Date   

Re: Storage CRT Modes Question

Craig Sawyers <c.sawyers@...>
 

I have yet to see a working Tektronix oscilloscope running properly in any storage mode, only in
normal mode which looks just like a conventional CRT. What does it look like in variable
persistence?
What I am getting at, is it similar to a conventional CRT in that the traces are illuminated on a
dark
screen? Then with the persistence control, I am controlling how long it takes the traces to fade
out??
This mode having the "normal" mode high contrast?

I have seen it other modes where the whole screen is lit dimly and the traces appear as darker lines
.
Low contrast. But until the scope, a 7834 is repaired, what I am seeing is really distorted.

Thanks, Stan KO6YB
On any of the Tektronix multimode storage scopes, forget totally anything to do with bistable. It is
what Tek eventually admitted was "low contrast" - which means a bright screen with a (slightly)
brighter trace. That is in contrast (!) to dedicated bistable mode oscilloscopes and computer screens
that Tek made, which were superbly high contrast. Low contrast bistable is a feature of the multimode
storage scopes only.

The problem is that the "first use" instructions in the 7834 manual have the user store in bistable
mode. The user sees a lousy contrast and winds the stored trace intensity up - and burns the trace it
into the screen. That is why most multimode storage CRT's have a faint burnt image on the screen.

So - only use the scope in variable persistence mode, either full screen or reduced scan. If you do
that you can store a single shot 1ns rise from a fast pulse generator.

Craig


Storage CRT Modes Question

brasscat
 

Hello the Forum,

I have yet to see a working Tektronix oscilloscope running properly in
any storage mode, only in normal mode which looks just like a
conventional CRT. What does it look like in variable persistence?
What I am getting at, is it similar to a conventional CRT in that the
traces are illuminated on a dark screen? Then with the persistence
control, I am controlling how long it takes the traces to fade out??
This mode having the "normal" mode high contrast?

I have seen it other modes where the whole screen is lit dimly and
the traces appear as darker lines . Low contrast. But until the scope,
a 7834 is repaired, what I am seeing is really distorted.

Thanks, Stan KO6YB


Re: Tek 7623A - Inverted and compressed Horizontal only from TB (was 7623A + 7A26 + 7B53)

Fabio Trevisan
 

On Wed, Mar 7, 2018 at 12:27 am, Roger Evans wrote:
Fabio,
If you look at the 7B53A manual schematic <8>, it shows the waveforms that
should appear on the A11, B11 backplane connectors and from there to the input
to U150. Are they both present and correct?
Regards,
Roger
Hi Roger,
Thanks... I didn't have chance to set it up properly on the bench for a probing session... That's probably my next step, when I'll also check the LVPS for actual voltages and ripple.
I did have chance to re-touch the Hor. Gain trimpot (R512) and found it was at its minimal setting... I turned it back and forth a few times, to be sure I wasn't having a problem of bad or no wiper contact and no... the trimpot is acting smoothly... and even at the maximum setting, the horizontal sweep increased to from 4.5 divisions to about 7 divisions. Still not enough, but at least it's responsive.
Rgrds,
Fabio


Re: Tek 7623A - Inverted and compressed Horizontal only from TB (was 7623A + 7A26 + 7B53)

Roger Evans
 

Fabio,

If you look at the 7B53A manual schematic <8>, it shows the waveforms that should appear on the A11, B11 backplane connectors and from there to the input to U150. Are they both present and correct?

Regards,

Roger


Re: Capacitors Question?

Ed Breya
 

I too have seen plenty of bad electrolytic caps in all sorts of gear, especially consumer electronics. The problems haven't necessarily been the same type or cause as the infamous bad SMT caps we find in that era of Tek stuff. In consumer gear, it may be from the plague, or due to maximizing cheapness, with caps that aren't rated sufficiently.

