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On Sun, Mar 31, 2024 at 5:04?AM <jking2603@...> wrote:

Hi Siggi,

I also don't think the problem is that you're not triggering. In AUTO mode

you should get sweeps even without a trigger, so more likely you have a
sweep problem.

Yes I agree after reading the Operating Manual more carefully yesterday I
really expected to be able to set auto trigger and have the behavior of
triggering appear at U500 TGA18 output.

The interactions between the display sequencer, the trigger hybrid and the
sweep hybrid are quite intricate.

I know this 2465 is not triggering because I have measured with the
HP1742A scope at
U500 TGA18 output and all that shows is a straight line DC voltage at
approx +2.3V. I did not exactly measure the value because it was so obvious
this was nothing like the trigger signal that should occur as specified on
the TP 29 Oscillogram, which shows (when trigger A is outputting) an
regular square trace at 3.0 mSec intervals between +3.0V and +4.0V.

In AUTO, yes, have you verified that the OSD displays AUTO trig?

Do you agree?

It confirms that sweeps are not being regularly initiated.

Try this, set the TIME/DIV control slow - maybe 50-500ms/DIV, enable all

the traces with POS controls about mid-range, then select SINGLE trigger.
Each time you toggle the mode control down, you should get a sweep.
I believe the AUTO sweep state machine is reset on settings changes (e.g.
TIME/DIV), but it needs the sweeps to run and to complete in order to
generate more than a single sweep command.

I tried the above and no sweeps.

That's ... interesting.

If not, it might be worth trying to swap the A/B sweep hybrids. Do take

note of
which is which, though, so that you can restore them to the right position.
" Noted: But do you think the change in sweep hybrids could fix what
appears to be a measured lack of trigger?

The sweep state machine is complicated. It involves the display sequencer,
the trigger hybrid and the sweep hybrids. Without triggers, the display
sequencer (DS) should be initiating AUTO sweeps in AUTO trigger mode. I
can't think of anything that would derail that, save for a problem in the
DS or the sweep hybrids. This isn't necessarily easy to diagnose without a
storage scope of some sort, as I believe (though I've never looked at this
signal) the DS's strobe for AUTO sweep is a momentary toggle. If the sweep
then doesn't subsequently run, none of the oscillograms are relevant.

" It took some time but I went carefully over the circuits. J101 and J102
is involved. The connectors are shown in the Options Service Manual. On my
units all the connecting wires appear to be in place transferring the
signal from the Buffer board to and from the A1 Board.

Sounds good - while these interconnects could cause the 05 POST error, I
don't think they'd inhibit AUTO sweeps.

As you suggested:
I also followed the TEK Service Manual Probable Causes of Trigger Error
messages. which says look at
for Test 5, Fail 04 or 44
A5 U2634A,
A5 U2335
U500 (Trigger)

and ended up back where you first advised we started at ; with the Sample
and Hold Op Amps; Not a surprise.

Right.

A5 U2634A Pin 1 is A TRIG LVL. With the HP1742A this measures a straight
line at about zero voltage.
So it is clear here a trigger is not occurring.

TRIG LVL should be DC, but you should be able to tweak the TRIG LVL control
on the front panel, and see a corresponding change in the TRIG LVL signal
on the A5 board. Is that the case, or no?

The Service manual further explains:
"
A comparator circuit in U650 detects when the ramp
crosses a predefined threshold voltage {approximately
+3 V]. When the threshold is reached, pin 10 of U650
{HRH} goes LO and the integrating capacitor is discharged.
At that same time, an internal counter that keeps track
of the holdoff ramp cycles is incremented. The ramps
continue to be generated and reset until the holdoff ramp
counter has counted the number of ramp cycles defined
by the sweep-rate-dependent holdoff data ?eld stored in
the Display Sequencer control register. At all sweep speeds
except 5 ns per division, the count is at least two holdoff
ramp cycles. The front~pane| variable HOLDOFF control
affects holdoff time by varying the HOLDOFF control
voltage to U165C {from the DAG}, changing the charging
rate of integrating capacitor C660.

When holdoff time requirements are met {determined
by the number of ramps counted}, the Display Sequencer
sets the THO [trigger holdoff] signal LO. This enables both
the A Sweep hybrid (U700) and the A Trigger circuitry
in U500. The Trigger circuit begins monitoring the selected
trigger source line and, when a triggering event is detected
that meets the triggering requirements defined by the
stored control data, initiates the A Sweep and sets the TSA
{trigger status, A Sweep} line to Display Sequencer U650
LO {indicating that the A Sweep has been triggered.


