Date   
Re: my repair attempt

ykochcal
 

Well that brought back some memories from 2013, Thanks for posting the
picture.

I did a repair of what looks like a similar pot from a B plugin
I bees waxed the screw and hole, then applied a small amount of epoxy to the
plastic and then wrapped the pot with wax free dental floss and applied more
epoxy to the outside, ( I think the picture is at this point), then came
back after the epoxy thickened some and applied a second layer.

I thought the "Wrap" was fairly effective at keeping it all together when I
tightened the allen. Should check to see how it's doing.

I would not have guessed that the plastic was delron but mine was well
oxidized and I am no plastic expert, I was thinking the wrap and epoxy being
all the way round would not have to really bond but just prevent expansion.

That was done for the shaft connection and back cover.

The ground lead and knob were just other epoxy day projects.

John

P.S. I did my first picture post to your folder, so I hope that is proper
picture Etiquette, if not delete, comment or move as you see fit.

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: Thursday, February 25, 2016 5:55 PM
To: TekScopes@...
Subject: [TekScopes] my repair attempt

The dreaded Delrin split has afflicted one channel of my 1A4.
Finally got around to it. I drilled out a roughly 5/32 hole and put in a
brass threaded insert and put some plastic bonder all around it. It's
supposed to bond Delrin with a bit of surface roughening.
The threaded insert was a little bit squished so the set screw puts some
expansion on the whole mess. Let's hope it lasts.

Re: 7834 horizontal jittery readout

 

On Fri, 26 Feb 2016 22:02:46 +0000, you wrote:

On 25/02/2016 22:02, David @DWH [TekScopes] wrote:
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?
Panic over. It wasn't jitter. Seems it just needed the focus settings
reset. Sorry for any trouble. This is 7834 with the rewound transformer.
Presumably resetting the -1955V and CRT bias must have messed things up
somewhat. Or maybe the other voltages weren't exactly as the old
transformer.

I couldn't compare the 7633 readout with the 7834 readout. Despite the
manual (I must have the wrong one) schematics being very similar the
board in my 7633 doesn't fit with the schematic. In particular around
the strobe source. Some of the diodes appear to have been replaced with
resistors.
No harm done. At least we found this before proceeding further.

One thing worth checking is the ground connections to the readout and
horizontal CRT amplifier boards.
I will do. It's performing well now but they do tend to loosen a bit in
time.

Something that was slightly puzzling. In the Performance check "G
Readout System". It says to remove Q3416 and check that the display
shows two rows of all zeros, it didn't. Mostly zeros mixed with a few
other characters and some gaps. I'm not sure what to make of it as it
seems to be displaying OK.
I am not sure if that is a problem or not. The identify command is
used to align the decoders so that the proper characters are
displayed.

You could swap U3429 with U3418 to see if that makes a difference. I
would also reseat all of the ICs and transistors. The IC sockets are
problematical.

Going back to the -1955 setting. On my HP1251B meter, on the range in
question the input impedance is 11.1M Ohms. It would be wouldn't it -
teach me not to read the manual. After calculation and setting to a
meter reading of 1.975 (1000:1 Tenma probe) things fell into place a bit
better.
I got caught by the same issue with my HP3478A when I first used my
high voltage probe to measure the cathode voltage on my 7834. I was
aware that this could be a problem with high performance multimeters
but to remind me in the future, I printed the table out from the
manual which shows what the input resistance is for different input
ranges and pasted it to the top of the multimeter's enclosure.

The reason caught it is that I did a sanity check using my handheld
DMMs and none of them agreed with the HP3478A but they agreed with
each other. The solution was to manually set the range on the
HP3478A.

Re: 468 sweep offset issue

Brian Bloom
 

That looks like 100 MHz of bandwidth to me.
I'm going to do some investigating as to why the signal amplitude dropped off when I had the 191 connected. I guess I should suspect the 191 even though it seemed fine when I checked it with the new digital. I'll try using the 067-0532-01 even though I have no clue if it's in need of repairs.

I'm just going to continue on with the calibration procedure for the 465. I'm hoping that I'll be able to adjust the 106's fast outputs enough with the 7854 to get the 468's comp adjustments back into the usable range. I'm still trying to figure out a way to get access to an EE lab at the university.


The only way I could get a readable display for risetime off of the TD pulser was by using the part of the rising edge after all of those nasty abberations and overshoot looking trash.
>>
>>I've never used a TD pulser before, so I don't know what I should be seeing exactly... but I doubt it's what's shown in the pictures. I drove the pulser per the datasheet instructions - @ 100Khz from 106s high amplitude output and into a thru termination to the HighZ scope input.

