Date   

Re: New Member Dead 7704

Jerry Massengale <jmassen418@...>
 

92% alcohol from walmart is fine with cotton swabs

On Thu, Jan 5, 2017 at 3:49 PM, volvoboy242@... [TekScopes] <
TekScopes@...> wrote:



I'll clean the contacts with CRC and a PEC pad, unless there is a better
way. I'll post an update later.

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



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


Re: Update on 2465

Joseph Tatum
 

Thanks Bill,

That is basically what happened to me. I took the readout board out and the little plastic card retainer popped out in two pieces. I have repaired it now. Stuck it together with my soldering iron then added some of the 3 sec, ultra violet cured glue. It waved about because that was broken plus I had removed the inner cover.

I had looked at Digikey but I need to learn how to navigate their catalog without just bringing up one page at a time. I will use the number you gave now. I did jumper in a fuse I had on hand and that fuse is all that was damaged.


Re: New Member Dead 7704

volvoboy242@...
 

I'll clean the contacts with CRC and a PEC pad, unless there is a better way. I'll post an update later.


Re: New Member Dead 7704

volvoboy242@...
 

Downloaded the pdf. You're right. I was twisting knobs at random.
I read through and set the scope as per TEK 7704 Instruction pdf initially but until wiggling, twisting and pushing every knob and switch, there was no activity at all on screen.
The youtube vid actually captured the first blip and was a surprise to me.
I expected to show you all a blank screen.
As for my knowledge of oscilloscopes, my erratic Velleman was used to diagnose intermittent automotive drivability issues.
Obsolete now, with data logging.


I did replace a power supply transistor in it once, which was a service bulletin from Velleman.
So I guess that would be my oscilloscope repair experience!


Re: Update on 2465

Bill Spratt
 

I also had that fuse blown by the readout board contacting the chassis. The card guide had broken and popped out so it wasn't constrained at all as I rotated the scope. I temporarily jumpered it to F1101 since I don't have the option that would use it. I used a replacement from Digi-Key for the 5V fuse (F1102) F3174CT-ND $0.75, FUSE BRD MNT 5A 125VAC/VDC AXIAL

Bill


Re: New Member Dead 7704

Jerry Massengale <jmassen418@...>
 

The readout is encoded by current through the interface and is sensitive to
poor contact. a good cleaning of the connectors at the rear of each module
is needed. also ensure the modules a latched in.


On Thu, Jan 5, 2017 at 11:31 AM, volvoboy242@... [TekScopes] <
TekScopes@...> wrote:



I have swapped the plugins around in their respective A/B slots but I
haven't tried swapping them from horizontal/vertical slots. I have wiggle
tested the plugins to see if bad contacts might be causing problems.
I tried wiggling what I think are the 10 number chips on the display board
as one or two of the characters seem to flicker intermittently.
What I did made no difference.
I'll give your suggestion a try.
The display works very intermittently and usually, the only way to see
anything on screen is with the beam finder.
I tried to pull a square wave off my handheld while the 7704 was "working"
but got this:
https://groups.yahoo.com/neo/groups/TekScopes/photos/photostream/lightbox/
462709026?orderBy=mtime&sortOrder=desc&photoFilter=ALL#zax/462709026
https://groups.yahoo.com/neo/groups/TekScopes/photos/photostream/lightbox/
462709026?orderBy=mtime&sortOrder=desc&photoFilter=ALL#zax/462709026


I downloaded the generic troubleshooting guide and the 7704 operating
manual.

I haven't found the manuals for my plugins yet.


The other time plugin I accidentally bought ( ) should arrive today.
I'll be able to switch back and forth for comparison.
I'll post results later.


It would probably help if I knew something about electronics, other then
having excellent unsoldering/soldering skills and being able to read a
DVOM!
I'm pretty sure that everything has to actually hit the screen of the CRT
before I can troubleshoot the rest of the scope.
Again, the boards inside look very clean, not stinky and nothing I can see
is burned or exploded.
I haven't touched anything with DVOM or scope as I wouldn't know what I
was looking at anyway.
If you guys want me to check something or try swapping something around,
let me know.
I'll post back with pics, videos or values....whatever you ask for.
I've got good hands but I'm a monkey with a Tek 7704.







Re: New Member Dead 7704

 

Your knowledge of soldering and a DVOM isn't going to help you to understand
an oscilloscope. Get a copy of "The XYZs of Oscilloscopes" and read it
thoroughly before doing anything else.

