Love the switch porn on the attenuator unit. Some high-purity IPA would clean a lot of the gunk off of your front panel, and it doesn't affect any of the paints or glues. It brings old plastic up really clean in combination with the rough side of a piece of un-dyed veg-tanned leather. The smooth side cleans up the BNCs better than new. Keep up the good work. The more of these instruments in full working order, the better!
One hint for 485 users: the calibration oscillator on this scope has a fast rise time (~1 ns), but only when terminated with 50 ohms. So you can test the vertical section in 50 ohm mode with a length of RG-58 coax, or put a terminator right at the calibration socket to test probes. Only the rising edge is fast, not the falling edge.
Nice video. I am a big old Tek fan myself. Always loved the looks of the 400 series, which I do not yet have. Looks like a real nice scope. Thanks for sharing your troubleshooting.
Looks pretty clean. Mine is missing the those rear plastic feet. Nice debugging of the front end. I was expecting that the glitches at the edges were due to reflections from the mistermination when using 1M input Z. I really need to jump into my 485 and clean up the attenuator contacts. Best method for this is to put some isopropyl on strips of white paper, and carefully drag them through the contacts in the "closed" position.
+w2aew Yes, luckily aside from a few of the front panel buttons, everything on the inside is pretty clean and seems to be working smoothly so far. I've heard of that technique for cleaning the finger contacts before; I think I read it somewhere on the EEVblog forums - actually, come to think of it, it was probably you. :) The effect that the HF gain pot had on the waveform edges was really the big clue to hunting this one down; tweaking it *almost* fixed the problem, but not quite. I could twiddle the HF gain on channel 2 and get it to give the same glitch effect, so I figured it was something to do with the related circuitry in channel 1.
+devttys0 I learned that alcohol & paper trick working on the inputs of my old 475A (boy, wish the trace bloom had never showed up as I loved that scope and should have held onto it!). Thanks for sharing the troubleshooting journey, pretty cool! 73 - Dino KL0S
Thanks for the video, I did not realize how easily the attenuattors could be removed. One of mine has a loose connector, so now I'll fix it. I can't believe you had a failed resistor, didn't think they really failed! My 485 had a problem in its horizontal section and I was very worried that it was a Tek custom chip. Luckily, it was just a bad 741 OP-amp. One nice thing about this scope is that includes the probe power supply for P6201 900 MHz FET probes. These probes have been getting very cheap recently on Ebay. $70 gives you the same performance as, for example, >$1000 each P6243 active probe.
I really enjoyed your Tektronix 485 adventure. Mine is roughly the same vintage and is plugging along fine after many years of use and abuse. It's really convenient when you have one working channel to use as a reference to revive the other misbehaving channel. Nice job finding that 47 ohm resistor that drifted up beyond 160 ohms and thanks for sharing this!
I've got one of these. You have to be really careful when pulling those connectors from the attenuators, as the board is very weak. Both are broken on mine. I had to solder wires all over the place, but it still works.
Nice Video- I have an old Tek scope that used to work I feel tempted to have a look at it now. Mine might be a power supply issue . In Australia 240 V and I think I had to do a repair once after forgetting to inspect input voltage I assumed the guy would set it for Australia it was shipped from the USA. It worked for a short while. I noticed the tolerance / allowable variation/ safety margin was less for 240 v than it was for 115v. I have a Hantek scope in the meantime. Hoping to reproduce Stanley Meyer water fractionation technology which I believe Bill Gates bought after his death 20th March 1998.
Very nice video. I have two of these beauties and one of them has contact issues with the little gold fingers but I see below where Alan talks about cleaning them with white paper and alcohol. Absolutely beautiful instruments and I paid about the same price for one of mine off Ebay from seller Chipxs. Thanks for posting.
Excellent video. Logical troubleshooting procedure and we can see everything clearly. We have one of these old workhorses on a shelf where I work. Now I want to play with it. Cheers from your newest subscriber. :)
You're lucky. I've had 100% success repairing 455, 465, 475, and many 500-series Tek scopes. However I had to give up on two 485's. One reason, they have a strange power supply circuit where if any voltage is a bit low or a bit high, the whole power supply shuts down. That makes troubleshooting very tricky. I spent about four hours on those 485's and got nowhere. Most 465's you can go directly to the main power supply capacitors and bridge rectifiers and sometimes a tantalum capacitor and that will be the problem. With a 485 you have to be a bit more strategic, with like voltage injection and such.
I got a 485 for a reasonably good price (I think). Who could you refer to me (a good deal/trustworthy) on a calibration and probably replacement of tired old catalytic capacitors. Thanks for all of your assistance & wisdom here.
Great video! I have a digital Tek TDS1002B since 2008 and I'm happy with it. Recently I run into the opportunity of buying a used Tek 465 (not the B version) for $150. Is it worth buying and having it nowadays?
My Tek485 works fine with DC coupling , but one channel does not work with AC coupling. The scope shows only very little voltage level. My first idea was the 2.2uf coupling C , but that is ok. There seem another tree switched by K1 but can not find C16.
