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

[grusus]

I have adjusted grid bias following service manual, just before making second video from previous post. But i think I have done this week ago, maybe two.
One thing i have done also after doing Q1001-Q1004 videos, I have change U1001 to lm324 just in case (had some free time, and got some in stock) I my scope there was NEC C324C. Maybe that is why adjustment was no longer correct.

Any further Ideas?

Many thanks for both of you guys for helping me.

CD4051 will arrive on friday, so I will change it.

I was wondering also:
My 130V AC line is approx 122V AC. Maybe there is something drawing excesive current and pulling +130VAC down to +122VAC. I don't think this will be causing the problem with flickering and ghosting, but?

Offtopic
I was consideriing to buy HV probe anyway, because some tube constructions that arrives in my workshop have 1,5-2kV anode voltage and i had no way to measure that.
My multimeter measures up to 1000V AC/DC and there were some situations that i have measured (and brymen showed correct value) about 1200V AC (with centertap) power transformer for tube amp 4xEL34 mono guitar amp. :-) 710 on anodes of each EL34. A lot :-)
/Offtopic

[rf+tech]

First thing, a comment about the videos. The ambient light level washes out the very faint detail on the scope screen, making it next to impossible to observe any detail in the video clips you have posted.

As for the +130 Vdc measuring below specification at 122 Vdc. No relation to the Z axis problem. I have not yet checked the schematics, but I seem to recall +130 Vdc supplies the deflection amplifiers.

Looking back at the other 2246 thread, the OP measured a variation of 4.5 to 4.4 Vdc, at the emitter of Q1001. The corresponding variation on your scope is 4.14 to 4.0 Vdc. The schematic indicates a normal variation of 1.1 Vdc.

Both scopes exhibit Z axis problems. Both scopes exhibit the same minimal Q1001 emitter voltage variation

With 4.46 Vdc on each Q base and 4.2 Vdc on each emitter, each transistor is biased off. When the emitter is pulled down by the corresponding active-low gate signal from U602, that particular transistor would be biased on and the buffered intensity setting passed on to the Z axis amplifier.

U602 is an ECL device, the intensity gate signals will only vary about 1 Volt in amplitude, between high and low states.

The very next step would be to measure the DC voltage variation at Q1002, Q1003, Q1004 emitters, to see if they mirror the Q1001 emitter measurement.

If this is the case, then it appears U602 is not gating the four transistors. Some portion of each signal bleeds through each transistor, producing the mash-up result observed.

Before concluding U602 is defective, address inputs A0 and A1 should be observed. Each of the four outputs should go low (ECL low being 1.95 to 1.63 Volts less than Vcc, or 3.35 to 3.57 Volts, with Vcc 5.2 Volts) [1], corresponding to addresses 00, 01, 10, 11. This is a bit difficult to perform, as it requires three channels of a four channel scope. Or a logic analyzer that is known to work with ECL logic levels.

As BΩL points out, trouble in the trigger logic could be responsible. Timing is everything in digital circuits and the RO anomaly can certainly be attributed to a timing (multiplex) defect.

[1] For reference, ECL high level is 0.96 to 0.81 Volts less than Vcc, or 4.24 to 4.39 Volts, with Vcc 5.2 Volts.

edited to correct ECL logic levels min/max for Vcc = 5.2 Vdc.

[grusus]

Before concluding U602 is defective, address inputs A0 and A1 should be observed. Each of the four outputs should go low (ECL low being 1.95 to 1.63 Volts less than Vcc, or 3.05 to 3.37 Volts, with Vcc 5.0 Volts) [1], corresponding to addresses 00, 01, 10, 11. This is a bit difficult to perform, as it requires three channels of a four channel scope. Or a logic analyzer that is known to work with ECL logic levels.

If my thinking is correct:
First probe on A0, Second on A1, third measuring pins 17-20 of U602?

I can do it with scope itself. It is operational and I have 3 channels working. Flickering is not a big deal as I will get 3 square waves?

If I am wrong, please correct me.

First thing, a comment about the videos. The ambient light level washes out the very faint detail on the scope screen, making it next to impossible to observe any detail in the video clips you have posted.

I am sorry for that. I will pay more attention to that in the future. I will make those videos again tomorrow and paste them here.

[rf+tech]

First probe on A0, Second on A1, third measuring pins 17-20 of U602?

