Tektronix 475 non A Repair and Restoration

A huge thank you again for all that continue to Join us in the lab for repairs and alignments. The channel would not exist with out all of you so thank you again for dropping by.
Here is a video detailing some more information • Tektronix 475 Troubles... The transistor that is bad is the 151 0367 00 [MPSH05]
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In this video we take a look at another 475 from the stack. This one is a non A unit and does not have the DMM44 on top but another step through the repair stack. As always I am in the comments section below and more is always on the way.
** Repair exposes the Tech to mains electric and should only be done by trained personnel. Errors can be fatal. **

[@coldfinger459sub0]

I absolutely love the look and feel of this old equipment. And believe it’s life should be extended and used for another generation.. But like you say, the service time is extensive . If I had to charge for my shop time at my company’s labor rate eight hours is a little over $1600 repair.. definitely a labor of love to Owns as a beautiful piece of equipment.

[@dennisbergman3896]

I have one of these, goes well for 5 minutes then the vertical trace goes to negative. Will keep it😊

[@darrenmurphy6251]

i love tek gear ,i had an ex bbc 7403n with 2x 7a18 verticle amps , only 50mhz and no readout but it was a joy to use, i was so smug (i was a teenager) showing friends what the vernier did on the 7b53 dual timebase and that i had 4 traces (using scart and showing rgb+sync) .trouble was it hated my familys damp drafty uk house it started drifting out of focus with a smell of corona discharge and all the plastics started crumbling. when bits of the attenuator barrels started falling out i scrapped it , moved to a hameg which i had no love for. now decades later i have several tek 2245a/2246a (24 series in uk are unobtainable ) even though i have a modern siglent dso

[@nopenadanowaynohow]

good to see you got back ok, and another great video!

[@larrybud]

What great video! Happy to have found you. Definitely deserve more subscribers!

[@fasthardware6293]

hey, im a big fan of your work, I love this old tek tronix devices, they are history, I bought a 7104 with 4 modules pre-installed , IT turns on the trace is very wide out of focus, I think you will be a good fit, to troubleshoot the main fraim and modules and salvage whats good, or even repair the whole thing , I dont need this Monster of an instrument, Im willing swap it out for a basic unit like the one in this video. I only do hobby electronic stuff. want me to email you pictures of my Main fraime ?

[@ReyciclismoMTB]

Watching another one of your videos but I have a real i nterest on this one because I have the same on. The only thing working is the intensity, I can't turn it off. Did several adjustments including grid biasI have a crisp trace bu nothing else. All rail voltages are dea on. So your input would be appreciated, i'm a scope noob, so I spend a lots of time on them A hobby. Thanks

[@joshuagraham2883]

My father's first job in the Navy was repairing and calibrating scopes. Towards the end of his life he went back to this as a hobby to pass the time. Before he died he tasked me with getting his collection of scopes back into circulation. Some of them are working and some are not. Of the twelve scopes nine are either model 475 or 475A. I want to figure out which scopes are working and which are not so I know which to sell as functional and which for parts. I know absolutely nothing about oscilloscopes. I had asked him to label which ones were and were not working but he couldn't in the end because his COPD wouldn't allow him to get into his workshop. He just couldn't make the walk without his blood oxygen bottoming out. Do you have a video or know of a resource that covers just testing basic function? I'm really at a loss trying to figure it out and any help you could give me would be greatly appreciated.

[@ZenwizardStudios]

My condolences for your loss. Yes there is a video on the channel that might be very helpful in this regard. The title of the video is “New Scopes 1st steps for a Checkin” A link to the video is here: kzbin.info/www/bejne/oafHaImbmJydmKM Pretty much ALL the 400 series scopes function the same way just vary in speed. The 485 is the odd ball that has some more settings on it and does not follow the standard form factor.

[@joshuagraham2883]

@ZenwizardStudios Thank you very much for the link, I'll check it out. And thank you for making all this information available. It looks like you've got a pretty good channel here

[@jeditoto3441]

Another great video!