It is obvious the above sequence is not happening.
This is seen as the reason why triggering is not occurring

AUTO sweeps don't rely on triggering, the timing of those (in the absence
of a trigger) is solely decided by the DS. If the sweep doesn't run,
however, you'd see no traces, and the trigger would never re-arm, so I
believe your no-sweeps condition is consistent with a sweep problem.
HOWEVER, please make sure - via the OSD - that the scope is set as you
expect it. There's no point speculating about whatsits if the scope is e.g.
set up for B-sweeps, and the OSD is the way to verify that the settings are
as you expect.

Even if Auto Triggering is set it will still induce the above by using the
Microprocessor to set ramp values to start the Triggering Sequence.

No, the MPU only sets the conditions for how auto sweeps and triggers are
initiated, it's FAR too slow to take any part in the actual sweep sequence.

Do you have any feedback before I start to work through I should

test as much I can in-situ the above components to see if I can find a
faulty component?.

I would suggest:
1. Verify via the OSD that the scope is set as you expect.
2. Swapping the sweep hybrids.
It's easy to do, and if you still have no sweeps, it's semi-conclusive
that you don't have a sweep hybrid problem.
(Absent common power supply or control issues).

At this point: Do you have any other further suggestions as to what could
be preventing Triggering?

Triggering is immaterial in AUTO sweep mode. The DS initiates AUTO sweeps,
though the trigger hybrid DOES have to pass them through.
I would think you should see at least a single AUTO sweep with very slow
time bases, if:
1. the trigger hybrid passes the DS's signal through.
2. the sweeps are functional.
3. the DS itself is not bad.

As you have two sweep hybrids, it's easier to diagnose the first than the
second, so I suggest you try and swap the sweep hybrids. To diagnose the DS
is potentially a nightmare, though I don't think I've ever heard of one go
bad - anyone?

Good luck,
Siggi

Hi Siggi,
Thank you again for your replies: Your feedback is really helpfull.
Now I understand why your English is rather similar to New Zealand English.

RESPONSE

I also don't think the problem is that you're not triggering. In AUTO mode

you should get sweeps even without a trigger, so more likely you have a
sweep problem.

Yes I agree after reading the Operating Manual more carefully yesterday I really expected to be able to set auto trigger and have the behavior of triggering appear at U500 TGA18 output.

I know this 2465 is not triggering because I have measured with the HP1742A scope at
U500 TGA18 output and all that shows is a straight line DC voltage at approx +2.3V. I did not exactly measure the value because it was so obvious this was nothing like the trigger signal that should occur as specified on the TP 29 Oscillogram, which shows (when trigger A is outputting) an regular square trace at 3.0 mSec intervals between +3.0V and +4.0V.

So that input to the U500 is absolutely not present for timings of 0.5mSec and 1.0mSec /DIV.

Same at TSG (trigger status A sweep) TP 33 for U650 Pin17. Just a flat line voltage where the specified oscillogram expects 0V to +5V every 3 mSec and 0V during the sweep.

So it confirms no trigger.

Do you agree?

Try this, set the TIME/DIV control slow - maybe 50-500ms/DIV, enable all

the traces with POS controls about mid-range, then select SINGLE trigger.
Each time you toggle the mode control down, you should get a sweep.
I believe the AUTO sweep state machine is reset on settings changes (e.g.
TIME/DIV), but it needs the sweeps to run and to complete in order to
generate more than a single sweep command.

I tried the above and no sweeps.

If not, it might be worth trying to swap the A/B sweep hybrids. Do take note of

which is which, though, so that you can restore them to the right position.
" Noted: But do you think the change in sweep hybrids could fix what appears to be a measured lack of trigger?

I'm not sure which options are provided with a 2465DMS,

"
Provided are:
GPIB Measurement System Option 10
150 MHZ Counter / Time / Trigger (CTT) with 17 Bit Word Recogniser Option 9,
4.5 Digit Auto Ranging DMM Option 01
"
but I remember chasing my tail on an
05 POST error on my 2467, because I hadn't reconnected the CTT option.
It turns out that some trigger signals run to options through J102 (see
schematic <5>). So if your scope has any options that reroute the trigger
signals, it's worth checking that the interconnects are good.

