I've dealt with this in industrial equipment. The copper tangs under the relays lose tension over time. When they are new, the tangs are bent out far enough so that they will bend a little angainst the contact pads to maintain connection. However, if the relays are left in the same position most of the time and that coupled with time, temperature cycling, and vibrations cause the tang to deform and lose tension gradually until they are only floating on the contacts. This is why the paper shim was able to restore a little connection, by pushing them slightly closer together. If you want a solid connection, you'll have to re-bend the tangs on the relays. That is much easier said than done but not impossible. Perhaps you could find a tiny shim to go behind each of the tang legs? Good luck and thanks for another great video!

I worked for an electronics engineer for a while in high school. He mainly used digital scopes but he always had that one bench in the corner with all the analog scopes on it. He would throw a sheet over them to keep dust off. I asked him why he keeps them and he just said "For when things get weird" and walked away.

I bought a pallet of about 20 of these scopes in the early 90's for $5.00. I didn't know what to do with them so I posted a notice at my university's engineering building and ended up selling most of them for $50-$100 each. Pretty nice return on investment! I miss old-style government auctions, mostly because people didn't know about them and you could get great stuff extremely CHEAP!

The way I was taught to clean those gold contacts is with a small strip of white printer paper and IPA. I have serviced quite a bit of old Tek equipment. I love Adrian's show, but I would strongly advise against scratching up the pads with a steel implement...

All of the pre-1990 Tek scopes are masterpieces of chassis design and circuit layout. The early tube-based CRT scopes are especially nicely laid out.

I think bending up the relay contacts will do the trick 100% since they are probably work hardned in the position they are now.

Hi Adrian , Ray Burke here , I use to work on the Tektronix Portable scope line. Most of the gold contacts shouldn't be scraped with tweesers, Tektronix in their manuals usually suggested using Isopropal Alchol and a this peace of paper in the service manual unsure about Deoxit? The problem with the CH 1 and CH2 Attenuators may be the outer mounting ring screwed to the Attenuators, using a thin open end wrench to carifully thghten them, they might be loose from connecting and disconnecting the scope probes. This could cause the signal to distort. You may contact the Tektronix support forums or the Beaverton Museum.

Tektronix are one of the finest made precision instruments ever made. These things were built to last.

That thing is forty years old. It's _amazing_ how well put together it is, and how good it still looks.

You should call the Vintage Tek museum in Beaverton. They will know how to fix this. Maybe do a field trip! It’s also a fabulous place to visit for sure.

The inside is a work of art, absolutely beautiful layout.

I chuckled when I saw the title of this video. Anyone that has worked in or familiar with the calibration industry will know how insane the electronics in instruments like this were. Big kudos to Adrian on this video tackling the issue! I was a young apprentice in the early 90s and I remember looking inside Tektronix scopes back then and feeling intimidated by the precision engineering. Although some might say an "easy" fix, there was a precise and logical approach to the solution. Hope that's all it was! Recently, my brain was blown by the fact that NASA had surface mount technology in the 1970s. I think I saw that somewhere on CuriousMarc's channel.

Thats a lovely scope. Everybody needs an analogue scope and a digital one, just like your multimeter :) Just a little warning, I used to make thick film circuits and if you are soldering to them you should use high silver content solder or the 60/40 will absorb the silver from the film traces

I’m not sure abrasion is necessary, but I’d totally consider squishing the spring pins on the relays since pressure helps the connection. Springs do weaken over time after all. It also sometimes behaves like there’s stray capacitance, so some of the pins might be losing contact but stay close enough to form some capacitance along with the circuit board etc. Either way reinforcing the pressure would be the simplest thing to try, since you noticed it’s pretty clean inside.

I had a very similar issue pop up in my LeCroy 9310 (with the gorgeous amber CRT). Long story short, after a total of 40 hours poking around in it, I decided to dump the Roms and have a friend look through them to see if we could find what controlled CH2s attenuation. Turns out that one of the 5 EPROMs had one janky bit of code and during the boot process it would internally switch to 1 Meg and there it stayed. Working on scopes of that era can be a real trip sometimes.

