Tektronix 2246 flickering screen, ch2 not working. (Ch2 fixed) New help needed!

[rf+tech]

I am not seeing the retrace.

I am seeing a diagonal stripe pattern of three or four intensity levels. Apply 1 MHz sine signal, level to fill six vertical divisions. Time-base set the same as for previous videos. The result on an analog scope would appear to be a solid band of light, the individual cycles will not be individually discernible. On the 2246, these diagonal stripes should be clearly visible.

Adjust the Holdoff to make the stripes nearly vertical, for easy counting. The number of stripes will be of interest. Does the number of stripes vary with holdoff?

Also of interest is the pulse width and count at U600-15. Refer to waveform 4D. At minimum holdoff, there are 50 pulses occurring during 4D high period. Note the discrepancy in sweep speed of 20 usec/div shown in the text above and the actual 10 usec/div in the photo. The latter is correct.

Please check the actual frequency of the 10 MHz clock on U600-1.

[grusus]

I am not seeing the retrace.

  I didn't post any vid and photo with visible retrace.

1MHz on input. I am changing timebase settings on video, and adjusting horizontal position:

https://photos.app.goo.gl/3VukWbH4Fjrazy5m8

I am seeing a diagonal stripe pattern of three or four intensity levels. Apply 1 MHz sine signal, level to fill six vertical divisions. Time-base set the same as for previous videos. The result on an analog scope would appear to be a solid band of light, the individual cycles will not be individually discernible. On the 2246, these diagonal stripes should be clearly visible.

Adjust the Holdoff to make the stripes nearly vertical, for easy counting. The number of stripes will be of interest. Does the number of stripes vary with holdoff?

If I understand you correctly: Is this what you want me to do? :-) I don't know about what diagonal stripes you are talking about ? I see only vertical.
I am adjusting holdoff from CCW to CW, and meantime trying to tune to stabilise those vertical stripes. Number of stripes vary with holdoff. 18,36,72 stripes. Scope at 0,1ms

https://photos.app.goo.gl/5Ld5EVAupkwPpv4PA

Also of interest is the pulse width and count at U600-15. Refer to waveform 4D. At minimum holdoff, there are 50 pulses occurring during 4D high period. Note the discrepancy in sweep speed of 20 usec/div shown in the text above and the actual 10 usec/div in the photo. The latter is correct.

Siemens is on 10 usec/div.

tek on 20usec/div: 50 pulses
https://photos.app.goo.gl/x6W8LTLKp2pCkriYA

tek on 10usec/div: 20 pulses
https://photos.app.goo.gl/GDsr4bSS2Wp28tFn9

tek on 5usec/div: 10 pulses
https://photos.app.goo.gl/WwtBghKVgPg723i9A

Please check the actual frequency of the 10 MHz clock on U600-1.

Spot on:
(0,2usec/div)

https://photos.app.goo.gl/U2b7Y1GX9m6x7wjBA

Also I have noticed few days ago (I forgot to mention. After repairing calibrator circuit there is no change), that time measurement on tek is 70% off actual input frequency. 1kHz input is measured as 1,7kHz - maybe it's off beacuse of bad calibration but will it be as much?

[rf+tech]

Please check the 10 MHz with a counter, for error that an oscilloscope cannot resolve.

What is the period of the stripes seen in the second video?

With R2419 disconnected, use an extra 1k resistor to tie the ROB input of U600-11 to +5V.
Disconnect R2420, connect ROR input of U600-12 through 1k to +5V.
This should be easy to accomplish at R2419 & R2420 locations, rather than on U600 pins.
With both ROR and ROB disabled, the RO should not be visible.

What effect does this have on the 1 kHz sine wave test signal?

[grusus]

Please check the 10 MHz with a counter, for error that an oscilloscope cannot resolve.

https://photos.app.goo.gl/YaRJLqcniEARwSuX6

What is the period of the stripes seen in the second video?

If I understand you correctly Bars are approx 15ns, blank spots are approx 40 ns when there are 18 stripes on screen.

With R2419 disconnected, use an extra 1k resistor to tie the ROB input of U600-11 to +5V.
Disconnect R2420, connect ROR input of U600-12 through 1k to +5V.
This should be easy to accomplish at R2419 & R2420 locations, rather than on U600 pins.
With both ROR and ROB disabled, the RO should not be visible.

What effect does this have on the 1 kHz sine wave test signal?

Firstly I am at 1kHz sine, then at 1MHz.

Both ROR and ROB pulled up to +5V
Hmmm. I don't know if you see that but When RO intensity is on there is ghost of trace generated by readout circuit. I am adjusting holdoff for almost whole video.

https://photos.app.goo.gl/559uVo4ARrr8iF839

Holdoff clk is from 130kHz to 70kHz depending on position.

[rf+tech]

My bad, the /ROB input needs to be tied to ground to disable RO blanking, not +5V. /ROR is disabled with +5V.

With RO blanking disabled, the RO intensity control should have no effect and the background signal should no longer be present.

