Obsolete and not standard parts now really makes me angry - Page 1
Forum section: electronics / repair

author: Vicus
author_rank: Regular Contributor
timestamp: July 30, 2025, 03:48:13 pm
content: Last of a long list of "similar but not the same and now, off course, discontinued" is a dual pnp transistor. Model number IMT4. It's used in a moltitude of Beyerdynamic microphone and isn't really that special apart the pinout. It's different from ANY dual pnp that's in production today. A stupid 50cent part that make me waste too many hours looking for something compatible. I'm tired, I'm really tired about this.And please don't link me some ebay auction, I belive in thrusted supliers.

author: jc101
author_rank: Frequent Contributor
timestamp: July 30, 2025, 04:02:28 pm
content: Is the ROHM IMT1A any good?https://www.mouser.co.uk/ProductDetail/ROHM-Semiconductor/IMT1AT110?qs=4kLU8WoGk0u%252BQ6RyJBZs5A%3D%3D&srsltid=AfmBOoonMXfTXjJxvHIQO4IkRrWD9s1o7co9_Xje2SMFhS5jMl06rpL5

author: bdunham7
author_rank: Super Contributor
timestamp: July 30, 2025, 04:11:14 pm
content: The part is discontinued so you'll have to deal with surplus suppliers. Octopart lists a number that appear to have stock although the minimum orders may be a bit much for you.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: July 30, 2025, 04:18:56 pm
content: Digikey proposes MMDT5401-7-F as substitutehttps://www.digikey.com/en/products/detail/diodes-incorporated/IMT4-7-F/1935698

author: jc101
author_rank: Frequent Contributor
timestamp: July 30, 2025, 04:19:54 pm
content: Quote from: Uunoctium on July 30, 2025, 04:18:56 pmCheck the pinout, Rohm seem to have a different layout to everyone else.

author: amyk
author_rank: Super Contributor
timestamp: July 31, 2025, 03:54:35 am
content: Nothing that steady hands, a tiny soldering iron tip, and some fine wire can't fix.

author: coppercone2
author_rank: Super Contributor
timestamp: July 31, 2025, 04:08:16 am
content: what we really need is a through hole part that is like a old style rivet, so there is round pads when you insert it through the bottom.Then it would be inserted into the PCB with a part on top. Only problem is that you would need blind viasReally this is a flat adapter problem.I think you can replace alot of parts 'nicely' if there is a good way to solder two PCB together. I think it would take no more then micro indexing pins to keep it aligned. Like 0.1mm brass rodsThe solution looks like "pipes" screensaverI have been experimenting with HMP solder. High melting point. It is unique because when you combine it with a regular solder, you can use HMP solder to make 'pads' or solid-non melting foot prints, that can be lapped/sanded to be flat and act as 'pads' that have a 3d shape. Then you can solder them down with regular solder.The problem with SMT adapter PCB is that they IMO do not have good pads for board to board contact. It seems to work alot better when you have some meat there.There is like a uprising amount of problems occurring from not being able to make a parts adapter for SMT parts that solders well.SMT to TH works great because the pins offset it. But when you have SMT to SMT its sloppy. Being able to put a feature on it with a Z-axis would make it... nice. The only options seem to be HMP solder or to make some micro-part that is soldered into a blind via, but the problem is.. you start running into problems with getting boards made (HDI)Having 'dummy' feed through SMT parts would be nice. Imagine you can get like a high temp plastic molded thing that had feed-through pins on it that stick out 1mm on both sides. So it looks like a ball bearing cage with ball bearings in it. Then you solder it to your adapter PCB with HMP solder, and use regular solder to solder on the part and to solder the adapter to the PCB.I wonder if you can just use HMP and solid metal balls with a BGA type design.I can't believe they went full steam ahead on pushing SMT parts without solving these problems.........

author: Vicus
author_rank: Regular Contributor
timestamp: July 31, 2025, 05:22:46 pm
content: Quote from: amyk on July 31, 2025, 03:54:35 amSo your theory is that some decide to use a part with a non standard pinout only to improve repair man soldering skills?

author: Vicus
author_rank: Regular Contributor
timestamp: July 31, 2025, 05:24:44 pm
content: Quote from: Uunoctium on July 30, 2025, 04:18:56 pmA substitute not pin to pin compatible. Thanks for nothing.

author: bdunham7
author_rank: Super Contributor
timestamp: July 31, 2025, 08:37:23 pm
content: If you weren't so grumpy I'd suggest looking at these:https://www.ebay.com/itm/401543197161?_skw=IMT4&itmmeta=01K1H31S6D71XJ42XCND8G11QYBut feel free to ignore that suggestion as well.

author: Vicus
author_rank: Regular Contributor
timestamp: July 31, 2025, 09:56:38 pm
content: Ignoring the price for a single dual transistor, I don't assume an ebay seller as a thrusted supplier.

author: Psi
author_rank: Super Contributor
timestamp: July 31, 2025, 10:01:11 pm
content: Not to be disheartening or unsupportive, I feel your pain, but you're supposed to design alternatives for every BOM item into the design before release to prod.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 01, 2025, 01:51:35 am
content: Many years ago, Siemens produced a 6 pin DIP optocoupler which was just like every other 6 pin DIP optocoupler, except, for some strange reason, it had a different pinout.What would have been an "easy fix" became a nightmare, as EU suppliers were notoriously slow at sending parts to Australia.

author: Psi
author_rank: Super Contributor
timestamp: August 01, 2025, 04:58:03 am
content: Different pinouts to try and 'lock you in' is a real thing.It's an important design step to check through all the similar parts on the market to see what pinout orders are the most common so you can go with that pinout. It's well worth the time and pays off later for availability/alternatives but also because you have more options to find the cheapest compatible part for each prod run.

author: David Hess
author_rank: Super Contributor
timestamp: August 01, 2025, 07:07:18 am
content: Unfortunately surface mount dual transistors have specialized pinouts for functions like differential pairs and cascode pairs, so there is no standard pinout.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 01, 2025, 08:18:08 am
content: The solution is to solder 2 pieces of Rohm 2SA1579 / 2SA1514K together. The IMT4 is nothing more than that.But that would be simplehttps://www.mouser.com/datasheet/2/348/rohm%20semiconductor_2sa1579-1201538.pdf