Somewhere around 400V is the typical input voltage limit for any real oscilloscope, old or new. Not in 50 Ohm mode though, this is usually limited to something like 5V. Note that these voltages are the limits with a 1x probe. I have repaired tons of these Tek scopes. The ones like this full of custom ASIC's are a pain because if those ASIC die it's mega bucks to replace them if you can find them at all. I've never seen this specific problem but I have replaced whole attenuater modules due to the ceramic PCB being cracked. I recommend taking a really close look at it, the relays, and the BNC (crusty connectors is very common even if they don't look so). One of the first things I do on these is Deoxit the entire front panel. Every knob, every switch, every connector, the power switch and other mechanical stuff back there. Most of the time this fixes all intermittent issues like this.

The difference between oscilloscope CRTs and TV / monitor CRTs is in the method of deflection. Oscilloscope CRTs use two pairs of charged plates to steer the beam instead of the usual deflection yoke. There are actually some very early TVs (late 1940s era) that used electrostatic deflection CRTs. On the digital board, the Motorola IC next to the EPROMs I'm 99% sure is a custom version of the 6800.

Try gently bending the contacts on the relays that meets the pcb they act like springs but the been in that position for about 40 years so with temperature changes they no longer make positive contact that should fix the flakey behavior for another 20 years. Just bend slightly.

Be very careful when touching, cleaning, and rubbing those open hybrid circuits, you can very easily damage the printed high-precision resistive ink printing, which will completely destroy the hybrid. I use to design, construct, and troubleshoot those types of hybrid circuit boards.

With the relay contacts being an issue, I'd go back in and give the contacts a tickle with a fibreglass pen, a very light touch though, if that doesn't do it, maybe bend the contacts very gently outwards from the relay modules to give them a bit more springiness, given over time they may have been bent inwards meaning they haven't got enough oomph to maintain a reliable connection... :)

Don't scape with metal, just use a fiberglass pencil, followed by De-Oxit to safely polish / clean the gold plated contacts. Sraping will lead to oxidation once the protective gold layer is completely removed.

I still have several Tek analog scopes from the 465 to the 2465 but I'm glad I no longer repair them as they were always a PIA. I remember taking the week long repair course Tektronix came and gave us technicians.

Back in the 80s I bought a cheap 1950s-era Dumont Cathode Ray Oscillograph. Good up to a megahertz or so. Having something like this Tek would have been a dream, though I eventually wound up using this exact model amng others at work for most of the 90s. I've never seen the inside of one, and all I can say is holy cow, is that thing ever packed full. Glad you were able to rescue it, very cool to watch.

I used this model daily back in the 90's while in the Navy. Loved them.

those digitally controlled analogue scopes were marvellous. The analogue stage was just a work of art, tolerances were just impossible at those high frequencies. I had a fully analogue Tektronics many years ago, it was "spent" but ok. One day I opened it and noticed like 1000 trimmers so I didn't even think of adjusting anything! Then I stumbled into a digitally-controller Fluke 100Mhz one. I opened it up and there was not a single trimmer to adjust, everything was done digitally! The best scope ever, but lacking digital buffer to stop the signal. On cleaning those pads, I am not sure I would use DeOxit. It might leave some protection behind which is fine for a C64 SID or VIC IC but might interfere with the tiny signals at high frequency of an oscilloscope's front end. One of the cleaners I am using is not recommended for signals below 1V for example. I would probably use isopropyl only and I'm sure Tektronics used something even better, likely in clean rooms! Without knowing much about those scopes, sounds like the relays might have develop some contact issues? I'm wondering whether a bath in isopropyl might help? As you said, you have to trust your instrument so right now that scope is probably useless. Great video as usual - what's your new camera?

