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Vintage 500 Series Tektronix scopes

If you wrap it in tough plastic, and seal the edges with parcel tape, and include silica desiccant inside, I think you'll find it'll survive for many years, the only problem being if the bag package gets damaged. You can get those plastic vacuum bags people use to store clothes in their loft, which are sturdy and have a strong double zip-lock type arrangement, and hold a mild vacuum for years. If one was big enough to slip the scope in, that'd do nicely.

Thinking about it that sounds like the best strategy. I’ve ordered some large (67 x 35”) heavy duty builders rubble bags that it should fit in (my maths is crap) and some silica gel. After I’ve finished washing it and allowed it to fully dry out over the next few weeks I’ll double-bag it with the gel and really tape the edges securely. It nicely postpones any decision.

If you do strip it for parts, concentrate on the bits that can't be replaced, so knobs, the front panel graphics, the transformers. The electronic bits will be replaceable (but expensive) but you'll be really annoyed if you damage a knob or something like that that is obviously visible from the outside!

The annoyance is being from different series/eras (530 vs. 540) they are not as similar as one might think/hope. If they were both in the same cosmetic condition I’d have picked the 533 as the restoration candidate as it is a more simple pure valve construction. All the big parts (transformer, HV, CRT etc) are different and not compatible.
 
The annoyance is being from different series/eras (530 vs. 540) they are not as similar as one might think/hope. If they were both in the same cosmetic condition I’d have picked the 533 as the restoration candidate as it is a more simple pure valve construction. All the big parts (transformer, HV, CRT etc) are different and not compatible.

Oh, that is annoying! In my world, i've got my dodgy TDS520A back up and running, and it was 'operator error' in that I have been moving parts between it and the broken TDS644A i'm trying to repair, and had managed to re-flash the wrong image to the 520A NVRAM, leading to a boot failure. Once I realised what was going on, it's all making a lot more sense, and i'm back to just the one broken scope.

The broken scope looks to have an issue with a custom ASIC which is not pulling a pin high during the initialisation, so i'm got the task of unsoldering it and replacing it. It may be that having removed it I find a corroded trace under the chip, so giving it a good clean is enough to get it working again. The replacement parts are non-existent, so it's a case of salvaging one from another scope. However, in this case, the scope itself has multiple of these parts, and I think I can re-purpose one which is used as a floppy controller to be the memory controller (they are the same ASIC but with multiple circuits which are activated by different input conditions).

This will (hopefully) lead to this failure being resolved, and the floppy controller not working, but since the machine doesn't have a floppy drive installed, fingers crossed it'll work out. The chips are SSOP packages, with lead spacing of 0.65mm so it's all a bit scary to remove these from the board, with 80 odd pins per package on 4 sides!

Given though that the reason to get this scope in the first place was to learn more about electronics, do some digging and improve my soldering chops, worst case it turns into a doner board for other projects.
 
Given though that the reason to get this scope in the first place was to learn more about electronics, do some digging and improve my soldering chops, worst case it turns into a doner board for other projects.

Interesting stuff, worthy of a thread IMO. It certainly sounds like it has far more to do with computer restoration than scope stuff at this point. The TDS range look like really good scopes.

PS I’ve searched all the usual places but has anyone any insight with regards to decoding Tektronix serial numbers? All my stuff has the serial in the 100xxx format. The 1 being Guernsey. Beyond that the number has to just be sequential for that model, e.g. my 543B has a lower serial to the clearly much older 533A and both are vastly lower than the CA plug-in. My suspicion is the Guernsey serials are different to the US ones and do not correlate to any revisions stated in the manual, though I’ve not proven this to myself yet. I’m pretty sure my scope dates from 1967-8 as all the Mullard date codes (which I can read) seem to be ‘67 unless the valve has been replaced (e.g. there are a couple of mid-1970s or later Mullards in there).
 
