Working on the HV Section of a 533A


 

Fresh off of several victories with my 7603 and plug-ins, I turned my attention tonight to the 533A and found the courage to peek inside the left half of the HV section (the section on the opposite side from the CRT, with the five 5642 rectifier tubes). The section was entirely covered in soot, which is expected where you have high voltage, but after I got done cleaning the soot off of everything a possibly serious problem became apparent: two of the ceramic terminal strips at one end of the row of rectifiers was still pitch black.

I have uploaded pictures of the HV section to this album: https://groups.io/g/TekScopes/album?id=266270

I have already ordered replacement ceramic terminal strips, but I don't really know what I'm doing. I assume that I will need to unsolder the rectifier tubes both to replace the terminal strips, and to verify that there isn't more damage to components beneath the rectifiers.

I'm also wondering if I'm going to need to replace those black axial leaded capacitors that can be seen in the foreground. I think that there are more like that elsewhere in the scope, but I have done a detailed inventory yet. If I need to replace them, what do I replace them with?

Any advice is appreciated.

-- Jeff Dutky


Brenda
 

Hi Jeff! Great to see you are working on your 533A! I have one as well, but it's in really bad shape on the inside. Those 2 back strips is perfectly normal. My 535A and my 545A is like that as well. I read somewhere on the forum that it's called corona dope, since that is where the 10KV is. I think that you will find that after a really good cleaning of the HV board that everything will be just fine. You really do want that coating to be on those last 2 strips, but don't worry, it's really hard to get off. As far as those 2 Black Beauties goes, most likely, those will be just fine. It's a "newer" scope as by this time, Tektronix got rid of the bad capacitors as your HV section has ceramic and those will be just fine as well. I have a few scopes that use these Black Beauties with the red writing to be fully functional. The ones with the yellow writing are most likely going to be very leaky.

Brenda


 

Brenda,

thanks for that tip; I had never heard of "corona dope" before, but a quick google search (on the correct term) reveals all.

Any idea how I would test be certain that everything is okay? I mean, I guess I can just power the instrument up and wait for the arcing to start, but maybe there are less reckless approaches?

I can guess that I won't simply be able to check resistances, because any leakage would be expected to be at high voltage. I am currently building a small HV power supply in order to test capacitor leakage, but it will only go up to 500 V, and I'm guessing that the voltage on those terminal strips is in the kV range.

-- Jeff Dutky


Brenda
 

Hi Jeff, I am glad that I was able to contribute this this forum.

I would have to say, in my opinion, since you started to clean that section, you should keep cleaning it until it is spotless. I have read from another post that you don't clean this section well, that you would actually create leakage and that would throw your HV into chaos. Once it's all clean and dry, you should be able to power it up without any problems. My 545A was filthy, more so than yours most likely was. Mine was covered in all that soot, but was covered in cigarette tar so I had to clean it. I mean, it was pure yellow and sticky and I am not that knowledgeable so I learned the hard way that all this smoke and tar gave me a LOT of HV issues. I am sure that others on this group will chime in as I am still learning about these old scopes with my 535A being my favorite. I would also advise to check and reseat the 12AU7A and the 6AU5GT tubes that are on the underside of the HV oscillator, at least that is what I would do myself.

Brenda


Mark Vincent
 

Jeff,

Brenda is right about the corona dope. Leave those strips in. Clean them to remove dust. I have not seen any of the black beauties any good. These are a wax condenser in a plastic case. I replace them on sight. The Good-all ones I also replace on sight. Replacements I use are Sprague Orange Drops or other high quality ones at 630V, e.g. Panasonic. Radial types work fine to replace axial.

Mark


Keith
 

Guessing you both know the trick about holding a little NE-51 or similar neon bulb in close proximity to the HV section to confirm its operation? If your HV section is working, the little neon will light up from the radiated energy.

Cool to see and an easy way old fashioned service trick to know something is there without having to resort to the high voltage probe, etc.


Keith
Coolblueglow


Mark Vincent
 

Keith,

I have not done that trick in some time. I have done it before. Great way to test for high voltage being present.

Mark


Harvey White
 

I've heard that you need to be careful how you solder to those ceramic strips.  What I did hear is that you do not put the iron tip in the notch.  Pleas check to make sure I got it right.