>This page shows what the output of the tunnel diode pulser should look
>like:

I didn't think it was right. Oh well, I only paid $30 for it among other things. I'll deal with figuring out what's wrong with it and fixing it later when I actually need it.

Re: 468 sweep offset issue

 

On 26 Feb 2016 20:02:59 -0800, you wrote:

I have checked the 465 risetime measurements for CH1 and CH2. I am adding photos.

I have one good desktop PC that has a DVI output, but it's buried under a bunch of stuff beside my workbench.... so I used my best 106 and also tried it with my 067-0681-01. I think my TD pulser might be in need of some major help. If it is bad and can be diagnosed, I have all of the necessary parts to repair it.

Rise time measurement setup:

-106 square wave gen (<1ns) connected through 42" RG58A , through 011-0049-01 thru termination and into either channel 1 or channel 2.

-106 set at 100Khz. Fast rise output used, except for when TD pulser was connected.

-Of course, the 465 is in X10mag for 5nS/div.
-Verticals set at .1V/div with VAR set for proper scale of waveform on display.

Both channels measure the same: 3.5nS.
That looks like 100 MHz of bandwidth to me.

The only way I could get a readable display for risetime off of the TD pulser was by using the part of the rising edge after all of those nasty abberations and overshoot looking trash.

I've never used a TD pulser before, so I don't know what I should be seeing exactly... but I doubt it's what's shown in the pictures. I drove the pulser per the datasheet instructions - @ 100Khz from 106s high amplitude output and into a thru termination to the HighZ scope input.
This page shows what the output of the tunnel diode pulser should look
like:

http://dabbledoo.weebly.com/pulse.html

Re: 468 sweep offset issue

Brian Bloom
 

I have checked the 465 risetime measurements for CH1 and CH2. I am adding photos.


I have one good desktop PC that has a DVI output, but it's buried under a bunch of stuff beside my workbench.... so I used my best 106 and also tried it with my 067-0681-01. I think my TD pulser might be in need of some major help. If it is bad and can be diagnosed, I have all of the necessary parts to repair it.


Rise time measurement setup:

-106 square wave gen (<1ns) connected through 42" RG58A , through 011-0049-01 thru termination and into either channel 1 or channel 2.

-106 set at 100Khz. Fast rise output used, except for when TD pulser was connected.

-Of course, the 465 is in X10mag for 5nS/div.
-Verticals set at .1V/div with VAR set for proper scale of waveform on display.

Both channels measure the same: 3.5nS.


The only way I could get a readable display for risetime off of the TD pulser was by using the part of the rising edge after all of those nasty abberations and overshoot looking trash.

I've never used a TD pulser before, so I don't know what I should be seeing exactly... but I doubt it's what's shown in the pictures. I drove the pulser per the datasheet instructions - @ 100Khz from 106s high amplitude output and into a thru termination to the HighZ scope input.

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

Re: 468 sweep offset issue

Brian Bloom
 

Once taken out of circuit, the original measures 2382ohm. Still within tolerance... However, with the 560K paralleled, it measures 2372ohm. Shows just how sensitive this circuit is!

Re: TDS 380 calibration and vertical scale problem

David Wilson
 

working on it

Re: 468 sweep offset issue

Brian Bloom
 

It now see another way to trim the sweep positions. R758 and R778+774
add a current into Q760 and Q772 which the sweep output voltages
subtract from. Trim the value of one of the resistors to move the
sweep slightly. A parallel resistance of about 300 kilohms will move
the trace one minor division.


BINGO!!!

I piggybacked a 300K onto R758 and now it's starting a fraction of a minor division before A sweep!

I think I'm going to trim it a bit more to get the sweep aligned as best I can.
I would say that 300K moved the B sweep near 0.9 of a minor division.
I'm going to try a 510K to see how much closer I can get it.

Once I've got it where I want it I will see if Mouser has the value I need in RN55 so I can replace it with a single resistor.

Thanks for the help! I think I will learn quite a lot with this group!

