Counterfeit or "refurbished"? (LT1084) - Page 1
Forum section: electronics / projects

author: jitter
author_rank: Frequent Contributor
timestamp: January 13, 2018, 06:45:01 pm
content: The company I work for has used the LT1084-CP5 (TO-3P) for a particular long running product for years.In those years thousands were used without a single failure and then all of a sudden DOA's started to be found during testing. Few and far between, but still remarkable for a component with 0% previous failure rate.After a bit of looking at thedatasheetI found that, sure enough, packages TO-3 and TO-3P have become obsolete.Time to look a little closer at the failed components.Visually there's some variation in the finish of the leads. Some look quite good, others have scoring and evoke an "oh-oh" response.First a look at a known genuine item:One of the worst looking new items in stock had a step and scoring across the leads visible to the naked eye:A look under the X-Ray machine - side by side with the genuine part - shows that the internals look identical. However, you should be able to spot the less than legitimate one without me telling you which is which:Based on this, would it be a reasonable assumption that these are genuine items that were salvaged and then had new leads grafted on?

author: wraper
author_rank: Unknown
timestamp: January 13, 2018, 06:50:49 pm
content: It's obviously used IC from e-waste. Look how legs look on X-RAY. Old legs were cut off to certain length and then new legs welded on and sanded. I would guess that marking was removed and reapplied as well to match date codes.

author: jitter
author_rank: Frequent Contributor
timestamp: January 14, 2018, 08:06:23 am
content: Yeah, thought so.But I'm really curious about what particular products these would have been salvaged from. I mean, a linear regulator in TO-3P shape capable of 5 A output wouldn't be something I'd expect to find in large numbers in consumer gear, right?

author: jitter
author_rank: Frequent Contributor
timestamp: January 15, 2018, 06:05:39 am
content: Quote from: blueskull on January 14, 2018, 08:34:05 amThat explains why there are people interested in salvaging or counterfeiting them.I still wonder about the source, though, as the batch we are currently using, which was obtained from a broker, was quite large.Linear Technology does continue the TO-220 package of the LT1084, capable of the same current, but I wonder about the thermals of that smaller package.

author: wraper
author_rank: Unknown
timestamp: January 15, 2018, 12:31:55 pm
content: Quote from: jitter on January 15, 2018, 06:05:39 amIt only matters if it dissipates a lot of power and is mounted on a large heatsink. Thermal resistance figures are in the datasheet.

author: jitter
author_rank: Frequent Contributor
timestamp: January 15, 2018, 07:46:42 pm
content: Yes, they are. Worst-case spec of the TO-220 is 0.4 K/W worse than the TO-3P, but that's junction to case.Surely the case to heatsink resistance (in the application a silicon thermal pad, no thermal compound) must be bigger in the TO-220 package?I think it could end up being 0.5-1 K/W worse than with the TO-3P.Power dissipation with the standard configuration (as we ship it) is nowhere near what it could be, but additional modules may be put in by the customer, some of which are rather power hungry.In the end it's up to the customer to decide. For now they chose to take the risk with the suspect batch.

author: wraper
author_rank: Unknown
timestamp: January 16, 2018, 07:08:14 am
content: Quote from: jitter on January 15, 2018, 07:46:42 pm, I guess someone needs to be sued by customers for knowingly using counterfeit components.