Date   
Re: 7834 horizontal jittery readout

 

I think that could be normal depending on what is being drawn at the
time. Does the photograph show the oscilloscope monitoring its own
readout?

What effect does changing the readout mode to gated have? The slide
switch for this is on the front panel to the immediate right of the
readout intensity control.

How does the readout behave when the sweep is very slow like
100ms/div?

It is normal for there to be some interaction between the horizontal
sweep and the readout which causes the readout to shift around
somewhat. The same goes for the vertical interaction.

On Thu, 25 Feb 2016 20:56:48 +0000, you wrote:

On 25/02/2016 20:54, Gordon @GordonW [TekScopes] wrote:
Checking TP12 and 13 on the readout board (x and y out) reveals a rather
odd waveformhttp://www.mgcsoft.com/tek/7834_tp12_readout_bd.jpg.
That's 2V not 200mV, it's a *10 probe.

Gordon

Re: 7834 horizontal jittery readout

Gordon <tekscopes@...>
 

On 25/02/2016 20:54, Gordon @GordonW [TekScopes] wrote:
Checking TP12 and 13 on the readout board (x and y out) reveals a rather
odd waveformhttp://www.mgcsoft.com/tek/7834_tp12_readout_bd.jpg.
That's 2V not 200mV, it's a *10 probe.

Gordon

7834 horizontal jittery readout

Gordon <tekscopes@...>
 

Hi All. Just trying to sort out a jittery readout on my 7834. The ramp outputs of the horizontal board look very stable and the trace itself doesn't appear to be jittery, at least nothing like the readout. In inches I'd say it's jittering about 0.040" maybe a bit less but only horizontally. The supplies don't appear to have significant ripple and putting an extra 4.7u on the 130V doesn't make any difference.

Checking TP12 and 13 on the readout board (x and y out) reveals a rather odd waveform http://www.mgcsoft.com/tek/7834_tp12_readout_bd.jpg. The waveforms in the manual aren't really clear enough. Could someone confirm whether or not the waveform is something like normal please.

Cheers

Gordon

Last few 11K plugs in left at Sphere

 

My thanks to all that responded about the 11K stuff we are clearing out. Shane at Avatar Metrology ran all the plug ins for everybody in his 11302A to be sure they were good, so there shouldn't be any surprises on arrival.

All the cal, blank and comparator plug ins and many of the others are gone, here's what's left:

1 ea. 11A34 (quad) US$50 (found another one!)
3 ea. 11A32 (dual) US$50 each
3 ea. 11A71 (fast 50 ohm single) US$70 each

I also have some bad (sorry, no idea what the issues were, just tagged bad, some missing covers) 11K plug ins, they are 11A32 and 11A52, US$25 each. still look good, and no visible internal damage. looks like we can ship 2 plug-ins expresspost to the US for about C$58, or by regular post for C$39.

I also have a lot of 11401 internal boards left (known good) if any help to somebody out there. There's also a bad 11302 frame that will go at stuff day, US$150, has a deflection problem, no other details. just failed about a year ago, was set aside, may be a psu problem. Too big and heavy to ship, so pick up at stuff day (april 9th) ONLY.

let me know if you can use any of these, YES, I will hold any stuff for pick up in April at stuff day if settled now.

Lots more Tek stuff to go on stuff day, I will try to advise on as much as I can here on the list before stuff day, but we are just in the middle of getting everything restored inside the building after having the floor replaced, (took 8 months), so not a lot of time to do that.

all the best,
walter & susan (walter2 -at- sphere.bc.ca)
sphere research corp.
http://www.sphere.bc.ca

Re: TDS 380 calibration and vertical scale problem

Gilles Drolet
 

Hi David
Remove as much colder as you can without scrapping the board and Just reflow the holes with chipquick and the part will come off the board.
Good luck
Gilles

On Thursday, February 25, 2016 10:31 AM, "david.wilson92@... [TekScopes]" <TekScopes@...> wrote:



  It looks like I am in a real bind desoldering ch2 hybrid from the mainboard. The joints are through hole and some of the joints I was able to get the solder off at the top but at the bottom there is suborn solder that just refuses the come out. I tried desoldering several times but not having much luck. Since I don't want to break anything I thought about putting it back back the way it is and just use as is. A partially working scope is better than a broken one.

I could use a soldering iron to flow solder back in the through hole and try to desolder once again. The board is about 4 mm thick approximately and so are the through hole joints.

