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Demo boards that display the Tektronix logo and other images on your analog
scopes in XY mode are once again available from the museum!



-Thomas

On Thu, Feb 27, 2025 at 09:52 PM, <saturn.v2000@...> wrote:

Oddly, the flicker I'm seeing on the green button indicators goes away with
signal input (using built-in 1khz calibrator tab).

If trigger mode is in "Auto Level" does moving the tigger mode to "Auto" and changing trigger level away from zero stop flickering?
Ozan

Hi

With reference to the display fading only.

You are probably seeing a little understood / acknowledged problem with the high value resistors around the CRT. They normally go high in value with applied voltage, this effect can take a considerable time to fully occur. 15 to 20 minuets is quite common.

To fix replace the resistors with high working voltage ones from the likes of the Vishay VR26 range.

George G6HIG UK On Friday 28 February 2025 at 04:18:38 GMT, saturn.v2000 via groups.io <saturn.v2000@...> wrote:

Hi All

Have two issues with my Tek 2246 scope display. Looking for common faults before digging in.

1) Display brightness fades after approx half hour after power on. Display geometry is fine, it just dims

2) Display seems to have a slight flicker . . . it's also noticeable on the green LED's illuminating buttons

Bought it in not working condition. Replaced rectifier in -15VDC supply. All now working well except these two issues.
All other supply voltages look steady, although have not taken time to look at any ripple/abnormalities.

Thanks in advance,
Mike

Thanks for the reply.

The "flicker" seems to go away with readouts turned off (clear display button).

Oddly, the flicker I'm seeing on the green button indicators goes away with signal input (using built-in 1khz calibrator tab).

The volts/div and sec/div readouts (which I don't think can be turned off) appear to have noise on them at all times, same with the other readouts
when those are turned on.

I realize there's a jitter adjustment for the readouts as per service manual, but would like to get opinions/advice first.

Mike,
The display flicker might be due to the on-screen readouts stealing the beam at times.
Does the flicker go away if you turn the readouts off?
--John Gord

Hi All

Have two issues with my Tek 2246 scope display. Looking for common faults before digging in.

1) Display brightness fades after approx half hour after power on. Display geometry is fine, it just dims

2) Display seems to have a slight flicker . . . it's also noticeable on the green LED's illuminating buttons

Bought it in not working condition. Replaced rectifier in -15VDC supply. All now working well except these two issues.
All other supply voltages look steady, although have not taken time to look at any ripple/abnormalities.

Thanks in advance,
Mike

Thanks Mark!

This is great info and I'm sure it will be very helpful to folks in the future. It is the kind of stuff that is above my pay grade. I figured there was SOMETHING newer and better, but I'm a tube guy so I had no confident idea how to confidently recommend such a device, so thanks for the tip. Glad to know that I don't have to steal another off my parts mule after all. :-)

It is so much easier to order stuff from Mouser or Digikey. So readers in the distant cyber future, here's the short version of this fix

1. Check your U4269 14 pin IC for waveforms as illustrated by # 87-91 from the manual.
2. If they are wrong at U4269, just pop out the 14pin chip and put in a PN3568, available from Mouser.

Wow, that was a lot faster than my original post! :-)

Cheers,

Keith

Keith,

Thanks for the help. I am sure ones here will need this information.

From the specs of the CA3046 at 120mc while the specs also say the range is 550mc, a PN3568 looks like a good replacement at higher specs than the original IC. You will need 5 transistors to do the job of the IC. These are rated at 80/60V, 600mc, higher current capacity and 625mW. The PN transistors are a current supply at Mouser.

Mark

I'll try to keep this brief, but this is an end to end diagnosis and repair description. Maybe this will help someone in the future who has a 465B or similar scope with a similar problem? Experienced techs will laugh at my ignorance, a chuckle which I both accept and invite. :-)

This post concerns the diagnosis and repair process of a Tektronix 465B, SN 37xxx, suffering from a display that was horizontally compressed and shifted far to the right. When operating, the display showed only 3 divisions trace width. In addition, the trace start could not be forced to go anywhere left of the centerline on the graticle. (THIS IS A CLUE!) All the typical sweep functions and vertical amplifier functionality appeared o.k. Just a horizontally shifted and compressed display. (THIS TOO IS A CLUE) The Beam Finder was not centering the beam either, but it was going center and just off the top of the screen. I noted this as a possible "other problem" as well as a symptom.

This scope had been working perfectly. It is my backup scope. Fired it up after a 6 month inactivity in climate controlled storage. No particular reason for failure noted

REPAIR PROCESS

ONE) Since it had been stored, I did the usual "clean the switches/exercise the switches". Nothing changed

TWO) Opened up the scope and started taking measurements. No board removal required. Just remove the case and face the scope screen to the right so it matches the orientation of the diagrams. I was pretty sure the PSU was right, thanks to relatively recent recap by my favorite scope tech, my brother Mike - but I checked PSU test points on A4 board anyway. Examine Figure 8-7 TP 4340, 4437, 4338, 4339 and 4439. All these voltages were exactly right. They are printed on the board there. I did not check CRT HV, since the beam was bright and sharp.

