Yet another mystery component - anyone recognize? - Page 1
Forum section: electronics / projects

author: Kremmen
author_rank: Super Contributor
timestamp: October 23, 2013, 10:59:22 am
content: The board comes out of an old CNC machine. The red sugar cube is the one that needs replacing. Yes, a small hint 48/24 so a converter it is.Here is the schematic where the components are marked as U2 and U3So it is quite certain that it is a 48 to 24 V converter of some kind. The specs would be interesting though. This board is vintage 1974 so it may or may not be a SMPS - i suspect maybe not.Manufacturer is Weber and that's all i know about it.Anyone?

author: Stonent
author_rank: Super Contributor
timestamp: October 23, 2013, 11:07:26 am
content: I'd go with small transformer.

author: Stefan
author_rank: Contributor
timestamp: October 23, 2013, 11:19:12 am
content: Hmm, everything looks quite DC to me.Pin 3 of U3 connects to the negative supply pin 35 of the board, and Pin 2 goes to the positive supply pin 36 (via a series resistor). Also there is a polarized cap between pin 2 and pin 3. Pin 1 drives a relay.Looks like a linear regulator to me. Pin 3 is ground, Pin 2 is the input and Pin 3 the output. I don't understand the series resistor though.Edit:come to think of it, the resistor could be a simple current limiter. The 24V relais won't need more than a few milliamps. I'd just try to put a TO220 type 48 to 24v regulator in there.Edit2:The big "DC" on the component might also be a hint that its not an AC transformer...

author: dr_p
author_rank: Frequent Contributor
timestamp: October 23, 2013, 11:50:05 am
content: My guess is some sort of voltage doubler with it's own oscillator, since it's powered from DC.edit: I got it the other way around, it seems to take 48V input and output 24V, so it's a voltage...halfer. I still think it's a charge pump implementation.

author: Kremmen
author_rank: Super Contributor
timestamp: October 23, 2013, 04:06:37 pm
content: Thanks everyone for your interest. The owner of the board took a risk and broke one of the mystery parts open. The cigar goes to Stefan for being spot on; it is a 3 component linear regulator - a transistor, resistor and zener.This was my suspicion as well, because switching tech was not that common in 1974. Well, that is cleared, now to find out what the black mystery boxes are...

author: MacAttak
author_rank: Unknown
timestamp: October 23, 2013, 05:56:48 pm
content: Quote from: Stefan on October 23, 2013, 11:19:12 amThe resistors are pull-ups.That bottom-most horizontal net connects up to +V right under d22 in the center of the schematic. And those resistors connect that +V rail (from pin 36) directly to pin 2 of those red boxes.edit: that was dumb, yes they are obviously current limiters.

author: MacAttak
author_rank: Unknown
timestamp: October 23, 2013, 06:18:17 pm
content: The black boxes are mind boggling. The relay solenoid from neighboring relays are connected to pin 5 - and we know that the other side of the solenoid is the output from the regulator - so pin 5 acts as the switch controller at the very least.Either pin 1 or 4 needs to be grounded - I'll guess that pin 1 is it.Op amp for speed control with the speed sense coming in via signal 8? And signals 6 and 7 are ground / power for the sensor?Also, what a Rube Goldberg series of relays! Wow, I guess this is how they had to implement milling controls when microcontrollers weren't available. All of those interleaved relays looks an awful lot like endstop logic, direction control, and the like.

author: SeanB
author_rank: Super Contributor
timestamp: October 23, 2013, 06:35:31 pm
content: Your black boxes are relay drivers, likely a delay unit either on turn on or turn off, as they do have the delay capacitor attached to them. Power it and see the voltage levels on the input and compare to the outputs, likely it will be a 5V TTL input and drive the 24V relay.

author: Kremmen
author_rank: Super Contributor
timestamp: October 23, 2013, 08:17:01 pm
content: Unfortunately i don't have these in my hands, not yet at least. The field guy however has - hmm - "opened" one of the black boxes and reports that there are a couple of transistors marked 3T2 and mfg is PI.. something. Also 4 carbon film resistors and what looks like an old school ceramic cap. If is all capsulated in translucent greenish stuff that may or may not come off.The studio team is also betting on some kind of delay circuit but that will become clearer once i actually get one into my hands. The funny aspect of the story is that these come out of a lathe where several boards have failed. As they are not available from anywhere the guy has kept buying lathes only to rip out this one board. So now he has like 5 unusable machines standing around, minus this board.Plan A is to remanufacture this board using modern tech. Should be a breeze once the mystery functions are sorted out. Not that they are all too mysterious but we need to get it right first time to avoid expensive bent metal.This board would actually be associated with joint motion endstops because those become problematic when this board fails. I have yet to see more of the schematics but there is little doubt that this is the case

author: lowimpedance
author_rank: Super Contributor
timestamp: October 23, 2013, 11:12:48 pm
content: Schaublin is not your average hack machine brand !!, and this guy has bought 5 others just to get the PCB !!!..I'll bet he would be only too happy to have a nice new revision of the cct. He could rebuild the other machines and easily make his money back selling them.

author: Kremmen
author_rank: Super Contributor
timestamp: October 24, 2013, 06:08:46 am
content: Yep!The field guy is coming in on Friday and we start doing an autopsy on the problem board. Like i said we are planning to re-implement it with modern components and restore all of the now idle machines to commission. That would make several people very happy