[Non-text portions of this message have been removed]

#yiv0467986494 #yiv0467986494 -- #yiv0467986494ygrp-mkp {border:1px solid #d8d8d8;font-family:Arial;margin:10px 0;padding:0 10px;}#yiv0467986494 #yiv0467986494ygrp-mkp hr {border:1px solid #d8d8d8;}#yiv0467986494 #yiv0467986494ygrp-mkp #yiv0467986494hd {color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px 0;}#yiv0467986494 #yiv0467986494ygrp-mkp #yiv0467986494ads {margin-bottom:10px;}#yiv0467986494 #yiv0467986494ygrp-mkp .yiv0467986494ad {padding:0 0;}#yiv0467986494 #yiv0467986494ygrp-mkp .yiv0467986494ad p {margin:0;}#yiv0467986494 #yiv0467986494ygrp-mkp .yiv0467986494ad a {color:#0000ff;text-decoration:none;}#yiv0467986494 #yiv0467986494ygrp-sponsor #yiv0467986494ygrp-lc {font-family:Arial;}#yiv0467986494 #yiv0467986494ygrp-sponsor #yiv0467986494ygrp-lc #yiv0467986494hd {margin:10px 0px;font-weight:700;font-size:78%;line-height:122%;}#yiv0467986494 #yiv0467986494ygrp-sponsor #yiv0467986494ygrp-lc .yiv0467986494ad {margin-bottom:10px;padding:0 0;}#yiv0467986494 #yiv0467986494actions {font-family:Verdana;font-size:11px;padding:10px 0;}#yiv0467986494 #yiv0467986494activity {background-color:#e0ecee;float:left;font-family:Verdana;font-size:10px;padding:10px;}#yiv0467986494 #yiv0467986494activity span {font-weight:700;}#yiv0467986494 #yiv0467986494activity span:first-child {text-transform:uppercase;}#yiv0467986494 #yiv0467986494activity span a {color:#5085b6;text-decoration:none;}#yiv0467986494 #yiv0467986494activity span span {color:#ff7900;}#yiv0467986494 #yiv0467986494activity span .yiv0467986494underline {text-decoration:underline;}#yiv0467986494 .yiv0467986494attach {clear:both;display:table;font-family:Arial;font-size:12px;padding:10px 0;width:400px;}#yiv0467986494 .yiv0467986494attach div a {text-decoration:none;}#yiv0467986494 .yiv0467986494attach img {border:none;padding-right:5px;}#yiv0467986494 .yiv0467986494attach label {display:block;margin-bottom:5px;}#yiv0467986494 .yiv0467986494attach label a {text-decoration:none;}#yiv0467986494 blockquote {margin:0 0 0 4px;}#yiv0467986494 .yiv0467986494bold {font-family:Arial;font-size:13px;font-weight:700;}#yiv0467986494 .yiv0467986494bold a {text-decoration:none;}#yiv0467986494 dd.yiv0467986494last p a {font-family:Verdana;font-weight:700;}#yiv0467986494 dd.yiv0467986494last p span {margin-right:10px;font-family:Verdana;font-weight:700;}#yiv0467986494 dd.yiv0467986494last p span.yiv0467986494yshortcuts {margin-right:0;}#yiv0467986494 div.yiv0467986494attach-table div div a {text-decoration:none;}#yiv0467986494 div.yiv0467986494attach-table {width:400px;}#yiv0467986494 div.yiv0467986494file-title a, #yiv0467986494 div.yiv0467986494file-title a:active, #yiv0467986494 div.yiv0467986494file-title a:hover, #yiv0467986494 div.yiv0467986494file-title a:visited {text-decoration:none;}#yiv0467986494 div.yiv0467986494photo-title a, #yiv0467986494 div.yiv0467986494photo-title a:active, #yiv0467986494 div.yiv0467986494photo-title a:hover, #yiv0467986494 div.yiv0467986494photo-title a:visited {text-decoration:none;}#yiv0467986494 div#yiv0467986494ygrp-mlmsg #yiv0467986494ygrp-msg p a span.yiv0467986494yshortcuts {font-family:Verdana;font-size:10px;font-weight:normal;}#yiv0467986494 .yiv0467986494green {color:#628c2a;}#yiv0467986494 .yiv0467986494MsoNormal {margin:0 0 0 0;}#yiv0467986494 o {font-size:0;}#yiv0467986494 #yiv0467986494photos div {float:left;width:72px;}#yiv0467986494 #yiv0467986494photos div div {border:1px solid #666666;height:62px;overflow:hidden;width:62px;}#yiv0467986494 #yiv0467986494photos div label {color:#666666;font-size:10px;overflow:hidden;text-align:center;white-space:nowrap;width:64px;}#yiv0467986494 #yiv0467986494reco-category {font-size:77%;}#yiv0467986494 #yiv0467986494reco-desc {font-size:77%;}#yiv0467986494 .yiv0467986494replbq {margin:4px;}#yiv0467986494 #yiv0467986494ygrp-actbar div a:first-child {margin-right:2px;padding-right:5px;}#yiv0467986494 #yiv0467986494ygrp-mlmsg {font-size:13px;font-family:Arial, helvetica, clean, sans-serif;}#yiv0467986494 #yiv0467986494ygrp-mlmsg table {font-size:inherit;font:100%;}#yiv0467986494 #yiv0467986494ygrp-mlmsg select, #yiv0467986494 input, #yiv0467986494 textarea {font:99% Arial, Helvetica, clean, sans-serif;}#yiv0467986494 #yiv0467986494ygrp-mlmsg pre, #yiv0467986494 code {font:115% monospace;}#yiv0467986494 #yiv0467986494ygrp-mlmsg * {line-height:1.22em;}#yiv0467986494 #yiv0467986494ygrp-mlmsg #yiv0467986494logo {padding-bottom:10px;}#yiv0467986494 #yiv0467986494ygrp-msg p a {font-family:Verdana;}#yiv0467986494 #yiv0467986494ygrp-msg p#yiv0467986494attach-count span {color:#1E66AE;font-weight:700;}#yiv0467986494 #yiv0467986494ygrp-reco #yiv0467986494reco-head {color:#ff7900;font-weight:700;}#yiv0467986494 #yiv0467986494ygrp-reco {margin-bottom:20px;padding:0px;}#yiv0467986494 #yiv0467986494ygrp-sponsor #yiv0467986494ov li a {font-size:130%;text-decoration:none;}#yiv0467986494 #yiv0467986494ygrp-sponsor #yiv0467986494ov li {font-size:77%;list-style-type:square;padding:6px 0;}#yiv0467986494 #yiv0467986494ygrp-sponsor #yiv0467986494ov ul {margin:0;padding:0 0 0 8px;}#yiv0467986494 #yiv0467986494ygrp-text {font-family:Georgia;}#yiv0467986494 #yiv0467986494ygrp-text p {margin:0 0 1em 0;}#yiv0467986494 #yiv0467986494ygrp-text tt {font-size:120%;}#yiv0467986494 #yiv0467986494ygrp-vital ul li:last-child {border-right:none !important;}#yiv0467986494




