Re: Tek 465 Negative 8 volt rail issues


Paul Amaranth
 

These caps dry out all the time, it's a very common problem.

The orginal cans are no longer available and, if you find some NOS
ones, they will probably dry out shortly if not already.

Get 105C snap caps and use one of the adapter board floating around to
match the footprint to the 4 terminal footprint of the original. Use
high quality caps by Nichicon, Panasonic, etc. Avoid cheap noname or
offbrand Chinese caps.

All 3 ground leads need to be jumpered since Tek used the can as a
jumper and the adapter boards take care of that for you. The adapter
boards make for a very professional repair. I hate seeing caps hanging
off the board hot glued to something.

If I have to replace one, I generally replace all of them. Then you
won't have to worry about it for 20 years.

By using very long leads on the adapter boards I have replaced the
caps in situ without pulling the main board by threading them down from
the top.

Unsoldering the main caps is fun, not. It's easy to overheat the board
and have trace separation. Be careful and use good desoldering tools
and technique for that. Some chipquick wouldn't hurt.

Paul

On Thu, Dec 24, 2020 at 05:59:34PM +0000, Dave Peterson via groups.io wrote:
Ed, how serendipitous.

I too am looking at a power supply cap issue. Haven't nailed it down yet, but similar line frequency "ripple". In my case the "ripple" is more like unregulated/unfiltered full-wave rectifier output on the 120v and/or 55v rectifier output - there's no significant capacitance. Question is, which cap.

What caught my eye here was "I have the caps on hand". Do you mean you have a stock of original 465 PS caps? Or do you mean you have a supply of modern caps?

I've looked at the "465 Power Supply Capacitor Replacement Guide", and am feeling a little more confident about attacking these caps. But I'm still on the fence about what route I would want to go. I'm very much the "ain't broke, don't fix" kind of guy, and I'll say I'm 51% biased towards keeping things as original as possible.

Curious to know what you meant by on hand, and if you have suggestions for sources.

Dave


On Thursday, December 24, 2020, 09:11:31 AM PST, Ed Pavlovic <kc9mmm@comcast.net> wrote:

I recently picked up a used Tek 465 scope for a price I liked and could pick
it up without having is shipped, and I'm getting started on checking it
over.  Everything works, although both traces even when grounded look like
there's an uncompensated probe attached.  But I figured I would look at the
low voltage power rails before I try to track down that issue.  Early 465,
with a B010XXX serial number, needs some cleaning and TLC.



All the test points for the rails except the -8 volt are within spec which
was low, so I hooked up a probe to the test point.  I'm getting a 1.75 volt
ripple at a frequency of 120 Hz, which makes me suspect the filter cap is
bad.  I have the caps on hand to replace all of those power supply caps on
all the rails, but before I go and do that, I just figured I would ask if I
should look at anything else on this power rail before I change the filter
cap so I don't kill it right away.  There's also a 33uf tantalum cap on that
rail to ground that I will replace as well as the service manual calls it
out as a 10 volt rated cap, which isn't much to spare on 8 volts.

I uploaded a photo to a folder I created of a shot of the ripple on the -8
volt rail here:



https://groups.io/g/TekScopes/photo/258534/0?p=Created,,,20,2,0,0



If the link doesn't work the name of the folder is "Tek 465 Negative 8 volt
rail" and there's only one picture in there.



Ed Pavlovic

KC9MMM













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Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows

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