Very informative. I'm a novice although I just succeeded in replacing the power caps on my vintage T912 scope. Question...what would cause a sine wave to sort of walk across the display? Is it an adjustment or an internal thingy? Thanks and keep up the good work.
Hi there , great video and clear explanations. One question in the beginning the trace has a halo effect how did u correct that ? I have the same effect on my 485 ..thanks !!!
The halo effect in the beginning of the video was just due to the intensity being turned up too high. It showed up worse on camera that it did in real life, but either way just turning the intensity down was the solution.
I have to assume you're from the northern hemisphere... Most of the video of the scope face while you were doing the troubleshooting looked 'upside down' from here.
can anyone tell me if tek 465B has no display but just green color is on the screen, where should I look for the fault? Which components should I check?
First, a well-deserved compliment: your videos (especially this one) are magnificent. I stumbled across them when searching for enlightenment on a Tek 485 I am reviving. If O.K. with you, I am enshrining you in my pantheon of electronic "how-to" gods like W2AEW (below) and Mr Carlson (or Mr Carlson's Lab). Second, I did not find your interspersal of "umms" and "ahhs" off-putting (until the commenter brought it to my attention). But please do not change! To do so would lose the spontaneity and sacrifice the genius of your advice. You want distracting? Try ferreting out nuggets of knowledge from an interminable 45-minute Martin[?] Lorton video on calibrating DMMs and workshop temperature. God love him, that lisping Midlands accent is truly annoying. Finally, help me Obi-wan, you are my only hope. (Actually, just asking a sanity check.) Here's what I posted over at ARF: Tek 485 CH 1 position control moves CH 1 trace right enough as the CH 2 position control moves the CH2 tace. HOWEVER the CH 1 position control ALSO moves the CH 2 trace when in CH 2 mode. In addition, the CH 1 position control moves BOTH treaches in the CHOP and ALT modes. The CH 2 position control only moves the CH 2 trace in those modes. ..something rotten in the state of Denmark, right? Thanks again for your marvelous videos; the 485 is truly a treasure!
+k6whp Call off the dogs! The problem was (preliminarily) a mis-seated J200 and J300 plugs on the A7 board. Removing it the two coax input plugs and re-seating them during the investigation seems to have restored the normal functionality. Now poring over the manual and schematic to make sure it was not some intermittent component I "bumped" into working. Still, videos are great and happy I "discovered" your work!
+devttys0 Alas, no. It proved to be a temporary remedy. (I suspected it might.) So the question becomes at what point does this crossover occur? Is it before the A7 board or on it. One thing certain is that I will be a lot more knowledgeable on the 485 after this problem is solved than I am now. Nudge, nudge, wink, wink.
+William Phinizy Bummer! If re-seating those connectors temporarily fixed it though, it sounds like it could very well be a loose or corroded connection somewhere. Maybe giving the board/connectors a wiggle test will help isolate the issue.
Nice video - how did you get the "smiley face" trace at the end? Looks like 2 square waves on top and part of a sine wave on the bottom, with maybe the H-sweep limited?
I'm happy you understood me and did not misinterpret it as harsh criticism. I know it is very difficult when doing unrehearsed/unscripted commentating. I have an iwatsu 5711 (quad channel 50 MHz) which sadly/fortunately does not have any problems. Weighs 20 pounds. Heavy SOB. Looking forward to seeing more vids from you. What do you focus on? (Theory/design/construction/troubleshooting...)
+George Tsiros I think many internet wars have simply been the result of the difficulty in translating one's tone of voice into black and white text. :) Constructive criticism is always welcome! I try to do a mix of practical theory and design, and of course troubleshooting/repair videos like this one, with a focus on analog circuits. I'm overdue for a theory/design video, so that will be coming up soon!
+Adil Malim There should be a knob on the front panel for adjusting the horizontal trace position, so you can center the trace. If that knob doesn't do anything, or if it moves the trace but the trace width is only half the the width of the screen, then you'll need to get the 'scope manual and look at the horizontal amplifier. There are usually internal adjustments that allow you to set the trace's horizontal width, it may be that this is out of calibration and just needs a tweak.
It's a carbon composition type. You mostly see them in older gear, not so much in new designs these days. www.eeweb.com/blog/andrew_carter/introduction-to-carbon-composition-resistors
Cool. I just got a defect HP 1725A free. Only see a flat trace. Can't wait to dig into it. I also bought a Fluke 80K-40 High Voltage Probe for €50,-. for that purpose. Question: What is a save way to discharge the crt? I think I will put an extra wire on the HV probe and connect the other end of the wire to the chassis. Then poke the probe underneath the cap. Do I need a resistor (10M) in series with it for that? Or can I just short it? I don't want to damage it.
+Joost B I usually stay away from the HV CRT stuff myself. :) I have seen other repairs where the CRT was discharged, always by shorting it to chassis ground (no resistor); my understanding is that while the voltage is large, the current is relatively small, so you shouldn't melt any wires by just shorting it out. Micro Center did a video on this (it's a TV CRT, but the same principles apply): ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-0X28FX_XxtU.html