[Non-text portions of this message have been removed]

Re: 468 sweep offset issue

 

On Thu, 25 Feb 2016 16:10:21 +0000, you wrote:

Hey there,

do you have a name we can call you by?

I took a look at the sweep generator schematics, and in your shoes I'd
start looking at the quiescent DC levels of the sweep generators. R970
trims the B sweep start voltage, and Q958/Q960 are the differential
amplifier that set the quiescent (start) voltage of the B sweep. You should
see the same voltage on the base (&emitter) of both transistors, and you
should be able to trim it with the trimmer. The schematic I got from
koo4b's site is pretty poor, but it looks like the base of Q958 is
annotated with +13.0V or +13.6V.
Somewhere in there (I didn't find it right quick) there's also a comparator
between the A sweep ramp and the delay pot's output voltage.
It's worth checking the quiescent state of the A sweep as well, as if
that's off, you may be looking at a stretched sweep that's out of range of
the delay pot at the start end.

... time passes ...

Interestingly it looks like the "B sweep start" trim sets the start voltage
for both sweeps, so if they're significantly off, there'll have to be a bad
component someplace. So, perhaps start by measuring the quiescent voltage
of the A/B sweeps - they ought to be at the same level.
Looking closer, according to figure 67, the A sweep ramp has ~11V range
(this is for - what - 12-15divs of sweep normally?), so a division off
smells like a diode drop :).
There is only one adjustment for the A and B sweep start voltage. The
comparator circuit they use for each one could have 10s to 100s of
millivolts of offset so potentially the start voltage could be offset
by that much. With a sensitivity of 1 sweep volt per division, a
sweep offset of more than a minor division (200 millivolts) is
possible.

The A and B sweep stop voltages are fixed at the same level although
independently referenced to the +5 volt supply and will have even more
offset. The stop points are not important as long as they are greater
than 10 divisions.

In summary, check the quiescent DC levels of the sweeps, they should be at
the same voltage. If not, look at the start voltage diff amp for the sweep
that's off.
If the sweeps are at the same quiescent voltage, you probably need to look
at the B sweep start comparator.

