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tektronix 465 question

I just bought a tek 465 scope on ebay, but am having a problem with it. For about half the time, everything works fine, but occasionally, and for no apparent reason, the scope will behave as if there is no incoming signal on either channel - time/div, horizontal position, intensity, etc can be changed, but vertical position cannot be, and nothing will display on the crt when a signal is applied to either channel. During such periods, setting A Trigger Source to a channel and then pressing the trig view button correctly displays the signal on that channel. Furthermore, and perhaps irrelevantly, the AC/GND/DC selector below CH 1's volts/div knob doesn't click like CH 2's does. The problem seems like it might be minor - a loose connection somewhere

- since at times the scope functions exactly as it should. any suggestions as to what could be wrong are very much appreciated - i don't have much experience with scopes, and certianly not with troubleshooting them. I also don't have a service manual yet, but am trying to find one on ebay. Thanks.

Reply to
keithcc
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"keithcc" wrote in news: snipped-for-privacy@o13g2000cwo.googlegroups.com:

You may have lost a roller bearing on the AC/DC/GND switch,or the lever has loosened on the switch shaft.

Maybe a bad trigger view/BW limit switch on the vertical pre-amp board.It's towards the rear of the PCB,near the delay line connection.It's heat-staked on,and has HF cam switch contacts that have a very low wiping force,and are suceptible to contamination,like films from plastics outgassing,cig smoke,dirt.

At TEK,we used to remove the plastic sw.frame,tear off the old contacts,bolt on new ones from a repair kit,and stake on a new sw.frame.Those parts are no longer available.

So,what you do is take a narrow strip of paper,slide it under a closed contact,and put a drop of 90% isopropyl alcohol on the paper,and carefully slide it back and forth to clean the contact and the PCB pad.If the contacts have lost tension,then you have to scavenge some from a parts board.

--
Jim Yanik
jyanik
at
kua.net
Reply to
Jim Yanik

do as Jim proposed: Clean the contacts and of course the rest of the o'scope (cause iif it's put away the housing, that's easy to do in one action).

and chck for bad caps in the LV supply -- electrolytics easily get dried out in these scopes during the years.

After doing this maintenance, the scope should still work when used occasionally when you will be long gone. The 465 are realy nice and affordable nowadays.

hth, Andreas

Reply to
tekamn

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