" It took some time but I went carefully over the circuits. J101 and J102 is involved. The connectors are shown in the Options Service Manual. On my units all the connecting wires appear to be in place transferring the signal from the Buffer board to and from the A1 Board.

As you suggested:
I also followed the TEK Service Manual Probable Causes of Trigger Error messages. which says look at
for Test 5, Fail 04 or 44
A5 U2634A,
A5 U2335
U500 (Trigger)

and ended up back where you first advised we started at ; with the Sample and Hold Op Amps; Not a surprise.

So it looks like a fault some where in th at region.

A5 U2634A Pin 1 is A TRIG LVL. With the HP1742A this measures a straight line at about zero voltage.
So it is clear here a trigger is not occurring.

A5 U2634A Pin 1 is feed by A5 U2335 Pin 12. This has also been measured as having no signal also
So it can be concluded that This MUX Signal #2 is not being conditioned by the Microprocessor or other circuits to have a value.

I cannot think of any other way to verify a trigger is not occurring.

From the Service Manual page 3-18 and 3-19
"
HOLDOFF RAMP.
The holdoff ramp circuit, used to
delay the start of a sweep until all circuits have recovered
from the previous sweep, is made up of U165C, Q154,
Q155, and associated components. Operational Amplifier
U165C and capacitor C180 form a sample-and-hoid buffer
used to set the charging current for holdoff-ramp inte-
grating capacitor C660. A control voltage from digital-to-
analog converter {DAC} U2234 {diagram 2} via multiplexer
U170 (diagram 4} is stored on C180. The stored voltage
level sets the base voltage for both Q154 and Q155 via
amplifier U165C. Transistors C1154 and (1155 form a
current~rnirror with nearly equal collector currents.
Transistor Q1154 is a current-to-voltage converter that
provides negative feedback to U165C, setting loop gain.
Transistor Q155 acts as a constant current source that
charges integrating capacitor C660, producing a linear
holdoff ramp.
"

The above circuits could also have a fault that is preventing the Trigger starting.

The Service manual further explains:
"
A comparator circuit in U650 detects when the ramp
crosses a predefined threshold voltage {approximately
+3 V]. When the threshold is reached, pin 10 of U650
{HRH} goes LO and the integrating capacitor is discharged.
At that same time, an internal counter that keeps track
of the holdoff ramp cycles is incremented. The ramps
continue to be generated and reset until the holdoff ramp
counter has counted the number of ramp cycles defined
by the sweep-rate-dependent holdoff data ?eld stored in
the Display Sequencer control register. At all sweep speeds
except 5 ns per division, the count is at least two holdoff
ramp cycles. The front~pane| variable HOLDOFF control
affects holdoff time by varying the HOLDOFF control
voltage to U165C {from the DAG}, changing the charging
rate of integrating capacitor C660.

When holdoff time requirements are met {determined
by the number of ramps counted}, the Display Sequencer
sets the THO [trigger holdoff] signal LO. This enables both
the A Sweep hybrid (U700) and the A Trigger circuitry
in U500. The Trigger circuit begins monitoring the selected
trigger source line and, when a triggering event is detected
that meets the triggering requirements defined by the
stored control data, initiates the A Sweep and sets the TSA
{trigger status, A Sweep} line to Display Sequencer U650
LO {indicating that the A Sweep has been triggered.


It is obvious the above sequence is not happening.
This is seen as the reason why triggering is not occurring

Even if Auto Triggering is set it will still induce the above by using the Microprocessor to set ramp values to start the Triggering Sequence.

So the components with the faults must likely will be be within the following list:

Operational Amplifier U165C, LM324J4
Q154 Silicon PNP 2N3906,
Q155 Silicon PNP 2N3906
and associated components / resistors.
capacitor C180
capacitor C660
Digital-to- analog converter {DAC} U2234
Multiplexer U170. TEK 156-0513-02
U500
U650

Do you have any feedback before I start to work through I should
test as much I can in-situ the above components to see if I can find a faulty component?.

At this point: Do you have any other further suggestions as to what could be preventing Triggering?

A couple of years ago, I had triggering issues with my 7B70. It turned out to be a bad tunnel diode (VR304). At that time, I was finding suitable tunnel diode replacements on eBay (1S2199); however, I'm not seeing those at the moment. Hopefully yours will turn out to be something else but, if not, then the 1S2199 diodes may resurface.

