Worked a few hours on the thing again today. Making progress.
CRT
- Tried "retro-brighting" the plastic clamp for the neck, the part that I was missing. Didn't work at all, so I will have to get used to its massive yellowing.
- Lost spacer : went to the H/W store, bought a 8mm OD anodized aluminium tube and cut a new spacer, 8mm long. Used my tiny precision files made in China, to deburr the thing and make it look nice. Super happy with the result, looks like I bought one !
- put everything back together, reinstalled the CRT and gave it a test. I tested a Zener diode so as to display a test pattern that would give me a horizontal and vertical line as a reference. I played with the red knob of the clamp, to rotate the CRT, and it worked just fine. Te CRT is perfectly held in place, no wobbling around anymore, and I can easily fine tune the rotation. Had no trouble at all lining up the Zener diode pattern exactly to the graticule !
See pics.
KNOB REPLACEMENT
Big knob used to select the series resistor for the base of the transistor under test. Seller put an incorrect knob in there. Grey instead of black, and also with a big hole in the center, probably destined to host a secondary small red knob, I presume.
Once I had removed this horrible knob, I was in for a nasty surprise, see pic. Underneath the knob, 2 HUGE scratches, VERY deep!!!
Probably the guy didn't have the correct imperial size 1/16" Allen key so attacked the knob from under using a flat screw driver or something, and went crazy with it...
Problem is that even with the knob in place, you can still see a little bit of the scratches, it can't hide it all
I replaced it with the proper knob, courtesy of my 531A donor as per usual.
Now come the good surprise : before, with the old knob I found it was behaving strangely: you could switch from the last position of the switch (highest base resistance, 22k ) to the first lowest resistance, 1 ohm) !! No stop ! I fond this crazy as one could easily by mistake blow the transistor under test in the blink of an eye ! I was bitching at Tektronix !
BUT... when I went to put the new knob in place, I had forgotten what position the old knob was in, so I reset the shat to put at one end. Screwed the new knob and.. hey presto, now you can't blow your tranny ! You can't switch carelessly from the highest to the lowest anymore ! Tek was not faulty, the old knob was imply not adjusted properly that's all ! Problem solved
So the seller once again demonstrated his "talent"... destroys the face plate while taking the old knob out. Then can't even be bothered to put the correct knob and to top it all can't even be bothered to align the knob properly, meaning basically he had no clue what base resistor he was using as the knob was displaying garbage !
this guy blows my mind, really does !!! And he teaches electronics to engineers he said !!
TEST PANEL
Well I call that the "Test panel" for lack of a better term... it's the "pod" at the bottom of the instrument that holds the sockets to fit the DUT. Well the bottom right corner of said panel is bent out of shape, it's sticking out. This also causes a binding post that so happens to live there, to consequently follow suit : it's not upright anymore, it's leaning a bit to the left, hence it no longer aligned with the other two binding posts above it. So I went to pull the panel out of the pod, hoping / thinking it would be easy and I could try to straighten the panel at my (mechanical) work bench.
Well it was not so easy...
There are four screw one can see from the outside, one in each corner.. I though OK let's just remove them and I can pull the panel. Nope. The top 2 screws you can remove. The bottom two you can loosen them but that's all, then they spin round, no luck. There is a nut behind the panel but it's not captive. Tilted the 575 on its side... oh there is a bottom cover one can remove. 3 screws. Then you get to see what's inside the pod, and you can remove the two nuts. But the panel still won't move at all.
For that you need to free the switch : removed its big retaining nut from the outside. 16mm ( 5/8"), but need a deep socket so as to be able to clear the bat of the toggle switch. Standard socket no joy. So how do you do ? Well lucky me, I had a deep socket for the spark plugs on my car... it so happens to also be 16mm, how cool !
So ow you can free the panel but... you can only lift it by a couple inches tops ! Because the bat of switch won't clear the panel, almost but not quite ! So the switch is keeping you prisoner !!! So to pull the panel for good, one would have to desolder the very many wires going to the switch, which was way more than I had planned on doing, and way more than I could do this evening. So I tried to straighten the panel in situ ! Put a couple layers of masking tape on it to avoid marking it, then grabbed a pair of pliers and had a go at it, crossing fingers and proceeding with caution as you can imagine.
Well it went well. I managed to bend the corner of the panel into shape without making it look worse than it already was. It's spotless too, tape did its job.
Well to be honest I should have bent it a tiny little bit more... The corner of the panel looks good now, not sticking out any more, but the binding post is still sliggggggggghtly misaligned, just a hair. So I think later on I will probably have another at it. But I am splitting hair really. It looks fine. If you don't know what to look for, you would never see it I bet !
So overall very happy with the result.
