Check the supply for the Wehnelt cylinder, PWR dead, bad contact, broken cable...
Wolfgang
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Hi all,
Forgive me for not having very much useful detail on this, but a friend has a scope that's unfocusable and produces a thick trace. My immediate reaction was maybe noise getting into the signal path from a faulty mains filter or maybe an internal component in the smps section failed, but he reckons he's ruled out the latter as apparently it's a linear supply. He doesn't have another scope to check the rails for noise with so he's kind of limited. Anyway, that was only my hunch, I don't know the precise model of scope this is; I just wondered if anyone would like to toss in their 2c worth if they've encountered this issue themselves and what might be the cause of it? thanks, cd.
Anything Tek one address:
Cheers!
Probably not. Noise, if you mean interference, would be affected by change of timescales. More likely, a HV electrode in the electrode gun is used for focus, and the adjustment is off because a high-ohms fixed resistor has failed, open circuit. Look for range-setting fixed resistors connected to the focus control, taking all precautions against HV and breakage of the glass...
Well, there's no real substitute for actual troubleshooting - but having said that, I understand some Tek's have had bad focus potentiometers, and there's always the possibility of a bad high-value resistor in such a circuit. A bad 2.2 meg resistor caused a B&K 'scope of mine to not quite focus. The focus pot ran out of range first. Replacing the resistor fixed it.
If you do attempt to troubleshoot, be aware there are some rather high voltages in such circuits.
Mark Z.
Model number ?
Not known, I'm afraid. And the person who was acting as intermediary between myself and the scope owner has declared he no longer wishes to spend a single second more on the issue, so all the suggestions so far have been passed on to the owner, but no more will be. Thanks, guys.
If it's a 2235, 2236, and I think the 2215, it's because they used a bunch of underrated 1/2 watt carbon comp resistors in the focus divider chain. Put too high a voltage on them and they shift in value.
Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)
First of all, you should have a service print on it..
Some clues..
If the width control seems to be operating in a different place than where It use to be, this indicates that HV is not where it should be, since this can cause a deeflection change.
The focus circuit voltage dividers may have failed and or the focus pots.
Another issue is over brightness etc....
But like I said, you need some points of reference to fo this sort of work.
Some of the analog tek scopes use custom hybrid boards and were prone to failure, good luck with that.
Jamie
Then offer the guy ten bucks for it. It would be damn hard to find any Tektronix scope worth less than ten bucks.
And then if you get a ten grand scope fro ten bucks, fukum. they bother you, get you to look into T?HEI?R problem and then bloww you off like that ?
I hope you do get a ten grand scope for ten bucks and enjoy the f*ck out of the $9,990. If so, pick me up some weed wouldya ?
I got some in my back yard, just growing all over, you're welcome to come over here and remove it!
I don't care what you have in mind for it! :)
Jamie
The Tek 2235 and its cousins have a fairly common problem show up. The focus chain uses high-value carbon-composition resistors, which tend to shift value with age... the focus pot runs out of range as a result.
I bought a 2235 with this problem at a local flea market for all of $60. An hour's work and a few replacement resistors fixed it.
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