The other problem commonly seen in these sweep generators is leaky or bad
FET. If you measure the voltage over R866, you should measure precisely
zero volts, as there should be no current (to mention) going through the
gate of Q867. The symptoms to a bad FET are usually more obvious, as in the
sweep hangs, goes backwards or is very non-linear, but it's easy to check
for this.
The sweep start voltage are independent of any offset in the sweep
integrators unless they are so broken that the start voltage cannot be
attained.

Re: 468 sweep offset issue

 

On 24 Feb 2016 18:18:13 -0800, you wrote:

There is only one apparent difference between the scopes other than the A/B sweep start misalignment.

On the "good" 468, B sweep ends 1 minor division before A sweep.

On the "bad" 468, A and B sweep end at exactly the same point.
The sweep lengths are not tightly controlled although it looks like
Tektronix went to some effort to make sure they were stable. They
only have to be "long enough" to cover more than 10 divisions.

The sweep stop voltage levels are fixed and the only adjustment which
alters them is a change in the regulated +5 volt supply. The
difference between the A and B sweep stop voltage could be 100s of
millivolts amounting to a couple of minor divisions.

Re: 468 sweep offset issue

Siggi
 

Hey there,

do you have a name we can call you by?

I took a look at the sweep generator schematics, and in your shoes I'd
start looking at the quiescent DC levels of the sweep generators. R970
trims the B sweep start voltage, and Q958/Q960 are the differential
amplifier that set the quiescent (start) voltage of the B sweep. You should
see the same voltage on the base (&emitter) of both transistors, and you
should be able to trim it with the trimmer. The schematic I got from
koo4b's site is pretty poor, but it looks like the base of Q958 is
annotated with +13.0V or +13.6V.
Somewhere in there (I didn't find it right quick) there's also a comparator
between the A sweep ramp and the delay pot's output voltage.
It's worth checking the quiescent state of the A sweep as well, as if
that's off, you may be looking at a stretched sweep that's out of range of
the delay pot at the start end.

... time passes ...

Interestingly it looks like the "B sweep start" trim sets the start voltage
for both sweeps, so if they're significantly off, there'll have to be a bad
component someplace. So, perhaps start by measuring the quiescent voltage
of the A/B sweeps - they ought to be at the same level.
Looking closer, according to figure 67, the A sweep ramp has ~11V range
(this is for - what - 12-15divs of sweep normally?), so a division off
smells like a diode drop :).

In summary, check the quiescent DC levels of the sweeps, they should be at
the same voltage. If not, look at the start voltage diff amp for the sweep
that's off.
If the sweeps are at the same quiescent voltage, you probably need to look
at the B sweep start comparator.

The other problem commonly seen in these sweep generators is leaky or bad
FET. If you measure the voltage over R866, you should measure precisely
zero volts, as there should be no current (to mention) going through the
gate of Q867. The symptoms to a bad FET are usually more obvious, as in the
sweep hangs, goes backwards or is very non-linear, but it's easy to check
for this.

Siggi

On Thu, 25 Feb 2016 at 00:33 analogaddict013@... [TekScopes] <
TekScopes@...> wrote:



I didn't get to do much today, but I checked the waveforms at the
disconnect amplifiers for A and B.

The waveforms sync up, but the A disconnect amplifier (at emitter) is .5V
high ( -2V instead of -2.5V) and the B disconnect amp ( at emitter) is .3V
high ( at -2.6V instead of -3V).

I'll do more tomorrow - hopefullly I will have the time to check the
entire sweep logic section and find the out of tolerance resistor(s). It
appears that is what I should be looking for... (am I correct?)



[Non-text portions of this message have been removed]


Re: 468 sweep offset issue

 

On 24 Feb 2016 15:53:50 -0800, you wrote:

I am not sure what you mean by voltage offset. With no sweep, there
is always a voltage offset because the blanked beam is located at the
left side of the CRT.
Is the bow on the right 1/4 of the CRT visible in your photos?
It is only slightly visible in the close up photo. It is most noticeable when I have the scope set up per the calibration procedure for Y axis and Geometry adjustment. I will upload a photo of the display symptoms shortly.
This may be just a characteristic of the CRT. Tektronix sometimes
specified a tolerance for geometric distortion inside and outside of
the center area. Toward the edges, you can usually find some geometry
error if you look closely enough.

According to the schematic for the horizontal amp, when the scope is set up in XY mode (as per the voltage measurement conditions) both plates should measure close to 52V. My 110V rail is 2V high, so it should measure 54V, but either way they should both be the same with the dot centered. Left plate measures 56.7V and Right plate measures 54.3V.
It is normal for the CRT to have some vertical and horizontal offset
to produce a centered beam. To compensate for this, the CRT
amplifiers may have a centering adjustments. x1 horizontal centering
on the 468 is adjusted with R551 shown on schematic 10 and x10
horizontal centering is adjusted with R578 shown on schematic 10.
There are separate vertical centering adjustments for each input which
do the same thing.