Yes, this is correct. Trigger on A0, sweep speed adjusted to show four cycles of A0. A1 should show two cycles.
The decode should be something like:

Code: [Select]

A0  A1 Gate output Low
L   L  pin 17
H   L  pin 18
L   H  pin 19
H   H  pin 20

The exact order may differ, the important detail is that only one of the four outputs are low at each of the four possible addresses.
When moving the third probe to another output, the position of that output low pulse should shift left or right of the first output probed. In this way, each of the four outputs should align with the corresponding address, as observed on channels one and two.

If you find the results to be confusing, that would be expected - A0 and A1 are part of a wider address bus and the trigger may actually need to be taken from pin 40 /SIN - assuming this pin function is "chip select". When this pin goes low, the address codes are intended for U602, as opposed to another IC sharing A0 and A1.

If further clarification is needed, just ask.

[grusus]

I did some measurements.
Q1002 E is +4,56 - +4,45
Q1003 E is +4,38 - + 4,29
Q1004 E is +4,36 - + 4,26

Checked A0 and A1, with pins 17-20 of U602. Only pin 17 is low, other 3 are high. When I change to B sweep 18 is low, others high. When I turn readout from full ccw to full cw trace is getting slightly lower(not on video)

Here is video of pin 20 of U602.
Top trace is A0, Middle is A1, bottom is pin 20.
https://photos.app.goo.gl/ZEK7gZi9n6mB1TTZ6

Going through pins 17-20. (This random dots on bottom trace is because of bad probe connection. It is hard to shoot video with one hand and measure with other one :-) )
Top trace is A0, Middle is A1, bottom is pin 17-20.
https://photos.app.goo.gl/dt1F4vMpkSrqr9KN8

A0 on pin 38 of U602 only, on digital scope:
https://photos.app.goo.gl/7Ev6gxwzNtJDnhVq5
https://photos.app.goo.gl/gtVKDSQtmhAZ2drA7

A1 on pin 39 of U602 only, on digital scope:
https://photos.app.goo.gl/NUVxnMxVKg6wxnSD7
https://photos.app.goo.gl/SAc1kvSvh8Qz3umM9
https://photos.app.goo.gl/JCAPhzqTk48s3yd79

Should they look like this? Especially A1?

EDIT
All in place:
https://photos.app.goo.gl/DxPyb9omd31whon7A

Q1001 out. Q1002, Q1003, Q1004 in place
https://photos.app.goo.gl/WDsMbpKdTror1Y7W9

Q002 out. Q1001, Q1003, Q1004 in place
https://photos.app.goo.gl/P5EFFHctmCq4d1xZ7

Q1004 out, Q1001, Q1002, Q1003 in place
https://photos.app.goo.gl/gvvR6U4PAzSD1gUK6

Q1001, Q1002, Q1004 out, Q1003 in place
https://photos.app.goo.gl/m6ys8G62jeMhdUwS6

All out.
https://photos.app.goo.gl/jM918cqxfUxy7Byd8

/EDIT

[rf+tech]

I owe you an apology about he videos.  It was my browser causing a problem where only the first few seconds would play, then repeat. This was short enough that the trace never appeared on screen, leading me to think it was too dim to see. Lights out, nobody home on this end.

The timebase setting is far too slow. Within the first few milliseconds, there are multiple high-low transitions occurring on A0 and A1. The timebase must be set to a much faster sweep (us or ns), so that each narrow pulse can be seen clearly. And external trigger connected to /SIN.

Please make a video of Q1002 (RO) in, Q1001, Q1003 and Q1004 out. It is expected that the RO will be free of flicker.

These emitter DC measurements are interesting. I wonder if the schematic values are actually the high and low DC levels expected, when the gate signal is off and on? This interpretation certainly fits with ECL levels. With the higher sweep speed, note if the gate outputs' high and low levels are displaced above zero Volts, by about 4.2 and 3.1 Volts respectively, with about 1.1 Volts peak-to-peak amplitude.

[grusus]

In my videos were lot of reflection so do not apologize :-).

Some photos:
Pin17: https://photos.app.goo.gl/NtrTs7vaotwJuZMQ7

Pin18: https://photos.app.goo.gl/gZ1d2wX1WLBYkZPK7

Pin19: https://photos.app.goo.gl/JVcxWVQkSZSJBV3b7

Pin20: https://photos.app.goo.gl/buu77qKE2dVrANnx5

I called my friend and he will lend me his 4 ch Uni-T digitall scope, but after my come back from hospital - next week.