If you ever have a question on analog test equipment, you should ask Mr. Carlson. He's my go-to radio repair guy, but he owns a plethora of analog stuff. I know you're a digital guy, but Mr. C and Shango066 are the best for this sort of stuff if you need a second opinion.

thanks a lot, fantastic video, i had one of them 2445 in my lab today, very much the same kind of relay problem, attenuator some points not doing their steps correctly, but we just worked the relays many many times it slowly got better, and now it just dont fail anymore :-)

Man that's an amazing piece of capable analog tech. My jaw dropped at some of the features.

We had these at school. As kids we had no idea what we were doing but it brought back so many memories!

Every one of these from the vacuum tube on up are built like tanks. Still great tools and are highly serviceable.

I love my 2230. Yes it's only 2 channel and 100MHz, but the analog/digital combo is just so cool to me. It's also the only functional 8088 machine I have haha. Seeing this 2445 was very cool!

thank you for everything you do!

This is one of those moments where I observe that technology has evolved backwards. This is really an amazing piece of technology of the 80s, extremely well constructed, something you rarely see in modern electronics.

Wow. Glad I discovered your channel. Excellent lesson in diagnostics. I know a ton about my 2445 and you haven’t even opened the case yet! Love it. (Mine works perfectly…but)

I love how the PCBs are literal "Resistor Cities"

I only just started watching, but make sure you replace the RIFA caps in the power supply, and the main filter caps too, when those start to get weak it puts too much ripple on the rails, which then causes the yellow axial tantalum caps to fail throughout the unit and short out. I've done some videos repairing my 2432A which is the same kind of design.

i love scopes. old or new. low end or high end. they are all fascinating (imo)

So cool i have the same ;) hope you get it working. If its the model with memory its great to change the battery inside so it dosent begin to leake. Love your channel keep up the good work :)

I bought a tex dual scope from Alabama Univercity trash at 2007.. They're great gadgets.. You're dominating subject very well.. Exactly..

My grandfather worked for Tek back in those days doing technical writing on the manuals. Always love seeing these old scopes. :)

Great job man!! This was a huge uphill battle. Your chances of success were slim, but you did an excellent job, and you know a lot more than you give yourself credit for. Keep at it and eventually she will be 100%. It's probably the BNC itself like others have pointed out, may be missing a tine. These are the best, and it's really wonderful when someone brings one back from the dead.

I remember having to use something similar to this back when I did some electronics courses, these analog oscilloscopes are built like tanks!

As a old and 8 years retired engineer in electrical (with Two exams in enginering (the second for an master of electronics) and 1.5 years studies in astronomi) this video gav me kind of years in my yes). Techtronix is This the shit, but last time I used one was in the mid seventies!!! So this was a very modern Techtronix for me😁👍! The inside of a Techtronix is real beautyfull of enginering quality. Any old engineer will Come to years and want to hug and kiss this fantastic beautyfull ❤️❤️❤️❤️😮😮😮😁😁😁👍👍👍. And as allways your videos are fantastic. And make The viewer feel good and Happy and you feels like an old really Nice friend to us. Thanks 1000 Times. And of course my old trust Amiga 1200 with a accelerator is still working just as my sons Amiga 1200 still is doing. He is also an engineer (in comp uting and software of course). And we also has Z 81s, Spectrums and Amiga 500,Amuga 500 plus and still working Commodore and old Ohilips monitor. So every time when I feel low after starting some PCs I just have to start my Amiga and feel glad and smile again. But anyhow thanks for your fantastic videos. 😁😁😁👍👍👍