Let's see how the test signals look with the RO control signals fully disabled.

[grusus]

ROB directly to ground, or through 1k resistor?

[rf+tech]

1k resistor.

[grusus]

Hmmm.
At first after starting scope there was no ghost of trace. It come on screen when I turned on more than 1 ch. They eventually didn't come off, even with only 1 ch active, nor after restart. Cold sprayed U600 and U602 did nothing, also major part of Processor board.
See video:

https://photos.app.goo.gl/ZcxqEbZbDCjDzPmh9

[rf+tech]

The objective at present is to completely disable all RO related signals and see if this removes the gaps and extraneous dots in the trace.

The residual RO dots are the result of Z-axis intensity modulation. Disconnecting Q1002 should prevent these from being visible.

However...

U600 cannot receive an RO Request and RO blanking is forced active, why are we seeing RO dots? Without commands, no RO dots should be generated.

If Q1002 does not eliminate the dots, try disconnecting Q1001, Q1003 and Q1004 to isolate the source path.

About the video: at the start, the waveform looks quite good. When the dots first appear, is the Holdoff being adjusted? This control is off-screen. Is it possible to put the camera on a small tripod, situated so all of the controls can be seen? This would greatly enhance interpretation and reduce the need to guess or ask questions.

The Tek 2445/2465 manual goes into much greater detail on the Display Sequencer theory of operation. These models use a different IC with some additional signals, but is conceptually the same.

Key points of operation are a full analog sweep of channel 1 (single channel active), followed by blanked retrace during trigger hold-off. Following retrace, the beam makes a fast horizontal sweep, while the character dots deflect the beam vertically. Z is unblanked to paint the individual dots. This entire process occurs during the hold-off period, which according to waveform 4D is about 58 usec. When the hold-off period ends, the next analog sweep occurs. So for a single channel active, there is one "frame" of analog sweep, followed by a "frame" of RO and cursors. It is not clear if a single RO frame follows after all active channel frames, or, if a channel-specific RO frame follows each channel, with multiple channels active. I would guess the latter, as the RO follows the measurement processor, which probably follows each channel in succsession.

For slow horizontal sweep speeds, where flicker of the analog sweep is visible, the RO portion is multiplexed into the analog sweep, to present flicker-free RO. Obviously, this makes for greater difficulty interpreting effects. The sweep speed transition point is not specified. 1 msec/cm, 10 msec total sweep time, might be on the edge. Perhaps a 5 or 10 kHz test signal should be used, to avoid the possibility of RO multiplexing.

Using Chop mode as default will introduce chopping artefacts into each analog sweep with two or more channels active. Chopping should automatically de-activate with only one channel active. Given the nature of the problem we are trying to solve, Chop mode only makes interpretation more difficult. Which portion of the gaps are due to intentional chopping action and which portion of the gaps are due to this problem we are trying to resolve? Alt mode should be used as the default. Reserve Chop mode for slow sweep multi-channel operation, where Alternating sweep makes it difficult to visually compare signals between multiple channels.

Here's an idea that is a bit outside of the box: use the M07192 in X-Y mode to display the respective signals from the 2246, and Z axis from the 2246. X from the input to the horizontal output amplifier, Y from the delay line input and Z from the waveform 7B point. Z may need to be capacitively coupled (100 nF), since the signal rides on +5.5 Vdc. This might reveal something interesting, as it eliminates the 2246 Z-axis and Autofocus amplifiers and CRT from the picture.

[grusus]

U600 cannot receive an RO Request and RO blanking is forced active, why are we seeing RO dots? Without commands, no RO dots should be generated.

Maybe U600 is going bad? Maybe it is not registering/interpreting ROB and/or ROR singals correctly. I don't know how warm it should get during normal operation, but compared to U602 and few other chips it is cool/cold.

Q1002,3,4 out - no change dots and trace are visible. Q1001 - as expected nothing on screen. No trace nor dots.

About the video: at the start, the waveform looks quite good. When the dots first appear, is the Holdoff being adjusted? This control is off-screen. Is it possible to put the camera on a small tripod, situated so all of the controls can be seen? This would greatly enhance interpretation and reduce the need to guess or ask questions.

Holdoff is adjusted from 0:40-1:03

Next video from tripod :-)

For slow horizontal sweep speeds, where flicker of the analog sweep is visible, the RO portion is multiplexed into the analog sweep, to present flicker-free RO. Obviously, this makes for greater difficulty interpreting effects. The sweep speed transition point is not specified. 1 msec/cm, 10 msec total sweep time, might be on the edge. Perhaps a 5 or 10 kHz test signal should be used, to avoid the possibility of RO multiplexing.

Dots of readout can be turned off by RO Intensity and also they dissappear with A intensity full CCW.