Q1002 in, Q1001,q1003,q1004 out.
https://photos.app.goo.gl/5Cn6457dNGijtag2A

These emitter DC measurements are interesting. I wonder if the schematic values are actually the high and low DC levels expected, when the gate signal is off and on? This interpretation certainly fits with ECL levels. With the higher sweep speed, note if the gate outputs' high and low levels are displaced above zero Volts, by about 4.2 and 3.1 Volts respectively, with about 1.1 Volts peak-to-peak amplitude.

I think i quite don't understand :-) At bases of q1001....4 there is only dc voltage. At C and E is square wave. with peak-to-peak approx 0,1-0,2V dependig which Q I am measuring.

[rf+tech]

At bases of q1001....4 there is only dc voltage.

Correct. The circled 4,2V and 3,1V on the schematic are the square wave voltage levels expected on the emitter. When U602 pin 20 is ECL high, the voltage should be 4,2V. When U602 pin 20 is ECL low, the voltage should be 3,1 Volts. A DMM cannot distinguish between the two and this is why I suspect these circled voltages may actually refer to waveform levels. It is not just a coincidence that the two voltages *are* ECL levels.

For clarity, CMOS logic low is zero to 1/3 Vdd and high is anything between 2/3 Vdd and Vdd.
TTL low is zero to +0,8 Volts and high is anything between +2,0 and +5 Volts.
ECL levels are as I explained previously.

When U602 pin 20 waveform is at an ECL low, the voltage level observed on the measuring scope should be 3,1V above the zero reference line. Similarly, the high portion of the waveform should be 4,2 Volts above the zero reference.

The objective is to measure the actual logic high and low levels, by counting divisions on the display, based on the number of divisions above zero reference, to the high and low portions of the gate waveform. With a vertical setting of 0,5 Volts/cm, 3,1 Volts would be 6,2 divisions above the zero reference on screen. If the probe being used is a 10x, then 0,5 Volts/cm is really 5 Volts/cm and 3,1 Volts would be 0,62 divisions.

At C and E is square wave. with peak-to-peak approx 0,1-0,2V depending which Q I am measuring.

If the total amplitude swing from high to low is only 0,1 to 0,2 Volts, then this is definitely a problem. The total amplitude should be 1,1 Volts. Q1001 through Q1004 are not being turned on by their corresponding gate signal. BJTs require about 0,65 Volts base-to-emitter minimum to turn on. 0,1 to 0,2 is inadequate.

The video of only Q1002 in circuit is half of what I expected. The RO intensity works and the other intensity controls have no effect.
The flicker is still present, but I am not ready to condemn U602 defective. Verifying the address timing is a challenging task. It would be nice find U602 is not being addressed correctly and failing to turn on its gate outputs when expected.

I have been studying the Readout System on sheet 9, looking for another possible cause. Waveforms 9A and 9B, /RO Blank and /RO Request, should be checked.

If you would like to take a break from this RO problem, here's something easy to address the channel 2 attenuator hybrid. Make up a chart of resistance measurements from AT117. No need to disconnect any leads.

Code: [Select]

pin 12 to pin 11
pin 11 to pin  9
pin 11 tp pin  1
pin  1 to pin  2
pin  9 to pins 8,10
pin 11 to pin  7
pin  7 to pin  6
pin  6 to pins 3,5
pin  4 to pins 3,5

Compare to AT127, to see if there are any significant differences.

Maybe your friend can smuggle his scope and your 2246 into the hospital?  Might make the time pass much more quickly. 

[grusus]

Q1001...4 base voltage to gnd is 5V
0,67-0,72 B-E voltage.  depending on Q. When A sweep i active only Q1004 B-E is 0,2V and vice versa with only B sweep.