Hi, if I still had hair on my head, I would lose it terribly 😂 I completely understand your approach, if you have no experience with such a device, but you didn't even do a basic inspection of the components (or you didn't show it in the video) and stuffing it with paper sent me to the ground . 1) the input part of the attenuator was not checked (it may be mechanically damaged, e.g. by hitting the BNC), the hybrid PCB may have been damaged 2) the attenuator and motherboard connectivity was not checked (there may be cold junctions) I almost died when I saw the gold surfaces being scratched by the metal and the pressure applied to the hybrid circuit board. Even the smallest scratch is a problem that cannot be effectively removed, as someone already wrote here - very carefully polish it with a piece of paper (you can also use a soft eraser on a pencil, but it leaves microscopic residues that need to be completely removed) impregnated with IPA and then treated with a suitable means (eg Kontakchemie Gold 2000). The fault itself tells us what is happening - decay of the rectangular signal, decrease or increase in voltage = incorrect function of the input divider of the attenuator (it is only an estimate, but it is the first thing I would check) 1) decay of the rectangular signal = problem with input compensation 2) voltage drop or rise = input divider error As I already wrote, this is just an idea without specific measurements, but another fact brings me to this idea - the anchored attenuator to the structure reacts to the movement of the BNC. I could of course be wrong and the fault could be elsewhere - without measurements any advice can only be guesswork, but I am the owner of a working 2465. Good luck finding the bug and have a nice day 🙂Tom

Wow, this scope is absolutely insane! I didn't realize there were analog scopes that have the features that this one has! I have a HP 54645A from around the late 90s to early 2000s, and even though that one is a digital sampling scope, it's feature set is more similar to this analog scope than I expected! Great find!

I have an old Tektronix scope that's 1000% analog - no fancy features. You've got the best of both worlds here. If I want voltage or time, I've got to count marks on the screen!

I suspect you have one or two hogged out center BNC connections on the input jacks. Explains to me why wiggling the probe plug affects it the way it does.

I love the old Tek scopes! I had one of those on my bench when I was in the Army back in the mid-'80s. I just looked and found that scope (refurbished and guaranteed working) online for about $200. (I'm tempted to get one for my own bench, to sit next to my 500 MHz Tek DSO I snagged "untested" for $200 on Ebay some years ago.) Speaking as an EE, the triangle(ish) waveform from the square wave signal is caused by capacitance in line. Yep; cruddy contacts can do that, and they can also cause low signal. So, I think that you are on the right track. BTW, DeoxIT has a formula specifically for gold contacts.

As someone who is only a novice at reading circuits I was impressed by your ability to seduce the problem by working your way through the circuit diagram. Must have taken a lot of practise to get to that point!

Probably cause I never understood it but during my first year in college in mid 90s we had to do an electronics class. I never picked anything up, struggled with it and we had to use analogue scopes. It all just seems so old fashioned and the scope just totally lost me. Now I still no nothing about electronics but the digital scopes really make me want one and to understand it. For me, the digital scope I feel changed it all. The digital scopes, when you see people using them properly and knowing what they are doing makes it so much more interesting than back in the days of college.

Great Work . Thank you very much for Sharing .

Great video! Love the analysis and repair. Definitely don't see these scopes around much. A couple weeks ago a friend recently gave me a 2245A scope from the mid 80s. (It's mostly identical but maxes at 100MHz.) I was amazed how much lighter weight the 2xxx series from the 80's is compared to the 70's 7603 scope I had years prior.

Man, I am so envious. I have an ancient Hitachi scope which does its job, but it's short on features and when I opened it for a good clean it's so barren inside. This Tektronix is a total work of art. I do have a modern Rigol digital scope, but I still love the instant response and feel of analog tech. It's great how much you can torture the analog stuff and have it survive.

Excellent debugging and repair

My first and oldest scope here, a Telequipment S43. Fully valve powered and in a case that you could drop a building onto and it will still work. Best part, you try and overload the input and the valves just hold their noses rather than give up the ghost like more modern replacements.

I love my Tek 2211, it's a digital/analog hybrid scope so you get the best of both worlds, though it's limited to 20MHz in digital mode, 50MHz in analog. Part of me wonders if those little spring contacts on the bottom of the relays are causing the issue, they could've lost tension over time, might be worth trying to gently bend them out a bit so they make better contact with the pads on the PCB.

I had one of these in my cubicle when I worked on microprocessor development systems in the 80's at Tektronix. Every engineer, HW and SW had them.