ELECTRICAL
I just noticed that if you test a transistor, and if you look very closely at the CRT for the horizontal parts of the curves... then you see that lines are not "solid"... they show like a tiny ripple all over them ! OK you say need to recap the power supply... maybe but as I said earlier, I have already tested the 3 main rails, -150/+100/+300 and they are all fine with very low ripple, it's within spec.
It does not do it when I test a diode... only with transistors.
I think I found the problem... think it's indeed a power supply, but not an obvious one.
As I had the 575 on i's side looking at the bottom of the test pod... my eyes inadvertently glimpsed at some canned caps, and noticed that two of them had a suspicious looking terminal ! See pic. The positive terminal is covered in ... I don't kn,ow what. Looks like these caps leaked. Looked them up in the schematic, and then it all made sense : they are not part of the 3 main supplies I had already tested good. No. These 2 caps are part of a gang of 4 identical smoothing caps all in parallel : x4 2000uF caps, that filter... the power supply that supplies the base current for the transistor under test ! So yeah, I can understand how these faulty caps could forward their ripple to the screen, and why it would not affect diodes, since in this case, a dipole, you are not using the Base Step Generator so not using this power supply !
So... that's cool, looks like I may well be soon fixing yet another problem, and make the display on this puppy even more betterer as some would say !
I will replace all 4 of these caps I think, not just the 2 faulty ones. Not going to put crapacitors so I need to order online, so will cost an arm in shipping/minimum order, for 2 Euros worth of caps, pfff.... what wouldn't I do for my little 575...
Will have to buy some more stuff to meet the minimum order... but no more than that.
BTW, I pulled the condom off of one of these cans, and it says 30th week of 1963. So mine is 58 years old !
Will probably be 60 by the time I am done restoring it....
Caps all rated at 20V.
CLEANING
Now that I fixed the test panel and knob.. thought it was about time to finish the job by giving the front of the instrument a good cleaning. Basic stuff, 30 minutes, no taking apart of anything, just some detergent with hot water in a spray bottle, a stiff tooth brush to clean all the crap on the knobs and every where... and off you go. 30 minutes later it now looks much better. Test panel is now so much more pleasing to look at ! Just compare before and after pics...
Now that it's clean I can see what defects / imperfections are left. Answer : all of them. That poor face plate is riddles with a myriad o very deep scratches, worn out spots, stains... it's hopeless, will have to leave with that. Again the poor 575 was in such a poor overall shape inside out the it was clear from day one that I could not do miracle and turn it into a concourse winner no matter how hard I try... it's worn out, can't fight that !
So the goal has alwyas been to make it look as good as possible, do everything that's reasonable, but that's about it.. I am no magician !
Anyway, I enjoy it much better already with what I fixed so far and this first pass at cleaning it, and anticipated the future improvement I will make to it's appearance as I go. So I think I can make it look quite decent and that will somewhat balance things out....
Test panel : as you can see, the paint is worn out / faded toward the left. I think because that's where people put their greasy fingers whenever they stick a tranny in the test socket. However, all is not lost ! I noticed that the artwork is NOT printed on the panel, as it is on the 500 scopes. No... look like Tek wanted to innovate with the curve tracer... all the artwork is actually engraved !
ALL of it... text, lines, symbols, absolutely everything. So basically I could fix the paintwork by just adding some more paint in the "grooves", then wiping the excess and that's it ? Will need to experiment and ask around what kind of paint is best suited for that application. Need to have it custom mixed too, to get the colour right... so not something to improvise, but sounds doable eh ?!
Then I looked at the face plate.... you won't believe it.... they went wild and also engraved the face plate too ! ALL OF IT ! There is not a single thing that is printed on the face plate ! Even the Tektronix logo and accompanying text, it's all engraved ! wtf:
SO !!! That means that ONE DAY, when I am retired and have lots of time, and some money to spend... I COULD fix this 575 after all ! I could just sand down allll the scratches and blemishes and ever defect, make it 100% perfect. Then I would have to send it to some specialized company so they can re-anodize it just like Tek did. Then I can go wild with black/red/blue paint and redo all the artwork, then a couple coasts of lacquer to protect it all, again like Tek did... and hey presto, a brand new face plate !!
I could also do the same all the chassis parts, most notable the lower deck, which are pitted/ corroded beyond recovery. Cleaning it will never make them look shiny and spotless again, forget it
So here too, I could just sand them to removed every bit of pitting, then anodizing, then I will have to redo all the printing on it (vacuum tubes types and part number mostly), then lacquer. Brand new chassis.
But that's just a dream, it's well beyond the scope/ambition and budget of this restoration. But that's OK. Everything I do now, is something I won't have to do later on if I decide to have another go at the restoration one day.
Well overall it was quite a day for my 575 I think. Made quite some progress. fixed a few things, diagnosed some others, gave it a good clean, now looking much better.... yes it's a good day for him !
A few pics and off to bed, it's 7AM FFS !