Re: 468 sweep offset issue

Brian Bloom
 

Well that didn't quite do it, but it definitely helped.
>
>>Now B sweep only "lags" A sweep by 0.5 minor divisions. It also ends the same amount before A sweep, where they were both ending at the same time. According to the measurements I took, the transistor-diode combinations were within 200uV of each other. The diode pair for A sweep is also within 200uV, as are Q760 and Q772.
>>
>>At least I am learning something practical about this type of circuit and how it reacts to matched and unmatched PN junction drops and such. I forgot to check the resistors again, and will do that tomorrow after work.
>>I guess if what has to be done to get this aligned is to trim the A sweep start circuit, I'll do it and figure out how to make it look clean.. I'll have to buy the trimmer, though, so I might as well buy an entire set of them. For now, maybe there's one that will work from the 475 main board or trigger board that I have laying around.
>>Probably should check for any out of tolerance resistors and any other unmatched components from A to B sweep start/miller runup, etc.

>It will be easiest to change one of the diodes and introduce a
deliberate mismatch to move the sweeps into alignment.

>How close are the sweep output voltages when both are reset? The best
way to measure this is between the collectors of Q967 and Q998.

>It now see another way to trim the sweep positions. R758 and R778+774
add a current into Q760 and Q772 which the sweep output voltages
subtract from. Trim the value of one of the resistors to move the
sweep slightly. A parallel resistance of about 300 kilohms will move
the trace one minor division.

Does it matter which diode I change out? If I change diodes again, should I try mismatching the diodes in the A sweep gen in an attempt to get it to delay slightly instead of trying to get B sweep to start sooner?

Forgive my ignorance in understanding this circuits functionality... I am going to read through your posts, the sweep gen theory of operation, and the related section in the Tek troubleshooting your scope book again to try and obtain a better understanding of it now that I have some more clues.

"How close are the sweep output voltages when both are reset? "
By "reset" do you mean their quiescent state? I can set it to single sweep, run one sweep, and then measure that if that's what you mean.

Putting a 300K parallel to R758 (2.37Kohm) would give me 2351ohms. This would raise the voltage of the B sweep rampslightly, thus causing the B sweep trace to move closer to the start point. Am I correct here? If doing so will move the sweep 1 minor division, then with me needing just a hair over half a minor division, I need to lower the resistance of R758 by about 11 ohms.

So if I need 2.36 ohms, what if I use a 510Kohm in parallel with R278? This would give me 2359ohms according to the math.

Am I correct in my thinking here?



I'm anxious to get to the point in my knowledge of circuits where I'm able to fully understand the operation of such circuits!!

Re: 468 sweep offset issue

Brian Bloom
 

Is the vertical deflection accurate?

Is the vertical deflection linear from the top to the bottom of the
CRT?

The bandwidth limiting switch activates two different sections shown
on schematic 3. At full bandwidth the two inductors are suppose to be
shorted out but what if just one of them was because one throw of one
pole of the switch was open?

You could measure the bandwidth at point TP322 or TP324 to see if the
problem is earlier or later in the vertical signal path.

Yes, the vertical deflection is accurate. I had just checked it against my 067-0502-01 amplitude calibrator.

Yes, vertical deflection is looking pretty good. I checked it when I began the cal procedure, which was checking the Y axis alignment and Geometry settings. I didn't change them at all since they were fine.

I'm able to visually inspect the switch contacts for BW limit, and they are functioning correctly. neither contacts you are referring to are sticking at all, and the ones on the front fully open and close as well.

I'll make a note on my "465 BW problem" checklist to check BW at TP322/TP324

Thus far, that list contains:

"
>>You are correct, I am mistaken. It is a 465. The manual I am using is also for a 465. I just slipped with the "B"...... Sorry for the confusion.

Ok, so there is no mystery here. You have a 465 with the discrete
vertical CRT amplifier.

Check the low voltage power supply levels including the -8, +15, and
+55 volt outputs.

I would also check bulk decoupling capacitors C4498 and C4499 on the
discrete vertical CRT amplifier board.

Check the voltage at the bases of the two cascode stages. There
should be +9.2 volts as marked on the schematic at the junction of
R4462 and R4463 and +15 volts at the junction of R4480, R4482, and
R4492.

Measure the values of the resistive trimmers R4427, R4425, R4422, and
R4438. Maybe one of them is open. This can be done in circuit
because each is in series with a capacitor. Be careful not to adjust
them however unless you want to do a full vertical calibration.


"

These were your instructions to the OP in the thread "465B Degraded Bandwidth". The OP never specified what the solution was or if he bothered to look for one. The thread ends abruptly with no conclusion.

