Date   

Re: Trying to bring back a AA501

Dave Wise
 

That happened here a few weeks ago. Fluke 8000A DMM. After a transient, it would only display even digits. Turned out the 7447 display driver developed an internal short on its 1's input. The MOS A/D chip was fine. Whew!

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Chuck Harris via Groups.Io <cfharris=erols.com@groups.io>
Sent: Sunday, January 05, 2020 10:36 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Trying to bring back a AA501

I am having trouble imagining how a 15V CMOS device could spontaneously
generate 5V on one of its outputs.... I can see ~0V, or ~15V, or even 7.5V,
but 5V is an odd value for a device that has no resistors in it.

Are you sure that it isn't being bullied around by whatever it is driving?
old style CMOS has very little drive capability.

-Chuck Harris


Re: 454 screen brightness issues?

Chuck Harris <cfharris@...>
 

I saw that once in a 2456B's CRT. An internal weld between
a strap and an element broke, leaving an open circuit on
the CRT's intensity (control) grid .

The symptom was the intensity started out low, readout seemed
fine, and the beam could be moved with the intensity control,
but the beam kept getting brighter and brighter.

-Chuck Harris

Mlynch001 wrote:

I'm
wondering if maybe the grid assembly was knocked loose during shipping
maybe? I'm not intimately familiar with the CRT construction, so maybe
someone more well-acquainted with Tek's CRTs could give me some idea of
what may be going on...
While fixing my newest 465 I recall seeing a post where a 465 had a similar problem. The OP found an internally disconnected Grid pin. Here is the post.

https://groups.io/g/TekScopes/topic/tek_465_intensity_problem/7656664


Re: tek 7xx4 series brightness dimming after power on

Chuck Harris <cfharris@...>
 

There is a 5uf, wet tantalum capacitor, C171, in the z-axis output amplifier
that sometimes degrades to a condition between open and shorted. It has direct
control over the intensity.

Also everything down stream of that capacitor is the very high impedance DC
restorer circuitry. Any resistor 1M or higher is a reliability problem... as
is any capacitor that it services.

-Chuck Harris

Alberto, IZ2EWV wrote:

Hello dear friends,
I own three beautiful oscilloscopes from the series 7000: a 7904A, a 7104 and - the most recent arrival - a 7854.
Some of them had common issues, after powering on (failure at the RC snubber and the AC line filter - which I replaced with new components and everything come back to normality.
I ask you about a behavior that is common to the 7904A and the 7854: at power on, the traces and the readouts are bright, but after some minutes they dim: to restore the brightness it’s a matter of little correction on the related controls.
By the way, I ask you if it is a normal situation (e.g. “normal” at the time that the equipment was younger, by memory of somebody of yours) or if it is a sign of aging of some component in the main power supply or in the HV power supply. In this latter option, I ask you advice to let me get closer to the problem (I have the service manuals).

Tnx es 73 de Alberto, IZ2EWV




Re: 454 screen brightness issues?

Mlynch001
 

I'm
wondering if maybe the grid assembly was knocked loose during shipping
maybe? I'm not intimately familiar with the CRT construction, so maybe
someone more well-acquainted with Tek's CRTs could give me some idea of
what may be going on...
While fixing my newest 465 I recall seeing a post where a 465 had a similar problem. The OP found an internally disconnected Grid pin. Here is the post.

https://groups.io/g/TekScopes/topic/tek_465_intensity_problem/7656664

FWIW, I received a 465 in near mint condition as part of the purchase of a 485. I took a 465 and a 2215 as a group to get the 485. The 465 had a similar problem. I usually clean and DeOxit all the switches on any old scope that I get before anything else is attempted. Although the switch felt good, the beam finder worked properly when fully depressed and appeared to be in the correct position when released, in reality the Beam Finder on this scope was evidently "sticking sightly on" and creating some weird intermediate connection in the circuit and this cause a similar issue to what you are seeing on your 454. After cleaning and DeOxit the scope came back to normal, so a very simple fix in this case..

Best of luck
--
Michael Lynch
Dardanelle, AR


Re: tek 7xx4 series brightness dimming after power on

Eric
 

The 7904A has a screen protect - anti burn circuit. Mine functions exactly
the same as well. The service manual calls this out though I forget which
page it is on.

On Mon, Jan 6, 2020, 10:33 AM Tom Bowers <pvhengineering@gmail.com> wrote:

Hello,

I have a 7904A and it works exactly as you describe. I consider that
normal, nothing to worry about. Just a minor annoyance.

