Oh a minter then, great find that some gorilla hasn't been at this one. For sure that adapter has been fitted since early on and preserved the dielectric.
Picture of the two bottom UHF connector so you can compare. Honestly I do'nt see the point of restoring these scopes unless you also replace all UHF connectors. The old ones look so crusty and ugly, it does not matter how much you clean the face and polish the knobs, the scope will only really come to life visually, once it has good looking UHF connectors. I noticed that when I restored my first type 317. Unfortunately replacing those UHF connectors is a lot work as you need to remove the face plate which of course requires to take every single element composing the front panel, out of the way. I remember that power switch being a pain. The 317 being very compact makes it all a nightmare. I am hoping my larger 500 scopes will be easier...
As for rework, I take that back ! I just flipped the scope on its side so I can pull the bottom cover and have a look in there... oops !
Nothing massively wrong mind you, but not perfect eitehr. Will need some rework, again, from me this time, to tidy things up a bit.
So what I spotted :
1) Of course the guy put a modern power cable in, but this was done properly, nothing to complain about. Unlike the job that was done on my 575 where the guy clearly attempted to murder me....
2) Guy rewired the primary of the main transformer to accommodate for the higher mains voltage we have these days. You can clearly see that the corresponding ceramic strip is full of flux residue + the jumper is hardly factory looking shall me say ! But what is a bit strange is that his jumper connectzs pin 8 and 3, which is not a valid combination according to the table printed on the transformer ?!
He should have wired 8 and 1 not 8 and 3. Looking at the schematic for the power supply, using pin 3 instead of 1 make for a higher voltage. Either the guy screwed up, or the other way around he was anal custom wired the primary to try to adjust as closely as possible to his local mains voltage. So would need to wire it properly between 8 and 1 as that's meant for 248 Volts which is what we get around here these days.
3) Next to the transformer, there are a couple small ceramic strips that hold the test points for the power rails (-150v, +100V, +300V and +400V UNREG ).
Strips also hold 3 beefy 10 ohm resistors, which Tek always pus in these scopes, in series with every rail, right after the full wave bridge rectifier.
One of those 3 10ohms resistors, clearly has been replaced with two 27ohms resistors soldered in parallel. Correct type of resistor, power rating less per resistor but since there 2 of them, seems appropriate. Value well... two 27 in // makes for 13.5 ohms instead of 10, close enough I guess he thought. I guess he didn't have a 10ohm at hand and/or not of the proper wattage. The solder joints look clearly how you doing, his iron clearly was not powerful enough for the job... so that would need redoing, with a proper 10ohms resistor as well of course.
This resistor belongs to the 300V rails, which also gives you the 400V UNREG rail. The latter's only purpose in life is to power the primary winding of the HT transformer for the CRT. I have had this rail fails on several hollow state Tek scope, so I guess that's what happened here as well, hence had to replace this resistor. If I were to remove the shield of the CRT circuit, I bet I would find some more rework/repair in this area as well...
I think the reason this circuitry likes to fail might be because there is a can cap in the CRT section in the upper deck, that filters this 400V UNREG rail. It's voltage rating has not much headroom to begin with, so when you plug the scope today on a 250V outlet, the cap that's already old and tired, sees a voltage that's actually in excess of its rating. But I am not sure it's all the story because there is also a 3.3K resistor in series with the supply, upstream of the cap, hence limiting the current to 120mA which should be plenty low enough to not cause the beefy 10ohms resistor in the power supply to blow.
So I don't know...
Anyway, I know it' s a common failure mode so am not surprised at all to see it here.
This is probably what prompted the guy to rewire the transformer, I would guess....
Which leads to the next question knowing how anal Vince can be......replacement of any/all rusty nuts and bolts ?
Again there is not rust on this scope so no hardware to replace !
Well other than the UHF connectors I mean.
I have never replaced any screws so far ! I am only considering it strongly for my 575 curve tracer because it's really in a terrible, terrible condition compared to any of my other Tek scopes !
So much stuff wrong with the 575, some being not fixable within reason/budget/time, that my reasoning is "let's try to improve as much stuff as reasonably possible, hoping it would make the few remaining issues more acceptable".... kind of mindset ! See ?
Obviouslty the nice thing is that the effort I put into researching this screw stuff for my 575, will then benefit all my other Tek scopes potentially, or any other old gear I might buy in the future. So it's not just for the 575.. it's also an "investment"
Anyway, could not help myself sorry, I powered the thing up, have no variac yet, SUE ME !!!
Went just fine
Scope basically works, but does some funky stuff of course, so needs some electrical debugging, most likely as always, a few caps and tubes to be replaced.. but all the fundamentals are good !
Cooling fan starts on the button, this alone is an achievement.. I have never managed to get it working properly in my restored 317... so might swap the motors !
I can display a signal, trace is sharp and bright, stable, trigger works perfectly, sweep too. Can display the calibrator output. Squares are clean, no undershoot nor ringing. Nice clean square wave. You will I hope appreciate the quality of the screen shot. ZERO reflection, excellent contrast, sharp clean trace... COURTESY of .... well I happen to have a viewing hood for the 317 !!!
Make a world of a difference when trying to take pics of the screen.
I wish I had a hood for my 500 / 5 inch scopes !!!
If I can't find one at a reasonable price, I might try and fabricate one.
What needs fixing :
1) Horizontal amp : trace spans only 50% of the width of the screen.
2) Vertical amp : DC balance out of wack + none of the attenuator settings are good, needs calibrating. Probably just tired 6AU6's again, that make all the attenuation settings out of wack in unison.
3) Now for the really funky stuff that I can't quite explain where it comes from. The trace gets distorted in the following way. It's most obvious when you feed no signal and just display a flat horizontal trace on the screen. So that's what I did. What happens is that when you use the Vertical control knob to move the trace up and down the screen, as you do so, the trace is not horizontal anymore. Instead it develops a "slope", it tilts a bit. The farther away you move the trace from the center line, the more pronounced the slope becomes. If throw the trace to say the upper edge of the screen, you get maybe I don't know, a 25+ degree angle. The issue is perfectly symmetrical : if you move the trace toward the bottom edge of the screen, it will develop a similar slope, just negative instead of positive.
I can't see how this could be cause by the H or V amps. It's like the CRT is doing it... maybe it got damaged during shipping, the internals of it got bent/out of shape and the beam is not deflected properly anymore. Not a big deal as I have 6 of these scopes so I am sure I will have a good CRT somewhere !
However the fact the problem is 100% symmetrical makes me think, just gut feeling, I am incompetent bear in mind, that it's probably not an internal damage. CRT HV problem ? It's certainly not low nor tired.. .trice if sharp and bright, even when I cranked up the sweep speed. I also had it running of well over an hour and still going strong. Could be TOO Strong maybe ? Could check that cathode and PDA level to make sure it's not too high.
However I am not sure the symptoms are compatible with a HV out of spec...
My best bet is just dirty contacts at the CRT neck connector. Had that in my 575 and it cause not these exact symptoms, but stuff in the same vein where the trace would get distorted depending on where it was located on the screen.
Some pics, then off to go do some work on the house, 3 interior doors / frames to paint. Bought expensive fancy lacquer from my local Pro Tollens paint shop... hoping the result will be worth it !
See you later....