Zero Line position is at very bottom of the crt. Coupling DC 1v/div
Collector:
Q1001...4: 5,8V to bottom of trace https://photos.app.goo.gl/fXVg9cgGWkFEpv1g6

Emiter: A sweep is active, no readout.
Q1001: 3,8 V to bottom of trace https://photos.app.goo.gl/NJa1jH7kFkRCFkPm7
Q1002: 4,5V https://photos.app.goo.gl/LpYPxe9EsiLikWwf9
Q1003: 4,4V https://photos.app.goo.gl/orG2o7E41NJGwnto6
Q1004: 4,4V https://photos.app.goo.gl/orG2o7E41NJGwnto6

9A: (U600 pin12) AC 10mv/div 1us/div When I turn cw readout intensity whole trace goes down.(not the amplitude)
https://photos.app.goo.gl/Va62yfrc8Lz4ac6J6

9B: (U600 pin11) AC 50mv/div 0,5us/div When i turn cw readout intensity whole trace goes up. (not the amplitude)
https://photos.app.goo.gl/JCWcLw8xvd4x9j3H6
https://photos.app.goo.gl/nv2qfZffCfkxJNTj7


At117&127

pin 12 to pin 11 492K inf
pin 11 to pin  9 0 0
pin 11 tp pin  1 0 0
pin  1 to pin  2 0 0
pin  9 to pins 8,10 inf inf
pin 11 to pin  7 4,5 4,2
pin  7 to pin  6 inf inf
pin  6 to pins 3,5 inf inf
pin  4 to pins 3,5 inf inf

Only noticable difference is on pin 12 to 11 (scope turned off). Maybe i will do some magic and cut trace after pin 12, put two 1m ohm resistor parallel and capacitor (measure it from AT117) with one in series :-) Just kidding :-)

Maybe your friend can smuggle his scope and your 2246 into the hospital?  Might make the time pass much more quickly. 

That would be perfect :-) Unfortunately due to Covid-19 restrictions there are no other people allowed to entry to hospital than patients. Even my wife cannot visit me in hospital.
No worries. I am going to hospital at june 30th(tuesday) and will be out at july 3rd or 6th (friday or monday) so not much time i will be off.

[rf+tech]

Now it is getting even more interesting. The waveforms at 9A and 9B should both be close to 5 Volts p-p.

I should mention that DC coupling must be used for all logic waveforms. AC coupling blocks the DC component, which is essential to DC measurement. Set the vertical to 1 V/cm, DC coupling, sweep 2 us for 9A and 50 us for 9B. Trigger set to negative-going and DC coupled. Let's see the DC level for 9A and 9B.

9A: (U600 pin12) AC 10mv/div 1us/div When I turn cw readout intensity whole trace goes down.(not the amplitude)

This is to be expected with AC coupling. When there is a step change in the DC level on the probe side of the scope input AC coupling capacitor, the other side of the capacitor responds by shifting the trace position.

Something I should ask, does this 2246 have two small watch cells in holders? The 2246 I repaired had a fair amount of corrosion damage, from leaking cells.

Q1001...4 base voltage to gnd is 5V

This is another problem. Vbb3, from U604 pin 11 should be 3,85 to 3,97 Vdc, and present on the cathode of CR1005. The anode of CR1005 should be one diode drop (about 0,65 Vdc) higher. Current flow through CR1005 and R1028 dictates the anode voltage cannot be 5 Volts, neither can the bases of Q1001-4. Something is open circuit, CR1005, U604 pin 11 or a copper track or jumper W1000.

AT127 - by all means, tack solder a 470k resistor external between 11 and 12. The high frequency response will suffer, but for a quick  confirmation, this is what I would do.

Thanks for sharing the dates of your upcoming "holiday." Do enjoy the attention of all the young ladies. 

edited to correct ECL Vbb3 voltage min/max, for Vcc = 5.2 Vdc.

[grusus]

Zero line at very bottom of the crt. V and s and trigger settings as you said in previous post.
RO intensity 12 o' clock

9A: https://photos.app.goo.gl/6ehPL4QWmazxthuu9

9B: https://photos.app.goo.gl/NYiVE8Zk1gM779w96

RO intensity off.

9A: (0,2V DC offset) ( 0 line in the middle of crt) https://photos.app.goo.gl/KBMfrirgywTKz5B17
and with 0,1V/div: https://photos.app.goo.gl/edUxCbnDQYeMdexw8

9B: (5,2V DC offset) https://photos.app.goo.gl/H92fiaosCDa5v6jF6

Something I should ask, does this 2246 have two small watch cells in holders? The 2246 I repaired had a fair amount of corrosion damage, from leaking cells.

Yep. I have change them, because they leaked. Only cell holders were affected. Cleaned everything. No trace damage is visible.

