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Nicko

Mon Oct 19 2009, 09:35PM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

So, I'm doing this project (see

) and trying to work out why something's not what it should be, when I decide to check that one of the tinylogic SOT-23 chips I'm using is really what it should be...

...and it wasn't...

(I had to use a microscope AND a test harness AND a logic analyser...)

So, I ring Farnell and complain - "How do you know it's not the right one?" thay ask. "Well, because the code on it is wrong and its logic isn't what it should be"... "oh"...

So, they check their dispatch bin, and lo and behold! They've got the wrong reel in there...

So, they send me new ones by UPS, but by then I've lost the best part of a day chasing smoke & mirrors... and I'm pissed off...

Lesson? SMDs look very alike, so be very aware that just because its a SOT-23 out of a pack marked SN74LVC1G32DBVR or something, doesn't mean to say that it is!

Rats...

Proud Mary

Mon Oct 19 2009, 09:40PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Golly, I never ever use them Nicko - precisely because they're difficult to make out even with a magnifying glass.

Dennis Rogers

Mon Oct 19 2009, 09:45PM

Registered Member #1837 Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65

Brutal. I've had similar problems at work with refurbished equipment. You trust the refurbished stuff is good and when your system still doesn't work you question your original diagnosis. After losing another day or two of troubleshooting you figure out that the refurbishers just don't know what they are doing. It's super frustrating but it also is the challenge you need to be on top of your game.

These are the super tough ones that I am most proud of when I fix them, but to the customer you are an idiot that took 3 days to fix the problem. I get no respect! (I fix elevators)

Coronafix

Mon Oct 19 2009, 10:26PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

There is a hobby supplier here in Oz called Jaycar and they are reknowned for having mislabelled chips. A friend of mine always takes his logic analyser in with him when he needs a part urgently. He asks for the whole bin and goes through them until he finds one that works.
Makes me wonder how many home hobbyists give up in frustration because they can't get a circuit to work no matter how many times they check their work. And it's probably a mislabelled chip.

doctor electrons

Mon Oct 19 2009, 11:28PM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

One thing that really sucks about this sort of thing is when manufacturers buy a certain amount of these things, they can put what ever number on
them that they want. I had some surface mount components once that had sony's phone number on them! No wonder i couldn't cross reference them!!
I feel your pain!

Steve Conner

Tue Oct 20 2009, 09:18AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I hate SMDs too. The worst thing is when some little SOT23 thing blows out and you don't have the schematics for the equipment, so you don't know what on earth the part actually was. (You can't test it to figure out what it is, because it isn't one of those any more, just a tiny frazzled lump.) In situations like this I end up typing the package code into a search engine, but it hardly ever works. Or tracing the schematic and trying to figure out what sort of a component you'd expect in there. On the whole, I prefer not to work on SMD boards unless it was something that I designed in the first place.

Harry recently sent me some lovely germanium transistors the size of .22 bullets, no microscopes needed there!

Proud Mary

Tue Oct 20 2009, 09:49AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Steve McConner wrote ...

Harry recently sent me some lovely germanium transistors the size of .22 bullets, no microscopes needed there!

And those were the small ones, Steve!

Steve Conner

Tue Oct 20 2009, 11:04AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yay, do you have any in TO-36 packages?

I first saw these in an old marine radio transmitter I was dismantling, there were a pair of them driving the high level modulator.

Z28Fistergod

Tue Oct 20 2009, 11:26AM

Registered Member #2040 Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180

I wonder if the imposters made it into any commercial products. I guess they probably have tests to prevent things like that. Could you imagine the PITA if you had to change out 1000 of those, or maybe it'd be more cost effective to just throw the old boards away...

Nicko

Tue Oct 20 2009, 12:02PM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

Just opened another pack - should be SN74LVC2G17DBVR - a SOT-23 double schmitt buffer, i.e. 6 pins (+/-ve, A1/Y1,A2/Y2) and guess what?

...they are SOT-23 allright, but only 3-pin devices, so these definitely are wrong too... heaven alone knows what they are, but I know where they are going... into the bin...

grumble. grumble...

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