1kHz input to tek:
https://photos.app.goo.gl/Z2F68RLn6j6QGcah8

10kHz input to tek: (look what retrace is doing with holdoff adj)
https://photos.app.goo.gl/o95oAKaH9bUMTKE57

100kHz input to tek:
https://photos.app.goo.gl/CFLUenhDUdnvpadV6

Here's an idea that is a bit outside of the box: use the M07192 in X-Y mode to display the respective signals from the 2246, and Z axis from the 2246. X from the input to the horizontal output amplifier, Y from the delay line input and Z from the waveform 7B point. Z may need to be capacitively coupled (100 nF), since the signal rides on +5.5 Vdc. This might reveal something interesting, as it eliminates the 2246 Z-axis and Autofocus amplifiers and CRT from the picture.

I can't do that. MO7192 has no external z input. tried with X-Y on X on TP 2I and y on 6H. nothing useful - just blurry line. Wen RO intensity is off - line gets thin, no blurr. That led me to do the following:
I decided to observe both TP on normal operating mode and RO dots are there:

https://photos.app.goo.gl/J3nSnWbewtFwXePEA

Tried to lift RO horizontal and vertical input W804 and R207 - no change.
I also tried to lift R215 (Vertical RO enable) - no change

That means to me, RO dots are inserted elsewhere before TP 2I and 6H and they are not from W804 and R207.

One of logical path to me is pin10 of U1001 to Pin 14 of U506. Then to AD mux bus.
Second, is that U602 pin20 is reflecting backwards to U602 17 and 18, but - there is no RO From U600...

Other thing is that RO enable goes out of U503 also to R502 and then to AD mux bus to U506.
There is also RO freeze from U173 to U502, Which need to have proper clock from U606 pin 12 (I don't know freq. it should be) that goes from U501. (I know that they are shift registers but maybe? SR0 are working as those are for attenuators. (U171 and U172) But maybe U173 is making some mess) I know i may be very very wrong, but:  it is me trying to understand this circuit :-)

[rf+tech]

That means to me, RO dots are inserted elsewhere before TP 2I and 6H and they are not from W804 and R207.

RO vertical position ENABLE signals are injected into vertical preamps U210-U240 (column B on sheet 2, R212, R222, R232, R242). They also control output switching of analog muxes U202 and U201.

RO vertical position ENABLE signals originate on diagram 9, location 1M, from U2403.

But wait, there's more. Look again at analog muxes U201 and U202. The same RO enable signals permit the respective channel vertical position signal to pass on to U280. Vertical signal and vertical signal position are summed before entering the delay line driver.

The RO vertical position signal, in through R207 and out through W202, is also summed with the above signals.

Tried to lift RO horizontal and vertical input W804 and R207 - no change.

This is very significant, even moreso considering that ROR is disabled and ROB is forced to blank.

Note how these dots follow the input sine wave, with a fixed offset. This tells us that the dots are not coming from the RO at all. The artefact is a fault of multiplexing and a DC offset would explain the dots following the input sine wave. The dot effect would correlate to an enable signal and the larger gaps could be caused by a much larger DC offset that drives the beam off screen.

Sanity check: adjust channel 1-4 position controls and trace separation control for 0 Vdc at the non-inverting inputs of U203a,b,c,d and U801 (diagram 2). Verify the output of each opamp is also 0 Vdc. No need to make channels 2,3,4 active, leave them off.

With 0 Vdc into muxes U201 and U202, check at W202 that there is no DC offset. If a DC offest is observed, lift R201-R204 and R206 one by one until all are disconnected and only W202 remains. Use both DMM and the M07192 for this test.

Let's follow this theory down to a conclusion.

[grusus]

Sanity check: adjust channel 1-4 position controls and trace separation control for 0 Vdc at the non-inverting inputs of U203a,b,c,d and U801 (diagram 2). Verify the output of each opamp is also 0 Vdc. No need to make channels 2,3,4 active, leave them off.

Done.

With 0 Vdc into muxes U201 and U202, check at W202 that there is no DC offset. If a DC offest is observed, lift R201-R204 and R206 one by one until all are disconnected and only W202 remains. Use both DMM and the M07192 for this test.

Nope. 0VDC on W202.

I decided to check W202 with scope.

When ch1 horizontal line is on RO dots, on U203A pin1  there is 0V and nothing on siemens scope. But check what is observed when vertical position is off center:

https://photos.app.goo.gl/ZWNdsyq39YJp7mNs9

I checked all inputs on U202 and this garbage is comming from pin 10. Next I have checked either side of R212. Higher signal was on U2403 side.

U2403 side:
https://photos.app.goo.gl/z6kWSnJbJYhTMWnt5

U600 side:
https://photos.app.goo.gl/iTJptGYDSQFsayHv8

I decided to desolder U2403 and put it into socket for ease of further removing and inserting.
After that, as expected no change - I didn't break anything :-)

But when U2403 is removed - no RO artifacts on any channell.
There are still cuts in traces.

Signal applied: sine 1kHz, 10kHz, 100kHz, 1MHz, 10Mhz.

https://photos.app.goo.gl/1taJjj89GxzNGwt17

Ok. Now we have signal not interferd by RO. Or maybe not? 