Harvey

On 7/19/2021 10:03 PM, Brenda via groups.io wrote:
Hi Jeff! Great to see you are working on your 533A! I have one as well, but it's in really bad shape on the inside. Those 2 back strips is perfectly normal. My 535A and my 545A is like that as well. I read somewhere on the forum that it's called corona dope, since that is where the 10KV is. I think that you will find that after a really good cleaning of the HV board that everything will be just fine. You really do want that coating to be on those last 2 strips, but don't worry, it's really hard to get off. As far as those 2 Black Beauties goes, most likely, those will be just fine. It's a "newer" scope as by this time, Tektronix got rid of the bad capacitors as your HV section has ceramic and those will be just fine as well. I have a few scopes that use these Black Beauties with the red writing to be fully functional. The ones with the yellow writing are most likely going to be very leaky.

Brenda





Renée
 

Jeff-
make sure you use silver bearing solder on the ceramic strips. sometimes the strips can be cleaned...but ya have new ones on the way moot point. too much heat too long will also cause the silver to come loose from the ceramic...use high heat get in and get out! ( don't ask how i know.....)
personally ,I have had mixed luck with the old oil/paper caps. I would look at those last they may be just fine. tek used pretty good ones!. however, ..If they are cracked they go otherwise... replacement - mylar have been fine in some of my restorations. some will say Orange drops....both will work fine and are most likely superior in the long run.
Renée

On 7/19/21 6:52 PM, Jeff Dutky wrote:
Fresh off of several victories with my 7603 and plug-ins, I turned my attention tonight to the 533A and found the courage to peek inside the left half of the HV section (the section on the opposite side from the CRT, with the five 5642 rectifier tubes). The section was entirely covered in soot, which is expected where you have high voltage, but after I got done cleaning the soot off of everything a possibly serious problem became apparent: two of the ceramic terminal strips at one end of the row of rectifiers was still pitch black.

I have uploaded pictures of the HV section to this album: https://groups.io/g/TekScopes/album?id=266270

I have already ordered replacement ceramic terminal strips, but I don't really know what I'm doing. I assume that I will need to unsolder the rectifier tubes both to replace the terminal strips, and to verify that there isn't more damage to components beneath the rectifiers.

I'm also wondering if I'm going to need to replace those black axial leaded capacitors that can be seen in the foreground. I think that there are more like that elsewhere in the scope, but I have done a detailed inventory yet. If I need to replace them, what do I replace them with?

Any advice is appreciated.

-- Jeff Dutky




 

Kieth,

That's an interesting trick to know about, but I already invested in a 40 kV probe (and heavy rubber gloves) back when I was working around the HV section of my 475. I think I'll stick to the HV probe. I haven't worked long enough around HV to lose my skittishness about it, and "holding a neon bulb near the HV section" while it's operating is well outside my comfort zone.

-- Jeff Dutky


 

Renée and Harvey,

The scope still has it's emergency spool of silver solder, apparently unused, but I also bought three 0.35 oz coils of Kester 62/36/2 silver solder when I was working on the 475 or 475A HV sections a few months ago.

When you say "high heat" Renée, what temperature are we talking about? I already replaced one blown resistor in the LV section, and I used my old Weller iron (the kind with the magnetic tips that you have to change to select the temperature). It was not easy to do, but I think some of that was because I did not clean the area very well before applying the heat. I also have a surface mount rework station with a soldering iron attached, and it allows me to adjust the temperature with a dial. What temperature should I be using on the ceramic strips?

I'm was already planning to test all the electrolytic cans, so testing the axial leaded caps is only a little more work. I'm glad that mylar caps will do as replacements, as I already happen to have a good supply of those that I have been using on some EICO instruments.

-- Jeff Dutky


Tim Phillips
 

Then there is the other trick of powering-on, if safe to do so, and turning
out the room lights for a few seconds. (Stand back)
This should show any arcing or flashovers in the HV compartment. Sometimes
a smell of Ozone,
I once did this with a 536, and one of the HV rectifier tubes was lit up
like a blue Neon sign.
Usual warnings apply: HV = High Vigilance !!