Re: 468 sweep offset issue

Brian Bloom
 

David,
>That 55 MHz bw is far too low; can you explain exactly how you are measuring it ?Is the Bw limit switch stuck on ?What vert sensitivity are you making the measurement on ?It should probably be done on the 5-10 mV position; no probe
>The generator should be terminated in 50 ohms, at the scope end.
Are both ch the same ?What is the risetime measurement ? Should be 3.5 nS (10/90) on a 465.
HankC, Boston WA1HOS


I am measuring it exactly how both the 465 manual and 468 manual specify. In the 468 manual volume 1 it is page 4-44. In the 465 manual it starts at the end of page 6-21.
I am using a fully functional 191 leveled sine gen - one of the recommended unit options for the cal procedures.
The line used is a 42 inch RG58A - Belden. new. properly terminated with 011-0049-01 direct into either channel.

I have tried it on every V div setting possible - up to 1V/div, and tried both channels. both channels are the exact same. At 100Mhz, I only have 2.2 divisions of deflection. When 191 output freq is dropped to 55Mhz, I have 3.5 divisions.


The procedure is as follows:
5uS timebase setting
untriggered display - A trig level fully CW
CH1 & CH2 vert 5mV/div

At 50khz reference signal from 191, set gen output voltage for 5 division display. Increase freq to 100Mhz. Check that there is at least 3.5 divisions of vertical deflection (ensuring 100Mhz+ bandwidth capability from vertical circuits)

Unless both CH1 and CH2 vertical circuits have the exact same fault, it must be after the signal is combined at the delay line driver.

Also, there are no stuck switches. This scope has been thoroughly cleaned and fully checked for mechanical problems. Enabling BW limit when at any VHF frequency drops the vertical deflection to one minor division or less.

I'll be checking the risetime measurement on it this evening sometime via the VGA/DVI output of a device (per David's instructions) and also will try using both of my poorly cal'd 106s. I want to get this 468 sweep lag thing resolved first while I've got everything laid out to do so.

Re: 7834 horizontal jittery readout

Gordon <tekscopes@...>
 

On 25/02/2016 22:02, David @DWH [TekScopes] wrote:
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?
Panic over. It wasn't jitter. Seems it just needed the focus settings reset. Sorry for any trouble. This is 7834 with the rewound transformer. Presumably resetting the -1955V and CRT bias must have messed things up somewhat. Or maybe the other voltages weren't exactly as the old transformer.

I couldn't compare the 7633 readout with the 7834 readout. Despite the manual (I must have the wrong one) schematics being very similar the board in my 7633 doesn't fit with the schematic. In particular around the strobe source. Some of the diodes appear to have been replaced with resistors.

One thing worth checking is the ground connections to the readout and
horizontal CRT amplifier boards.
I will do. It's performing well now but they do tend to loosen a bit in time.

Something that was slightly puzzling. In the Performance check "G Readout System". It says to remove Q3416 and check that the display shows two rows of all zeros, it didn't. Mostly zeros mixed with a few other characters and some gaps. I'm not sure what to make of it as it seems to be displaying OK.

Going back to the -1955 setting. On my HP1251B meter, on the range in question the input impedance is 11.1M Ohms. It would be wouldn't it - teach me not to read the manual. After calculation and setting to a meter reading of 1.975 (1000:1 Tenma probe) things fell into place a bit better.

Sorry again for the trouble.

Cheers

Gordon

Re: 7834 horizontal jittery readout

 

On Thu, 25 Feb 2016 23:41:25 +0000, you wrote:

On 25/02/2016 22:02, David @DWH [TekScopes] wrote:
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?
Thanks and no, that's a 7633.

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.
It doesn't affect the jitter as I've noticed.

How does the readout behave when the sweep is very slow like
100ms/div?
I'll check again tomorrow but I don't think it makes any difference.

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.
Yes, I've seen that but this is more. It's very noticeable. I'll take a
pic of the jitter tomorrow - if it shows up well enough on a pic.

I'm not 100% sure it isn't affecting the trace as well. It's enough to
make the readout a bit difficult to read but rather hard to tell on a
trace. I'll try a triangle waveform tomorrow, it might show up better if
the trace is affected as well.

Cheers

Gordon
The readout on my older 7834 has quite a bit of horizontal and
vertical jitter but it is all caused by thermal imbalance in the
amplifiers so the magnitude depends largely on the sweep speed and
displayed waveform. Most of my 7000 mainframes and 22xx oscilloscopes
display this behavior to one extent or another. Some 7000 mainframes
have adjustments for this as Dallas mentioned but not the 7834 or at
least they are not well documented.

