1960s pellet parts - Page 1
Forum section: electronics / projects

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 20, 2020, 06:49:38 pm
content: So I collect plugins for 500 series Tektronix scopes. One of those plugins is a 1GHz sampler called the 1S1.Last week I discovered that the 1S1 actually uses embedded components in the PCB itself.This isn't mentioned in the 1S1 manual, but if you look at the input to the sampling bridge (R4 R5 C4 C5) and look up the Tek part numbers, they are odd.There is a Tek document that does mention these parts.http://w140.com/tekwiki/images/f/f7/Tek_1s1_field_training_package.pdf"The circular pellet parts are inserted in the board before plating.They are bonded into the board and then plated over. The board is thenetched in the usual manner, leaving the location of the parts practicallyinvisible to the eye"Wow. Now I never looked that closely at the PCB to notice that certain parts aren't there, since the failures were always further down the signal chain.Googling for "pellet parts" doesn't yield much except for pellet stoves and pet food pellets.What could these parts be? Something like a 0402 part inserted into an unplated hole which is then plugged with conductive filler and plated over? Capacitors to ground I could picture, but how do you embed a series resistor into a trace?This obviously wasn't beyond 1960s tech, but I've never heard of them used in 1960s Tektronix stuff. The faster plugins like the 1S2 don't mention it either but now I have to find out!I have an itch to completely strip a 1S1 apart, removing the PCB from the chassis and seeing what my naked eye can't see.The closest thing I saw was what's called "leadless" capacitors which are just a stack of dielectric with electrodes soldered directly to the board.

author: RoGeorge
author_rank: Super Contributor
timestamp: June 20, 2020, 07:11:41 pm
content: Quote from: Alex Eisenhut on June 20, 2020, 06:49:38 pmWow indeed!I'll be very curious, too, to find out more.Since on the page 210 of 218, in the schematic diagram, the R4 R5 C4 C5 have an asterisk explained as "denotes an integral part of the PCB & can not be replaced", I guess Google won't know much about them. The best source will be to find an engineer who designed/manufactured that PCB, and ask about more info, and only if there is no NDA about that.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 20, 2020, 07:30:20 pm
content: You can get PCBs with embedded components (mostly R and C chips), and some other things. Or say, carbon ink screened around vias, for inline terminators. Don't know quite how specialized or common these processes are (e.g., IBM did it first, because of course they did, good luck to anyone else?). I know several US fabs that mention it so it's not entirely non-standard, but you'll likely want to be sitting down to read the quote.Next best I think is beam lead SMTs, which aren't supposed to be so much SMT'd, as wire bonded or welded, on hybrids; but can still be soldered if you don't mind the tiny pitch.Tim

author: edpalmer42
author_rank: Super Contributor
timestamp: June 20, 2020, 07:32:30 pm
content: Quote from: RoGeorge on June 20, 2020, 07:11:41 pmNo worries. Bob will tell you anything you need to know.QuoteI can't believe they actually gave a guy's name. Yes, he was a real person.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 20, 2020, 07:36:24 pm
content: Hah, guessing ol' Bob was extremely confident in the performance of his unconventional solution...Tim

author: edpalmer42
author_rank: Super Contributor
timestamp: June 20, 2020, 07:43:57 pm
content: Quote from: T3sl4co1l on June 20, 2020, 07:36:24 pmMore than that! Both he and his bossesexpectedthat he would remain in that job for a very long time. Today, nobody would make that assumption in their wildest dreams.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 20, 2020, 08:08:34 pm
content: Quote from: T3sl4co1l on June 20, 2020, 07:36:24 pmWell he certainly wasn't wrong about the "invisible to the naked eye" part...

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 20, 2020, 08:22:58 pm
content: Quote from: edpalmer42 on June 20, 2020, 07:32:30 pmSHHHH!!!COMPANY CONFIDENTIAL-FOR INTERNAL USE ONLY

author: LaserSteve
author_rank: Super Contributor
timestamp: June 20, 2020, 10:08:24 pm
content: Why are you surprised, they had an in house ceramics plant for decades.Steve

author: exe
author_rank: Unknown
timestamp: June 21, 2020, 02:04:24 pm
content: Any photos of that board area?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 21, 2020, 07:25:21 pm
content: I took a picture but it's not the greatest.Interesting. My 1S1 manual doesn't call out embedded components, but the schematic matches my s/n 001897 1S1 which came from McDonell-Douglas (makers of the F-15! w00t!)The schematic in the field training package has different values for C88/C89, and are also called out as embedded components. (So in some 1S1s it's more than just R4 C4 R5 C5.)As you can see my 1S1 has the 15pF ceramic caps.I think that the vias/solder blobs pointed by the red arrows are actually where the two pellets are inserted from the other side.I'll bet that R4//C4 is one pellet, and R5-C5 is another.I'd have to remove the PCB and look underneath but that is not in my plans right now.LaserSteve: I don't see the connection. Tektronix also made their own PCBs and CRTs. That doesn't mean I'd expect to have embedded components in a PCB.Edit: A simple test occurred to me, remove the connection from the delay line and check the resistance from the center pin to the input of the bridge. It measures 6.3 ohms, not 4. Shows that there's indeed something there!

author: duak
author_rank: Super Contributor
timestamp: June 21, 2020, 10:51:36 pm
content: Is the PCB the standard 1/16" thick material? Somewhere I've got an old board from the 60s that has some cylindrical surface mount parts although I think they were somewhat longer than 1/16".About M-D - McDonnell also made the F-4 Phantom, and the Mercury and Gemini capsules. As it happens, when I was with MacDonald-Dettwiler I worked with a fellow who was with McDonnell Aircraft in the mid-60's during those programs. I believe he was in an electronics lab there and could very well have used that 1S1. He was also there for the infamous accident involving two astronauts:https://en.wikipedia.org/wiki/1966_NASA_T-38_crashCheers,

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 22, 2020, 12:48:29 am
content: Here is the whole PCB. It is a FR-4 style regular old PCB with glass weave and everything. It looks like the usual 1.5mm 62 mils. The only difference with modern PCBs is that whatever resin they used is more sensitive to heat and the board measles easily. But that doesn't change the function.You can see a cable bundle making a u-turn in the upper left corner, there's a screw under there. I don't like moving the cables too much, but I need to remove all the screws to lift the PCB.There's a sheet metal plate right under the PCB.

author: amyk
author_rank: Super Contributor
timestamp: June 22, 2020, 02:27:41 am
content: I think it was more of an anti-reverse-engineering trick than anything else. The extra parts might be hiding under R7/R8 --- the PCB layout in the PDF linked in the OP shows the input going to another island under them, and in the picture I see something odd in the gap between them.

author: LaserSteve
author_rank: Super Contributor
timestamp: June 22, 2020, 04:29:52 am
content: The connection. Is, having good ceramacists. In house would get you to SMT and hybrids early on.In an area where ceramic hybrids were just being invented.Steve