OK worked a bit on the thing, not much but what's done is done...
Fixed a couple items from the "mechanical" trouble-list...
1)
Added missing screw to the triangular stiffener, LHS, between lower deck and rear panel. Courtesy of the 531A as usual. Well to my dismay I didn't find the 100% correct screw, somehow. I mean it's the same shape, head, dimensions etc, but the surface finish on the head is slightly looking yellowing if you pay attention (visible on the pic too). It's very slight, but enough for your brain to notice something's "off".
Not that pronounced so I won't lose sleep over it, but I would still like to find a screw with the proper finish. I guess I will just have to visit one of my other scopes... bummer. Trying to take as many parts off of the 531A and leave the other scopes alone, but I don't think I will have a choice here.
Anyway, it's much better than with a missing screw, so am happy with it for now
2)
The missing beam / stiffener, top right of the cabinet, that goes from the panel all the way to the back. I was about to salvage it from the 531A. However it would not fit as is, because the cabinet of the 575 is actually 2 inches shorter than that of a regular" 500 scope. However given the shape of it, i.e a basic extruded shape (no joggling at the end for example, or any machining), I could literally just cut to length !
Then just drill couple holes for the screws holding it to the chassis, and that's it. So I was starting to look closely at the holes on the chassis of the 575, and noticed something odd.... the hole are.... not.... countersunk ! But they HAVE to be in order for the screw to fit ! It's just not possible otherwise !!! So that had me baffled.. only explanation is that there NEVER was a beam in there, despite the logic, and despite the hole being present ! I t was hard to believe but the evidence was there, pretty compelling... so I rushed to Tekwiki to check pics of the 575.... and what do you know... pics do NOT show a beam on the left side either ! Checked again, this time for B&W pics in the service manual... still no beam !
Then checked the 531A... THE SAME !!!
So all this time I thought I missing an obvious, huge piece of the chassis, and in fact there was nothing missing to begin with !
So that's one problem "fixed" kind of !
Then turned my attention to the 4 crapacitors soon to be replaced.
I pulled / desoldered a few wires so I can take them all out of circuit to make reliable/meaningful measurements. Before touching any wire, made sure to take a good close-up pic of all the wiring pertaining to these caps, so I can put it back properly... my memory is not that great and after only one hour I cna come back to the bench and already start wondering where the hell THIS wore goes to !
So since it will take a few days for the caps to arrive, no choice... PICTURE !
Then I could measure them all one by one.
1) Capacitance : they are rated at 2000uF but no indication of tolerance on the cans or part list... but from memory on other scopes, it can be as wild as -50/+100% !!!
3 of them read 3000uF and one read 2680uF.
2) Shorted / discharged all the caps, the moved on to DC resistance check. This one was a bit weird. At first, it's a short for a split second then very quickly climbs up to 3K or so, the slows down dramatically and slowly keeps climbing. After a few seconds it gets to 20 or 30K, then stops there. Not good. Then if I remove the probes, and put them back on like almost immediately, a second or two, then it now reads much higher. Depending on caps, 750K or 1.5M or 3M tops. But it does not climb. It just reads this value instantly and sticks to it.
No sure I understand 100% what's going on. However what I do understand is that the max they will read is in the order of 1M give or take, which can't be good for a capacitor eh ?!.....
So they do need to go indeed !
Tried to remove on these caps just to see how easy it goes. It's a nightmare : The 4 ground tabs go through a narrow slit in the base that's screwed to the chassis, then the tabs are twisted to lock the cap onto the base. OK so I though I just need to remove the solder, straighten the 4 tabs and it should come out just fine.... nope, forget it. The tabs impossible to straighten well enough to even remotely hope for them to go back through the narrow slit they were inserted into when new. Plus, the tabs are perverse and feature a "locking" mechanism, so to speak. It's like two little "spikes" on either side of the tab, they "expand" when you twit the tab to lock it, and then act as an ratchet thing... you can twist one one, it's locked, then the spikes fighting and keep the tab from being twisted back in the other direction. Plus, doing this in situ just makes things more difficult.. and you have FOUR oof these monstrous tabs per can... and TEN cans in the instrument, should you wish to pull them all ! So instead I had to resort to removing the two screws that hold the base onto the deck, problem solved. However access to the head of tehse screws, top side of teh deck, is absolutely terrible. I managed to get one cap out as an exercise... but that's it. I will put it back where it can from, and won't touch the other cans, like ever.
So the new caps will have to be soldered bottom side, I am not going to go though the trouble of "restuffing" the cans. Will just pull one wire to disconnect them, then solder the new caps straight to the tabs. Like MED did on his 547. It's ugly, looks out of place, looks not period, but... I will have to live with it...
Second thought.... OK maybe it's possible to remove these cans.. just had another look. It's kind of a domino game : now that I have removed one, it gives me access to the screw of the next can, then the next, and so on. As for the second row of cans, hidden in the center of the scope, the screw that's behind the cans is 100% inaccessible because there is a large aluminium panel all over that area... it's the sub-chassis for the collector sweep stuff, on the other side of the chassis ! So.... if I remove this entire sub-chassis, then I can get access to the screws and remove the cans. But removing the chassis is not a 2 second job... it's tied to a big transformer, so some wires to pull, and also tied to the front of the chassis, the face plate, because it hold 3 rotary switches. Knobs are connected to the switched via shaft couplers, so you need to free those 3 couplers, in situ, with crap access.. one is close to you it's OK, but the last two are buried in the center of the scope.. normal Allen Wrench won't do ti, no access. Only way is to get a dedicated 1/16" screw driver, and a long one so you can reach the couplers without having to shove your hand inside the scope or else you don't see what you are doing and you don't have space to manoeuver / turn the screw driver....
So I ordered a crew driver... cheapest I could find was an extremely ugly looking "WERA" branded thing, looks like a Rigol style wise, but for screw drivers...
https://www.amazon.fr/Wera-Kraftform-Tournevis-argent-05118076001/dp/B001555FYK/ref=sr_1_5?__mk_fr_FR=%C3%85M%C3%85%C5%BD%C3%95%C3%91&dchild=1&keywords=1%2F16+tournevis&qid=1631748425&sr=8-56 euros plus 5 for shipping, but at the checkout Amazon said I have nothing to pay at still had some Euros left from an old coupon/voucher my ex-company gave me. So free screwdriver for Vince. Ugly one, but free..... no here is hoping it's gonna do that job ! Have a 1/16" tiny Allen wrench and the size is ACTUALLY is, is 1,5mm instead of 1,6... so it can't grab the head, it spins round and round in it !
On the SAME set of wrenches, I have also METRIC wrenches. I tried the 1.5mm one, hence should have the exame same problem, too small... and I do, using ONE side of the wrench (the small side)... but somehow the OTHER side (long side) of that same wrench... fits PERFECTLY !
So... cheap wrenches can be pretty much useless, beware !
Anyway, I have order the caps. Didn't get them from Farnell to save money (minimum order 35 Euros for free shipping). So I searched a few smaller suppliers to see if they had decent caps, and then checked how much they charged for shipping... overall the best deal was not from a French shop, but from Reichelt in Germany. 13 Euros delivered for 10 caps, top quality, Nippon-Chemicon, 105°C rated for 10.000 hours. No 2000uF 20V as originals were, so grabbed closest, 2200uF (+/- 20%) 25V.
Also ordered the cheap component tester, can't wait to play with this thing, like millions before me already have !
OK that's it for today... now waiting on the things I ordered...