I am still wondering why I can make dots stop moving by adjusting Scale Ilumination :-).
The only logical explanation to me is: When turning SI on, there is very small voltage drop on +15V line (about 0,15V), that can make some change in voltages in calibrator circuit, as it is also connected to +15 V line. Or maybe sth else that is also on +15V line.

[rf+tech]

Good idea to remove U2403. I cut that part just before my last post. Bend pin 1 of U2403 out, to disconnect the enable signal, connect this pin directly to ground and retest.

Since U2403 is the source, the real question now: are the bits on address buses A0-A4 correct, implying U2403 has a decoding problem? This is where a logic analyzer would be handy. Or a spare 74HCT374.

The hold-off effect observed from about 2:20 to the end is the same as seen on a Tek 2465, very minimal.

The retrace blanking on the 2246 is too slow at turn-on. With 1 MHz input to the 2246, use the M07192 to observe waveform 7G, diagram 7. This is the totem pole driver output to the CRT grid. Note the DC levels, relative to ground.

I am still wondering why I can make dots stop moving by adjusting Scale Ilumination :-).

Your conclusion of power supply loading is correct. The measured difference is 1% of the supply rail. An RC oscillator will show a small shift in frequency.

For reference, the Tek 24x5 series also exhibit subtle Z-axis dashes in the sweep. The number observed is much higher, probably 50 to 100, with a single cycle of 1 kHz displayed. Intensity has to be set low and even then they are barely visible. Hold-off and RO intensity have no effect, but Focus does. De-focus makes the dashes and gaps a bit easier to observe, they are about 60/40 to 70/30 mark/space ratio. My suspicion is that these are caused by residual ripple in the -HV CRT cathode supply. The mark/space boundary is that of sine wave Z-axis modulation, not square-wave sharp.

[grusus]

Good idea to remove U2403. I cut that part just before my last post. Bend pin 1 of U2403 out, to disconnect the enable signal, connect this pin directly to ground and retest.

Since U2403 is the source, the real question now: are the bits on address buses A0-A4 correct, implying U2403 has a decoding problem? This is where a logic analyzer would be handy. Or a spare 74HCT374.

If I bend pin 1 and connect it to ground, behaviour is the same as without that chip, but no Vertical position or trace separation is working.

It is not the problem to order one, it is cheap(0,3$) and available. I am just waiting to place bigger order - not only one chip because of shipping cost. I Was thinking also about buying some logic analyzer but are those cheap one for 10-25$ worth anything? I cannot afford now a more costly one for 300-500$ It is more likely for me to buy digital scope like Rigol ds1054Z  now - because I will use it more often than a good logic analyzer.

The retrace blanking on the 2246 is too slow at turn-on. With 1 MHz input to the 2246, use the M07192 to observe waveform 7G, diagram 7. This is the totem pole driver output to the CRT grid. Note the DC levels, relative to ground.

15-70V with a intensity fully cw. Always minimum at 15V max varies with A intensity:

siemens at 10v/div 2us/div
tek has 1 Mhz on input. A intensity at full cw
https://photos.app.goo.gl/qhVDejdjcqgHJHy28

holdoff at min, trigger level in the middle.
https://photos.app.goo.gl/ARiA91nBnufZeLLc8

Your conclusion of power supply loading is correct. The measured difference is 1% of the supply rail. An RC oscillator will show a small shift in frequency.

That's exactly what I thought.

I was messing out with scope and noticed maybe sth usefull, maybe not:

Look at traces when dots are stopped, and changed to chop mode:
https://photos.app.goo.gl/SahrsMDKyyDkFQZGA

Same on higher sweep:
https://photos.app.goo.gl/UpHwK9PyuNujYu2T7

[rf+tech]

If I bend pin 1 and connect it to ground, behaviour is the same as without that chip, but no Vertical position or trace separation is working.

This behaviour is to be expected and it is good to know the result is the same as removing U2403. What does the sine wave look like?

15-70V with a intensity fully cw. Always minimum at 15V max varies with A intensity:

Adjust A intensity for 40 Volts on the Siemens. What does the 2246 sweep intensity look like?

Look at traces when dots are stopped, and changed to chop mode

Chopping artefacts are to be expected. Selecting chop mode is incorrect usage, in these tests.

Note how intensity grows slowly, in the below cropped image of the 1 MHz sine wave. Sweep is 0.5 usec/cm, intensity change over two cycles implies a rise-time of about 2 us. Set the Siemens to 0.5 usec/cm and show the positive going rise from +15 Volts to +40 Volts. This corresponds to unblanking. Check this with both channels on the Siemens and use the channel that shows the best square wave response. Then change the Siemens triggering to show the fall from +40 Volts, to +15 Volts. This corresponds to blanking for retrace.  We are interested in the 10% to 90% transition times and the corner squareness. A faster scope would be preferred.

While you are at it, check waveform 7F frequency, to see if this correlates to the slow unblanking and retrace blanking.