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That’s as good as I can be bothered getting the 533A. Nowhere near as filthy as it started, but nowhere near as clean as I’ve got the 543B. Once I’ve given the case parts a bath it is good enough to bag-up and store.
 

I’ve been watching a fair few videos on this guy’s channel as he seems to really know what he’s doing with vintage Tek scopes. There are full restorations on several including the monster dual beam 555. Over the course of his channel he seems to have shifted mindset between replacing caps to reforming them, and interestingly he doesn’t have any problem with the ‘Black Beauties’ and views them as a film cap (which the red print ones kind of are from what I can make out). He is far more disciplined and methodical than I was in that he checked and reformed every cap before powering up. I think I was very lucky indeed nothing exploded! One blindingly obvious tip that didn’t occur to me is that if you pull out the time delay relay tube it will just sit there on its heaters indefinitely allowing you to get some measurements etc. Nice to know for the future!

I have all the caps to hand to replace the ‘Black Beauties’ but as the scope seems to be mostly working and all rail voltages seem right I’m tempted to sit on them and do nothing.

I do still have some issues, most notably the plug-in bay socket seems really imprecise. It will often glitch or the trace even vanish if I tap on the plug-in front panel (either CA or G). I have cleaned the sockets and plugs as much as is possible with Deoxit, cotton buds etc, it is all absolutely spotless, but obviously worn (the gold coating has worn off). I wish I could find a NOS socket to swap in. There is one advertised on eBay, but it is not right, clearly very closely related, but not the same type as the moulding and mounting-points are entirely different. Still half tempted to buy it to see if I could transfer the pins across…

I also had/have an issue with the ‘Normal/Single/Reset’ sweep function. Initially it behaved as ‘Normal Sweep’ in all positions, though pushing it all the way to ‘Reset’ got the ‘Reset’ light to blink on for a split second. It is an exposed relay type switch and a dirty and tired looking one. I’ve tweaked the leaves of the relays so it is now working as it should be (the centre position obviously wasn’t making contact on one pair of leaves), but I don’t think it is going to stay done long term as it just lacks ‘spring’. At least I know what the issue is and can rob the switch off the 533A if absolutely necessary.
 
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Here’s the sweep switch. Pic taken before I took it to bits to flatten out a couple of the leaves that weren’t making good contacts. Got it back working properly again, but how reliable it will be I’ve no idea. Next time I’ll desolder it rather than dismantling it hanging from its wires, that likely cost me far more time than it saved!
 
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I couldn’t resist this Type Z plug-in on eBay (original listing here). It was absolutely filthy and in unknown working condition, but no one had harvested the valves so by the time eBay offered my a fiver off ‘seller offer’ (it was in my watch list) I hit the button. £46.99 landed, so less than the potential value of the valves alone. It has cosmetically cleaned up very nicely and after a lot of internal contact cleaning seems to be working as far as I understand it. The controls do what I kind of expect them to anyway. It is a fascinating thing, crazy expensive in its day ($525 in 1962!), and very interesting in construction with ‘turret attenuators’, which I had to dismantle to clean. All a good learning curve. Manual and details for anyone interested on the truly wonderful Tek Wiki.

This means I now have a working CA, G and Z plug-in, enough for two in the stand and one in the scope, so a fully working display set!

PS I can never get the CRT to photograph well, it looks way, way better in person!
 
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I have very limited knowledge of electronics, but I have always thought oscilloscopes were fascinating things. Back in the 60s there was a British built amplifier (I can’t recall the brand) that included a small 2inch dia oscilloscope screen in the front panel to show the waveform of what you were listening to. I liked this idea and since I was working for a university at the time I borrowed an oscilloscope and hooked it up to the 33, 303 I was using to see what music looked like. Orchestral music was all jaggy with overtones complicating the waveform but Milt Jackson’s vibraharp put out a pure sine wave, which surprised me.
 
Here’s a couple of internal shots of the Type Z as it is such an odd thing:

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This shows the ‘turret attenuators’ which are kind of a reverse stepped attenuator where the resistors are internal and the whole thing rotates, rather than the more usual fixed resistors and rotating contact blades. I’d never heard of this before.