[@nickfatsis9607]

I can see 2 separate inputs, and 2 separate vertical controls, but I can only see 1 horizontal control, how would you display both channels, using 2 different timebases on screen at the same time?

[@ZenwizardStudios]

That is a limitation of the 4xx series scopes although it can be done a bit with the delayed time base. For true dual sweeps either a dual beam scope is needed or one of the 4 bay 7xxx mainframes. These can support 2 vertical and 2 time bases.

[@nickfatsis9607]

@@ZenwizardStudios I find it odd that the manufacturer would make them this way, they've given 2 channels X and Y, why not make them with separate timebases?

[@ZenwizardStudios]

Similar issues to what plagues engineers today. Space, Cost, Use. In terms of space the trigger and timing boards take up most of the right side of the scope. These also use some extraordinarily expressive components. Mainly the tunnel diodes and timing capacitors. In terms of cost in 1977 a 475 sold for $2,900 the slightly faster time base the 7B80 sold for $745 almost 1/3 the cost of the scope. Adding a full second time base would have been cost prohibitive. Use, The 400 series scopes were mainly intended for service tech and their primary focus was on portability. The 485 still today holds the crown of the fastest analog scope that fits under a plane seat.

[@user-ik6ei7jn8r]

Hi Zen. I turned on my 475 after some period of non-use, and notice noisy traces. Nothing is connected to the input BNC, and it still shows some kind of pulses on the beam. The trigger light turns on at that ghost voltage. The BW switch doesn't help much, sometimes it calms the beam, but mostly it has no effect. If this is a malfunction, where would you look for it first? Greetings from channel followers.

[@ZenwizardStudios]

the 400 series scopes is plagued with switch contact aging issues. I would start as with all things a good switch cleaning *LOTS of them in the 4xx scopes) and checking the power supply rails for proper voltage and ripple as always use caution around elevated voltages.

[@user-ik6ei7jn8r]

Thanks for the response. I've been scrolling through the forums, it seems that the 475 is particularly susceptible to this issue, probably due to bandwidth. Somehow I don't believe that the problem is in the vertical inputs, because the thing also happens with the switch set to GND. If I can't find anything else, I would try reducing the sensitivity of the trigger.

[@grahambambrook313]

Which are the transistors you replace as a matter of course? I have one of these 'scopes which I will hopefully get around to looking at soon. I know the 10x light on channel 2 doesn't work for some reason but other than that it seems to do the right things. Time will tell, no doubt. Thanks for all you do.

[@ZenwizardStudios]

Here is a video detailing some more information kzbin.info/www/bejne/nXa7ioWGg9Sbr6M The transistor that is bad is the 151 0367 00 [MPSH05]. This was not used in the 465 or the 485 so that is good.

[@grahambambrook313]

@@ZenwizardStudios Cheers, many thanks.

[@THOMMGB]

@@ZenwizardStudios Hi, I'm learning a lot from watching your videos. I have a 455 with problems. (I have not been able to find any 455 repair videos.) So, just to be clear, were you saying that my 455 doesn't have the transistor problems like the 475? I'm blowing a fuse, but it is powering up, somewhat. (Amber screen only lights up) Any advice? Thanks a lot.

[@ZenwizardStudios]

@@THOMMGBI have changed my thinking on the "bad" transistors after a lot of discussion with the Tek scopes group and some additional testing on my part. With the symptoms of blowing the fuse and not powering up I would start in the power supply. There are about 8 power rails in a 4xx scope and they go ALL EVERYWARE. My first thoughts are shorted tant cap dragging down one of the rails. There might be and ohm out chart for testing the power rails to ground in the service manual. This should be done with no power on the circuits. It is bad to feed power in to the resistance ranges of meters. Some go pop. With a power fuse blowing there could also be some issues in the bulk filters. Zen

[@THOMMGB]

@@ZenwizardStudios Zen, Thank you for the quick reply! If I am able to get my 455 working again, I’ll be sure to let you know what the problem(s) were. Is there a Tektronix repair forum that you can recommend?