Is my Tektronics 465B working correctly? - help a NUB

[GroupJ]

I just purchased a Tek 465B on ebay.  Came with one 1x probe with no ground clip.  I find the following issues:

1) Focus knob is frozen (or locked) - won't turn easily (I don't want to force it)  The trace is sort of focused but not pin point sharp - I can add photos if that helps.  I assume the knob drives a pot?  Is it possible someone locked the shaft to prevent someone from (screwing up) changing the focus?  Any suggestions on what to look for?  Is the pot easy to get to?

2)Main concern - trace is "jittery" meaning the intensity of the trace is not steady.  At its worst it looks like the trace is turning on and off at about a 10 hz rate.  The trace is stable - it does not move in x or y.  The jitter gets better or worse with movement of the Time/Div knob.  At some point I can always get the jitter to go away (and have a steady intensity trace) but seldom does this align with where I want the Time/Div setting.  Is this normal?  I can still read the trace with the jitter but it is annoying.  I haven't used a scope in 30 years, and my memory maybe (is) going, but I recall these scopes should have a rock solid trace.  I see this jitter when I sample the calibrator signal and I see it on both inputs.  I also see it with input set to AC, GRD, or DC .

Appreciate any help available.

[alm]

1. I don't think so. I'm thinking a bent pot shaft or very dirty/broken pot. I'd certainly not force it but disassemble and investigate.

2. My first guess would be bad cap causing power supply ripple.

[David Hess]

The focus knob goes to a long plastic shaft to a plastic high voltage potentiometer, so definitely do not force it.  It needs to be inspected.

[GroupJ]

Thanks for the info.  Any estimate on what it might cost in parts to re-cap the scope - I just re-caped a small CRT driver board and that was about $15 in caps - I suspect the 465B will take a lot of Caps.  I might be better off returning this scope - I have a 30 day trial and paid $150 for it.

[james_s]

It depends on which caps are bad, you might only need to replace a few of them in the power supply. Don't just blindly replace all of the caps, I've seen that a lot of times where someone replaces good quality parts that are still in good condition with cheap junk. Sometimes they replace a specialized part that has special characteristics with something generic and then it doesn't work right.

The focus pot is probably just gummed up with 40 year old grease, a shot of pot cleaner ought to free it up.

Is your sweep set to alt? That will make the trace flash on and off. Make sure you RTFM and learn how to use the scope properly before you waste the seller's time and money returning an instrument that may be perfectly good.

[med6753]

Jammed focus control is a common issue on 400 series scopes that I've seen several times. A spray of deoxit where the shaft meets the pot body will free it up.

Without seeing exactly what your intensity is doing can't really offer a will fix it solution but you could try spraying some deoxit directly on the intensity control even though it's a sealed pot. The deoxit will find it's way in there. Work the pot back and forth several times.

If you suspect PSU issues check the ripple on all the supply rails. Max allowable ripple is listed in the manual. If you don't have a manual go to TekWiki and download a copy. Make sure it's for the 465B, not the 465 (They are not the same). 

 

[bdunham7]

465B will take a lot of Caps.  I might be better off returning this scope - I have a 30 day trial and paid $150 for it.

I believe there are 40 or so caps that merit replacing.  Identifying, measuring and looking up the caps is probably the most work. If it is in otherwise good shape and mostly works, it sounds like a good project.  It's unfortunate that you can't acquire projects like that for nearly free anymore, but in todays market $150 isn't a bad deal.