547 Restoration conundrum #photo-notice


Jason A.
 

Hello fellow Tek fans,

I'm in the midst of what are hopefully some of the finishing touches to my 547 restoration and I've hit one thing that is perplexing me as I have found no mention of this specific issue - and hopefully I'm not just missing the correct search term. After some extremely helpful recommendations from Chuck on the HV section of my 547, I have eliminated all but one of my display oddities. Everything is leaning slightly up and to the left. See photos here:

https://groups.io/g/TekScopes/album?id=264243

A little history - until recently the geometry was seriously compromised on my 547. I replaced the HV diodes with solid state ones per this forum and TekWiki's mention of it being a recommendation from the late-great Jim Williams, finishing out that modification with replacing the 56K-ohm resistor R803 up to a 68K to keep the 12AU7's plate at the correct voltage. I just tonight finished replacing the last 2 resistors on the HV section of the 547 and that has made an amazing difference in both geometry and trace definition/focus/clarity. The final adjustment I would like to make is to get rid of the display-wide slant.

If anyone has any recommendations on what I am missing, I would love to hear from you.

Thanks everyone and especially Chuck for helping point me in the right direction on the resistors.

Jason


Morris Odell
 

Have you tried the trace rotation control? It's the screwdriver adjustment in the centre of the Astigmatism knob..

Morris


Jason A.
 

Hi Morris,

Thank you for the suggestion. Yes I have given that a try as well, but sadly that makes everything go askew. I set it with the input shorted to get a straight line across the center graticule and it appears the trace rotation is set correctly to get the tops and bottoms of the waveforms where they need to be.

I keep wondering if the shield around the picture tube is maybe somehow magentized or something like a trimmer capacitor on one of the horizontal stages (generator/amplifier) is throwing things off.

It is really something of a head-scratcher.

Thank you and best regards,
Jason


Keith
 

Some of the other guys or gals here can comment with far more authority than me on this topic, but maybe this is the mystery magnet alignment thing? Chuck? Others? I seem to remember something about little tweaker magnets put on some Tek CRT necks? I thought I read they were literally taped there to deal with weird nonlinear astigmatisms? Seems like someone talked about the tape drying out and magnets falling off, resulting in display linearity problems.

Or, have I been using my 100W soldering iron for a coffee warmer too much?

Also, had some discussion and got an education here lately about the mu-metal shield and how fragile it actually is. If it gets whacked, dropped or banged up - even a little - it loses its effectiveness. (But maybe my head is what has taken one to many blows, and I’m grasping at straws?)

Maybe your Mu-Metal shield is damaged and not doing its job, allowing some stray magnetic fields in the scope to mess things up? I mean, they put those shields on there for a reason, right?

I know that’s a long shot - just hoping for your sake that the real answer is not “something is misaligned in the CRT due to rough handling”

Again, this entire line of thinking on my part may be the result of lead poisoning...😂


Keith


Michael W. Lynch
 

On Mon, May 17, 2021 at 07:49 PM, Jason A. wrote:


I'm in the midst of what are hopefully some of the finishing touches to my 547
restoration and I've hit one thing that is perplexing me as I have found no
mention of this specific issue - and hopefully I'm not just missing the
correct search term. After some extremely helpful recommendations from Chuck
on the HV section of my 547, I have eliminated all but one of my display
oddities. Everything is leaning slightly up and to the left.
Jason,

I had a 475 that had a similar defect in the trace.

Link to discussion here: https://groups.io/g/TekScopes/message/170272

I ultimately discovered that one of the glass support rods in the gun assembly had been broken by an impact at some time in the past.

Link to Photos on TEKScopes here: https://groups.io/g/TekScopes/album?id=251792

Before you spend a lot of time looking at the electronics and trying to adjust the defect out of the scope , I would suggest a careful examination of the CRT for some sort of internal damage. As I learned in this instance, a CRT can be damaged ever so slightly inside and still produce a fine looking trace, but one that is also useless because of the distortion. I hope that this is not your problem.

Best of luck to you.

--
Michael Lynch
Dardanelle, AR


Leon Robinson
 

If there is damage internal to the CRT it might be possible to use external magnets (small) to make corrections.  It would take a considerable amount of experimentation. 


Leon Robinson  K5JLR

-------- Original message --------
From: "Michael W. Lynch via groups.io" <mlynch003=yahoo.com@groups.io>
Date: 05/21/2021 9:45 AM (GMT-06:00)
To: TekScopes@groups.io
Subject: Re: [TekScopes] 547 Restoration conundrum #photo-notice

On Mon, May 17, 2021 at 07:49 PM, Jason A. wrote:


I'm in the midst of what are hopefully some of the finishing touches to my 547
restoration and I've hit one thing that is perplexing me as I have found no
mention of this specific issue - and hopefully I'm not just missing the
correct search term. After some extremely helpful recommendations from Chuck
on the HV section of my 547, I have eliminated all but one of my display
oddities. Everything is leaning slightly up and to the left.
Jason,

I had a 475 that had a similar defect in the trace.

Link to discussion here:  https://groups.io/g/TekScopes/message/170272

I ultimately discovered that one of the glass support rods in the gun assembly had been broken by an impact at some time in the past.

Link to Photos on TEKScopes here:  https://groups.io/g/TekScopes/album?id=251792

Before you spend a lot of time looking at the electronics and trying to adjust the defect out of the scope , I would suggest a careful examination of the CRT for some sort of internal damage.  As I learned in this instance, a CRT can be damaged ever so slightly inside and still produce a fine looking trace, but one that is also useless because of the distortion.  I hope that this is not your problem.

Best of luck to you.

--
Michael Lynch
Dardanelle, AR


Jason A.
 

Thank you for the recommendations all!

I took a look at the neck as best I could without fully removing it and I don't see any spare magnets or damage inside the tube neck itself. That said, I will need to get it removed to fully inspect it and I haven't had sufficient time for that yet. The Mu metal shield doesn't look like it's suffered any trauma that I can see. At one point in time, I used to have a tape head demagnetizer - I'm pretty sure it has been relegated to the bottom of a box somewhere probably 20 years ago. Once I can put my hands on it, I may try running it over the outside of the shield unless anyone knows this to be a bad idea. Otherwise, I think what I may do is live with it until I can find another CRT for mine. So long as I know what it is doing wrong I can accommodate it in my observations. At some point I will want it to be more correct but for now it sounds like I'll have to wait for a decent CRT to show up to fully fix it or at least fully troubleshoot it.

I really appreciate all the discussion and links to the 475 with similar issues. I'll be curious to see if I can find anything amiss in the neck once I get the CRT out of the shield.