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.

 

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.

 

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