There is one thing:
My processor board is different from manual. It is not covered in service manual that i use. I cannot find correct one.

https://photos.app.goo.gl/UQzj2Mvck7KNMwtW6

Getting back to q1001-q1004:

Cr1005 cathode is 3,858 V (same on U604 pin 11), Anode 4,45 V
R1028 one side is 5,18 V other is 4,46 V

Ring out everything from U604 pin 11 to bases of q1001-4 looks fine.
W1000 has continuity.
I am litle suspicious about CR1005. 0,6 V drop diode test, 0,99V drop backwards. Tested in circuit.

AT127
This is another story.
I just put new solder to pins 11 and 12 and values are good now. Checked one more time at117 and at127 and values are same. Still no trace on ch2. When I hit beam find button it shows it on very bottom (if ch2 is inverted it goes to the top). Position does nothing. Something is bad with vertical preamp for this channel.
I am wondering if U122 is bad. I think, even this is tek part, it can be fixable.
https://photos.app.goo.gl/3wDtDcViJRzAvd1L6

[rf+tech]

Okay, it looks like there may be two things causing some confusion. The +5 Vdc supply is actually +5.2 Volts and the scope vertical gain may not agree with your DMM.

About 9A - is it not possible to set the triggering for a stable display? When triggered correctly, it should be possible to see a low pulse of 2 us width, as shown in the manual.

9B is triggered cleanly, but the sweep speed is too slow. Try 2 ns and 50 ns for 9A and 9B. It is very difficult to male out the sweep speed units in the manual photos.

The high and low levels for 9A and 9B look good.

For U122, apply the same resistance measurement technique and compare with U112. If you do not already have them, locate a set of needle multimeter probes, also known as back-probes. These are tiny enough to probe within the ceramic hybrid without accidental shorts.

Locate U220 - place DMM red lead on pin 14, black lead on pin 13. With scope on, no signal on channel 2, turn the vertical position control from ccw to middle and to cw. The expected behavior is that the DMM will show a decreasing voltage difference that passes through zero Volts near middle and increases with opposite polarity.

CR1005 should be okay, the voltage drops all look good.

I see how your processor differs from the board in the 2246 I repaired in 2017. Interesting.

[grusus]

9A:  triggered on rising edge (I can't do it on falling edge) Previously it was on falling edge.
2us: https://photos.app.goo.gl/kmoGdKzSCoCY8MnV7
1us: https://photos.app.goo.gl/d1bukCsgSPAV8ppJA
.5us: https://photos.app.goo.gl/jrBM8t5KHPjsyunE9

9B:
20us: https://photos.app.goo.gl/3qebDvUWVrrUG3o68
10us: https://photos.app.goo.gl/AVFUTe3Tbr9bH8Lm9
5us: https://photos.app.goo.gl/bsu3n9p5iNtw1o5V7
2us: https://photos.app.goo.gl/VqcHGZN9wMdMhBNc9
1us: https://photos.app.goo.gl/4cCYM4gm8dz98U3BA
0,5us: https://photos.app.goo.gl/q4VMtxaw1ckya37F9


Scope I am using is Siemens oscillar M07192 (another old scope, from 70's propably - i bought it 14 years ago used when I was studying electrotechnics at University). No documentation is there. No calibration guide. I didn't want to mess arround with calibration. I am just getting to know how to do it from tek2246 service manual. I 'd better trust my DMM than this scope for voltage mettering :-) I am looking forward to calibrate this siemens scope in future, after 2246 repair.

U112 measured the same as U112

Pin13&14 of U220 ch 2 no input, normal +1,38 to +1,39 (from ccw to cw)
ch2 inverted: -1,37 to -1,38V

Pin 13 to gnd is 5,93V
Pin14 to gnd is 7,3V

On u210 those are equal  6,6V

hmmm.
I was looking at schematic 2 - There is some kind of mixing RO with CH1-4 - vertical position switching. I am wondering if here could be source of all problems: U280,U202 maybe? What do you think?


I know this processor board assembly (g-8928-03) was used in very early tek 2246 units. Also they were used in tek 2245 (bit earlier assy g-8928-02) not 2245a (they have same as in 2246 service manual). I tried to find service manual for 2245 but there is only for 2245a.

[rf+tech]

9A and 9B look like the service manual waveforms, good job.

The variable control  I am referring to on the M07192 is the red knob in the center of the channel 1 and channel 2 vertical step attenuators, on the front panel. The marking is Verst Fein. Turn this ccw out of detent and note how the display amplitude varies in a continuous manner. This is what I am referring to, to get the scope and DMM to agree. This has no effect on the present state of calibration. This control is there for user convenience.