THREE) Upon visual inspection of the A4 board, I found a couple of suspect looking tantalums which I shotgunned in there because I could - but to no avail. C4441 in particular looked bad. Screen still offset. Noted a couple of resistors on A4 that looked like they were running warm as well. R4368 and R4369, and noted them for future attention. Checked Axial Electrolytic C4461 by lifting one end. LCR meter said cap was o.k., so I put it back as is.

FOUR) Checked the following trim-pots on A4 board. NOTE: IF YOU ADJUST THESE YOU WILL HAVE TO RECALIBRATE SOME - Move with discretion and note positions so you can at least get them back close.

XGain control, R4381 - no effect on horizontal width, i.e. inoperative (THIS TOO WAS A CLUE!)
X10 gain R4275 - working but off to the right as expected.
X1 Gain R4274 - working, showed a very small adjustment range (as expected with a horizontally squashed display)

Note that these Bourns trim pots are known to fail. If they fail, your display will go black. Ask me how I know. :-) But mine were fine this time.

FIVE - FIRST PROGRESS) I finally got smart and ran a diagnostic test I got here on TekScopes I/O. The test is simple. Put the scope in X/Y mode and supplied the front-panel calibration oscillator to the x/y inputs. This is a good tip, posted on this forum somewhere, and repeated here. I quote below the exact language of the test routine.

"""""Put the scope in x-y mode (to bypass all the sweep generator circuits) and drive both x and y with the calibration source on the front panel (it's just a handy signal source). If you a.) still see width compression there, the problem is downstream of the sweep generator. If you b.) no longer see width compression, then the problem lies before the deflection amplifier.""""""

I observed condition a.) Therefore, something wrong "downstream" of sweep generator itself, in the horizontal amplifier post sweep circuit. Now I finally knew where to start looking.

I checked the +15 and -8 voltages at the front panel position indicator potentiometer and observed that they seemed reasonable when the pot was turned. That put me firmly on the A4 board itself. I re-read Section 465B manual section 3-19 and 3-20, and the description of the "Input Paraphase Amplifier" / "Gain Setting Cascode Amplifier" and associated driver transistors. I looked at the A4 board physical layout, Figure 8-7 in the manual. I looked at the A4 Schematic which is #10, and is missing from some PDF versions of the manul, like the one at Tek Wiki. So download the file called "missing pages" there at Tek Wiki. :-) Note that the A4 board schematic is also scattered around in various other places on other board drawings. It is a little hard to follow as a PDF, IMO. Paper might be easier for this one. A bit of a head scratcher, but it is all in there.

WHERE I SHOULD HAVE STARTED: At this point, based on the results of above and especially advice from the Scope Whisperer (my brother Mike L., here on the TekScopes group) I scoped the waveform checks #87-91 from the manual. You'll find the manual's page of waveforms right after the A&B Timing Switch Diagram #9. For physical location of the test points, check Figure 8-7 A4 Interface Circuit Board, location i 5. You'll see it there. U4269. That's where you take those readings for waveform 87-91. That 14 pin DIP integrated circuit.

These waveform checks are scope measurements of the expected waveform performance of the Input Paraphase Amplifier and the Gain Setting Cascode Amplifier mentioned in section 3-19 of the manual. These are both part of a 14 pin DIP, common part CA3046, Tek part 156-0048-003, schematic devices U4269A-E (it is a "five transistor array" on a 14 pin dip). If you haven't already, you should hope yours is in a socket. :-) If it is not you are probably pulling your A4 board. :-/

PROGRESS! I quickly observed that something was wonky there at U4269, as about half of those predicted sawtooth waveforms were missing or way wrong. I checked the various discrete driver transistors downstream of the 14 pin DIP and they were faithfully trying to reproduce the wonky signals from U2469. I looked upstream and it looked kind of o.k. to me as well (I'm no expert). So the CA4036 Chip was very suspect. Fortunately, mine was SOCKETED! :-) yea!

PARTS ACQUISITION: I searched my pats bin - no dice. I looked online in the usual places, and quickly saw that true Tek "selected" parts were not real common on eBay, etc. Some were rather pricey.

You are looking for a CA3046 when you look for a replacement. Note that this is the number for the "improved version" in scopes S/N B03920 and above. For Older scopes like mine they specify another similar device, Tek P/N 156-0179-00, but you can ignore that as the Tek 156-0048-03 is "improved" and drop in substitute. Note that all of these CA3046 devices apparently have a fairly poor reputation in the Tek community, even though Tek was "selecting" them. Makes you wonder how bad the unselected ones were! :-) Tek specifies 04713 Motorola as the manufacturer, and a mfg. P/N of SC77161B, which is less useful today, but might help a few of you sort through your parts bins.