Good day , thank you for the video , this oscilloscope of 1983 , as I understood , and there are relays in the volt division unit in it , I went to study in the 2nd grade in those years , in 1992 I worked as a repairman and I had an analog oscilloscope with a CRT kinescope , in these sensors it is necessary to measure ESR metr all electrolytic capacitors, thanks for the video, all the best

You have repaired things with an oscilloscope many times, but this is the first time the thing you repair is an oscilloscope.

I worked oscopes in USAF PME Lab had a great time doing that. Great to a repair.

Always down for another episode of Adrian's Analog Attic!

I absolutely coveted that scope when i was in high school.. it's amazing how far we've come with test equipment like this lately, i now have a vastly more capable scope for probably 10% of what that Tek originally cost. I still covet the old analog stuff though!

This is a truly great peace of equipment then but still now.

i went back to college in 96-98 and we had the same model in our labs they were still in production in the early 90's

Tektronix scopes are absolute beasts.

tektronix scopes are a challenge to repair, I have had several over the years, and use them at work as well.

Use Q-tips with polishing compound on the PCB. Clean up with alcohol. Use a skinny straight pick to "tweak" the fingers to apply more tension. Use the relay slider to allow both sides to be adjusted. Clean fingers with alcohol. Use extreme caution on fingers. Two scopes fixed.

Definitely faulty relay contacts - I've seen the same issue on plenty of other small signal relays when they get old, and they can be intermittent each time you switch them as well as with physical force applied. A combination of oxidation on the tips of the relay contacts and/or a loss of spring tension mean the moving contacts don't make reliable contact anymore. Not much you can do about it apart from replace the relays. Probably very hard to find the relays but if you could you could fix it 100%. The poor high frequency response (triangle wave) in the earlier parts of the video is an interesting one - high bandwidth scopes like this use a dual signal path - very early in the input signal path the signal is split into low frequencies and high frequencies, (with a crossover point somewhere around 10-100Khz) amplified separately in parallel by two different amplification chains using very different design techniques optimised for their respective frequency ranges and then mixed together again later in the signal chain after a significant amount of amplification has occurred. This is done because it's nearly impossible to design a single path pre-amp circuit that can work all the way from DC to 150Mhz while maintaining extremely flat frequency response, extremely high sensitivity and low noise. So the majority of that 150Mhz is handled by a pre-amp following RF amplifier design practices which can work from a few tens of Khz up to 150Mhz, the low frequency amplification is typically handled by an op amp circuit and this circuit is also responsible for precisely controlling and regulating the DC offset when you turn the vertical axis offset control. As soon as I saw that roll off at a few tens of Khz I immediately assumed the high frequency portion of the signal chain was non-functional so what you were seeing was just the low frequency (probably opamp) amplification stage working by itself. Rather than being faulty as such it looks like it was simply disconnected due to the poor contact issues.

used these in school when i took my two year electronics technician course back in the early 90's

I have several Tektronix scopes, and I have recapped all but one, as I have not decided what I am going to do with it. I too have a 2445 scope, and I find it to be a nice, inexpensive scope! In fact, many of the different Tek scopes have come down in price, due to the upgrading many industries have made! When I recap the scopes, I focus on the electrolytics, as they dry out, leak and change value. Afterwards, I have no fear of trusting them letting out the magic smoke, or worse! I was using an HP scope without changing the caps, and it ended up shorting out one of the power supply caps, and it let out some smoke, but it didn't hurt the PC board or other components, thankfully, so I am quite anal about changing caps now.

Oh baby, opening that thing up looks like opening an old Ham Radio. Super interesting and extremely complicated inside! Totally different, obviously, but just as busy in there!!

Bend the relay contacts out a little bit so they press down on the PCB with more force.

That's the model scope i used in college in the mid 80's (or one that looked just like it). Excellent o-scope. There's something about a good analog scope that you just don't get with a digital scope. I take it back, our scopes didn't have OSD. That was a newer design. It had to be digilog for OSD, the ones i used were pure analog.

47:52 - loved and taken care of isn't immune to wear but it is great that you got it mostly back up and usable again.