The horizontal position control is off-center to the right side of the display by approx 2 divisions.
Also, when I center the trace in a normal timebase setting and then switch it into XY, the dot is positioned that same 2 division to right offset.
This should be corrected by the procedure on page 4-64 if the
horizontal position control is already centered. Tektronix appears to
have left that out.

Are you referring to the start point of the A and B sweeps not being
exactly aligned?
The alignment depends on circuit tolerances and there may be no
adjustment for it. At high sweep speeds, it is normal for the start
of the sweep to creep to the right somewhat.
I can probably suggest where it can be trimmed out if we determine
that there is no actual fault.
Yes, I am referring to the A and B sweeps not being aligned. My other 468 doesn't have this problem at any timebase settings. (That one needs more work than the one being discussed.)

What really bothers me about it, and also has me slightly confused, is how to properly adjust the sweep start and sweep cal settings when taking this problem into account.

As per the horizontal cal procedure (it's the first step in this section):
-Set timebase A to 1ms and B to 5us
-Set delay time to 1.00
-Input 1ms time markers
-Adjust so the pulse displayed on B sweep starts at the beginning of the sweep & start of 2nd time marker from A sweep display**

The pulse on B sweep is not displayed if I set it to where I believe it should be - which is coinciding with the start of A sweep (which is the first time marker)
If I don't have it set exactly there, won't B sweep end up being out of tolerance?

I suppose I'll have to go through the waveforms again now that I have a digital scope and see if everything syncs up with the sync pulse, A and/or B sweep start, and blanking/unblanking. When I had checked them with my 465, everything appeared to be correct. Some waveforms just had minor differences in their voltage levels when compared against the manual spec, but seemed OK when compared against the other 468.
Their calibration procedure is pretty complicated and Tektronix does
not say what the goal is unfortunately. I suspect some of the steps
could be done in a different order for better results.

I definitely want to fix this and get them aligned. I guess I'm a bit OCD...
I sometimes trim the values of various parts or match transistors to
fix problems like these.

There is only one Sweep Start adjustment for both sweeps and based on
the design shown on schematic 8, there could be 100s of millivolts of
difference between the start points of the sweep generators do to the
matching of CR953/CR954 and CRsomething/CRsomething shown on schematic
8. Differential amplifier/comparators made up of Q958/Q960 and
Q987A/Q987B control the sweep start voltages. Oddly enough, the A
sweep uses a dual transistor which will have better matching while the
B sweep uses two separate transistors; I wonder why.

With an estimated CRT deflection of 1 volt per division at the sweep
output, a difference of 1 minor division or more is possible and your
first photograph shows an offset between the sweeps which is within
the design tolerances.

We have diagnosed other 465B type oscilloscopes here which had as much
offset between the sweeps.

If you want to trim the offset out, then I can make suggestion for how
to do it but it will require modifying the circuit slightly.

I just have a couple things to do and then I can get another picture or two uploaded, then do some waveform checking.

Re: Tek 555 part needed.

zerousair
 

Just to close this out: The HV supply I received from a person here from one of his 555's has fixed the lower beam problem. Stabilized correctly at -1350 volts. I haven't disassembled the old supply and checked all the caps yet or ohmed the burnt transformer.

Re: TDS 380 calibration and vertical scale problem

David Wilson
 

It looks like I am in a real bind desoldering ch2 hybrid from the mainboard. The joints are through hole and some of the joints I was able to get the solder off at the top but at the bottom there is suborn solder that just refuses the come out. I tried desoldering several times but not having much luck. Since I don't want to break anything I thought about putting it back back the way it is and just use as is. A partially working scope is better than a broken one.

I could use a soldering iron to flow solder back in the through hole and try to desolder once again. The board is about 4 mm thick approximately and so are the through hole joints.

Re: 468 sweep offset issue

Brian Bloom
 

I didn't get to do much today, but I checked the waveforms at the disconnect amplifiers for A and B.

The waveforms sync up, but the A disconnect amplifier (at emitter) is .5V high ( -2V instead of -2.5V) and the B disconnect amp ( at emitter) is .3V high ( at -2.6V instead of -3V).

I'll do more tomorrow - hopefullly I will have the time to check the entire sweep logic section and find the out of tolerance resistor(s). It appears that is what I should be looking for... (am I correct?)

Re: 468 sweep offset issue

Brian Bloom
 

Hi,
>since you are saying one is ok and this one is out a little…..check all all the settings of every knob on the >timebase side and compare knob to knob…...….both a and b and start/end and hold off to make sure you are >seeing what you think….