Tom Bowers


On Mon, Jan 6, 2020 at 8:29 AM Alberto, IZ2EWV <iz2ewv@gmail.com> wrote:

Hello dear friends,
I own three beautiful oscilloscopes from the series 7000: a 7904A, a 7104
and - the most recent arrival - a 7854.
Some of them had common issues, after powering on (failure at the RC
snubber and the AC line filter - which I replaced with new components and
everything come back to normality.
I ask you about a behavior that is common to the 7904A and the 7854: at
power on, the traces and the readouts are bright, but after some minutes
they dim: to restore the brightness it’s a matter of little correction on
the related controls.
By the way, I ask you if it is a normal situation (e.g. “normal” at the
time that the equipment was younger, by memory of somebody of yours) or
if
it is a sign of aging of some component in the main power supply or in
the
HV power supply. In this latter option, I ask you advice to let me get
closer to the problem (I have the service manuals).

Tnx es 73 de Alberto, IZ2EWV






Re: tek 7xx4 series brightness dimming after power on

Tom Bowers
 

Hello,

I have a 7904A and it works exactly as you describe. I consider that
normal, nothing to worry about. Just a minor annoyance.

Tom Bowers

On Mon, Jan 6, 2020 at 8:29 AM Alberto, IZ2EWV <iz2ewv@gmail.com> wrote:

Hello dear friends,
I own three beautiful oscilloscopes from the series 7000: a 7904A, a 7104
and - the most recent arrival - a 7854.
Some of them had common issues, after powering on (failure at the RC
snubber and the AC line filter - which I replaced with new components and
everything come back to normality.
I ask you about a behavior that is common to the 7904A and the 7854: at
power on, the traces and the readouts are bright, but after some minutes
they dim: to restore the brightness it’s a matter of little correction on
the related controls.
By the way, I ask you if it is a normal situation (e.g. “normal” at the
time that the equipment was younger, by memory of somebody of yours) or if
it is a sign of aging of some component in the main power supply or in the
HV power supply. In this latter option, I ask you advice to let me get
closer to the problem (I have the service manuals).

Tnx es 73 de Alberto, IZ2EWV




tek 7xx4 series brightness dimming after power on

Alberto, IZ2EWV
 

Hello dear friends,
I own three beautiful oscilloscopes from the series 7000: a 7904A, a 7104 and - the most recent arrival - a 7854.
Some of them had common issues, after powering on (failure at the RC snubber and the AC line filter - which I replaced with new components and everything come back to normality.
I ask you about a behavior that is common to the 7904A and the 7854: at power on, the traces and the readouts are bright, but after some minutes they dim: to restore the brightness it’s a matter of little correction on the related controls.
By the way, I ask you if it is a normal situation (e.g. “normal” at the time that the equipment was younger, by memory of somebody of yours) or if it is a sign of aging of some component in the main power supply or in the HV power supply. In this latter option, I ask you advice to let me get closer to the problem (I have the service manuals).

Tnx es 73 de Alberto, IZ2EWV


Re: Logic families

Mlynch001
 

On Sun, Jan 5, 2020 at 09:12 AM, Lawrance A. Schneider wrote:


Thank you Arden! I learned a lot by reading it.

Mr. Lynch, you wrote: I have an older TI Logic Cross reference that crosses
over many of the older Logic IC’s.

Could you post it?

Thank you, larry
Larry,

Here is that Older TI Logic Cross Reference link:

https://www.ti.com/lit/ml/scyb017a/scyb017a.pdf

I find this useful from time to time.



--
Michael Lynch
Dardanelle, AR


Re: 'Solder Rot'

Geoffrey Thomas
 

I would guess it had not been soldered correctly from the factory. I've had a intermittently faulty HP monitor that had the same problem, the component lead just hadn't "wetted" correctly. One soldered joint later, perfect.

Geoff.

On 06/01/2020 12:32, Tim Phillips wrote:
from Tim P (UK)
The posts re '465M junker' remind me of a post I sent a couple of years
ago. I had a 1S1 plug-in that was intermittent, sometimes OK, sometimes
just would not sample.
Did the usual things, re-seat transistors, clean switches, check sampling
bridge etc. Finally, I lifted the PCBs, thinking maybe a wire-clipping or
solder blob had got between the PCB and the chassis. Close examination with
a jewellers loupe and bright light showed a bad joint, where the solder
seemed to have parted from a transistor socket - there was a visible gap
between the solder fillet and the pin, not broken but as if the solder had
'shrunk'. Found a few other cases also. I guess solder ages like most
things, or sort-of-crystallises.
Tim


Re: Tektronix 570 Vacuum Tube Curve Tracer on eBay

Dan Cordova <danny_cordov@...>
 

There is one bomb which has a tube based radar.  It is being modernized and tubes will be replaced on the new version.

On Monday, January 6, 2020, 06:19:04 AM PST, Geoffrey Thomas <geoffreythomas@onetel.com> wrote:

I recall reading somewhere (years ago) that some military receivers were
running a few amps in the front end to protect against emp.
Anybody verify or was it an apocryphal tale/April fool article?

Geoff.