U112 measured the same as U112

Do I understand correctly that the resistance between the various pins measure the same?

Channel 2 vertical position signal, -2,5 to +2,5 Vdc goes to U203B pin 5. The same voltage should be present on U203B pin7 and on U202 pin 5, which multiplexes other vertical position signals, that then drive U280. Had I looked at this, it would have been obvious the vertical position controls have no effect on U112 and U122. 

Can you take another photo of U122 that is even closer and with a little more light? It should be easy to create a schematic of this hybrid. I agree it may be repairable and I am suspecting the problem may be an open feedback path. Some of the silver SOT-23 numbers are familiar, Motorola/ON Semi parts.

I was looking at schematic 2 - There is some kind of mixing RO with CH1-4 - vertical position switching. I am wondering if here could be source of all problems: U280,U202 maybe? What do you think?

We can certainly try to see what is happening here. Preset channel 1,2,3,4 and Trace Separation to middle of rotation. Alt. sweep 10 us/cm, channel ,2,3,4 on, no input.

Connect channel 2 of the M07192 to W201, this will be the trigger signal, positive-going. Set the sweep to 50 us/cm. We want to see two ENable pulses. If my math is correct, there should be 400 us between the two pulses, since each sweep requires 100 us times 4 channels.

With M07192 channel 1 (0,5 Volt/cm) probe on U202 pin 14, turn channel 1 position ccw, cw, back to middle. Repeat for channel 3 and 4. Then turn channel 2. If my theory is correct, there will be 1/4 of the waveform that varies in amplitude, for each channel. The time displacement corresponds to the active channel. 0-100us = channel1, 100-200 us = channel 2, etc.

How the readout for each channel is interleaved or overlaid with the channel vertical position level is not clear from the schematic. It may be necessary to read the theory of operation, to understand how the RO is overlaid with the vertical signals. We'll just have to see what the first waveforms reveal.

[grusus]

The variable control  I am referring to on the M07192 is the red knob in the center of the channel 1 and channel 2 vertical step attenuators, on the front panel. The marking is Verst Fein. Turn this ccw out of detent and note how the display amplitude varies in a continuous manner. This is what I am referring to, to get the scope and DMM to agree. This has no effect on the present state of calibration. This control is there for user convenience.

This does what it should :-) https://photos.app.goo.gl/LRWDXj8kBWeJtksu9

When I was making photos of trace 9A and 9B it was slightly off detent (approx 15 degrees) I doesn't have lock function, so adjusting v/div sometime makes red knob turns with it. I overlooked that. I will "calibrate" scope to DMM with var on scope tomorrow and make again 9A and 9B.

Do I understand correctly that the resistance between the various pins measure the same?

Yes. I made a mistake. Should be U122 measured same as U112.

Channel 2 vertical position signal, -2,5 to +2,5 Vdc goes to U203B pin 5. The same voltage should be present on U203B pin7

Voltages are spot on.

U202:
On pin 5 is 0,9V, but i think that You were thinking about pin 14- Voltage spot on.

Pin 13 is output for channel 2 an it is from +1,1V to -1,1V same as on pin 1 - for 1st channel.

We can certainly try to see what is happening here. Preset channel 1,2,3,4 and Trace Separation to middle of rotation. Alt. sweep 10 us/cm, channel ,2,3,4 on, no input.

Connect channel 2 of the M07192 to W201, this will be the trigger signal, positive-going. Set the sweep to 50 us/cm. We want to see two ENable pulses. If my math is correct, there should be 400 us between the two pulses, since each sweep requires 100 us times 4 channels.

With M07192 channel 1 (0,5 Volt/cm) probe on U202 pin 14, turn channel 1 position ccw, cw, back to middle. Repeat for channel 3 and 4. Then turn channel 2. If my theory is correct, there will be 1/4 of the waveform that varies in amplitude, for each channel. The time displacement corresponds to the active channel. 0-100us = channel1, 100-200 us = channel 2, etc.

And here we are hitting the wall.
This is not a dual trace scope :-(
It has 2 channels but only one trace is present on the screen. Maybe it is broken, but I have never make him to view 2 traces at the same time. We have to wait until next week when I will have digital scope.
Although Siemens has ext trigger function so maybe this will help.

Can you take another photo of U122 that is even closer and with a little more light?