>jim

There is only one apparent difference between the scopes other than the A/B sweep start misalignment.

On the "good" 468, B sweep ends 1 minor division before A sweep.
On the "bad" 468, A and B sweep end at exactly the same point.

Other than that, there are no other differences that stand out.


I am going to upload some more pictures that I took just to confirm that what I am seeing is normal. It is the same on both scopes: ( I put info for each photo in the comments)

All about classic Tektronix CRT o'scopes https://groups.yahoo.com/neo/groups/TekScopes/photos/albums/1461836945

https://groups.yahoo.com/neo/groups/TekScopes/photos/albums/1461836945

All about classic Tektronix CRT o'scopes https://groups.yahoo.com/neo/groups/TekScopes/photos/albums/1461836945 All about classic Tektronix CRT oscilloscopes, their use, repair, and collecting. (If you want to join, please make sure you write something relevan...



View on groups.yahoo.com https://groups.yahoo.com/neo/groups/TekScopes/photos/albums/1461836945
Preview by Yahoo






Also, I had myself a little bit confused. The bowing problem is with the 468 that I am not currently working on.

Re: 468 sweep offset issue

Jim Popwell <jpopwell@...>
 

Hi,

since you are saying one is ok and this one is out a little…..check all all the settings of every knob on the timebase side and compare knob to knob…...….both a and b and start/end and hold off to make sure you are seeing what you think….

jim

On Feb 24, 2016, at 3:53 PM, analogaddict013@... [TekScopes] <TekScopes@...> wrote:

I am not sure what you mean by voltage offset. With no sweep, there
is always a voltage offset because the blanked beam is located at the
left side of the CRT.
Is the bow on the right 1/4 of the CRT visible in your photos?
It is only slightly visible in the close up photo. It is most noticeable when I have the scope set up per the calibration procedure for Y axis and Geometry adjustment. I will upload a photo of the display symptoms shortly.

According to the schematic for the horizontal amp, when the scope is set up in XY mode (as per the voltage measurement conditions) both plates should measure close to 52V. My 110V rail is 2V high, so it should measure 54V, but either way they should both be the same with the dot centered. Left plate measures 56.7V and Right plate measures 54.3V.
The horizontal position control is off-center to the right side of the display by approx 2 divisions.
Also, when I center the trace in a normal timebase setting and then switch it into XY, the dot is positioned that same 2 division to right offset.

Are you referring to the start point of the A and B sweeps not being
exactly aligned?
The alignment depends on circuit tolerances and there may be no
adjustment for it. At high sweep speeds, it is normal for the start
of the sweep to creep to the right somewhat.
I can probably suggest where it can be trimmed out if we determine
that there is no actual fault.
Yes, I am referring to the A and B sweeps not being aligned. My other 468 doesn't have this problem at any timebase settings. (That one needs more work than the one being discussed.)

What really bothers me about it, and also has me slightly confused, is how to properly adjust the sweep start and sweep cal settings when taking this problem into account.

As per the horizontal cal procedure (it's the first step in this section):
-Set timebase A to 1ms and B to 5us
-Set delay time to 1.00
-Input 1ms time markers
-Adjust so the pulse displayed on B sweep starts at the beginning of the sweep & start of 2nd time marker from A sweep display**

The pulse on B sweep is not displayed if I set it to where I believe it should be - which is coinciding with the start of A sweep (which is the first time marker)
If I don't have it set exactly there, won't B sweep end up being out of tolerance?

I suppose I'll have to go through the waveforms again now that I have a digital scope and see if everything syncs up with the sync pulse, A and/or B sweep start, and blanking/unblanking. When I had checked them with my 465, everything appeared to be correct. Some waveforms just had minor differences in their voltage levels when compared against the manual spec, but seemed OK when compared against the other 468.

I definitely want to fix this and get them aligned. I guess I'm a bit OCD...

I just have a couple things to do and then I can get another picture or two uploaded, then do some waveform checking.





[Non-text portions of this message have been removed]




[Non-text portions of this message have been removed]

Re: Tek 7854 Info, Repair, Restore

Brian Bloom
 

You would not need the 7S11 at all but using the 7S12 as a sampling
>sweep requires the S-53 Trigger Recognizer head which is shown in the
>photo. This configuration gives roughly the capability of a 7T11
>without the random sampling capability so a delay line would be needed
>to see the triggering edge.

>I think the delay line is more rare and expensive than a 7S14 which is
>why I recommended the later. The 7T11 and 7T11A do away with needing
>the delay line as well because of their random sampling capability but
>are more difficult to use than a 7S14.