As for cheap logic analyzers, the Saleae Logic 16 clones are worth the price of admission. Sigrok pulseview supports these and many different LA models and clones.

And before I forget (again) thank you for using the tripod.  This enables me to see everything as if I am looking over your shoulder.

Edit:

Here, hold my beer while I do some math:

Waveform 7F shows 61 usec per cycle. 18 times 61 usec equals 1.098 msec. Here's the source of the 18 dots we have seen in the 1 kHz sine wave. The rise and fall times sure look like they correlate to the slow blanking and unblanking.

[grusus]

This behaviour is to be expected and it is good to know the result is the same as removing U2403. What does the sine wave look like?

To me it is the same. No difference if U2403 is removed or in circuit with pin 1 grounded.

Adjust A intensity for 40 Volts on the Siemens. What does the 2246 sweep intensity look like?

Brighter than I will normally use:
https://photos.app.goo.gl/kk45TrDJi2WRzuXb8

Chopping artefacts are to be expected. Selecting chop mode is incorrect usage, in these tests.

I know, but you never know when you discover something usefull or interesting 

Note how intensity grows slowly, in the below cropped image of the 1 MHz sine wave. Sweep is 0.5 usec/cm, intensity change over two cycles implies a rise-time of about 2 us. Set the Siemens to 0.5 usec/cm and show the positive going rise from +15 Volts to +40 Volts. This corresponds to unblanking. Check this with both channels on the Siemens and use the channel that shows the best square wave response. Then change the Siemens triggering to show the fall from +40 Volts, to +15 Volts. This corresponds to blanking for retrace.  We are interested in the 10% to 90% transition times and the corner squareness. A faster scope would be preferred.

For reference this is 1MHz square at Siemens input with 50 terminator:
https://photos.app.goo.gl/EtiShHAnpDesNLx87

rising 0,5usec/div:
https://photos.app.goo.gl/WXjS7RktxQGy6mZB8

rising 0,5usec/div with x5 mode:
https://photos.app.goo.gl/sUfjKkuvFup4EHkY9

falling 0,5usec/div:
https://photos.app.goo.gl/nvuPVcza9xUHS7Eu8

falling 0,5usec/div + x5 mode:
https://photos.app.goo.gl/P6dtpXHmnM8hgWMP9

While you are at it, check waveform 7F frequency, to see if this correlates to the slow unblanking and retrace blanking.

7F 5usec/div:
https://photos.app.goo.gl/cB3RVWCJ1Yag2Suf7

and with x5 mode:
https://photos.app.goo.gl/tb9PRr9Gt7aSj1Vc7
https://photos.app.goo.gl/5xYFjFwnPKSprLtk6

As for cheap logic analyzers, the Saleae Logic 16 clones are worth the price of admission. Sigrok pulseview supports these and many different LA models and clones.

I will check and order one.

And before I forget (again) thank you for using the tripod.  This enables me to see everything as if I am looking over your shoulder.

No need to thanks, that was my duty. 

Waveform 7F shows 61 usec per cycle. 18 times 61 usec equals 1.098 msec. Here's the source of the 18 dots we have seen in the 1 kHz sine wave. The rise and fall times sure look like they correlate to the slow blanking and unblanking.

But where is blanking frequency generated? U600?

[rf+tech]

The Z-axis rise and fall times look to be about 0.15 usec and correspond to a bandwidth of 19 MHz.

The manual does not specify a risetime for the Z-axis input. Based on what we are seeing, it looks compromised.

Refer to the Z-axis response adjustment, paragraph 6 on page 5-5. Check if C2704 can sharpen the waveform, as monitored on the Siemens. The reference square wave looks nice and sharp on the Siemens but without the graticule visible, the risetime cannot be estimated. Some scale illumination would be helpful.

But where is blanking frequency generated? U600?

If you are referring to the A and B sweep blanking signals, U600 is correct. U600 should still be providing blanking control to U602, for A and B sweeps. The RO control inputs to U600 are currently disabled, to eliminate their influence. In turn, U602 pins 17 and 18 control Q1001 and Q1004, respectively. I have lost track of which transistors are currently disconnected. For the moment, just Q1002, to prevent RO blanking pulses.

The 18 blanking gaps and dots correlate with the 130 Vac signal (7F) and this appears to be modulating the CRT grid in an unintended manner. It appears that the 130 Vac signal is intended to dynamically alter both the control grid and focus grid bias, in sync. Try disconnecting W1288, to remove the 130 Vac signal.

The CRT heater is driven with 6.3 Vac, at the same frequency as the 130 Vac signal, both derived from the main switching power supply. A most unfortunate condition to discover would be a heater to cathode short in the CRT.

[grusus]

The Z-axis rise and fall times look to be about 0.15 usec and correspond to a bandwidth of 19 MHz.

The manual does not specify a risetime for the Z-axis input. Based on what we are seeing, it looks compromised.

Maybe that's because Bandwidth limit is on?