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Here’s the other side which is far more conventional looking. It is about as clean as I can get it short of a full jet-wash. I think clean enough. Much to my surprise it makes good contact in the chassis as the interface plug was very badly tarnished. I worked on that one thing for at least 45 minutes bringing it back before trying it!

PS Never seen the EMI amp before, though some Marantz tuners/receivers had built in scopes. I think there was a silver-face Pioneer oscilloscope for one of their rack series too.
 
Here’s a couple of internal shots of the Type Z as it is such an odd thing:

52797490636_3eed948811_b.jpg


This shows the ‘turret attenuators’ which are kind of a reverse stepped attenuator where the resistors are internal and the whole thing rotates, rather than the more usual fixed resistors and rotating contact blades. I’d never heard of this before.

52796918167_9b58306bf0_b.jpg


Here’s the other side which is far more conventional looking. It is about as clean as I can get it short of a full jet-wash. I think clean enough. Much to my surprise it makes good contact in the chassis as the interface plug was very badly tarnished. I worked on that one thing for at least 45 minutes bringing it back before trying it!

PS Never seen the EMI amp before, though some Marantz tuners/receivers had built in scopes. I think there was a silver-face Pioneer oscilloscope for one of their rack series too.

The turret attenuators are similar in principle to the 13 channel turret tuners on old 405 line TV sets where individual tuned circuits were fixed to the rotor and connected for the appropriate channel.
 
That's proper tech!

I'm still working on 'old' but 'not that old' Tektronix scopes for fun.

I've just got a TDS3014B back up and running - this one had a failed power supply, and failing memory (battery backed up SRAM which has past it's use by date).

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These scopes can be hacked to 500Mhz bandwidth - this one is showing a sub 700ps rise time on a 10Mhz fast edged pulse generator, so hack successful.

The power supplies for these are a bit weird, they are always on, with the power button enabling the output voltage to make it to the power distribution board. This is because there was an optional battery pack, so the scope would charge the battery even when off, but the downside is that the not hugely efficient power supply is generating heat which knackers the plastics in the case, and damages the capacitors.

The power supply had blown everything on the feedback side, the isolator had stopped isolating, so large voltages reached bits they shouldn't, so it was a complete mess.

The battery backed up SRAM are unobtainable, so it's a case of fashioning a replacement from components which can be found. These DS1742W memory were easy enough to replace once i'd made the mis-play of ordering 5v memory rather than the 3.3v required...

Behind the scope is a new to me microscope for soldering work which has really helped as i've found myself struggling with small SMD components in the more recent things i've been working on, and behind that, more victims.

I've currently got a TDS210 that fails to start, another TDS3014B which had a short on its processor board, and a TDS644A which has triggering problems on its acquisition board.
 
It is amazing/quite disturbing that scopes of that generation (which looks like a new one to me!) are at the point of needing serious restoration surgery! Post a few pics of the guts next time you have one apart for rework. I’m curious what is in there. I’m assuming pretty much a single board computer with some proper scope inputs and protection up front. I’d still have hoped Tektronix used top quality caps with really long service-life etc even now in the SMD-era.

What’s the slot that kind of looks a bit like a 3.5” floppy on the front? Looks way, way too new to have one of those!

It is amazing just how solid these old valve Tek scopes are, they are beautiful things with a build quality beyond anything else I’ve seen, but I’d not choose to actually use one in real trouble shooting. The little Hameg HM303 does at least as much and is way more manageable, and something like the TDS range adds way, way more information and storage (useful for fault-finding computers that don’t want to boot!) etc. Just a shame the long-term reliability seems to have suffered. I’m amazed how much 500 series valve stuff just still works. All I’ve really done to the 543B is a ridiculous amount of cleaning, hours and hours and hours, replaced two or three tiny little caps, and stuck some oil in the fan. That’s about it!
 


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