Tim

On Tue, 20 Jul 2021 at 05:13, Jeff Dutky <jeff.dutky@gmail.com> wrote:

Renée and Harvey,

The scope still has it's emergency spool of silver solder, apparently
unused, but I also bought three 0.35 oz coils of Kester 62/36/2 silver
solder when I was working on the 475 or 475A HV sections a few months ago.

When you say "high heat" Renée, what temperature are we talking about? I
already replaced one blown resistor in the LV section, and I used my old
Weller iron (the kind with the magnetic tips that you have to change to
select the temperature). It was not easy to do, but I think some of that
was because I did not clean the area very well before applying the heat. I
also have a surface mount rework station with a soldering iron attached,
and it allows me to adjust the temperature with a dial. What temperature
should I be using on the ceramic strips?

I'm was already planning to test all the electrolytic cans, so testing the
axial leaded caps is only a little more work. I'm glad that mylar caps will
do as replacements, as I already happen to have a good supply of those that
I have been using on some EICO instruments.

-- Jeff Dutky






Renée
 

Jeff-
what i used and found worked best is the old 100/140W weller solder gun, actual temp? I do not know , in and out fast. I am sure one of the chisel tips would also work if they have enough mass. the ones available at work were too low temp for the job and not enough heat quick transfer. So...I ended up bringing my own tools from my shop.
a little extra rosin also helps , but start with clean leads and surfaces ( scotch brite pad works great here) .
on the caps note the outside foil side and try and match locations. the mylars may or may not have an outside foil. orange drops do sometimes not marked.
test/verify with a scope and your hand...
Renée

On 7/19/21 9:13 PM, Jeff Dutky wrote:
Renée and Harvey,

The scope still has it's emergency spool of silver solder, apparently unused, but I also bought three 0.35 oz coils of Kester 62/36/2 silver solder when I was working on the 475 or 475A HV sections a few months ago.

When you say "high heat" Renée, what temperature are we talking about? I already replaced one blown resistor in the LV section, and I used my old Weller iron (the kind with the magnetic tips that you have to change to select the temperature). It was not easy to do, but I think some of that was because I did not clean the area very well before applying the heat. I also have a surface mount rework station with a soldering iron attached, and it allows me to adjust the temperature with a dial. What temperature should I be using on the ceramic strips?

I'm was already planning to test all the electrolytic cans, so testing the axial leaded caps is only a little more work. I'm glad that mylar caps will do as replacements, as I already happen to have a good supply of those that I have been using on some EICO instruments.

-- Jeff Dutky




 

Renée,

What I've got is a Weller TC202 with a TC201P iron that I inherited from my father, with three tips (long conical #8, screwdriver #7, and narrow screwdriver #6). From a Weller tech sheet I found online it looks like these are 800°F, 700°F and 600*F respectively. I was using one of the screwdriver tips when I was having trouble with the ceramic strip, so I should try the long conical tip instead (which will let me get into the terminal slot better than the screwdriver tips did. I was using them because I had heard that the broader tip transferred heat better, but maybe an extra 100 or 200 degress is worth more than surface conduction).

I should also order a few extra tips: the ones I have belonged to my father and date from some time in the 80s, and they already had a fair amount of use when they came to me.

I'll be sure to get myself some scotch brite pads too.

-- Jeff Dutky


Keith
 

Hi Jeff,
Well, glad you are cautious...we don’t need any “did you hear about Jeff...” posts popping up. 😂

Still, and fwiw, you don’t have to get very close with the neon bulb, in fact, not as close as you get with your HV probe, and of course you can still wear your rubber gloves with the neon bulb too. Personally I find it quite safe, as I’m merely hovering a nonconductive object several inches away from the general area, versus putting contact pressure and therefore pushing my hands toward a definite live multi-kV point with a probe. But I surely get your point, safety first!

And of course since you have the probe, why not use it and get the data, instead of just an indicator of possible function. (He said...enviously)

Because SOME OF US (eye-roll) aren’t lucky enough to have a snazzy 40k HV probe 🤣

Cheers!
Keith


Harvey White
 

Put the neon lamp at the end of a one foot plastic rod.