It boils down (so to speak) to three failure types, regardless of component style - leakers, puffers, and just plain bad. Leakers are the worst because of the possible damage done by the electrolyte. Puffers are obviously shot - puffed up from too much internal pressure and possibly with safety vent features opened up. They may also be leakers, but most I've seen had no juices around, just dry and open. Just plain bad ones may happen due to various common and normal failures always associated with caps, and are the hardest to find because they show no obvious physical symptoms. I've also had leakers that did no damage at all, and were easy to find by the wet spots around them that would shine, or gather dust. The damage risk depends on the electrolyte and time.

BTW there is an extreme form of puffer - one that has the can blown off entirely. I've seen that once or twice.

Ed


Re: Capacitors Question?

 

A large part of my business is TV repair. The modern LCD TV motherboards are just as unreliable as the older 80's - 90's first generation SMD motherboards.
It is the norm that I have to replace ALL the SMD electrolytics on a 2-year-old LCD TV, to get it back to working condition (Other service centers tell the customer "You need a new board").

This high failure rate is due to mainly ONE cause - the SMD baking process.
All SMD components are glued onto the PCB, and then baked in an oven at about 300C to flow the solder onto the joints.
Just imagine what that does to the electrolyte inside the caps.

Maybe Vishay, Nichicon and Panasonic caps are built to withstand that heat and pressure during baking, but when was the last time you saw any of those quality caps inside a consumer-grade TV?

So, as long as baking PCB's is an integral part of production, the problem of short lifetimes of SMD electrolytics is NOT going to go away any time soon.


Re: Capacitors Question?

toby@...
 

On 2018-03-06 4:25 PM, Chuck Harris wrote:
Not to put too fine a point on my nitpicking, but
AFAIK, the capacitor plague applied only to radial
leaded, low ESR electrolytic capacitors, not to
SMD electrolytic capacitors.

The problem mostly appeared on computer motherboards,
and on graphics cards. The electrolyte would etch
through the factory applied anodize coating, which
was the capacitor's dielectric. When this dielectric
layer was thin enough, the leakage current the capacitor
drew would climb, and the capacitor would get hot.

The heat made the electrolyte boil, and the cap would
blow out its bottom rubber plug, leaving the cap all
akimbo, or it would "dome up" the the explosion relief
on the top, or sides, of the capacitor.
I've seen it on dozens of LCD inverter boards. In my unlearned opinion,
though some specific plagues may have occurred, it's a general problem
due to the cheapest electrolytics ("CapXon" brand stands out) being
built into consumer/office products, simply making them disposable after
a couple of years.

My introduction to the whole issue was when an ex-boss put his very nice
twin Samsung LCDs in the dumpster. I took them home and gave them a new
lease of life with $2 of caps. Fixed dozens more after that.
http://badcaps.net is a useful resource.

--T


-Chuck Harris

Dennis Tillman W7PF wrote:
Hi Michael,

Don't do anything until you read this article which explains the problem in detail:
https://en.wikipedia.org/wiki/Capacitor_plague

Dennis Tillman W7PF


-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: Tuesday, March 06, 2018 11:26 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Capacitors Question?

The problem will never really be completely solved, as long as manufacture involves putting a plastic/rubber sealed, liquid filled, component into an oven heated to soldering temperatures as a means soldering its leads to the board. You are heating up a lot of things that don't want to be heated up, just to solder a couple of tiny little tabs to the board. Heat them a little too hot, or a little too long (same thing), and the seal will be damaged, and won't keep the electrolyte inside of the capacitor.



Re: SG505 THD issues

EJP
 

I asked this question about a hundred years ago: my AA501/01/02 doesn't have R1038, the 3H adjustment. Instead it has a tripod of two resistors and a diode (or possibly a small capacitor, can't see it clearly). When I asked it before somebody responded that it was a known production modification. Does anybody remember or know anything about this?

EJP


Re: Capacitors Question?

Mlynch001
 

Well, I am going to keep a close watch on this machine. It takes all of 5 minutes to get it out of the case and I can spend an hour or so inspecting the boards and caps every so often and before any performance issues rear their ugly heads. .