So new pics:

7G: sec/div same as before
https://photos.app.goo.gl/9AthSiuVDTpXaBoc6
https://photos.app.goo.gl/pinRxVGvvPTM4nS17
https://photos.app.goo.gl/g27jEfNoUz3Zgzfj6
https://photos.app.goo.gl/TWPgthTTeew1PdeR6


7F: sec/div same as before
https://photos.app.goo.gl/zuxy8yr7HSFKRg4D6
https://photos.app.goo.gl/MDiSfnE7ifpEToVv7
https://photos.app.goo.gl/SwCP5SvKuQUbPdrm7

Refer to the Z-axis response adjustment, paragraph 6 on page 5-5. Check if C2704 can sharpen the waveform, as monitored on the Siemens. The reference square wave looks nice and sharp on the Siemens

I adjusted that 2-3 weeks ago. Generally I went throu whole adjustment procedure in SM for this scope.


Only Q1002 out.

The 18 blanking gaps and dots correlate with the 130 Vac signal (7F) and this appears to be modulating the CRT grid in an unintended manner. It appears that the 130 Vac signal is intended to dynamically alter both the control grid and focus grid bias, in sync. Try disconnecting W1288, to remove the 130 Vac signal.

The CRT heater is driven with 6.3 Vac, at the same frequency as the 130 Vac signal, both derived from the main switching power supply. A most unfortunate condition to discover would be a heater to cathode short in the CRT.

Heater to cathode is 5M in circuit. I will remove CRT tomorrow and check again for sure, but I think there is no short.
edit:
yes R2267 is making it to be 5.1M diag 11 8M


Here is very quick vid because there is no brightness control and I don't want to burn crt, or overload/overheat sth.
1kHz sine at input.
I don't see dots now in traces but focus is very rough.
I am adjusting holdoff during video, and changing base time. Retrace is visible sometimes. Look:

https://photos.app.goo.gl/JEvsL4bFySzGxQ6bA

So, now I am wondering what does it mean?


Will 24mhz 8ch saleae clone be enought, or I should get 16ch version? 8 ch can be delivered in 2 days. 16ch is from aliexpress and it is 2-3 weeks delivery.
https://pl.aliexpress.com/item/32780046572.html?spm=a2g0o.productlist.0.0.589a1821tnmNz1&s=p&ad_pvid=2020080918105216458788844781500002479693_1&algo_pvid=7850c058-078d-4625-8d5a-def708b21cdb&algo_expid=7850c058-078d-4625-8d5a-def708b21cdb-0&btsid=0b0a01f815970218528896097ef776&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

And also bandwidth per channel. LA1010 is 16 MHz per ch with 16 ch active. LA1016 is 100MHz per channel witch 16 ch active.

[rf+tech]

Had I looked at the -HV supply, I would have known about R2267. It was getting late.

R2267 is making it to be 5.1M diag 11 8M

5.1 and 11.8 Ohms, not MOhms.

So, now I am wondering what does it mean?

It means I needed to go to bed and sleep on it.

There is a lot going on in this circuit and the 130Vac drive is critical to proper operation as it forms the CRT grid supply. 130 Vac is coupled through C2713, R2722, C2712 and R2721 to CR2701 anode. The negative half cycle forward biases CR2701, establishing a negative charge on C2711. R2724 creates a long discharge time constant with C2711. The positive half cycle, through R2723, forward biases CR2702 which clamps the positive half cycle to the CRT cathode, at -2.7 kVdc. The total negative charge on C2711, as determined by grid bias pot setting, then holds the grid just enough negative wrt the cathode to extinguish the beam.

Z-axis signal coupled through C2711 raises the grid voltage closer to the cathode, reducing the grid-to-cathode difference and allows beam current to flow, in proportion to the intensity control setting, which establishes the Z-axis signal amplitude.

So the non-uniform sweep intensity, visible retrace, dark spots in the trace and their timing which coincides with the 130 Vac signal, now seem to point to a problem in this area. Either C2711 isn't getting sufficient charge, or its charge is being bled off very quickly.

Anticipating the possibility of a defective diode, I have looked into the FDH5004 and find it appears to be an epoxy encapsulated variant of the glass 1N486, which has a Vrrm of 250 V, If_max of 200 mA and Ir_max of 50 nA (all at 25C). This reverse leakage current rating is two orders of magnitude lower than the 5.0 uA of the 1N400x series. BAV21 is a much closer match: Vrrm 250 V, If_max 250 mA and Ir_max of 100 nA.

Now for the auto-focus. The 130 Vac signal establishes a negative charge on C2719, in the same manner as for the grid supply. Z-axis signal amplitude modifies the focus grid voltage just the same as the Z-axis modifies the grid voltage. As intensity increases, focus voltage is automatically compensated for the higher beam current. This circuit appears to have no trouble keeping the beam well focused and some part swapping with the grid circuit would certainly be appropriate.