I just haven't been able to find any 7T11, 7T11A, or 7S14 plugins thus far. There are a few 7S12, S53, sampling plugins, and 7M11 plugins available right now, though.

Re: 468 sweep offset issue

Brian Bloom
 

I am not sure what you mean by voltage offset. With no sweep, there
>is always a voltage offset because the blanked beam is located at the
>left side of the CRT.

>Is the bow on the right 1/4 of the CRT visible in your photos?

It is only slightly visible in the close up photo. It is most noticeable when I have the scope set up per the calibration procedure for Y axis and Geometry adjustment. I will upload a photo of the display symptoms shortly.

According to the schematic for the horizontal amp, when the scope is set up in XY mode (as per the voltage measurement conditions) both plates should measure close to 52V. My 110V rail is 2V high, so it should measure 54V, but either way they should both be the same with the dot centered. Left plate measures 56.7V and Right plate measures 54.3V.
The horizontal position control is off-center to the right side of the display by approx 2 divisions.
Also, when I center the trace in a normal timebase setting and then switch it into XY, the dot is positioned that same 2 division to right offset.

>Are you referring to the start point of the A and B sweeps not being
>exactly aligned?

>The alignment depends on circuit tolerances and there may be no
>adjustment for it. At high sweep speeds, it is normal for the start
>of the sweep to creep to the right somewhat.

>I can probably suggest where it can be trimmed out if we determine
>that there is no actual fault.

Yes, I am referring to the A and B sweeps not being aligned. My other 468 doesn't have this problem at any timebase settings. (That one needs more work than the one being discussed.)

What really bothers me about it, and also has me slightly confused, is how to properly adjust the sweep start and sweep cal settings when taking this problem into account.

As per the horizontal cal procedure (it's the first step in this section):
-Set timebase A to 1ms and B to 5us
-Set delay time to 1.00
-Input 1ms time markers
-Adjust so the pulse displayed on B sweep starts at the beginning of the sweep & start of 2nd time marker from A sweep display**

The pulse on B sweep is not displayed if I set it to where I believe it should be - which is coinciding with the start of A sweep (which is the first time marker)
If I don't have it set exactly there, won't B sweep end up being out of tolerance?

I suppose I'll have to go through the waveforms again now that I have a digital scope and see if everything syncs up with the sync pulse, A and/or B sweep start, and blanking/unblanking. When I had checked them with my 465, everything appeared to be correct. Some waveforms just had minor differences in their voltage levels when compared against the manual spec, but seemed OK when compared against the other 468.

I definitely want to fix this and get them aligned. I guess I'm a bit OCD...

I just have a couple things to do and then I can get another picture or two uploaded, then do some waveform checking.

Re: Tek 7854 Info, Repair, Restore

 

You would not need the 7S11 at all but using the 7S12 as a sampling
sweep requires the S-53 Trigger Recognizer head which is shown in the
photo. This configuration gives roughly the capability of a 7T11
without the random sampling capability so a delay line would be needed
to see the triggering edge.

I think the delay line is more rare and expensive than a 7S14 which is
why I recommended the later. The 7T11 and 7T11A do away with needing
the delay line as well because of their random sampling capability but
are more difficult to use than a 7S14.

On 24 Feb 2016 15:26:27 -0800, you wrote:

Would it be possible to use a 7S12 as the timebase for a 7S11 in order to calibrate a 106 square wave gen? If so, would I need the 7M11 delay line?

I got the idea from one of Peter's Tekwiki images.

http://w140.com/tekwiki/wiki/File:7s12-7s11-1ghz-store.jpg http://w140.com/tekwiki/wiki/File:7s12-7s11-1ghz-store.jpg

Re: Need Help Fixing A Couple of 2445 Scopes

Michael
 

Hi,

I haven't seen a 2445, but I think it is pretty much like a 2465. The 4-pin
connector does indeed connect to the back of the GPIB board.

I think that the other connector goes to the power supply board A2A1. There
are two connectors that come up from the bottom of the case from the main
board. They have different pin spacing and are keyed. They connect pretty much
side by side to the A2A1 board.

There are some photos on the eevblog forum from my teardown of my 2465BCT in
the category "Test Equipment", topic: "Tektronix 2465B oscilloscope teardown".
The url is
http://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/550/
which contains the photos of some of my teardown. Part of that is pictures of
how the 4-pin connector is connected and pictures of the inside after the A3 /
A2A2 boards have been removed. You can see the large white connector coming up
from the bottom. The wires go inside the metal post to keep the options from
pinching them and the two connectors that come up from the bottom connect to
the A2A1 board.