Michael Lynch

mlynch002@...

TEK 2440A
TEK TDS360
TEK TDS460A


Re: Capacitors Question?

Glenn Little
 

When it starts to show problems, there will probably already be board damage.
That scope is 20 years old, well past the design life of the capacitors which was probably 2000 hours.

At the first sign of trouble with a Panasonic DVC pro tape deck, all board capacitors were changed.
The cost of the repair was far better than trying to find a functional replacement board.

Glenn

On 3/6/2018 11:50 AM, Mlynch001 wrote:
We all know the horror stories about the leaky capacitors in TEK Scopes. This may have been answered, however, I cannot find this in a search. I am thinking that the first Surface mounted caps were used in the late 80's and early 90's and these were the ones that had serious electrolyte leakage issues. My question is, about WHEN was this issue solved so that these types of caps were no longer a serious problem? I have a TDS460A that has an inspection date on the CRT of mid 1998 and the caps on the main board look beautiful. Solder joints are clean and bright, there is no apparent leakage or corrosion present. The scope works fine, so I do not want to mess with it unless it begins to exhibit problems.

Michael Lynch

mlynch002@gmail.com

TEK 2440A
TEK TDS360
TEK TDS460A


--
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Amateur Callsign: WB4UIV wb4uiv@arrl.net AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"


Re: Tek 7623A - Inverted and compressed Horizontal only from TB (was 7623A + 7A26 + 7B53)

Fabio Trevisan
 

<dadhills@mindspring.com> wrote:

Someone switched the wires to the horizontal deflection plates on the CRT?

Dave
Hi Dave... Nope... Deflection plate wires are in their right place and...
besides, readout is not inverted.
Thanks for the headsup.
Rgrds,
FT




Re: Tek 7623A - Inverted and compressed Horizontal only from TB (was 7623A + 7A26 + 7B53)

Dave Hills
 

Never mind, just saw the readout is OK.  Sorry, my bad
Dave


Re: Tek 7623A - Inverted and compressed Horizontal only from TB (was 7623A + 7A26 + 7B53)

Dave Hills
 

Someone switched the wires to the horizontal deflection plates on the CRT?

Dave


Re: Capacitors Question?

Mlynch001
 

Thank You Dennis!


Re: Capacitors Question?

Mlynch001
 

Chuck,
As I understand the issue, it is ALL capacitors in almost all equipment manufactured in late 80's to early 90's, I have seen video of destroyed boards in various types of equipment, including TEKTRONIX Scopes, with leaky SMD electrolytic caps. I was concerned enough that I took my machine apart and gave it a good going over. Regardless, the boards look great and solder joints in my machine are shiny, like chrome. They are really nice, with no sign of even the slightest corrosion. I looked them over with a Magnifying glass and a good strong light. This made me feel really good about the machine. Also the fact that this is a fairly late version of the TDS460A series, probably cannot hurt. I appreciate all the advice and guidance.


Tek 7623A - Inverted and compressed Horizontal only from TB (was 7623A + 7A26 + 7B53)

Fabio Trevisan
 
Edited

Hello guys,
After having purchased that of my previous topic (see subject), and initially discussed its issues, I'll separate now the topics.
Here, I focus on the rather funny behavior of the Horizontal axis... as follows:
1. It's compressed... Full sweep covers only about 3.5 divisions.
2. It moves backwards (right to left)
3. Problem doesn't affect readout (readout is correctly spanning the whole screen width and it's not inverted).

What is already checked / ruled out:
a. It's not the TB plugin... I have 2 TBs (of which, one wasn't working initially, but I found what was wrong with it), and both exhibits the same behavior, leading me to conclude that the problem is in the mainframe hor. amplifier.
b. Pressing x10 on the plugin, makes the sweep extends beyond screen, which leads to conclude that the Hor. amplifier is well capable of the output voltage span.
c. Either at x1 or at X10, the sweep is linear... (although compressed)
b. I already checked the harmonica connector P501 going into the A6 HOR. AMP. board and it's not inverted. Damn! I could bet it was it... But not!
c. I already removed and re-seated the Hor. Channel Switcher IC (U510). The socket is the dreaded Texas, but it doesn't seem there's a bad contact issue here (U510 pins are gold plated).