If the jitter is caused by thermal imbalance, then it should abate
when their is no horizontal or vertical movement of the beam.

One thing worth checking is the ground connections to the readout and
horizontal CRT amplifier boards. I seem to remember having similar
problems caused by a ground loop or improper shielding when a ground
was disconnected for whatever reason. The readout board outputs are
single ended making them susceptible to this.

Re: 7834 horizontal jittery readout

 

On Fri, 26 Feb 2016 09:29:02 +0000, you wrote:

On 25/02/2016 23:41, Gordon @GordonW [TekScopes] wrote:

Thanks and no, that's a 7633
Duh. While drifting off last night it dawned on me that the 7633 is
going to be very similar.

Gordon
From the perspective of your photograph, I think they look identical.
I looked specifically for the reduced scan graticule and once I saw
that, I figured it was the 7834. The quality of the display looks
very similar to my older green 7834 but that could be caused by the
camera's color balance.

Re: SC503 storage mode

 

On 26 Feb 2016 07:39:49 -0800, you wrote:

As regards bistables: I've got a 434, a 577 D1 (bipolar storage) curve tracer, a 7623A and a 7633. I remember playing with them a few years ago.

I just drew out my 434 (split screen bistable with enhanced mode), which has been dormant for about two years and I played with it a little. A few memories came back and I could verify the following:

After switch on, the collimation of the flood gun is wrong; the display background is uneven and blooms badly.
After a while, things become better; the screen becomes darker. After about 20 minutes, things stabllise and the system becomes usable.
I have seen the same with the other instruments in bistable mode after a long period of non-use.
The 7623A needed some adjustment but became pretty usable after that.

In my experience, storage systems benefited more from adjustments after years of not being used than other subsystems. Aging of the CRT seems to continue, even when not used. This also held for variable persistence systems, though to a lesser extent. Apart from the 'scopes already mentioned, I have checked and adjusted my 464's, 466 and 7834. Bistable is usable but gives the worst results in terms of image quality (and usefulness).

With all analog storage 'scopes, it is important to allow sufficient time for stabilisation and recovery. This is as important while calibrating/adjusting as it is after a longer period of non-use. Bistable is more finicky than the other modes.

Raymond
The storage performance of my 7834 did not improve much with
calibration and its bistable mode has such low contrast that it is
unusable although variable persistence mode works great. I have not
run it for more than a couple of hours but maybe I should; leaving my
7603 on for a few days helped it a lot.

I considered experimenting to improve the 7834 but decided it would be
a waste of time unless I could correct its CRT geometry problem which
I was never able to do.

Re: SC503 storage mode

 

Storage as is shown in that video is about as good as it gets on the 434 and bistable in general.

HP 1741A and the faster-storage HP 1744A are nice storage 'scopes. They do variable persistence only; not even non-storage, just short persistence.
My favorite analog storage 'scopes are the 7834 (never seen a 7934) and the 466. Pretty fast single-shot storage, that last one, slightly faster than 7633 AFAIR.

I think there's agood chance that you'll revive the storage part of the SC503 by trying to get familiar with its operation and *carefullly* adjusting electrical parameters to do with storage.

Raymond

Re: SC503 storage mode

Malcolm Hunter
 

On 26 February 2016 at 15:50, jerry massengale @jmassen418
[TekScopes] <TekScopes@...> wrote:


I have had several DC503s and they mostly worked like you showed, I did
have one though that was almost perfect. There is an adjustment procedure
that is absolutely necessary to have any chance of success. It will never
be as good as an hp1741 or a 7834.

​To be honest, it's a really nice analogue scope. If I can get the trace
intensity up at low timebase speeds I'll​ be happy. The storage mode would
just be a bonus, so it won't be the end of the world if I can't get it
working.

Malcolm


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

Re: SC503 storage mode

Malcolm Hunter
 

On 26 February 2016 at 15:39, @Raymond [TekScopes] <
TekScopes@...> wrote:

I just drew out my 434 (split screen bistable with enhanced mode), which
has been dormant for about two years and I played with it a little. A few
memories came back and I could verify the following:

After switch on, the collimation of the flood gun is wrong; the display
background is uneven and blooms badly.
After a while, things become better; the screen becomes darker. After
about 20 minutes, things stabllise and the system becomes usable.
I have seen the same with the other instruments in bistable mode after a
long period of non-use.
The 7623A needed some adjustment but became pretty usable after that.