Good luck with it,
Barry - N4BUQ

Adam,

You may have bad tunnel diodes. Check the ESR of the condensers. They may need to be replaced.

Mark

Hi all,

I just acquired a 7704A with plugins (7A26, 7CT1N, and two 7B70s). Everything more-or-less works, although I'll have some mainframe questions eventually.

For the moment, I'm trying to figure out why one of the 7B70s won't trigger on anything other than a square wave/pulse. Note that I've cleaned the cam switch contacts with alcohol/paper, reseated all transistors on the trigger board, relays check good, and the trigger amplifier transistors aren't shorted or open (using a DMM diode test).

Using FG502 as input source:

With 7A26 on 0.5V/div, EXT trigger displays a stable waveform with a 1.25 Vpp square wave. INT trigger displays a stable waveform with 2Vpp from the FG502.

With lower output voltage from the FG502 on either trigger, the TRIG light is on, but no waveform is displayed, so I assume it's triggering on noise? If I adjust the trigger pot until the TRIG light goes off, I can see the envelope of the waveform, so it's not like the signal vanished.

With the 7A26 on 1V/div, EXT works with 1.25Vpp, but INT requires 4Vpp to display the waveform. I do not understand this interaction with the vertical amplifier, but the INT trigger only gives a stable waveform if the signal is 4x the vertical V/div setting. EXT only requires 1.25 Vpp.

The other oddity is that it will not trigger on a sine or triangle wave, although it will display them if I use the external trigger output from the FG502. I'd assumed it was a dead transistor in the trigger amplifier until I realized this, and now I'm wondering about a bad tunnel diode? No extender, so I'm kind of limited on tracing for the moment.

thanks,
Adam

I also like the 44 page preview. It really gives a good idea of what's in the book and they style of the book. I'll buy it as soon as it's in stock. :)

I blush.... THANKS!!!!!

The vintageTEK museum bought one for display at the museum and one to give to Tektronix President Chris Bohn yesterday.

Dave

On Fri, Mar 29, 2024 at 12:24?AM <jking2603@...> wrote:

END OF SETUP
#####################################################################

Your setup looks good to me, you should be getting AUTO sweeps and traces
at these settings.
However, in your shoes, I'd ALWAYS verify that the OSD agrees with the
control settings. As this scope is largely drive-by-wire, problems with the
front panel control switches could lead to the scope being in a different
mode than what the controls indicate. I believe the OSD will indicate all
significant mode settings, which (I suspect) was done for documentation
purposes - so that a photograph of the CRT would show all significant
settings.

At this point I see no reason to ever to deviate from the TEK advised
setup.
I an firstly interested only in bring back CH1 trace so see no reason to
unlock time sweep controls or to alter anything.

Sounds like a plan.

Into CHN5B of U500 Trigger resistors read incorrect values.
R644 measures 2.21K [and is colour coded yellow, purple, red = 4.7K] Spec
4.7K
R646 measures 2.21K [and is colour coded yellow, brown , red = 4.1K ] Spec
4.12K
DO YOU THINK THESE WRONG RESISTERS COULD BE A CAUSE OF THE NO TRIGGER?

Most likely these resistors measure low in-circuit as they're effectively
in parallel with power off.
I also don't think the problem is that you're not triggering. In AUTO mode
you should get sweeps even without a trigger, so more likely you have a
sweep problem.

OUTCOME:

No traces appear for CH1 or CH2 or CH3 or CH4 for 0.5 msec / div or 1 msec
/ div

Try this, set the TIME/DIV control slow - maybe 50-500ms/DIV, enable all
the traces with POS controls about mid-range, then select SINGLE trigger.
Each time you toggle the mode control down, you should get a sweep. If not,
it might be worth trying to swap the A/B sweep hybrids. Do take note of
which is which, though, so that you can restore them to the right position.
I believe the AUTO sweep state machine is reset on settings changes (e.g.
TIME/DIV), but it needs the sweeps to run and to complete in order to
generate more than a single sweep command.

Other than that, I think working through the diagnosis trees in the service
manual is a great idea. The engineers who wrote the manual obviously knew
much more than I do, both about the scope and about fault diagnosing and
servicing it :).