Something else I would like to see beforehand are the Z-axis waveforms 7B and 7G, simultaneously on the Siemens. My interest is in comparing the squareness in and out, to see if this Z-axis driver amplifier has suffered a loss of bandwidth.

Which reminds me, the 20 MHz BW Limit only affects the vertical amplifier.

Will 24mhz 8ch saleae clone be enough?

Yes, until the day arrives where more channels and higher sampling rate are needed. Anticipating the arrival of that day, the LA1016 would be a wiser choice.

[grusus]

5.1 and 11.8 Ohms, not MOhms.

In Poland it Was late too. Why I saw 5M? 

Also Heater to cathode is not 5M It is approx 1K. Wrong wires.

It means I needed to go to bed and sleep on it.

Good idea :-)

There is a lot going on in this circuit and the 130Vac drive is critical to proper operation as it forms the CRT grid supply. 130 Vac is coupled through C2713, R2722, C2712 and R2721 to CR2701 anode. The negative half cycle forward biases CR2701, establishing a negative charge on C2711. R2724 creates a long discharge time constant with C2711. The positive half cycle, through R2723, forward biases CR2702 which clamps the positive half cycle to the CRT cathode, at -2.7 kVdc. The total negative charge on C2711, as determined by grid bias pot setting, then holds the grid just enough negative wrt the cathode to extinguish the beam.

Z-axis signal coupled through C2711 raises the grid voltage closer to the cathode, reducing the grid-to-cathode difference and allows beam current to flow, in proportion to the intensity control setting, which establishes the Z-axis signal amplitude.

So the non-uniform sweep intensity, visible retrace, dark spots in the trace and their timing which coincides with the 130 Vac signal, now seem to point to a problem in this area. Either C2711 isn't getting sufficient charge, or its charge is being bled off very quickly.

I was considering changing all hv caps while changing all electrolytics but they are rated at 4kV. I found in Poland only 3kV caps and they are ceramic disc caps. Thats why I decided to leave them as is. I will search for propper caps and buy them. Also I can use 4,7n +4,7n in parallel, or 6,8n+3,3n. Those are 4kV ceramic capacitors.
Other thing - 130VAC in my case is 122.

Anticipating the possibility of a defective diode, I have looked into the FDH5004 and find it appears to be an epoxy encapsulated variant of the glass 1N486, which has a Vrrm of 250 V, If_max of 200 mA and Ir_max of 50 nA (all at 25C). This reverse leakage current rating is two orders of magnitude lower than the 5.0 uA of the 1N400x series. BAV21 is a much closer match: Vrrm 250 V, If_max 250 mA and Ir_max of 100 nA.

In my scope CCR2701-4 were 1N4936 - as I have them in stock, I changed them today, because it will be hard to tell if diode is leaking. No change of behaviour.

Something else I would like to see beforehand are the Z-axis waveforms 7B and 7G, simultaneously on the Siemens. My interest is in comparing the squareness in and out, to see if this Z-axis driver amplifier has suffered a loss of bandwidth.

1k at input of tek:
7b - top
7G - bottom.
https://photos.app.goo.gl/j37oHN2hKdWLuKYy9

1M at input of tek. (siemens at 0,5usec/div)
https://photos.app.goo.gl/7ZCWdonNjsvY1a529
x5
https://photos.app.goo.gl/bkK4MJtaapHRbsUM6

https://photos.app.goo.gl/bUKrFjhcdiRo7Anf7
x5
https://photos.app.goo.gl/JkY9rnnUMWUcUmD67

Which reminds me, the 20 MHz BW Limit only affects the vertical amplifier.

That should be obvious to me.

Yes, until the day arrives where more channels and higher sampling rate are needed. Anticipating the arrival of that day, the LA1016 would be a wiser choice.

LA1016 ordered.

[rf+tech]

Both input and output rise and fall do not look at all good. The rounded leading edge of the Z-axis output flat top corresponds to beam turn-on and should be just as sharp as the initial corner of the rise from zero.

For ease of comparison, let's see the 1 MHz square wave against the Z-axis input signal. Then repeat with Z-axis output signal. Raise the sweep speed so the initial rise (with positive trigger) spans at least 1 division, preferably 2 divisions. Then change to negative trigger and show the falling edge. No need to use 5X magnification.

Align both signals at -2,5 divisions below center, adjust vertical setting and variable gain to place the tops of both signals at +2,5 divisions. This will make the 10% and 90% points coincide with -2 and +2 divisions and simplify rise & fall time measurement.

The overlaid signals will help quantify the M07192 limited rise time against the Z-axis measurement. If it is possible to borrow another 100 MHz scope, that would be very beneficial.

[grusus]

Both input and output rise and fall do not look at all good. The rounded leading edge of the Z-axis output flat top corresponds to beam turn-on and should be just as sharp as the initial corner of the rise from zero.

I was also worried about it.

For ease of comparison, let's see the 1 MHz square wave against the Z-axis input signal. Then repeat with Z-axis output signal. Raise the sweep speed so the initial rise (with positive trigger) spans at least 1 division, preferably 2 divisions. Then change to negative trigger and show the falling edge. No need to use 5X magnification.