Well done

It's really a surprisingly capable scope for its age, could be really handy to have around if it didn't have those issues. I definitely feel like those contacts were only tangentially related to the root problem, so hopefully a "grey beard" will appear in the comments with some good advice on how to further troubleshoot/fix the problem.

Pretty similar to the scope I had at my bench in the '90s, but it wasn't fancy enough to have those 'paddle' switches on the front.

I LOVE YOUR VIDEOS!

By the way, if you press both delta-V and delta-t cursor control buttons it switches to frequency display 🙂 The most instructions are written on the front panel itself.

Try checking the actual coax/BNC connector. There should be a nut (like on a potentiometer shaft). Make sure it’s tight, but not stupidly tight. Also, check the wire from the center conductor to the attenuator, and resolder if needed. 😊

may I recommend having the relays ultrasonically-cleaned? and under NO circumstances do you "scratch the surface" of a gold-plated contact and MOST DEFINITELY do NOT apply solder (unless you use that which is provided on a small spindle in the rear of the unit; it is SPECIAL!!!) if the contact is pitted, you can clean it with de-ox or iso-propyl alcohol.. then try applying a small piece of gold leaf in-between the contact and its mate, but NEVER EVER scratch the plating away as what you experience WILL occur due to thermal actions.. (you basically DESTROYED the contacts!).

Well I'm sort of glad I found this video. My 2465 does the same thing only on channel 2. When you were talking about tapping it on the bottom, I was like "Hey wiggle the input just a bit!" It's a 50 minuet video, so that probably translates to 20 hours of frustration in real time. From the looks of it it almost seems like a thin piece of plastic cut from flat spot on a square bottle or something, would put better pressure on the relays. If I'm going to be aggravated for quite some hours, I think I will look into @Unfinished80 bend the tab solution. Thanks. Subbed and liked. that's the least I can do :?)

That's a blast from the distant past for me. I had one on my workbench as a RF tech. It cost at least a couple month's salary when new I'll second the comments about bending the spring contacts. Ideally you need replacement relays HOWEVER you can reset their tension if you're very careful (there are tools for doing this - essentially a piece of stainless steel with a couple of slots to bend the things) - just don't overbend the spring contacts or you'll work harden them and they lose tension entirely Judging from what I saw in the video., the relay carrier has a foam pressure strip beind the relays, That may have collapsed over the last 40 years too

I was screaming "dry joint" all the way from 33:10, did you not hear me? Try reflowing the PCB joints. Also try swapping the modules to see if the faults transfer over.

Maybe the leads got pulled hard when connected at some point. It does seem like a mechanical issue. Perhaps you could try swapping the relays around and see if it helps. Perhaps you can get some modes working better. Otherwise try to bend the metal bits out a little bit. Maybe there are cracks in the solder on the BNC plugs too. I'm sure you can find a way, Adrian! ;)

I used this scope when I was doing technician work on minicomputers from 1984-1986 before the company switched to DSOs when I left in 1989 😉

That's one cool piece of hardware.

37:00 get a fiberglass-pen! They are perfect for tasks like this and are really soft to the material.

Well Done!

flexing your relay contacts so they make a more positive connection to the module board will correct the issue without the need for the paper.

I was looking at old CRT scopes but soon realised that they could be unreliable and power hungry so I bought myself a Hantek DSO5072p. It's got more features than I'll ever use.. I was thinking that maybe Adrian could get a couple of those attenuation boxes from a scrap scope. There must be plenty of old tektronix scopes around. Great video BTW.

Enjoyed. Couldn't tell from video, but a lot of those old relays aren't sealed... and the bad connection is on the inside, not the external gold pins etc. If you don't want to brave cleaning them... you could see if you have enough working ones to restore only 1 channel. Also, have that signal generator too. It's fine for audio signals, I don't recommend for higher frequencies.

It time index 3:40 you talk about the duration using the coursers to figure out the frequency. If you push both buttons, the Delta V and the Delta T, at once it will give you the frequency.

Nice old scope. I've got a tech 2225 that is still in use, great scope for what it is...