Actually, here's another thought.
You took the scope apart to service the power supply. I'm not sure which
options are provided with a 2465DMS, but I remember chasing my tail on an
05 POST error on my 2467, because I hadn't reconnected the CTT option. It
turns out that some trigger signals run to options through J102 (see
schematic <5>). So if your scope has any options that reroute the trigger
signals, it's worth checking that the interconnects are good.

Hi Siggi,
Thank you for your reply which again is very helpful.
Thank you also to Jean Paul for your observation feedback.

First off good morning from Dunedin New Zealand in the South Pacific.


Now I now list the exact specification of the setup for Testing.
I have strictly followed the TEK Manual 2465 Revised Jun 1983.
[The reason is all the Test Plots Oscillograms are based on a specific setup for a test described in that Version of The Service Manual. (For B Sweep There are required variations to the First setup). Because of the design mixture digital and analog obtaining the correct oscillogram is for some of plots critically absolutely dependent on the manual test setup being exactly followed. Prior to 5 days ago I was using the HP1742A for random sampling. Unusual values this week took me back to re read the Test Setup again where I Discovered that:
- the 1 KHz feed of a T Piece being joined to both CH1 and CH2 and the triggering of the test oscilloscope had to be linked to this feedline.
- the 1 KHz was not +100mV to -100mV but required to revised to 0.0mV to +200mV
Changing to this feed arrangement significantly changed some measured values of some Test Points.]

Serial number is B040292 and Dates Codes on label on EPOM U2378 is dated 85/07.

I also discovered that the Low Power Voltage Supply Board was different to the 1983 Manual and appeared the same as the layout in the 2465A service manuals.

For that reason the Service Manual below revised OCT 84 is probably a better match that the the Jun 83 Service Manual.


TEST SETUP NOW USED

Specification by TEK is:
Connect a 200-mV, 1-kHz squarewave signal from a signal generator to each Vertical Channel as appropriate via a BNC T -connector, a SO-O BNC cable and a dual input coupler.

SETUP NOW APPLIED TO PUT SIGNAL IS DIFFERENT
Connect a 200-mV, 1-kHz squarewave (0.0 mV TO 200 mV) signal from a
signal generator to BNC T -connector at Vertical CH1 and
a 470 mm long 50 ohm RG58 cable from BNC T -connector to CH2 and
another BNC T -connector and 470 mm long 50 ohm RG58 cable to the TEST OSCILLOSCOPE HP1742A external trigger
[I describe this so accurately because I have expert knowledge in deigning HF antennas and the length of the longer feedlines I have used can make significant difference to the signals received at Attenuator 2.

SETTINGS CONTINUED
CH1 connected by PUSHED IN
CH2 not connected by OUT
CH3 not connected by OUT
CH4 not connected by OUT

TRIGGER
MODE AUTO
CH 1 and CH2 1 MOhm DC
SOURCE VERT
COUPLING DC NOISE


SETTINGS CONTINUED
VERTICAL MODE CH1
Input Coupling CH 1 and CH2 1 MOhm DC

VOLTS/DIV CH1 and CH2 50mV

A and B SEC/DIV 0.5 ms (knobs locked)
A/B sweep speeds aligned

TEST OSCILLOSCOPE SETUP
Triggered the test oscilloscope on the rising edge of the 1-kHz signal and, using a X10 probe
with the test oscilloscope.

END OF SETUP
#####################################################################

If ever I need to deviate from the above setup I will record the change in a message.
At this point I see no reason to ever to deviate from the TEK advised setup.
I an firstly interested only in bring back CH1 trace so see no reason to unlock time sweep controls or to alter anything.

I have set
Input Coupling CH 1 and CH2 1 MOhm DC
because this was what TEK stated should be set.

Also note:
Looks like 1M to ground does measure 1M as as grounding condition [It measures 0L]
From the 0L I have assumed there is defect with 1M to ground settings

Into CHN5B of U500 Trigger resistors read incorrect values.
R644 measures 2.21K [and is colour coded yellow, purple, red = 4.7K] Spec 4.7K
R646 measures 2.21K [and is colour coded yellow, brown , red = 4.1K ] Spec 4.12K
DO YOU THINK THESE WRONG RESISTERS COULD BE A CAUSE OF THE NO TRIGGER?
When the RIFA capacitor gave way and smoke started to come out I was sitting in front of the scope. I turned the power off right away. It seems to me the Resistors would not have changed values when the input power was experiencing a loss of supply. Therefor i have assumed that these resistors would be down on value when the scope was previously functioning showing CH traces about 3 years ago.
############################################################################

SUMMARY OF RECENT MEASUREMENTS RECORDED ON CIRCUIT DIAGRAMS






OUTCOME:
No traces appear for CH1 or CH2 or CH3 or CH4 for 0.5 msec / div or 1 msec / div

Oh nevermind, it mentions it in a different service manual version.