You can download it here
http://info.tek.com/rs/584-WPH-840/images/XYZs-of-Oscilloscopes_03W_8605_7.p
df

From your YouTube video it appears you are just randomly turning knobs and
buttons. Read the section of the 7704 manual called "First Time Operation"
and set the scope and plugins up accordingly. You will need a BNC to BNC
cable to connect the vertical plugin to the calibrator.

Now each time you start the scope you will be in a known good state that
should result (when all is finally OK with the scope) in a square wave
waveform on the CRT.

Once you have the cable you need and you have set the scope up properly
according to the First Time Operation instructions take a picture or a
YouTube video of what happens on the CRT. Also take a picture of the entire
front of the scope so we can verify it is setup properly.

Never mind about the readout. That is a minor problem for now. Getting a
good display is your big problem. After seeing the pictures I don't think
swapping the 7B53 over to a vertical slot will tell us anything more.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: Thursday, January 05, 2017 9:31 AM
To: TekScopes@...
Subject: [TekScopes] Re: New Member Dead 7704

I have swapped the plugins around in their respective A/B slots but I
haven't tried swapping them from horizontal/vertical slots. I have wiggle
tested the plugins to see if bad contacts might be causing problems.
I tried wiggling what I think are the 10 number chips on the display board
as one or two of the characters seem to flicker intermittently.
What I did made no difference.
I'll give your suggestion a try.
The display works very intermittently and usually, the only way to see
anything on screen is with the beam finder.
I tried to pull a square wave off my handheld while the 7704 was "working"
but got this:

https://groups.yahoo.com/neo/groups/TekScopes/photos/photostream/lightbox/46
2709026?orderBy=mtime&sortOrder=desc&photoFilter=ALL#zax/462709026
https://groups.yahoo.com/neo/groups/TekScopes/photos/photostream/lightbox/46
2709026?orderBy=mtime&sortOrder=desc&photoFilter=ALL#zax/462709026


I downloaded the generic troubleshooting guide and the 7704 operating
manual.

I haven't found the manuals for my plugins yet.


The other time plugin I accidentally bought ( ) should arrive today.
I'll be able to switch back and forth for comparison.
I'll post results later.


It would probably help if I knew something about electronics, other then
having excellent unsoldering/soldering skills and being able to read a DVOM!
I'm pretty sure that everything has to actually hit the screen of the CRT
before I can troubleshoot the rest of the scope.
Again, the boards inside look very clean, not stinky and nothing I can see
is burned or exploded.
I haven't touched anything with DVOM or scope as I wouldn't know what I was
looking at anyway.
If you guys want me to check something or try swapping something around,
let me know.
I'll post back with pics, videos or values....whatever you ask for.
I've got good hands but I'm a monkey with a Tek 7704.








------------------------------------
Posted by: volvoboy242@...
------------------------------------


------------------------------------

Yahoo Groups Links


Re: TDS754D CRT

David Wilson
 

I had my eyes on that LCD kit you mentioned. Have you or anyone had experience with this kit?


Re: TDS754D CRT

Bruce Lane
 

It might be caps, but it might also be the transformer itself starting
to go bad. You might want to (for the long run) consider replacing the
entire CRT assembly with a nice flat-panel LCD.

http://www.newscope.info/home.html/2001/9001.html

No matter what, happy tweaking.

On 05-Jan-17 08:43, david.wilson92@... [TekScopes] wrote:
I am debating with myself and I think I need your help.

This concerns the CRT and driver board. I'm about to removing this part for inspection. Looking down from the top I don't notice anything broken or burnt visually.

I read that a high pitch sound coming from the fly back transformer is a indication that it is failing. I read that a dim crt usually means it is getting tired, though sometimes it might be the driver board typically it is the crt.

I read on a crt tv forum that a delay before a picture should already come in is a indicator of a dried / bad capacitor. Recapping the board might fix the delay before picture but it might not fix the wining sound or dim picture I seem to have. When I recapped the TDS380 the picture was noticeably sharper.

Since the display still works I could go ahead and recap it and get what I can out of it. Maybe finding a decent CRT is really all I need to get things going like new again. Maybe, don't know about the flyback.

Picture is stable by the way. Noticing no wobble or jitter.

So what is your take on the fly back transformer? Should I recap the board?

