paint over the incorrect number to avoid any confusion, either than or print some labels.

author: VK3DRB
author_rank: Super Contributor
timestamp: October 23, 2015, 11:02:51 pm
content: The ambiguity is derived from lack of common sense by the IC packaging developers. Even so at least they had date codes. These days, date codes are rarely found in IC's. Good luck determining which are the 3 characters if they exist (which you can probably locate and decipher find using the data sheet. Its pretty much open up a box these days and there is little forensics about when it was manufactured which is a bit of a shame.Taking it a step further it would be nice to know the names those who make products. Give it a personal touch. Maybe Apple should have special edition blood red iPhones in memory of those employees who later committed suicide at Foxconn. Call it the Gou Tai-ming Special Edition.

author: TerraHertz
author_rank: Super Contributor
timestamp: October 24, 2015, 04:09:50 am
content: Instructions unclear, didn't specify *which* junk box.Pics are boxes of ICs that are mostly not part of my actual stock. I've worked at a few places that manufactured in quantity, and typically now and then they'd clear out the storeroom of stuff they figured they were never going to use.I never could resist salvaging boxes full of rails of new ICs that were being binned. So I have these piles of very very useless ICs. Most not particularly antique. Standard TTL and LSTTL parts I mostly stored sorted elsewhere, so that's not 'junk'.The last two pics are of some older stuff. Some transistors in funny old packages. And some ECL chips, bought as spares for the HP 1630G logical analyzer I used most of my career.

author: TerraHertz
author_rank: Super Contributor
timestamp: October 24, 2015, 06:01:09 am
content: Quote from: wilfred on October 24, 2015, 04:40:27 amEach row is one type. These were all pulls from sockets in a pile of identical boards. L to R they are:AY38910A68A21HD46505SP-18255AC-268A09EQuoteNot quite what I meant. Which was: I already had a stock of most LS/TTL parts I could want. Then I got these rails (yes tubes) as well. I mostly didn't bother going through them, since these quantities wouldn't fit in my ordered parts storage system anyway. Better to leave them in the rails. Also, lazy. Though I did go through them all and fix instances where tubes had a missing end stop, so ICs were falling out loose. Someone had been even lazier than me.I just now grabbed a sample handful of tubes at random from one of the boxes. Most tubes are full, some nearly empty. Part numbers:UDN2944W740782S123DS8922SN7517574LS7474LS193 (2 tubes)74HC37374LS32 (2.5 tubes)74HCT2374HC573 (2 tubes)74LS13974LS14MC1488I had done a stock list for most of my 'sorted' stuff, but gave up when faced with these boxes. So really, no idea. When I (rarely) need something not in my main store, then I dig through these. Sometimes lucky.It would take hours (days?) to stocktake this pile, and there's little point. So I don't.Ha ha... anyone remember Scrooge McDuck, and his swimming pool of money in a vault? I could almost do that with EPROMs. Slight exaggeration, but not by much. The gaming industry used sooooo many EPROMs, and they rarely bothered to erase them. Just use new blank ones....

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 24, 2015, 06:05:27 am
content: And you thought diving into money would hurt..!Tim

author: jitter
author_rank: Frequent Contributor
timestamp: October 24, 2015, 07:17:23 am
content: Quote from: VK3DRB on October 23, 2015, 11:02:51 pmYes, OP's confusion is probably only with ICs carrying datcodes of 1974...QuoteI beg to differ. Any IC that has enough space to carry a datecode has one, and that's still plenty. Even if there's no space on the IC, they will have a datecode, or lot trace code (or both) on the factory original packaging.QuoteMany manufacturers still fit a 4 digit datecode in the YYWW-scheme. Some choose to do a YWW-scheme in which a letter has been used from 2010, so e.g. "950" means week 50, 2009 and "F14" means week 14, 2015. And then there's TI with their YM-scheme (embedded in the lot trace code, at the start, also for BB) in which there's always a numeral indicating the year and a numeral or letter for the month, so "21" would mean January 2012 and "4A" would mean October 2014 (if of current production, of course, they might also be a decade old...).QuoteGranted, once a factory package has been discarded there's no way to know with the small ICs. It's why the company I work for does lot tracking as a matter of course.Datecodes aren't everything. For real tracking the lot trace code must be used. Recently I noticed we had two reels of the same brand and type of relay in stock, both of which had the same datecode, but the lot trace codes were different.

author: mark-r
author_rank: Contributor
timestamp: October 24, 2015, 08:05:59 pm
content: Love those old power transistors, so many weird case designs.What's the collective noun for AY-3-8910s? A cacophony of AY-3-8910s, maybe?

author: VK3DRB
author_rank: Super Contributor
timestamp: October 25, 2015, 02:27:29 am
content: Quote from: jitter on October 24, 2015, 07:17:23 amYes, the lot trace code in important. Recently out of about 100 boards, two boards had Vishay tantalums go up in smoke (well within their voltage rating and inrush current slew rate). The labelling looked dodgy on some of those capacitor, so suspecting counterfeit Chinese parts had polluted the batch. I contacted Vishay and our PCA manufacturer adn supplied photos. The photos raised suspicions with but without the lot trace code it came to a dead end. No others have failed since, thanks goodness. Excessive heat during reflow can de-rate tantalums, but I doubt that was the problem. No more have failed yet. Touch wood.

author: jitter
author_rank: Frequent Contributor
timestamp: October 25, 2015, 07:45:11 am
content: Quote from: VK3DRB on October 25, 2015, 02:27:29 amEven with correctly derated tantalums (rated voltage at least twice nominal voltage), I believe that a small percentage (say 0.01-0.1%) of early failures is still to be expected.We also use a lot of tantalums and very occasionally find one that didn't survive the soldering process.Tantalums are becoming more expensive as the raw material isn't abundantly available anymore or from regions in the world with questionable attitudes towards human rights.Newer designs seem to steer clear of tantalums, using ceramics or polymer caps instead.The rise in price will probably also make the counterfeiters happy... so beware...Many of the tantalums we use are big enough to carry a code that I believe to be a lot trace code (or at least part of it) like in the picture below. Your's didn't have it?

author: VK3DRB
author_rank: Super Contributor
timestamp: October 25, 2015, 09:24:50 am
content: Quote from: jitter on October 25, 2015, 07:45:11 amI don't believe so. The edge of the characters were actually off the surface of the tantalum caps and the printing was inconsistent, hence why I got suspicious.Some time ago a colleague bought six power FETs on the grey market, and they all failed immediately. There was nothing wrong with the circuit around the device. So I scratched my head a bit as to why they failed. After looking closely devices, I suspected they were counterfeit. Comparing to the datasheet, it was apparent the original laser etched characters were ground off to a shiny surface and new characters were etched in. I found my colleague a suitable replacement and they worked no problems at all.The media here reported a few years ago the market is flooded with dodgy parts and a lot of these end up hidden in Chinese made products, unbeknown to the westerners who are duped into buying them. The parts are melted off their boards in filthy sweatshops and in the street often using child slave labour, without any regard to safety. No wonder we in the West cannot compete because we use genuine parts, respect basic human rights, and do not tolerate slavery.

author: Godzil
author_rank: Frequent Contributor
timestamp: October 29, 2015, 10:51:15 am
content: Quote from: joeqsmith on October 24, 2015, 09:15:52 pmWow I love your collection, so sexy