The manual mentions to adjust R519 to the voltage stated on the "CRT TAG". I do not know what that is and I looked more in the manual and still couldn't find that that is.

Perhaps you know?

Benjamin

On Thu, Mar 28, 2024 at 10:34?AM <jking2603@...> wrote:

On Mon, Mar 25, 2024 at 12:09 PM, Sigur?ur ?sgeirsson wrote:

I can swap the Pre-Amps as you suggest but first please read the following
and provide confirmation advice.

All Hybrids have been removed, and treated with Deoxt D100IT and Deoxit
Gold. No change of Functions resulted.

1. At this time I cannot see any of CH1, CH2, CH3, CH4 traces at all.
It is like I am driving a car and I cannot see through the windscreen.
It seems to me that:
-if I can restore the traces even if they are garbled the distorted traces
may provide valuable information or a better idea of what is not
functioning,
- Fault finding by verifying basic functions are occurring should lead to
more exact idea of what function critical is not occurring.
-So my first step am working on now is verifying if there is a gap in
critical information into the basic network for traces showing onto the
Cathode Ray Tube.

You have the OSD, which means that a whole lot of the machinery is working.
For the OSD to work, your channel switch has to work somewhat at least, the
horizontal, the vertical and the Z-axis all have to work. You do also get
something in XY mode, which again means that almost everything to do with
signal routing and deflection has to be working.

It's not yet clear to me what your test settings are, and so whether you
should expect to see a trace or traces, nor whether you should be able to
get triggering. I apologize in advance if I'm preaching to the choir here,
but in your first video you were in XY mode, and it's not clear to me
whether that's still the case. Note that the skirt of the TIME/DIV control
selects the A-sweep state, while the knob shows the B-sweep state. In
addition, the relative positions of both, plus whether the knob is in or
out also selects different modes of A/B or ALT sweeps.

To normalize this, you want the A/B sweep speeds aligned and the knob
pushed in. In this state, the skirt moves with the knob whether you rotate
CW or CCW - if that's not the state you've been testing in, then not seeing
traces might be WAI.
IIRC, to get to this state, you rotate the TIME/DIV knob CCW until the
indicator on the knob aligns with the skirt, making sure the knob is
pressed in. Now you're in A-sweep mode or XY, depending on the position
indicated by the skirt. From there you can pick a reasonable TIME/DIV
setting to play with the traces - something like 1ms/DIV is probably good.
You'll then want to set AUTO TRIG and trigger off CH1, the trigger coupling
and level should be immaterial, as you should be able to see AUTO sweeps at
this setting.
Input coupling on CH1-4 is immaterial, in this mode, but GND should give
you flat traces (and additionally engages AUTO TRIG implicitly IIRC).

If this produces traces (it should) then we can move on to chasing the
phantom signal and/or diagnosing the trigger failure.

Jeff swapping preamps I doubt if that will solve it

Follow the troubleshooting flow charts in the service manual.

For the manual, all the PDFs have faulty images or hard to print eg foldout B size schematics

We always get an original printed Tektronix service manual for the exact model and serial
Try vintage Tektronix Museum and Qservice in Greece.

eBay has some on occasion $20..70 Artech sells better pdf and printed reproductions.

Bon chance

Jon

On Mon, Mar 25, 2024 at 12:09 PM, Sigur?ur ?sgeirsson wrote:

I can swap the Pre-Amps as you suggest but first please read the following and provide confirmation advice.

All Hybrids have been removed, and treated with Deoxt D100IT and Deoxit Gold. No change of Functions resulted.

1. At this time I cannot see any of CH1, CH2, CH3, CH4 traces at all.
It is like I am driving a car and I cannot see through the windscreen.
It seems to me that:
-if I can restore the traces even if they are garbled the distorted traces may provide valuable information or a better idea of what is not functioning,
- Fault finding by verifying basic functions are occurring should lead to more exact idea of what function critical is not occurring.
-So my first step am working on now is verifying if there is a gap in critical information into the basic network for traces showing onto the Cathode Ray Tube.