Thanks

------------------------------------
Posted by: david.wilson92@...
------------------------------------


------------------------------------

Yahoo Groups Links



--
---
Bruce Lane, ARS KC7GR
http://www.bluefeathertech.com
kyrrin (at) bluefeathertech dot com
"Quando Omni Flunkus Moritati" (Red Green)


Re: TDS754D CRT

David Wilson
 

Based on my findings both are color driver boards and have a somewhat similar physical layout.

I posted a picture of the driver board if you would like to take a look.

671-2373-589-1344-02

How do you measure capacitor ripple?


Re: TDS754D CRT

 

Hello,

On late CRT TVs there was also cathode current measurement that could delay
the time to bring a picture up when the CRT was worn (Philips).

For whining sounds poke around with a chopstick at any ferrite core, the
most common cause is a loose core. Bad capacitors can be a cause too, not
limited to electrolytics.

Measuring ripple across electrolytics should give you a clue before
actually replacing them.
Beware of electrolytics in the flyback primary drive path.

Often a failing flyback will come with other symptoms: Heat, smells,
blooming picture or measurable oscillations on at least one winding.

Does this scope use the same CRT driver board as the TDS 544?

Paul



Le jeudi 5 janvier 2017, david.wilson92@... [TekScopes] <
TekScopes@...> a écrit :

I am debating with myself and I think I need your help.

This concerns the CRT and driver board. I'm about to removing this part
for inspection. Looking down from the top I don't notice anything broken or
burnt visually.

I read that a high pitch sound coming from the fly back transformer is a
indication that it is failing. I read that a dim crt usually means it is
getting tired, though sometimes it might be the driver board typically it
is the crt.

I read on a crt tv forum that a delay before a picture should already come
in is a indicator of a dried / bad capacitor. Recapping the board might fix
the delay before picture but it might not fix the wining sound or dim
picture I seem to have. When I recapped the TDS380 the picture was
noticeably sharper.

Since the display still works I could go ahead and recap it and get what I
can out of it. Maybe finding a decent CRT is really all I need to get
things going like new again. Maybe, don't know about the flyback.

Picture is stable by the way. Noticing no wobble or jitter.

So what is your take on the fly back transformer? Should I recap the board?

Thanks

------------------------------------
Posted by: david.wilson92@... <javascript:;>
------------------------------------


------------------------------------

Yahoo Groups Links




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


Re: New Member Dead 7704

volvoboy242@...
 

I have swapped the plugins around in their respective A/B slots but I haven't tried swapping them from horizontal/vertical slots. I have wiggle tested the plugins to see if bad contacts might be causing problems.
I tried wiggling what I think are the 10 number chips on the display board as one or two of the characters seem to flicker intermittently.
What I did made no difference.
I'll give your suggestion a try.
The display works very intermittently and usually, the only way to see anything on screen is with the beam finder.
I tried to pull a square wave off my handheld while the 7704 was "working" but got this:
https://groups.yahoo.com/neo/groups/TekScopes/photos/photostream/lightbox/462709026?orderBy=mtime&sortOrder=desc&photoFilter=ALL#zax/462709026 https://groups.yahoo.com/neo/groups/TekScopes/photos/photostream/lightbox/462709026?orderBy=mtime&sortOrder=desc&photoFilter=ALL#zax/462709026


I downloaded the generic troubleshooting guide and the 7704 operating manual.

I haven't found the manuals for my plugins yet.


The other time plugin I accidentally bought ( ) should arrive today.
I'll be able to switch back and forth for comparison.
I'll post results later.


It would probably help if I knew something about electronics, other then having excellent unsoldering/soldering skills and being able to read a DVOM!
I'm pretty sure that everything has to actually hit the screen of the CRT before I can troubleshoot the rest of the scope.
Again, the boards inside look very clean, not stinky and nothing I can see is burned or exploded.
I haven't touched anything with DVOM or scope as I wouldn't know what I was looking at anyway.
If you guys want me to check something or try swapping something around, let me know.
I'll post back with pics, videos or values....whatever you ask for.
I've got good hands but I'm a monkey with a Tek 7704.


Re: Update on 2465

Chuck Harris
 

That the 2465 has a quadrapole lens comes from a combination
of observation... I have a busted CRT... and reading about it
in one of the tek magazines.

When you look at your 485, do notice that the CRT's screen is
the same size as the 454A's, 36% smaller than the 2465.

That 36% is very significant in terms of spot size.