Harvey

On 7/20/2021 8:24 AM, Keith wrote:
Hi Jeff,
Well, glad you are cautious...we don’t need any “did you hear about Jeff...” posts popping up. 😂

Still, and fwiw, you don’t have to get very close with the neon bulb, in fact, not as close as you get with your HV probe, and of course you can still wear your rubber gloves with the neon bulb too. Personally I find it quite safe, as I’m merely hovering a nonconductive object several inches away from the general area, versus putting contact pressure and therefore pushing my hands toward a definite live multi-kV point with a probe. But I surely get your point, safety first!

And of course since you have the probe, why not use it and get the data, instead of just an indicator of possible function. (He said...enviously)

Because SOME OF US (eye-roll) aren’t lucky enough to have a snazzy 40k HV probe 🤣

Cheers!
Keith





Dave Wise
 

531/535/541/545 are the first generation of 500-series scope. 533 is second-gen, 533A is third. Black Beauty and Good-All from this era use plastic film insulation just like modern caps. In general they are no more likely to be bad than a modern cap.
That said, some also contain a layer of paper (Sprague trademark “DiFilm”), which by now has caused the cap’s Dissipation Factor to increase. In most applications, it doesn’t matter.
The 1nF cap that resonates the transformer primary is sensitive to DF however, and a lossy one can prevent oscillation. Something to watch for but not in the “front row” of suspects. If you have a bad cap in the HV section, it’s most likely to be one of the 10kV-20kV “doorknobs”. Now and then they short-circuit. The ceramic disks Tek used are very high quality, better in some ways than modern caps unless you really shell out the dollars.

My 500-series mainframes are still using their original electrolytic caps. If it was my scope, I’d just power the thing up.
If you test the electrolytics in-circuit, remove all the tubes first. (Note where each one goes, some are aged/screened/matched.) Otherwise you will ruin some by puncturing the heater-cathode insulation. That’s why Tek uses a time-delay relay.

It’s good you’re cleaning the ceramic strips; there are a couple of “sore spots” where high potential between adjacent terminals causes silver migration which will eventually arc over and (at the least) ruin the strip. The SNAP! made me jump a foot. Rather than replace the strip (lower left corner of the B sweep chassis, that’s not present in your model), I started an experiment by grinding off the flashed-on silver and painting the spot with corona dope. Not to suppress corona but to forestall further migration. I don’t know if it helps, ask in ten years.

Be sure you’re not leaving any conductive residue behind, it will just hurry the strip to its doom sooner.

HTH,
Dave Wise
535, 535A, 545, 547

From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Mark Vincent via groups.io
Sent: Monday, July 19, 2021 7:32 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Working on the HV Section of a 533A

Jeff,

Brenda is right about the corona dope. Leave those strips in. Clean them to remove dust. I have not seen any of the black beauties any good. These are a wax condenser in a plastic case. I replace them on sight. The Good-all ones I also replace on sight. Replacements I use are Sprague Orange Drops or other high quality ones at 630V, e.g. Panasonic. Radial types work fine to replace axial.

Mark


Renée
 

Jeff-
working on older parts the oxide on the leads impedes "solder-ability", so just a gentle cleaning. scotch-brite(red/green/grey), I use whatever is nearby (green/grey at the bench).
Re the tips they do go bad with time/use I would run with the screwdriver, the long conical generally does not have the mass to do fast transfer of heat. it is not so much the temp ( to a point) as is the quick heat/in&out, try the 800 it may work but beware of burning the rosin. too much heat is just as bad as not enough. Those high temps were not allowed ( and for good reason) to be found in the rework area or at our engineering benches the govt oversight would have a fit, I caused enough grief with procedures that got things done and fixed properly before my ECN could be approved. I hid most of my unapproved tools 99% of the time.
I like the Weller gun for tip interchangeability and one could shape the tip as needed. they are not ESD safe! as you know every tool has its applications and limitations. ( they are inexpensive now days ~$5 used at garage sales etc...best one has nuts to hold the tips but beware of stripped threads...they kept making modifications to the attachment point until it worked poorly )
Renée

On 7/20/21 12:15 AM, Jeff Dutky wrote:
Renée,

What I've got is a Weller TC202 with a TC201P iron that I inherited from my father, with three tips (long conical #8, screwdriver #7, and narrow screwdriver #6). From a Weller tech sheet I found online it looks like these are 800°F, 700°F and 600*F respectively. I was using one of the screwdriver tips when I was having trouble with the ceramic strip, so I should try the long conical tip instead (which will let me get into the terminal slot better than the screwdriver tips did. I was using them because I had heard that the broader tip transferred heat better, but maybe an extra 100 or 200 degress is worth more than surface conduction).