Signal from 7B and 7G is not 1MHz. It is more like 200kHz.

1MHz at tek input. 

200kHz at MO7192 CH2.

7B:
0,5us/div:
https://photos.app.goo.gl/9zBqwyRtfkPPw93Z7
https://photos.app.goo.gl/rRPBCxsnHYK3q4VR6

0,2us/div:
https://photos.app.goo.gl/SHuZy453kDsG1scLA
https://photos.app.goo.gl/NxoWEMRb3WScsvXU6

7G:
0,5us/div:
https://photos.app.goo.gl/c9bfUHgRmowsJMrW8
https://photos.app.goo.gl/iyjUcUWepYuyEUYn9

0,2us/div:
https://photos.app.goo.gl/4VScVo2CbXrrGoA9A
https://photos.app.goo.gl/ccxEv4YrxhhqcZhj7

If it is possible to borrow another 100 MHz scope, that would be very beneficial.

I will call my friend, if he doesn't need it I will borrow it.
 
///Edit: He will be back from holiday on sunday, so I can get it on monday. He said: no borrow time limit.

Just another thing that may or may not be usefull:
When I hit single sequence trigger button, trace is also cutted.
quick video: 1kHz input sine.
https://photos.app.goo.gl/AS2VQWPp2f1RRpVUA

[rf+tech]

I'm reading both transitions as about 60 ns, no difference input to output.

Move back one stage and show Q1001 emitter against square wave. 0.2 us/div and 0.1 us/div, for better resolution. Move the horizontal position just far enough to align the rising 10% point on the center vertical line, or, the rising 90% point. This useful technique makes reading the 10-90 difference a bit easier.

Once the setup is complete and a photo is taken, turn off the 2246 and allow it to cool down completely. There were some videos early on that showed a gradual change in the beam intensity over the first few seconds, when the 2246 was first turned on. After an hour or so, with the camera ready, capture the M07192 display when the 2246 is first turned on.

Bandwidth and rise time are inter-related, for analog scopes Tr(ns) = 0.35(1/BW). So 60 ns = 5.8 MHz, seriously degraded. Z-axis rise time does not appear as a specification, rather Tek makes reference to "usable bandwidth." The 465 (100 MHz, 3,5 ns Tr) states 50 MHz. Both 2445 and 2465 state 20 MHz. Using 20 MHz as a lower BW limit, Tr = 17.5 ns and for 50 MHz as an upper BW limit, Tr = 7 ns.

Refer to TM page 1-9 "External Z-axis Input" specs, use the 200kHz square wave to verify both thresholds. Then set the square wave amplitude for 5 Volts into both Z and channel 1 (cable from gen to tee at Z, then to ch 1 with terminator).

With the M07192, show the square wave into rear panel Z input on one channel and 7B on the other channel. Same setup with overlaid traces, -2.5 div to +2.5 div.

Just another thing that may or may not be usefull:
When I hit single sequence trigger button, trace is also cutted.
quick video: 1kHz input sine.

Notice there are 16 gaps per 1 ms cycle. The gaps repeat with a period of 62.5 us, which coincides with the scope's inverter power supply.

[grusus]

Move back one stage and show Q1001 emitter against square wave. 0.2 us/div and 0.1 us/div, for better resolution. Move the horizontal position just far enough to align the rising 10% point on the center vertical line, or, the rising 90% point. This useful technique makes reading the 10-90 difference a bit easier.

All at 0,2us/div - this max on MO7192
https://photos.app.goo.gl/vTMQi7RhVtaWKyHt6
https://photos.app.goo.gl/JYa3B35ts5nUs2Gw9

Once the setup is complete and a photo is taken, turn off the 2246 and allow it to cool down completely. There were some videos early on that showed a gradual change in the beam intensity over the first few seconds, when the 2246 was first turned on. After an hour or so, with the camera ready, capture the M07192 display when the 2246 is first turned on.

After 2 h: https://photos.app.goo.gl/5pix8S9gYjGDXhXG7
Starting point is 0,5us/div to see both rising and falling edge.

Refer to TM page 1-9 "External Z-axis Input" specs, use the 200kHz square wave to verify both thresholds. Then set the square wave amplitude for 5 Volts into both Z and channel 1 (cable from gen to tee at Z, then to ch 1 with terminator).

Z behaves as in specs but with terminator removed. Otherwise voltages must be +40% - +50% +/-

https://photos.app.goo.gl/rVPQimrAS5bR95Cg7
https://photos.app.goo.gl/6vGAyRCpqYVBYfSQ8

Notice there are 16 gaps per 1 ms cycle. The gaps repeat with a period of 62.5 us, which coincides with the scope's inverter power supply.

I decided to look at +130V ac and it looks like this:
5V/div x10 probe 20us/div:
https://photos.app.goo.gl/C3mpCW2Ne48GDrcL6

I was thinking if maybe PSU is failing.