What has been already advised and I`m pending to check:
a. L.V. Power supply voltages and ripple. I know, that should have been my first stop.. but as soon as i opened it, I found the FAN was stuck (dried out, sticky oil) so I fixed that ahead of everything else.
b. Probing around the Horizontal Channel switcher IC (U510) and check if all voltages are present.

QUESTIONS:
=> What is the nominal deflection factor of the 7000 series mainframe inputs (Diff Volt / Div. of deflection). I tried to find it on the specs, but it only says a blunt: "Compatible with all 7000 series plug-in units"
=> Is this IC 155-0022-00 a common failure?

I am posting pictures under title Tek7623a B060527...
https://groups.io/g/TekScopes/album?id=35474

Thanks for any advice and Rgrds,

Fabio


Re: What calibration items to buy.

Harvey White
 

On Tue, 6 Mar 2018 16:32:03 -0500, you wrote:

Close, but how about this scenario:
I'll guess.

I have a 5-1/2 dig DMM (dc) with 200mv low range.
OK, then LSD displayed = 10 uv.

I have a voltage ref standard with 1uv resolution.
Got one of them, too.
I know the std is good in the 10uv slot but may be off in the 1mv.
Then anything involving that digit is suspect, which carries over to
the next digit in what I'd say is a possible 1 digit error.
Can I calibrate the DMM to it’s full spec?
I'd say no. The last digit is uncertain (could be anything), which I
think could cause the next digit (100 uv) to be off by one.
Or am I missing something.
What if the DMM was 2v low range?
And 5 1/2 digits the lsb is 100 uv, see above with uncertainty about
the 100 uv digit.

Note I don’t need to prove cal to anyone but myself.
Well, that's what I think will happen. Let's see if I got it right.

Harvey


Sent from kjo iPhone



Re: SG505 THD issues

Craig Sawyers <c.sawyers@...>
 

I don't think so. By subterfuge I can get it to measure .0008%, at 100kHz with tiltering, as the
AA501
only goes up to 300kHz. Dennis' statement is further evidence.

But I am going to revisit the AA501's calibration, as there is a 3HD adjustment that I've never
made.
Well yes - if you filter of course you are going to see a lower reading, as you will if you use
weighting.

The numbers I quoted were straight from the AA501 manual. But if you think that your SG505's are
misbehaving nonetheless then so be it.

You'll know for certain if you knock up a twin-T passive filter at say 1kHz (or any other frequency
that takes your fancy) and look at the harmonics on a spectrum analyser. But that is the only way you
will know, because any other way will just give a system level measurement (i.e. of the SG505 and
AA501 taken together)

Craig


Re: What calibration items to buy.

Kevin Oconnor
 

Close, but how about this scenario:
I have a 5-1/2 dig DMM (dc) with 200mv low range.
I have a voltage ref standard with 1uv resolution.
I know the std is good in the 10uv slot but may be off in the 1mv.
Can I calibrate the DMM to it’s full spec?
Or am I missing something.
What if the DMM was 2v low range?
Note I don’t need to prove cal to anyone but myself.

Sent from kjo iPhone


Re: OT: Homebrew scanning electron microscopes

Chuck Harris <cfharris@...>
 

Think of the STM as being more like dragging a phonograph
needle over the atoms in the surface of a material. The
STM needle doesn't actually touch, but comes as close as
possible to touching without actually doing so. it can
see the actual atoms in a gold object.

-Chuck Harris

Brad Thompson wrote:

Hello--

Apropos of an earlier discussion, I came across the following web page:

http://www.opencircuits.com/Atomic_microscope

Very interesting, and no need for a high vacuum(?).

73--

Brad AA1IP

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