I have verified Data is getting through to Test points 56 & 57. That is vertical trace data is sent to U900.

By probing with the HP1742A I have established that:
- Horizontal scans from U700 and U 900 are not occurring and are just straight line DC voltages,
- That no Trigger Signal occurs and U500 out is are just straight line 0.0 DC voltage,
- From reading the Theory of operation a Trigger Signal

When holdoff time requirements are met (determined by

the number of ramps counted), the Display Sequencer sets
the THO (trigger holdoff) signal LO. This enables both the
A Sweep hybrid (U700) and the A Trigger circuitry in U500.
The Trigger circuit begins monitoring the selected trigger
source line and, when a triggering event is detected that
meets the triggering requirements defined by the stored
control data, initiates the A Sweep and sets the TSA
(trigger status, A Sweep) line to Display Sequencer U650
LO (indicating that the A Sweep has been triggered)<

So until
THO (trigger holdoff) signal become LO
A Horizontal Trace cannot occur or will be seen.

Reading the theory of operation it becomes a little more obvious that
- error trap routines may still disable trace scans as you logically might expect,
- that signals are on a bus and the Sequencer require that the right digits to arrive in the right place and right sequence to get a sensible plot.

I am understanding better the circuit diagrams by annotating (using Visio) links from diagram to diagram of each signal, and systematically recording expected specifications and measured values.
This will then give a block diagram (of functions) all the signals that must be present at various components.
The Tek drawings located in a PDF are very difficult to follow.
Annotated drawings enables looking at the entire network and identifying what is missing or incorrect.

Then I can measure at each point with the 'Test Scope HP1742A' on the circuit to verify:
A. Is the signal present?
B. Does the signal verify to be in limits of say +- 20% of the values show on the oscillograms?

I have further just measured and determined
CH5N input to U500 measures
at
TP 46 measures +0.5V to -0.5V @16.7
Specification is: +1v to -7V @16.7 mSec
Measured Only 12% of expected

But down stream of this

Circuit 9 Line Supply
at TP 82 Spec is:
+0.4V to -0.4V @ 16.7 mSec

so the value seen is close to the expected downstream source

So right now Im mystified why TP 46 can grow to become as large as Spec +1v to -7V @16.7 mSec
But this maybe 'a red hearing' and a completely unimportant waste of time.

The next steps proposed after restoring trace of from CH1 are finding are: below.

1. '>From what

I read of your message, it seems the phantom signal is present on the
negative differential output of the preamp.'

I have put up videos so you can look at them. It looks like there is a Phantom signal at Test Points 54 and 55.
Can you please verify YOU DO can see a phantom signal?

2. > then I'd try and switch the preamp hybrids between channels 1 and 2, and see whether the

problem follows the preamp. Make sure you know which preamp is which, as if
you switch them, you'll likely upset the calibration of the scope.
If this is a fault in the output stage of the preamp, then that would
explain why you can't trigger on the phantom signal, as IIRC the trigger
feed is a separate output from the preamp.

This still wouldn't explain the 05 POST failure you're seeing, but it would
be a step in the right direction.

I await your response and then swap the pre-amps if you still recommend as the first course of action.

Yours sincerely
Jeff King

Here's fresh link to the manual.



Jerry
W2Ji

Benjamin, typical flood gun bias.

See service manual for HV/STG adjustments and checks.

Also any scioe shieed around esp from epay may have internal damages to the CRT.

Serv man should give a quick test proceedute to verify the CRT and STG function.

Jon

Amazing, I saw one of these this morning at radio club coffee from someone who worked at Aussie Burroughs a while back. Its in pristine condition too.
Looking a the specs its a good thing. He will enjoy it. The discussion and information here was greatfuly received too.

Maxwelloau

Forgot to add images: /g/TekScopes/album?id=293980

Hi, I recently bought a Tek 314 from eBay, and everything in the scope works, except the storage function I believe.

Whenever I go into store mode, there is "noise" in the background. And the stored waveform isn't all that discernable.

There is some burn-in on the scope screen so maybe this causes it?

This "noise" doesn't happen on my tek 7613.