Tektronix 475 - buying used tomorrow, good ways to test w/o probes?

[Solidus_n313]

Hello all, ive finally decided to join the forums after thoroughly enjoying daves' channel (especially teardown tuesdays), and ive recently had the necessity (or desire ) to finally get a "new" oscilloscope (last one i had was a hitachi V-222, lost to water damage years ago). the oscilloscope i hopefully am able to acquire is the classic Tektronix 475 http://toronto.en.craigslist.ca/tor/eld/3954765908.html

i know the standard quick checks of checking that both channels display, trace looks clean at null, tapping on the top of the unit to make sure the verticle doesnt jump around and making sure all knobs and functions appear work fine and BNC's arent corroded.

the issue i have is that the unit does not come with any probes and i dont have any of my own anymore, so is there any other way to verify that the unit does in fact work properly and is worth investing the money in this unit? i dont really want to let a 475 pass at this price, especially considering finding a good scope in canada locally is almost impossible, and i dont want to pay more for shipping than the unit itself

also if possible, please advise if a makeshift DIY probe will be sufficient to test w/o a major concern of noise that could haunt me in the future

Much appreciated for any information,
Mathew

[Bored@Work]

Almost any piece of wire should be ok to connect the probe test output of the oscilloscope to one of the input channels. Don't expect a perfect test signal though. Repeat with the second channel. Bringing a wire with a BNC plug attached to one side and an alligator clip to the other side should be the luxury version for that test.

[elliott]

Also, be sure to let it run for a while, to be sure it is stable. I bought one that would be perfect for about 10 minutes, but eventually the traces would start drifting up. I still haven't gotten around to fixing it because I found a much better one.

[Rerouter]

also play with th trigger options on all the sweep speeds, mine had some dirty contacts so would not trigger on 200,20,2uS etc

[Solidus_n313]

thanks all, luckily im at work, and we have some loose BNC conns, so i can make up a temporary probe...now to find an alligator clip under the desk if im lucky

great heads up on the sweep speeds and to let the unit run, didnt even think of the duration, ill have to monitor the unit temp as well now that i think of it

ive never used a tektronix before so ive just been trying to absorb as much info on YT of user/reviews and leafing through the "bible" for the unit, LOTS of available documentation which is really nice.

also, from what ive heard, replacement parts aren't too hard to find, is that correct? (obviously depends on the part im sure) calibration shouldnt be an issue on this either once i get some real probes

[Marc M.]

Another simple item to check is the brightness of the CRT and any signs of burning.  In good working order, at lower sweep speeds there should be more than enough brightness when turned up.  It's also not uncommon to find screens with burn in, usually across the center.  If the CRT lacks brightness or is burnt, I'd take a pass.  The CRT's are getting difficult to find and cost as much or more than a complete working scope in good condition.

Another very common issue in the Tek 4x5 scopes to be aware of is bad caps.  I've acquired several 4x5 scopes over the years and they all had bad tantalum caps (always shorted) here and there.  The symptoms varied but in every case one or more of the supply rails were low/dead.  I think twice it took out the regulator and/or associated circuitry.  Also, many owners replace the main filter caps right off the bat, although the 3 or 4 I've had all the filters were good.  I think there are also some issues with the fans going bad.  If you do purchase this scope, I suggest that you take the time to lubricate the bearings or bushings in the fan with a good quality oil (Not WD-40 ).  The Yahoo Tektronix forum is a great resource for researching common issues with older Tek gear.  Once you get them straightened out, they are some of the best portable analog scopes ever produced.

[Solidus_n313]

Can someone PLEASE get Dave to add a "thanks" button?!?

seriously though, these are great responses. ive been out of the scope game for quite some time now, and while i havent forgotten everything, it was a bit daunting to drop the cash and time/effort to jump back in. looks like ill be a regular around here now

and Marc, thanks for that great future investment advice, im definately gonna open it up at that shop before i purchase to check the caps and filters. hopefully the CRT is in good shape.

well the countdown is 6 hours until i can pick it up, the end of my work shift will feel much longer now until i can check this thing out

[Solidus_n313]

OK well I picked it up, its in better functioning condition than I thought, with some cosmetic damage (knobs mostly) but when I got there and was testing it, they had a 2nd one that isn't working as well with some good replacement parts, so they sold me both for $150

The top one works, but the bottom one wasn't displaying a signal...when I got it home and did some more testing, pressed the beam finder, a noisy dot showed up hopefully after a little troubleshooting, I can get both in working condition.

Internals look nice and clean too, and the last calibration date listed for both is 1981 :p

[echen1024]

When I normally test the scopes at my local surplus store, I either bring wire, or just stuff my finger into the BNC connector and see if something shows up. That way, at least you know if the acquisition hardware is good.

[alm]

A working 475 plus a (worst case) parts unit for $150 is an excellent deal in my opinion. Especially with local pick-up.

[Marc M.]

The top one works, but the bottom one wasn't displaying a signal...when I got it home and did some more testing, pressed the beam finder, a noisy dot showed up hopefully after a little troubleshooting, I can get both in working condition.

Check your supply rails.  I know one  of the scopes I worked on had the same symptom - no horizontal scanning.  IIRC, there were a couple of shorted tantalum caps on the horizontal amplifier board.  I pulled the board and monitored resistance between the bad rail and ground while pulling 1 leg of each tantalum cap until the short went away.  Then re-installed the caps one by one looking for further shorts.  Found another one or two that way. 

Also, be very careful about using contact cleaner with these scopes.  The PCB material they used is very sensitive to it.  There are warnings in the service manual (available @ Bama) and I think it may be printed on the boards. It's OK to use CC on the pots and external switches (keep it off the boards!), but not on any of the cam switches.  To clean those contacts I used paper wetted with IPA.  They are very fragile and easily damaged so extreme care needs to be exercised when cleaning them.

Great score!

[Bryan]

Go to the Yahoo newsgroups and join  tekscopes. The place where all tek owners go for support and repair tips.

http://tech.groups.yahoo.com/group/TekScopes/messages

[Solidus_n313]

yeah i did that just after i picked these up just waiting for the group owner to approve