Anyway, as I looked around plenty of non-selected modern manufacturing versions of the CA3046 Device were available at low cost. It is used in a lot of stuff. :-) I hopefully opined that new production CA3046 are probably better than 1970's vintage of the same...so that was an option even though they are not "Tek selected" (haha). Another option might be the CA3045 which is a "ceramic version" of the above. But I would have to wait at least two days and we can't do that, can we? :-)

So another option for me was to harvest one from a donor scope. I have a 2445B parts mule scope. On a lark, I examined the 2445B manual and noticed that the 2445B ALSO used this very same device...at least five of them - same exact Tek P/N 156-0048-03. When I went to my mule, I discovered that a yet more "improved version" of CA4036 was used in the later serial numbered 2445B scopes, namely device type CA4336. I examined my parts mule. Sure enough, five CA4336 there on the A1 board of the 2445B. Sadly they were not socketed. In a stroke of good fortune, I noticed one of them, U550 was right at the edge of the board and accessible. I broke out the solder sucker and wick and managed to carefully remove U550 without ruining it (I hoped)

I inserted the rescued CA4336 chip into my 465 and turned it on. No magic smoke, just a normal display again. Bottom line CA4336 = CA4036 for this application.

Thanks to my brother Mike for the great help, and to whomever published that X/Y diagnostic test tip here on the forum more than 10 years ago.

No idea why my original CA4036 chip failed. As I said, they are apparently weak by design. I'm might rescue a couple more CA4336 off my parts mule, just in case.

Now to fix the beam finder and a quick calibration.

Keith
coolblueglow

On Thu, Feb 27, 2025 at 03:03 AM, TugboatDave wrote:

Now what I would like to know is if anybody has tried this substitution and
was it successful?

The info on TekWiki is obviously wrong.
154-0838-00 was used only 2213 and 2215.
154-0861-00 was used in 2213A, 2215A, 2235 and 2236.

Check out this old post on the same subject: /g/TekScopes/message/7170

/H?kan

Hi Dave,

Can't answer your question on the substitution,
but I believe that I have a good used CRT for the scope that you
have. Let me know off the list if you would like it and we'll make a
deal. IIRC, I believe that it's the same tube in the 2235 and 2236
scope.

Let me know.



Kim Herron W8ZV
w8zv@...
www.goldenradioservice.com
616-677-3706



--
Kim Herron
W8ZV
w8zv at goldenradioservice dot com
www.goldenradioservice.com

It is a well known issue in the 224x series scopes power supply that any original rectifier diodes marked ZM or ZS tend to get leaky or fail over time. There is a total of 17 diodes that should be replaced and MUR160 600V 1Amp 50nS diodes (Mouser PN 863-MUR160G) is a good choice, although any fast 1-amp rated diode will also do. Just don't try to use common 1N400x diodes.

Before you close up your scope, I suggest you check for any additional suspect diodes (probably they all will need to be replaced) and get it done now to be on the safe side, otherwise there is a good chance that over time you might have yet another shorted diode causing problems.

And while you have access to the big main board, check the voltage on the Lithium battery and see if it might need replacement. Anything under 3.0V is suspect and should be replaced. Fortunately in this scope series there is no calibration data at risk, the battery just holds any settings information so the scope can power up in the same configuration used before powering it down.

Hi all,
and thank you Mark and Gerald for the files and the hints. I found out, that the EMI Filter is blown. But I think it's not so easy to repair, because it's filled with epoxy.
Perhaps I will find a small filter and put it inside the original EMI Box. Not a problem.
Hopefully it will work afterwards.

闯ü谤驳别苍

The input is a sine wave. The wave form cause is a single component.

That didn’t take you very long. You get an A+.

Hi chaps.

I suppose this is the final update, as found a shorted 47?F 20v cap (C6033) on the A62 board, and now the 492 appears to be working again (although I don't yet know how to use it, to be sure).

Anyway... Fantastic!

Must finally be getting somewhere with my 'diagnose and repair' abilities. Lol...


Thanks again to Mark and Albert, as after looking at the complexity of the instrument, I was honestly not gonna follow this through.


James

Hi Benny,
I'm interested in replacing the rear feet on my 'ol Tektronics 475. Do you still print them? Price on 4?
Thanks
Stan W8SRD

Hello All,
Back Story:
Bought a cheap 2213A off Marketplace with fuzzy display issue,
Fixed issue by replacing focus resistors,
discovered screen damage in that there was trace distortion in lower half of display,
started looking for new CRT,
Found a part #154-0838-00 CRT on Ebay, according to Tekwiki this CRT is compatible,
My current CRT is part#154-0861-00 but I order it anyway (price is right),
get replacement CRT and discover that the HV lead is different and the trace rotation coil is smaller,
double check part numbers and find out Tekwiki led me astray and their CRT number index is in error,
CRT is out of a 2213
Today:
I have done some research and it seems that the HV voltage is higher on the proper 2213A tube.
Now what I would like to know is if anybody has tried this substitution and was it successful?
Failing that is there any tips on where to find a #154-0861-00 tube,
They seem scarce on Ebay.
Thanks in advance for any help or suggestions

Are the voltage’s adjusted with the VR’s on the plug-in Or is it an adjustment inside the scope itself?

What are???
Nothing quoted for context.

Glenn

--
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