I should also order a few extra tips: the ones I have belonged to my father and date from some time in the 80s, and they already had a fair amount of use when they came to me.

I'll be sure to get myself some scotch brite pads too.

-- Jeff Dutky




.


Dave Wise
 

I use a TC-201 with 700F screwdriver tip. You want mass more than temperature. Silver-bearing solder. In and out quick. Careful not to wedge the tip in the slot, it will break it.

FWIW,
Dave Wise

From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Renée via groups.io
Sent: Tuesday, July 20, 2021 8:22 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Working on the HV Section of a 533A

Jeff-
working on older parts the oxide on the leads impedes "solder-ability",
so just a gentle cleaning. scotch-brite(red/green/grey), I use whatever
is nearby (green/grey at the bench).
Re the tips they do go bad with time/use I would run with the
screwdriver, the long conical generally does not have the mass to do
fast transfer of heat. it is not so much the temp ( to a point) as is
the quick heat/in&out, try the 800 it may work but beware of burning the
rosin. too much heat is just as bad as not enough. Those high temps were
not allowed ( and for good reason) to be found in the rework area or at
our engineering benches the govt oversight would have a fit, I caused
enough grief with procedures that got things done and fixed properly
before my ECN could be approved. I hid most of my unapproved tools 99%
of the time.
I like the Weller gun for tip interchangeability and one could shape the
tip as needed. they are not ESD safe! as you know every tool has its
applications and limitations. ( they are inexpensive now days ~$5 used
at garage sales etc...best one has nuts to hold the tips but beware of
stripped threads...they kept making modifications to the attachment
point until it worked poorly )
Renée


On 7/20/21 12:15 AM, Jeff Dutky wrote:
Renée,

What I've got is a Weller TC202 with a TC201P iron that I inherited from my father, with three tips (long conical #8, screwdriver #7, and narrow screwdriver #6). From a Weller tech sheet I found online it looks like these are 800°F, 700°F and 600*F respectively. I was using one of the screwdriver tips when I was having trouble with the ceramic strip, so I should try the long conical tip instead (which will let me get into the terminal slot better than the screwdriver tips did. I was using them because I had heard that the broader tip transferred heat better, but maybe an extra 100 or 200 degress is worth more than surface conduction).

I should also order a few extra tips: the ones I have belonged to my father and date from some time in the 80s, and they already had a fair amount of use when they came to me.

I'll be sure to get myself some scotch brite pads too.

-- Jeff Dutky





.


 

Dave,

I suspect that all three of the tips I have are worn out. I discovered two tips, still in their bags, in a plastic "parts deresser" (plastic drawers for electronic parts, cheap a Radio Shack, back in the day). One is a long conical point (my favorite style) 700°F tip, and the other is a 600°F screwdriver tip (though it looks conical to me). I also ordered a half dozen new Weller tips on Amazon of various styles and temperatures, including a pretty broad "sloped" tip (but it's 800°F, so maybe not appropriate for most work). I'll be sure to order a couple more 600°F tips, if I can find them in broader styles.

The TC201 is very nice to use. My father had another, much cheaper soldering iron (or "pencil") that plugged directly into the wall (the two prong power cord came straight out the back of the handle). The TC202 seemed like ridiculous extravagance back in 1985. The fact that you could just unscrew the outer sleeve and swap the tips was astonishing. I'm still sorry that I didn't know how to take care of the tips properly, or they would probably still be in good condition.

I've watched a few videos about proper care of your soldering iron and tips, and I'm going to give a go at correctly cleaning and tinning the tips I already have, but I'll be more focused on keeping the new ones in better condition.

-- Jeff Dutky