Here you are:
https://photos.app.goo.gl/wkqinhz7Fepd4Sc27
https://photos.app.goo.gl/f7y39KPpPoQsUdmN9

Wait... are those cracked solder joints on pins 1-15? I did measurement on pads not on pins 
I wil reflow them and check tomorrow.

[grusus]

Reflow did nothing.

I found in google that siemens scope should show 2 independent traces. So I have two broken scopes :-)

[grusus]

I have done some diggin.

W201 50us with RO on: https://photos.app.goo.gl/YYDaUyNt6YUuWrgy5

With ro off it is flat unitl I activate more than 1 ch.

5ms/div
Also it blanks as screen is intermitent. https://photos.app.goo.gl/AhdK2SBdvxTFfgSL7

Also noticed that it is only intermitent at ,5V div. ch1.
https://photos.app.goo.gl/bSMSyMd6WVcGJMuN7

W201 in chop mode 2us/div: https://photos.app.goo.gl/WZCrqALqmbYGSz8h6
and with ro int turned on: https://photos.app.goo.gl/amsmCSrRDQczxSyH6

Pin 5 of U202: Cannot trigger it better.
https://photos.app.goo.gl/HLxLDQRtSVchcXF28
https://photos.app.goo.gl/A98kgL4hpkpZk2wMA

U280 pin 7 and 14 is trace position. Each of flat lines corresponds to ch1-ch4. They move within same ranges for all 4 ch.

0,1V/div 5ms/div
https://photos.app.goo.gl/3bXUWSwUbeBe89Zd7

When RO intensity is turned on then:
https://photos.app.goo.gl/fpYtv8GoSerbXaoJ6

Pin14 of U202 is only DC voltage - flat trace.

[rf+tech]

These waveforms are pretty much what I expected and I don't see anything unusual that could relate to the RO problem. I would like to see

When RO intensity is turned on then:
https://photos.app.goo.gl/fpYtv8GoSerbXaoJ6

With a faster sweep such that channel 1 expands to fill the screen. Channels 2,3,4 off. The vertical intervals where the beam deflects downward to the RO position, are of interest.

Now that you are gaining more experience with the M07192, we should revisit U602 pins 17,18,19,20. Each intensity gate signal should be switching between 3.1 Vdc and 4.2 Vdc, above zero reference. Ideally, only Q1002 should be installed. The other transistors should be left out, to exclude their contribution to the Z-axis amplifier. The RO shoudl be the only thing visible.

I found in google that siemens scope should show 2 independent traces. So I have two broken scopes :-)

Ahh, but an old school analog scope is so much easier to repair.    No schematics? No problem. When you are back home from your "holiday" in the hospital, start a new thread.

If you are already familiar with push-pull amplifiers, this is exactly how the vertical channels function. Since the one channel is working, it is established that the vertical deflection amplifier is working. The problem exists in the preamplifier for the other channel - its output is most likely "railed", the beam is pushed very far off the top or bottom of the screen. This is very easy to confirm, with just a DMM.

[grusus]

With a faster sweep such that channel 1 expands to fill the screen. Channels 2,3,4 off. The vertical intervals where the beam deflects downward to the RO position, are of interest.

2ms/div only ch1 active. (when 4 ch are active each time portion is divided into 4, when 2 ch are active, same ammount of time is divided by 2. etc.
https://photos.app.goo.gl/6YBDpbBhspKcL9L6A
It is shaking. I cannot stabilize it better. Also trace in the middle looks like it is running square wave.

If you'd like even faster sweep - please let me know.

Now that you are gaining more experience with the M07192, we should revisit U602 pins 17,18,19,20. Each intensity gate signal should be switching between 3.1 Vdc and 4.2 Vdc, above zero reference. Ideally, only Q1002 should be installed. The other transistors should be left out, to exclude their contribution to the Z-axis amplifier. The RO shoudl be the only thing visible.

Only Q1002 present.