After seeing that signal at 4:57, I almost immediately knew what the problem was. I have a Tek scope as well, not the same model. I have a Tek 475 from the 70s. It's fully analog and has no ditigal components. You can add a digital DM44 as an option but mine didn't have that. Back to the point. One day I noticed my 475 made some really funky signals when a square wave was applied. The signal looked identical to yours. But this only happened when the channel was coupled to AC. This was only on channel 2 though. Channel 1 worked perfect. When channel 2 was coupled to DC, the signal looked like a square wave, and not a strange triangle wave. So of course I went trouble shooting and probing around the vertical section of the scope with another oscilloscope to see exactly where the signal goes funky. On the input BNC the signal looked fine, so that rules out a bad BNC. The output of the vertical amplifier looked funky though. So it was not the CRT or any parts after the vertical amplifier. I then probed the output of the attenuators. AHA! The signal looked funky! So I opened up the shielded can and started probing there. The 475 doesn't need to have the entire attenuator module removed as you can access all the points you need to test by just removing 6 screws and a shield. This made it so I can probe the signals in the attenuators. I probes the input to the attenuators and the signals looked funky. This limited the problem down to only the very front part of the scope. The coupling switches. So checked then and found the signal going into the capacitor for the AC coupling looked fine, but the signal coming out not. My first guess was the capacitor went bad. So I replaced it and used a modern equivalent. It worked perfect. End of the story right? *W R O N G* . The AC coupling started going funky again after a few hours, so I poped it back open. The AC input cap on the 475 uses 3 pins instead of 2. One for one plate of the capacitor, one for the other, and one for the metal can surrounding it. My modern cap didn't have the shield so I thought that might be the problem so I popped the old cap back in to take some measurements to find a suitable modern replacement, but the scope started working fine again! Turns out it was just a faulty connection from the capacitor and the attenuator board. You see, the 475 and other 400 series Tek scopes used socketed devices. Eervy single transistor is socketed, every IC, and some capacitors. The contacts of the sockets where the faulty part. Apparently, nickel plated copper and gold sockets don't work as the nickel corrodes and tarnishes. All I had to do was plate the leads with a tin layer of solder and everything worked fine. I don't recommend solder plating for your scope though. But bad contacts is what caused this triangle wavefrom for a square wave.

The problem is probably inside the relays. Relay contacts do not last forever, they can oxidize or be damaged by repeated cycling or even arcing. Although arcing is probably not your issue here. But the chance of fixing or polishing the contact points in a relay that small are pretty much non-existent. A bigger relay i would suggest using a slip of paper as a very mild abrasive, and just push the contacts together with the paper between and then gently pulling the paper out. But again, those relays are so small it would be hard to access the contacts without breaking something.

According to the tektronix wiki one of these would have costed ~$10,000 in todays money, so it's safe to say they were pretty high end when new. There was also a 300Mhz version of this same scope that was even more expensive.

I love my 2445Bs (3) and my 2465B (1). As far as I can tell, one of each works completely. One '45B mostly works. The other generates a stationary spot, telling me that at least the HV PS is working. The scope has two PS modules, one low voltage and one high voltage. There is a large DIP chip, U800 on the mainboard, that will overheat if you operate the scope outside the case. And eBay has parts for the attenuators and hybrids. The attenuators are going for about $40.

Thanks for a good learning experience. A follow-up video would be cool. Did you find a replacement module? Time to tear down the modules and / or try getting some replacement relays? I'm genuinely curious. Thanks for sharing!

For a while I had a Tektronix 7600-series mainframe scope. It was beautiful, and was both an excellenet analogue scope and also fulfilled my poorly-hidden urge to have so, so many buttons to fiddle with. So! Many! Clicky! Things! And they all did useful things! Unfortunately it was very old and starting to break down --- the trigger didn't, very often, and the focus was drifting. Plus, it was vast, weighing 14kg and being about 75cm long. Eventually I had to give it away and get a modern Rigol storage scope, which is much less satisfying to use. Fun fact: the 7600 scopes could draw text on the screen --- but didn't have a CPU!