The 485, doesn't have any lens for increasing the deflection
sensitivity, so, that too helps the impression of size.

Another factor that makes the 2465 look fuzzy is all of the
switching that is going on to handle the display readout.
That switching causes a tiny, almost imperceptible tail on
the trace every time the beam flits away from the trace to
draw part of the readout. The trace looks better with the
readout off.

Try comparing your 2465 at 20MHz BWL, with the 485 at 20MHz
BWL. Take a measurement of the beam diameter at the same
intensity, and compare it to the 2465. In my experience,
the 2465's is about a third larger.

-Chuck Harris

Sigurður Ásgeirsson siggi@... [TekScopes] wrote:

Hey Chuck,

thanks for the correction - can you share where you come by this
information?
Naively I looked at the HV and CRT circuits, and took the -900V line from
the HV supply towards the front of the CRT neck to go to an expansion mesh.
Hmmm, maybe just a case of RTFM :). The -900 is termed "slot lens voltage"
in the Cathode Supply section of the Theory of Operation.

Incidentally find that there's no contest between the spot size and trace
clarity between my 2465 and my 485, the 485 has a much clearer trace. At
one point I routed the X/Y/Z from my HP8566B's display unit to a scope for
diagnostics of the display unit, and the 485 was the only scope I own that
was able to resolve the detail. See <https://goo.gl/photos/21ASGFDsU2Zd9qA66>
I believe that display is 1024x1024.
Maybe this is just a sign that my 2465 needs some TLC, though after I got
the 2467 she'd be better with someone who'd use her more, probably :).
The dot size on my 2467 is quite absurd in comparison to either of those -
though it wins hands down on brightness (which is the MCP trade-off).

Siggi


Re: TDS754D CRT

David Wilson
 

I am debating with myself and I think I need your help.

This concerns the CRT and driver board. I'm about to removing this part for inspection. Looking down from the top I don't notice anything broken or burnt visually.

I read that a high pitch sound coming from the fly back transformer is a indication that it is failing. I read that a dim crt usually means it is getting tired, though sometimes it might be the driver board typically it is the crt.

I read on a crt tv forum that a delay before a picture should already come in is a indicator of a dried / bad capacitor. Recapping the board might fix the delay before picture but it might not fix the wining sound or dim picture I seem to have. When I recapped the TDS380 the picture was noticeably sharper.

Since the display still works I could go ahead and recap it and get what I can out of it. Maybe finding a decent CRT is really all I need to get things going like new again. Maybe, don't know about the flyback.

Picture is stable by the way. Noticing no wobble or jitter.

So what is your take on the fly back transformer? Should I recap the board?

Thanks


Re: Update on 2465

Joseph Tatum
 

Thanks Chuck, That is what Siggi says also. I did expect the beam to sharpen more but I understand your explanation and, as you say, is no big deal.


Re: Update on 2465

Joseph Tatum
 

Hello Siggi,

OK I actually was expecting the very sharply focused trace like the 454. Not really a problem as it it does focus. As to the focus pot, I would just have expected the focal adj to come more to the center rotation of the pot.

At this point I have to hold off for a while pursuing the original problem. With the inner cover off the readout board is pretty loose and I think it must have touched the ground when I moved the scope. One of the 5V fuses (F1102) is blown. Seems hard to find axial lead 5A fuse like it without ordering from Taiwan or Hong Kong. I may be able to tack in a larger fuse until I can get a proper replacement.


Re: Update on 2465

Siggi
 

Hey Chuck,

thanks for the correction - can you share where you come by this
information?
Naively I looked at the HV and CRT circuits, and took the -900V line from
the HV supply towards the front of the CRT neck to go to an expansion mesh.
Hmmm, maybe just a case of RTFM :). The -900 is termed "slot lens voltage"
in the Cathode Supply section of the Theory of Operation.

Incidentally find that there's no contest between the spot size and trace
clarity between my 2465 and my 485, the 485 has a much clearer trace. At
one point I routed the X/Y/Z from my HP8566B's display unit to a scope for
diagnostics of the display unit, and the 485 was the only scope I own that
was able to resolve the detail. See <https://goo.gl/photos/21ASGFDsU2Zd9qA66>
I believe that display is 1024x1024.
Maybe this is just a sign that my 2465 needs some TLC, though after I got
the 2467 she'd be better with someone who'd use her more, probably :).
The dot size on my 2467 is quite absurd in comparison to either of those -
though it wins hands down on brightness (which is the MCP trade-off).