DC coupling 1v/div - zero level at very bottom of crt (first grid horizontal line from bottom)
Pin17-18-19 are same: (DMM = 4,11VDC)
5ms/div: https://photos.app.goo.gl/QjAo8rtstNdmZdio6
With readout: https://photos.app.goo.gl/CSJ1BVhD9US49DQz8
5us/div: https://photos.app.goo.gl/W1fETRyLoZKBSY7e7

Pin 20: (DMM = 4,5VDC)
With readout:
5us/div: https://photos.app.goo.gl/7M75xZBWG3MjuWkS7
2us/div: https://photos.app.goo.gl/jJUd2mVXr9vedU798
1us/div: https://photos.app.goo.gl/gq3oeEHz9WHWboeH8

If you are already familiar with push-pull amplifiers, this is exactly how the vertical channels function. Since the one channel is working, it is established that the vertical deflection amplifier is working. The problem exists in the preamplifier for the other channel - its output is most likely "railed", the beam is pushed very far off the top or bottom of the screen. This is very easy to confirm, with just a DMM.

Yes I am. When you input signal for ch1 trace is there. Also for ch2. Problem is that there is only one trace at same time and channels interacts to each other (you can change position of trace for ch2 with ch1 knob and vice versa) Also changing volts/div for ch2 changes position of ch1 trace and vice versa. So I think both channels are mixed together in not right way, but remember, I am noob in scope repairs :-). I will start new topic for siemens scope when I will be back.

[grusus]

I am back!!!

[rf+tech]

The break has given me a new perspective on the RO problem. As I was reviewing the various videos, something finally clicked. The RO anomaly is actually part of a larger problem. The random vertical lines are a clue.

From the theory of operation of the Vertical Preamps and Output Amplifier:

The signal current for the enabled channel (vertical channel plus its position offset) or the readout position current (enabled to the summing node during text and cursor displays) is applied to the Delay-Line Driver.

The important detail here is that the vertical displacement of the beam is the result of summing current from all four preamps, U210...U240. Disabled channels are *not* disconnected. I now suspect that non-working channel 2 preamp U220 is contributing garbage into the delay line driver and this is the cause of the random vertical lines. The RO jitter and shimmy is a side effect.

The best way to test this hypothesis would be to disconnect one end of R250E and R251E, effectively disconnecting the output of U220.

--

The waveform with only Q1002 installed looks very good, levels are correct. U602 is free to go, after posting bail.    Q1001,3,5 can be reinstalled.

[grusus]

R250&R251 are integrated 4 resistors in one. I cannot pull out one leg of each one. If I will desolder whole R250 and R251 none of ch1-4 will work. I can desolder whole R250 and R251, bend legs for section E end solder it back in. Maybe remove U220? Of course, if without R250 and R251 RO jitter will be gone, we will proof that problem is before R250 & R251 in circuit.

[rf+tech]

Arg, resistor pack.

Another option is to disconnect the RO vertical and horizontal signals, ahead of the vertical preamps and horizontal preamp. Removing one end of R207, near location 7C on Sheet 2, will disconnect the vertical dot position signal from the RO Display.

Similarly, disconnecting one end of R807, between 4B and 5B on Sheet 6, will disconnect the horizontal dot position signal.

[grusus]

I have removed R250& R251.
Result:
https://photos.app.goo.gl/SE1GHKUyBsrCN4hu7

I did some hacking with single 82R resistors and connected everything exept signals from ch2.
https://photos.app.goo.gl/e3afstQL859aTzD77

Now flat line from ch2 is present but no traces ofc.
 
Flicker is still there.

R207 and R807. I must locate them, because in this area board layout from manual doesn't match reality.

[rf+tech]

There is much unknown information to make a conclusion. The artifacts in the sine wave can be induced by selecting Chop mode and fast sweep speed. The beam has to deflect to each vertical channel position repeatedly, all within a single sweep. The result will be chopped up signals.

Alternate mode displays one channel per sweep. Using ALT with fast sweep eliminates the chopping effect. Chop mode is best for slow sweep speed.

Information essential to correct interpretation:
Sweep speed setting?
Chop/Alt mode setting?
Signal frequency?

Having a "before" and "after" video for comparison, with the exact same settings, signal, etc., would be of great help. It is becoming very time consuming to have to go back through this thread and try to locate another video for reference, that has different conditions, and try to interpret new videos.

The video with 82 Ohm resistors installed suggests that U220 may not be the cause. Then again, this could be the result of Chop mode and fast sweep.

To locate R207 and R807, measure resistance from W2302 pin 2 to U202 pin 4 - 714 Ohms is expected. With one probe on W2302 pin 2, see if it is possible to find where the resistance drops to 357 Ohms.

W2302 pin 1 to U802 pin 1 should be somewhere between 75 Ohms and 575 Ohms, depending on pot R823 setting.