SN74141 chip issues - fake/bad batch, or is this 'a thing'?

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6 months 1 week ago #12914 by meq123
Just been finishing up my Nixie clock Christmas present and hit a major snag. I did a trial run with the nixies (Z753M's) and things were not good. The tubes were faintly glowing with multiple digits foggily lit, and although you could see something changing every second, you couldn't tell which digit was being selected. Crap! These were new board layouts for both the carrier and the controller (based on Ian's classic model) so I immediately suspected bad track(s)/layout somewhere, but after spending an hour or so reviewing & tracing, I could not find any errors. Then I swapped a controller from an older clock over to this, and apart from finding that one of the tubes seems to be bad (another story) the clock worked! So that eliminated the tube carrier PCB and I started to concentrate on the controller. I checked the HT voltage, and found only ~130V. Hmmm. Well to cut an (already) long story short, I did a bunch more debugging based on posts I'd seen here after searching for High V issues, but could not find anything. But while doing that, I accidentally touched the 74141 chip and found it was very hot to the touch - this despite no tubes attached. Hmmm. I pulled the chip and boom, HT went back up to ~180V. So then I swapped the 74141 with another, then another, of the batch of 5 I bought off AliExpress. Every single one did the same thing. Aggh. So as a last verificationI swapped the K155ID1 from the working controller into this one. Boom again, it worked!

SO, after all that prose, are 74141's NOT a good choice for this (I had thought they were compatible) or do I have a fake/bad batch from some lousy vendor? Meanwhile I've ordered K155's from a US eBay vendor. Hoping I get them in time.

I wait for your opinions with Antici... ... ... pation!

Thanks, Mark

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6 months 1 week ago #12915 by Ian
That's a bummer.

I don't have a lot of insight for you, unfortunately. It's clear that the so called 74141 is breaking down under the voltage, and everything is more or less transmitting HV to ground.

Are you sure that these are 74141s? Did you try the alcohol rub to see if they have been re-badged? Do they look obviously second-hand or tampered with?

I have had something like this before, when I bought a bunch of K155ID1s, but received K115ID1s, which are for lower voltage use like in VFDs circuits.

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6 months 1 week ago #12916 by meq123
No, they *look* perfectly genuine. I just tried rubbing the lettering with iso-alc but it was solid. I guess they are just bad.

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6 months 1 week ago - 6 months 1 week ago #12917 by Ty_Eeberfest
74141 is a perfectly reasonable choice. 74141 / 7441 / K155ID1 are all interchangeable in these clock circuits. There are minor differences between them but nothing that matters.

74141s have become quite scarce and therefore expensive. I would expect to pay at least twice the price of K155ID1s, probably even more. If your 74141s were priced similarly to K155ID1s that would be a pretty good indication that they are fake. Every real 74141 I've seen has a white Texas Instruments logo next to the part number and date code. Do yours have that?

Look into it later when the dust is clearing off the crater.
Last edit: 6 months 1 week ago by Ty_Eeberfest.

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6 months 1 week ago - 6 months 1 week ago #12918 by meq123
Looks OK to my inexperienced eye...



Oh and this was the issue I was trying to debug ('scuse the dead tube):

Attachments:
Last edit: 6 months 1 week ago by meq123.

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6 months 1 week ago #12919 by Ty_Eeberfest
The apparent mold flash on the notch end of the package strikes me as odd. Don't recall ever seeing that on an IC before. Not sure if it signifies anything or not but it does raise questions in my mind about the origin of the part. Is it a reject from TI or a poorly made clone or what? I'm really not sure.

Unfortunately I can't find any real 74141s in my parts piles to compare with.

Look into it later when the dust is clearing off the crater.

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