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Possibly dumb question regarding a 5111

Dave Seiter
 

Last week a buddy of mine gave me a 5111 to look into (he got it cheap, didn't know if it worked, has never used a scope before, but wants to learn when he gets time.  I traded a working Dumont R1062 for it).  
It was really grimy inside, but I got a trace right away, and the storage worked, but obviously had a few issues.  Once, I smelled something burning at one point, and got a small plume of smoke out of the HV section before I was able to shut it off.  Strangely enough, I couldn't find the source of the smoke, even after I cleaned the entire scope up.  
The question is this (and this is the first split screen storage scope I've played with):  The storage is obviously split into upper and lower halves of the screen.  Do the vertical amps do the same thing?  The reason I ask is that both vertical amps only work on the lower half of the screen.  The two pdf manuals I have don't really address vertical centering at all in the usage sections, so I doubt it's the case, but the 4 5xxx V amps I have all behave the same way- the center of vertical adjustment is in the center of the lower half of the screen, and the trace will never adjust more than 1/10 of a division above the center line.
I've adjusted all the power supplies, and the voltage measurements throughout the vertical deflection system, while not being spot on, are near enough that they're "ok".  The scope is an earlier version (the LV board doesn't have the row of fuses), and I've found circuit differences from both of the pdfs I've been using  (and I hate debugging using pdfs!!!)
One bit of odd behavior that might be related:  whenever a trace is at the top of it's travel (center screen), and the intensity gets turned down to below normal viewing levels, the trace will start to move down the screen as the intensity fades out, eventually going off the bottom edge of the screen.  Never seen that behavior on a Tek scope before.  
Is it possible that the storage system is actually limiting trace movement in some way?  Just thought of that.  Not sure how that would work, but I'm not all that familiar with storage scopes either, only having one that works correctly (T912).

-Dave

 

On Mon, Jul 15, 2019 at 06:30 AM, Dave Seiter wrote:


One bit of odd behavior that might be related:  whenever a trace is at the top of it's travel (center screen), and the intensity gets turned down to
below normal viewing levels, the trace will start to move down the screen as the intensity fades out, eventually going off the bottom edge of the screen. 
Never seen that behavior on a Tek scope before.
I've seen similar behavior when one of the connections to the vertical deflection plates (V amp output) has become open.
So that would be the first thing I'd check. In your case it would be pins 11 and 12 in the CRT socket.
This could also explain why you can't get the trace above center.

/Håkan

Albert Otten
 

I can confirm this, Håkan. For some reason I experimented with a 7704A, one plate disconnected, no signal on the other plate. After a sudden change in Position the dot follows but it takes some time before the dot settles at the new position. Apparently the voltage (charge) at the open plate creeps slowly to a new equilibrium. That equilibrium also shifts slowly when Intensity is changed.
(Speculation: When Intensity is turned down the disconnected plate catches less electrons I think and becomes more positive. Then Dave's 5111 trace drifting to the bottom indicates that the lower plate is disconnected.)

Albert

On Mon, Jul 15, 2019 at 12:49 PM, zenith5106 wrote:


On Mon, Jul 15, 2019 at 06:30 AM, Dave Seiter wrote:


One bit of odd behavior that might be related:  whenever a trace is at the
top of it's travel (center screen), and the intensity gets turned down to
below normal viewing levels, the trace will start to move down the screen as
the intensity fades out, eventually going off the bottom edge of the
screen. 
Never seen that behavior on a Tek scope before.
I've seen similar behavior when one of the connections to the vertical
deflection plates (V amp output) has become open.
So that would be the first thing I'd check. In your case it would be pins 11
and 12 in the CRT socket.
This could also explain why you can't get the trace above center.

/Håkan

Dave Seiter
 

That was it!  The continuity of the two wires checked out, and the pins looked good, so I tried seating the CRT socket as well as possible.  Turns out that the thicker wires prevent the socket from going on all the way.  Exerting more force on the side with the smaller diameter wires seated them better, and it now works.  (For a few seconds, I was wondering if the break was inside the CRT)
For the record, this solved the half-screen-only issue, the trace droop caused by reducing the intensity, solved some weird delays (reaction of trace vs controls), greatly improved the shape/geometry of low to medium speed traces, and of course, allows the calibration of the vertical axis.
That's not something I would have thought of.
Thanks to both of you!
-Dave

On Monday, July 15, 2019, 12:41:20 PM PDT, Albert Otten <aodiversen@...> wrote:

I can confirm this, Håkan. For some reason I experimented with a 7704A, one plate disconnected, no signal on the other plate. After a sudden change in Position the dot follows but it takes some time before the dot settles at the new position. Apparently the voltage (charge) at the open plate creeps slowly to a new equilibrium. That equilibrium also shifts slowly when Intensity is changed.
(Speculation:  When Intensity is turned down the disconnected plate catches less electrons I think and becomes more positive. Then Dave's 5111 trace drifting to the bottom indicates that the lower plate is disconnected.)

Albert

On Mon, Jul 15, 2019 at 12:49 PM, zenith5106 wrote:


On Mon, Jul 15, 2019 at 06:30 AM, Dave Seiter wrote:


One bit of odd behavior that might be related:  whenever a trace is at the
top of it's travel (center screen), and the intensity gets turned down to
below normal viewing levels, the trace will start to move down the screen as
  the intensity fades out, eventually going off the bottom edge of the
screen. 
Never seen that behavior on a Tek scope before.
I've seen similar behavior when one of the connections to the vertical
deflection plates (V amp output) has become open.
So that would be the first thing I'd check. In your case it would be pins 11
and 12 in the CRT socket.
This could also explain why you can't get the trace above center.

/Håkan