Tek RM17 scope repair updateWell it's fixed but I need to tidy up the replacement of the 3 section electrolytic can cap in the power supply, that was causing the pre-amp to misbehave.
Papa Smurf would just solder the new caps underneath the chassis and leave the old can in place, for convenience, but I thought I would use that scope as an opportunity to see if I can do something cleaner.
I would like to remove the old can, and make a little PCB with the same shape as the old mounting plate that's bolted to the chassis. Either made of metal or insulated depending whether you want the common of the cap, to be floating, or connected to the chassis / ground.
It would also be a good exercise to get more time on Kicad, to help me learn it, as I am trying to.
So I go to remove that cap. Desoldering the 3 wires from it was the easy part...
Then you need to get to the two nuts that hold it to the chassis..... first there is this big trim pot that's in the way, so you need to desolder it from the ceramic strip, then remove the two screws that secure its mounting bracket to the chassis, and get that assembly out of the way.
Then you still can't get access to the top nut because a harness is right above it. So you try to lift it a bit and get a spanner on the nut... but you can't use the ring part of the spanner, cause the spanner can't get of course flat enough because of all the stuff surroundng the bolt. So you can only use the open ended part, at an important angle, and with only 60° angle resolution you can't really get it on there, it's not fun.
But... you only need to work it a little bit, just enough to loosen the nut. Then you can finish the job from the other side of the chassis, with the screw head... but well, that's only possible if you have a LONG / non standard screw driver, because the caps are tall and right next to the chassis sides which are tall. Luckily I had recently bought a long one, well, 150mm, longest I found at the local H/W store, in anticipation for adjusting a particular trimmer in my Rochar Nixie DMM, where you need a long reach to set one of the trimmers.
So I could get that top nut eventually.
So then the bottom nut... oh, it's even worse. Even the open end of the spanner can't be maneuvered on the nut, so you do need to get a socket on the nut... but there are components soldered "in the air" together, right above that nut !
So need to desolder that first and carefully bend the components a bit to get them out of the way. Then I could get a socket on it.... of course freaking Imperial size, but I did get a set of Imperial spanners and sockets, 5 years ago when I restored my first Tek scope
So I had at long last that cap on the bench, phew.
But still not out of trouble. I now need to remove the mounting plate from the cap, so I can take measurements.
So I need to desolder the plate from the cap, one tab. It's twisted / locked as well. So you first need to remove allll the solder from it, if you want to have a chance of being able to straighten that tab so it can hopefully get out of the slit in the mounting plate, that it was inserted into.
So I need to hold that cap firmly while I am working on it.... but I don't have a vice ! Well I do, but I can't use it because its C clamp does not open wide enough, so it's unable to grab the edge of the bench. So it's useless.
So had to hold that cap onto the bench with two fingers while using the other fingers to hold the solder wick, and the iron in the other hand. But... iron was not powerful enough (50Watt Weller Magnastat) to melt BOTH the solder on the tab AND the wick together. Without wick, I could melt the solder. But as soon as I applied the wick, too much thermal mass, iron quit.
Added some flux, helped, eventually managed to pull that mounting plate off the cap, phew.
Then I will have to do it all in reverse when in installing the new cap(s).
It's a lot of fun.... probably why Smurf in Chief doesn't bother....
But it's an exercise, I want to do it at least once, then decide if I want to keep doing that or not. But at least it will give me some experience and new options for future can cap replacements. Having more options in your tool box is never a bad thing, is it...
OK so now the challenge is to draw the outline of the mounting plate in Kicad !!!
I need to draw circles, and draw tangents to connect them together so I can draw the ovoid outline of the plate. Then the cap has 3 sections / terminals in it, so I need to arrange the 3 terminals in an equilateral triangle shape, and be able to rotate that triangle at a random but accurate angle so I can line it up as required.
I am not even sure Kicad PCB editor can do that ?!
I guess I will find out....
Maybe you can do it in a mechanical CAD program, and import the DXF file into Kicad ?!
I see the new Kicad v6 is out now. Maybe it has more drawing options / tools / wizards than the latest v5 I am using currently.
Oh boy, wish me luck !!!
So I need :
- A more powerful soldering iron
- A small vice that can be quickly and easily be secured to the bench.
- A PhD in Kicad PCB design to be able to draw the shape that I need to draw.... and then hope that JLCPCB or else, will be able to route it / cut it out....
19H45 here, time to go cook something to eat.
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