In my experience, storage systems benefited more from adjustments after
years of not being used than other subsystems. Aging of the CRT seems to
continue, even when not used. This also held for variable persistence
systems, though to a lesser extent. Apart from the 'scopes already
mentioned, I have checked and adjusted my 464's, 466 and 7834. Bistable is
usable but gives the worst results in terms of image quality (and
usefulness).

With all analog storage 'scopes, it is important to allow sufficient time
for stabilisation and recovery. This is as important while
calibrating/adjusting as it is after a longer period of non-use. Bistable
is more finicky than the other modes.
​I did find a YouTube video of ​a 434 yesterday, just to get some idea of
what my SC503 should be doing

https://www.youtube.com/watch?v=q7wYnLD_UxA <- Here

I have the SC503 service manual ready to download now, so I'll have a look
this evening to see what adjustments can be made. I have a TM503 with the
sides off - I'll see how I get on with that.

Malcolm


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

Re: SC503 storage mode

 

Hi,


I have had several DC503s and they mostly worked like you showed, I did have one though that was almost perfect. There is an adjustment procedure that is absolutely necessary to have any chance of success. It will never be as good as an hp1741 or a 7834.


Jerry Massengale

-----Original Message-----
From: David @DWH [TekScopes] <TekScopes@...>
To: TekScopes <TekScopes@...>
Sent: Fri, Feb 26, 2016 8:19 am
Subject: Re: [TekScopes] SC503 storage mode






Wow, I thought the SC503 was variable persistence. In the words of
Adam Savage, "well, there's your problem!" Ignore what I said about
the view time control.

I am not familiar with how the SC503 should look in storage mode but
from your video, it appears that there are at least two problems; the
slow sweep speeds should be brighter and bistable storage mode is not
storing at all although that is difficult to tell from your video. In
bistable storage mode, the writing rate is low so you either have to
have a repeating trace to store or you need to use a slower sweep
speed when doing single sweeps which of course is not going to work
with the current brightness problem at slow sweeps. The CRT cathode
voltage is no doubt correct but I think the flood gun or storage
calibration is wrong indicating a circuit problem unless someone
misadjusted it.

Someone else with experience with the SC503 or even bistable storage
will have a better idea but I would start I would start by checking
the various power supply voltages and then working on the non-storage
intensity problem at slow sweep speeds.

I did not have any trouble with the link once I removed the question
mark at the end. Did Yahoo add that?

On Fri, 26 Feb 2016 09:02:19 +0000, you wrote:

?Here's a video of both issues, which I hope should explain them:

https://drive.google.com/open?id=0B2-hICzIGrsSM0J1VUlOQ0pGdmc?

Re: 468 sweep offset issue

 

On 25 Feb 2016 15:27:39 -0800, you wrote:

Also, a quick question regarding bandwidth problems:

My 465 only has 55Mhz bandwidth on either channel... I noticed this when I decided to calibrate it. What >would be a likely culprit? Other than that issue, my 465 is in fantastic condition and runs great. I haven't >changed a single part on it since I got it last year. I also did not touch any of the LF/HF comp adjustments in >the vertical section!!
My noob mind started thinking that it could be some of the RC's in the signal path, but I haven't yet learned >enough about circuit functionality, HF/VHF, etc yet. I'm still studying "Electronics for Engineers" and >refreshing my math skills...
I forgot to mention - the procedure for checking bandwidth is the same
between the 465 and 468. This part of the cal procedure is on page 4-44.
In order to determine the bandwidth capability, I reduced the output
frequency on the 191 leveled sinewave gen until the 465 display was 3.5
vertical divisions in amplitude. That point was at 55Mhz. It should not have
reduced to less than 3.5 vertical divisions until beyond 100Mhz.
The output on my 191 is good. I checked it with a freq counter that was
checked against a double OCXO. ( STP2145A )
I found the topic "465B Degraded Bandwidth" through my search for the 465B topic relating to the sweep start misalignment. :-)

I suspect this topic will have the resolution to my bandwidth problem and am going to read through it for ideas.
Is the vertical deflection accurate?

Is the vertical deflection linear from the top to the bottom of the
CRT?

The bandwidth limiting switch activates two different sections shown
on schematic 3. At full bandwidth the two inductors are suppose to be
shorted out but what if just one of them was because one throw of one
pole of the switch was open?

You could measure the bandwidth at point TP322 or TP324 to see if the
problem is earlier or later in the vertical signal path.