11401 Tek Scope : spent a few more hours with the thing, trying to investigate my minor problems, just for fun...
1)
Slightly dim CRT : " fixed "... found a menu where you can adjust brightness. It was set to only 60%. If you set it to 100% boy it's briiiiiight.... Set it to 70% to get it just bit brighter but not too much... zero burn marks / ghosting on this 32 year old CRT so I would rather it stays that way...
2)
Inoperative " Power On " status light on the front panel. First made the assumption it was an LED, so checked with DMM in diode mode. Said open both ways. Checked in resistance mode, 27Meg both ways... chances of a status LED going open is next to nil I guess, so might be a tiny incandescent bulb ? I guess that would make more sense since the two wires going to it are both black, no "polarity", and on the PCB where it plugs to, the pins also don't give any indication of polarity whatsoever. Checked those pins with the DMM... shows 5Vdc. So I guess that's an incandescent bulb, unobtainium I imagine, but it's round and calipers say about 5mm in diameter so.... could possibly replace it with a standard green 5mm LED ?!........ worth a try I guess.
3)
Defective probe calibrator, shows 300mVdc and no AC. This is fed by a semi-rigid coax cable, very long, that sneaks its way under the video board towards the back of the scope, then plunges between the plugins backplane and PSU, to emerge on the other side of the scope, to connect to one of the two large boards under there. See pics.
No schematics in the service manual sadly... so tried to follow traces on the PCB, backwards. It goes first to a diode, which tests good. No signal on the other side of the diode / anode. Then the anode goes to two components. A flat blue thingie that's probably some kind of capacitor ?! Then it also goes to a 3K resistor, which tests good too. Still no signal on the resistor. And that's about it because then it goes to an inner/hidden layer in the PCB, so I am screwed !
All that the manual can tell me is that I am supposed to get 6Vpp.
4)
Scope is still hard of hearing : rarely powers up first time. Either it does not react at all, or it freezes at random places in the boot process. However it always eventually completes boot, and once it does, it works just fine for hours on end, no worries. Still zero POST errors, and zero fault as well when I manually run the extended tests suite from the Utility menu.
So I am reasonably hopeful that it's just a PSU problem, that has therefore a decent chance of being diagnosed and fixed... rather than a problem anywhere else, where the chances of diagnosing it, never mind fixing it... are slim to say the least....
Skimmed the service manual, looks like there are only two power rails, +5V for the TTL stuff, and -5.2V ... for some fast ECL logic somewhere, I guess. Can't believe that there are only two rails in this scope but... looking at the 3 largest boards in this scope, ie the 3 I can actually see, covering the top and bottom of the scope... they have a very distinct power connector, can't miss it, and they have only 2 or 3 wires, carrying indeed only +5V and -5.2V ! Wow.... how simple.
I checked both rails, they are perfect. Spot on, and next to zero ripple. As sweet as one could possibly want them to be.
So I doubt the big filter caps are gone in this PSU.... they clearly do their job.
So must be something to do with the power on timing/sequence maybe ? Maybe they are too slow to establish, and that disturbs the digital board ? I don't know... something wrong with the PSU other that merely voltage levels and ripple.
Anyway, no time to work on this scope for now, but when I do clearly I will have to attack the PSU. It's made of 3 things : a main shielded block, and 2 more boards. Tek calls them the "regulator" board and the "rectifier" board... they are stacked on one another, and both of them are under the main block. This ensemble is not accessible at all... requires dismantling the scope. So would need to take the scope apart, and check with a scope how the rails are doing at power up, if they are lazy or glitchy or what...
I can have a very limited peek at the inside of the PSU block, through vents. I can see some big electrolytic caps and they all look brand spanking new. No obvious sign of bulging at the least. Quite a few electrolytic caps on the boards (other than the PSU I mean), but it's all through-hole and they all look like new. It's too old to have any of the dreaded first gen SMD electrolytic.... unlike my TDS 544A, ahem...
So that's good !
What else... scope has a "health" counter : keeps track of operating time and number of power cycles. See pic.
12,460 Hours total, and 1363 power-ups. so 9+ hours per cycle in average. So basically scope was running all day for a few years...then got retired... Cal stickers on the thing indicate it was last calibrated in 2006 IIRC.
Hardcopy / Printer : .... scope showing its age ! Only printer options I am given are : either 8 or 24 pin dot matrix output, that's it ! Doesn't even specify printer brand or model, just says " 8 pin " or " 24 pin ".. so I guess that means back in the day all dot matrix printers used the same protocol / language ?!
Maybe some Firmware update might give me more printer drivers...