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Products => Test Equipment => Topic started by: twjdeboer on October 12, 2013, 08:37:37 pm

Title: 1977 Tektronix 465 retro goodness [Fixed!]
Post by: twjdeboer on October 12, 2013, 08:37:37 pm
Hello everyone,

let me introduce myself for my first post, is there a special part of the forum to do this? I'm a student at the TU Delft in The Netherlands. My specialization is in Mechanical Engineering, but my heart is in Electronics. I plan on doing a Masters in Mechatronics or something similar. My passion has started after a project in Mechatronics in which I had to relearn a lot about electronics, about a year ago. While I was doing this I stumbled upon the EEVblog on Youtube. I've been hooked ever since. My English is not terrible, but please correct me if I make any grave errors, I can always learn!

In this time I've done a few projects and build some stuff. While building a small collection of devices and components I decided to acquire an old Analog Oscilloscope. After some searching on Marktplaats (our local Ebay) I found a good and working Tektronix 465 oscilloscope as well as a Newtronics 200MSPC AM-FM-Sweep/Pulse/Function-Generator (their words, not mine), about which the internet knows nothing at all. All in all I paid 95 euros for both, the guy was happy to see it part with someone who was enthousiastic and I got a brand old scope!

After some playing around I decided to stress test the scope by leaving it on for about two hours straight. It still functioned but ran quite hot (as I would expect is normal during operation). The next time I turned it on: Nothing. No trace, nothing. Fearing for the CRT I bashed the Beam Finder button and saw a glimpse of green. The CRT was safe. Queue the DMM and voltage check. The -8 volts was only reading -6. Bingo. I would've liked to run the signal through an oscilloscope to check it for irregularities, but I only have one |O. I was able to find the original service manual from artek manuals and bought it for about 4 dollars, as it would help a bunch. Then I left the project for a month or two, because I was scared of breaking stuff and the -2450 volts segment right besides the -8.

(https://dl.dropboxusercontent.com/u/43019582/Foto%27s/EEVblog/2013-10-05%2014.25.50.jpg)

(https://dl.dropboxusercontent.com/u/43019582/Foto%27s/EEVblog/2013-10-05%2014.26.14.jpg)

I wanted to fix the issue without having to take the entire thing apart, which can be a pain, so I wiggled the rectifier until it fell off. I could now measure the AC volts and attach a new rectifier, with amps measurement in between. I measured 11 volts AC (the coil produces power for a +5 rail and a -8 DC) and 500 mA, so this was all okay. I decided to tackle the big Filter Cap (labeled 1977, which is older than I am) 3000 uF worth. After some 'percussive maintainance', I was able to desolder it without damaging the board too much. (I managed to take one trace off entirely) I replaced it with a local dealer's 3300 uF, which should be okay. I also replaced the bridge rectifier, as I had broken it myself. (It was still okay diode-wise)

(https://dl.dropboxusercontent.com/u/43019582/Foto%27s/EEVblog/2013-10-05%2016.54.24.jpg)

(https://dl.dropboxusercontent.com/u/43019582/Foto%27s/EEVblog/2013-10-05%2016.54.53.jpg)

The result is a working Oscilloscope, which is only a bit out of cal. Notice the replacement wire and new Rectifier!

(https://dl.dropboxusercontent.com/u/43019582/Foto%27s/EEVblog/IMG-20131005-WA0000.jpg)

Bonus Newtronics generator, about which I will post some questions later!

Thanks for reading! Hope to keep learning from everyone of you, because I couldn't have done this without you, especially Dave)
Title: Re: 1977 Tektronix 465 retro goodness [Fixed!]
Post by: miceuz on October 12, 2013, 08:52:44 pm
So what was the culprit? A cap?

I had a go on a HAMEG HM 605 a couple of weeks ago - as trivial as dead electrolytics. http://wemakethings.net/2013/09/29/hameg-fix/ (http://wemakethings.net/2013/09/29/hameg-fix/)
Title: Re: 1977 Tektronix 465 retro goodness [Fixed!]
Post by: twjdeboer on October 12, 2013, 09:14:24 pm
 :palm:

I had to retype part of the story, because my Chrome decided to fail on me. (it was a PEBKAC-error) I left out the bit where the 3000 uF cap was completely dead as can be. It worked like a treat immediately after replacing it. I did leave a bit of stripped metal inside, which in turn caused channel two to malfunction, but I found out rather quickly and got it out.

I still need to fix the Delayed timebase though, the knob turns completely free when I pull it for the B-trigger and my signal looks really squished together. I think it's either broken or I need to learn how to properly use it.
Title: Re: 1977 Tektronix 465 retro goodness [Fixed!]
Post by: PaulAm on October 13, 2013, 12:10:25 am
The filter caps failing open is a pretty common fault with these scopes.  Well, they're 30 years old, so it's not much of a surprise.

I had a 465 where the delayed sweep just rotated.  That's a fairly complicated mechanical arrangement with the two switches.  On the one I was working on, I had to end up replacing the whole board.  I think you need to pull the trigger board to be able to get the sweep board out.  I have no clue how they broke that.
Title: Re: 1977 Tektronix 465 retro goodness [Fixed!]
Post by: twjdeboer on October 13, 2013, 08:59:35 am
One of the other knobs is missing the plastic, so I think it has seen quite a bit of abuse. I will think about getting the boards out, but I probably won't need the delayed sweep anyway.

As for any other broken caps. Do you think it would be worth getting one of these ESR meters?

http://clientes.netvisao.pt/greenpal/evb1.htm (http://clientes.netvisao.pt/greenpal/evb1.htm)
Title: Re: 1977 Tektronix 465 retro goodness [Fixed!]
Post by: PaulAm on October 13, 2013, 03:34:43 pm
I built a simple ESR meter for $10; it's been handy on occasion.  If you have another scope the obvious ripple when checking ps caps is a big tip off.

On the other hand, never turn down an excuse to buy more toys.