You also have the fan power line that connects to the feed through capacitor
on the back, near the fan and the processor board.

There are four power wires. The two on the bottom go from the 115/230 switch
to the bottom two lugs on the A2A1 board. The two from the fuse holder go to
the top two lugs. The wire coming out of the end of the fuse goes to the lug
on the right (facing the A2A1 board), and the other goes to the lug on the
left. That doesn't quite match up with the schematic, but that is the way mine
was wired and it works. You have to be careful, those power wires are
difficult to get in place with no working room (loosen the back panel a bit
will help). It is easy to damage the fuse holder. I broke mine, but super glue
fixed it. There is also a ground wire from the A2A1 board that connects to the
back of the case.


Mike

Here's the problem. There are more insides, inside since this scope has
the GPIB Option, the problem is that I don't know where all of the wires go.
I think I got all but one cable plugged in in the right places, but I have
one end of one cable left, and I can't figure out where it goes.


The four conductor cable (all white wires) from the mode light panel
above the CRT, Does it plug into the four conductor terminal down low on the solder side of the GPIB board?


The cable that really has me stuck is a (seven?) single row conductor
cable with all white wires. One end seems to go on the Expansion
Motherboard that fits inverted on the top of the scope chassis, next to a 34
ribbon connector cable that goes to the A5 Control Board. Where does the
other end of this cable go? I can't seem to see any open plugs where it would fit.

Re: Tek 7854 Info, Repair, Restore

Brian Bloom
 

Would it be possible to use a 7S12 as the timebase for a 7S11 in order to calibrate a 106 square wave gen? If so, would I need the 7M11 delay line?

I got the idea from one of Peter's Tekwiki images.

http://w140.com/tekwiki/wiki/File:7s12-7s11-1ghz-store.jpg http://w140.com/tekwiki/wiki/File:7s12-7s11-1ghz-store.jpg

Re: 468 sweep offset issue

 

On 23 Feb 2016 19:13:28 -0800, you wrote:

I have been slowly working on getting this 468 fixed, back into spec, and calibrated.
Physically, it is mint. There's no damage anywhere.

I had to replace 3 of the PSU capacitors: the 55V, the 5V, and the -8V.
In the time where I hadn't the slightest clue what I was doing, I replaced lots of parts that I didn't need to - It has all new capacitors. New tantalums, new lytics, new poly HV caps... even new ceramics. I was very, very careful to make sure that I used the correct values for everything - and not to mix anything up.

There are still a couple of things left to resolve:

- There is a voltage offset between the horizontal deflection plates, which I believe is causing the vertical elements of the traces on the far right 1/4 of the CRT to have a slight bow to them. The Y axis and Geometry adjustments are not able to resolve this. I have not yet tracked down the source of the issue here.
I am not sure what you mean by voltage offset. With no sweep, there
is always a voltage offset because the blanked beam is located at the
left side of the CRT.

Is the bow on the right 1/4 of the CRT visible in your photos?

- The B sweep and A sweep do not sync at the start of the sweep. The sync pulse is correct. I have checked all of the waveforms numerous times trying to isolate the problem, but I believe this is a problem in the timebase section (according to "Tek: troubleshooting your oscilloscope") - making it a royal pain for a beginner like me to track down.
**This is the issue that is giving me all of the trouble**
Are you referring to the start point of the A and B sweeps not being
exactly aligned?

The alignment depends on circuit tolerances and there may be no
adjustment for it. At high sweep speeds, it is normal for the start
of the sweep to creep to the right somewhat.

I can probably suggest where it can be trimmed out if we determine
that there is no actual fault.

I have swapped out the trigger board and also the timebase board in an effort to at least isolate the fault to a specific block. The problem must reside on the main board. My guess is that it's going to be in the sweep logic circuitry.

I have been using the "Tektronix: troubleshooting your oscilloscope" book. I have read the theory of operation for this scope a couple of times. I have even read the circuit description section of my 465 manual to try and get a better understanding of the basic functionality of these scopes.

I'm hoping that I will have an easier time troubleshooting since I bought a new digital scope.
I'm confident that I'll be able to track down the problem with the horizontal amp , but this sweep start offset is driving me nuts and I just cannot figure it out! Will someone please point me in the right direction?

Pics of the problem:
https://groups.yahoo.com/neo/groups/TekScopes/photos/albums/1461836945/lightbox/1384398865?orderBy=ordinal&sortOrder=asc&photoFilter=ALL https://groups.yahoo.com/neo/groups/TekScopes/photos/albums/1461836945/lightbox/1384398865?orderBy=ordinal&sortOrder=asc&photoFilter=ALL