Siggi

On Thu, 5 Jan 2017 at 10:14 Chuck Harris cfharris@... [TekScopes] <
TekScopes@...> wrote:



A minor nit: The 2465 family CRT does *not* have an
expansion mesh lens!

It uses a "box" lens based on a quadrapole design.

The quadrapole lens eliminates most of the distortion
and all of the flaring exhibited by the expansion mesh,
to the point where the beam size after expansion is almost
exactly the same as it would be with a longer CRT that
has no lens.

The 2465 family has a much shorter (2 inches) CRT with
a much larger (36% more area) screen than does the 454A.

If you could expand the 454A's screen the 36% from
8cm x 6.4ch to the 2465's 10cm x 8cm, the 454's dot
would be much larger than the 2465's.

The reason most people think the 2465 has a larger,
fuzzier beam, is because the beam incorporates all of
the extra noise due to its 400MHz deflection amplifier
bandwidth.

Reduce the bandwidth to 20MHz, and the beam size is
very compact.

-Chuck Harris


Re: TDS754D CRT

David Wilson
 

uppon taking the 754D apart I had a difficult time removing the front panel and I believe I developed a trick to remove it easier. On the right side remove the panel and carefully work your left to the CRT. A small flat screw driver will help the difficult tabs at the CRT end, gradually work with it and it will eventually come off. Helpful advice that seemed to work for me.


Re: Update on 2465

Chuck Harris
 

A minor nit: The 2465 family CRT does *not* have an
expansion mesh lens!

It uses a "box" lens based on a quadrapole design.

The quadrapole lens eliminates most of the distortion
and all of the flaring exhibited by the expansion mesh,
to the point where the beam size after expansion is almost
exactly the same as it would be with a longer CRT that
has no lens.

The 2465 family has a much shorter (2 inches) CRT with
a much larger (36% more area) screen than does the 454A.

If you could expand the 454A's screen the 36% from
8cm x 6.4ch to the 2465's 10cm x 8cm, the 454's dot
would be much larger than the 2465's.

The reason most people think the 2465 has a larger,
fuzzier beam, is because the beam incorporates all of
the extra noise due to its 400MHz deflection amplifier
bandwidth.

Reduce the bandwidth to 20MHz, and the beam size is
very compact.

-Chuck Harris

Sigurður Ásgeirsson siggi@... [TekScopes] wrote:

On Wed, 4 Jan 2017 at 06:45 tatumj1@... [TekScopes] <
TekScopes@...> wrote:
Also, you shouldn't expect the 2465 to match your 454A for trace clarity or
dot size, as the 2465's CRT has an expansion mesh.


Re: Update on 2465

Siggi
 

On Wed, 4 Jan 2017 at 06:45 tatumj1@... [TekScopes] <
TekScopes@...> wrote:



Good morning Siggi. It seems that the symptoms on this scope have
constantly changed from the time I turned it on. At first it only flashed a
few panel LEDs. Now, after warm up, seems to work close to normally, tend
now to think it may be the caps, As it gradually moves closer to working
properly, the distorted trace moves toward normal. I do think someone has
changed some of the caps. I don't think Tektronix installed the power
supply caps standing off the board on long leads more than 1/4 inch above
the board surface.

Intermittent trouble is the worst, I hope you get this sorted.
I am printing out all your responses to use as trouble shooting guide. I
appreciate your help very much.

My pleasure - please let us know what you find.
This has nothing to do with the problem we have been chasing, but I
noticed that the focus control only brings the screen into focus near the
full counter clockwise position of the pot. I am looking in the manual at
the focus control circuit for an adjustment for this.

There is a CRT adjustment procedure in the service manual. Section 5
starts with power supplies, then goes on to the CRT.
The CRT adjustment procedure will have a bunch of interacting adjustments -
it could be e.g. that the geometry pot has drifted. It may also help for a
scope that's been stored for a long time, to let the CRT "bake" for a few
hours to days with a low-intensity beam. See e.g. <
http://www.eevblog.com/forum/testgear/dim-oscilloscope-screen/msg554039/#msg554039
.
Also, you shouldn't expect the 2465 to match your 454A for trace clarity or
dot size, as the 2465's CRT has an expansion mesh.

I've only been through the CRT adjustment for my 2467, which has a very
different CRT, and it's been a couple of years, so I can't help much there.