On 06/01/2020 01:59, Roy Thistle wrote:
On Sun, Jan  5, 2020 at 11:25 AM, Greg Muir wrote:


the vacuum tube equipment still possessed by the military for use when EMP
from a nuclear blast renders a portion of the solid-state hardware useless.
Hi Greg:
Although obviously I am privy to very little information about what the "military" has, or does not have... I am doubtful, if the military keeps any vacuum tube type equipment because of "transistorized" = solid state equipment failing due to NEMP. The reason I say this is that... at least the high EMF generated by the Type 1 pulse of a NEMP event requires relatively long conductors to couple energy. Small conducting paths; small inductor values, fully metallically shielded, and enclosed cases... besides other common EMP hardening measures... significantly null out NEMP effects.
That said... militaries are working on... and due claim to have... EMP weapons that act to produce extremely large local EMP pulse that can disable/destroy EMP hardened gear very locally... or so they say.
Cheers. Best regards and wishes.
Roy


Re: Tektronix 2465 for sale ...

tekscopegroup@...
 

On Mon, Jan 6, 2020 at 06:04 AM, Ancel wrote:
In the Caribbean
By any chance are you in SXM?


Re: Tektronix 570 Vacuum Tube Curve Tracer on eBay

Geoffrey Thomas
 

I recall reading somewhere (years ago) that some military receivers were running a few amps in the front end to protect against emp.
Anybody verify or was it an apocryphal tale/April fool article?

Geoff.

On 06/01/2020 01:59, Roy Thistle wrote:
On Sun, Jan 5, 2020 at 11:25 AM, Greg Muir wrote:


the vacuum tube equipment still possessed by the military for use when EMP
from a nuclear blast renders a portion of the solid-state hardware useless.
Hi Greg:
Although obviously I am privy to very little information about what the "military" has, or does not have... I am doubtful, if the military keeps any vacuum tube type equipment because of "transistorized" = solid state equipment failing due to NEMP. The reason I say this is that... at least the high EMF generated by the Type 1 pulse of a NEMP event requires relatively long conductors to couple energy. Small conducting paths; small inductor values, fully metallically shielded, and enclosed cases... besides other common EMP hardening measures... significantly null out NEMP effects.
That said... militaries are working on... and due claim to have... EMP weapons that act to produce extremely large local EMP pulse that can disable/destroy EMP hardened gear very locally... or so they say.
Cheers. Best regards and wishes.
Roy


Re: Tektronix 2465 for sale ...

 

In the Caribbean


Re: Tektronix 2245a Flickering Trace

Tony Fleming
 

First of all Harvey, Happy New Year 2020 and wishes of lots of health and
great ELECTRONS in your life!
If it wasn't for you, my scope would not work, so I trust you and wish you
are my neighbor!
Anyway, thanks for helping everyone here, including me. ( tonysfun.com and
click on MY VIDEOS to see how micro-knowledge functions in my very small
brain! ... ha ha ha)

Lastly, I wish you all HAPPY NEW YEAR 2020 and POSITIVE ELECTRON'S in your
life and scopes!

Tony

On Sun, Jan 5, 2020 at 10:35 PM Harvey White <madyn@dragonworks.info> wrote:

There are some tests you can do with a partially working scope, but you
are going to be very limited.

1) assuming horizontal sweep problems, you use an external ramp or the
"other" sweep if you have a dual sweep model.

2) if you have a horizontal amplifier problem, using the scope in XY
mode, even with the calibrator, can give you some idea of whether or not
it's the sweep or the amplifier.

3) if you have a dual channel scope, you can use a working channel to
debug the separate part of the vertical amplifier

These generally end up being go/no-go tests and are somewhat crude.

Function generators can make a very crude horizontal sweep. If they're
gated, then a gated ramp might work as a sweep.

Very crude, but better than nothing.

Generally, unless you have a scope specifically designed for self
diagnosis, you're better off with another, completely working, scope.

Even then, a scope designed for self diagnosis makes certain assumptions
about what's working, especially once you get past the "is the CPU
working...."

Harvey


On 1/4/2020 4:29 PM, Panos wrote:
I have read enough service manuals for the oscilloscopes, and till today
I didn't find any of them to mention, that someone can use the same faulty
scope (partially or totally) to repair his self.
But as always we can hope for something like that. After all, don't
they say that hope dies always last? :-)

In my opinion if you have time to play then do it by that way. But if
you want really to repair it, then proceed it with another oscilloscope.






Re: 'Solder Rot'

EricJ
 

It absolutely does. I was just reading a paper about this the other day. Several factors contribute to circuit failure due to aging. One being that the solder bond weakens apparently due to inter-metallic layer growth over time. There was a whole section dedicated to testing shear strength of aged surface mount joints. Leaded solder did much better than lead-free at retaining bond strength in those cases.

Several other factors mentioned and tested were the weakening of foil layers' (tracks and pads) adhesion to the boards (roughly halved over time), vias coming loose and separating from the fiberglass surface of the boards (apparently very common on heavy copper sections of the board due to thermal expansion of the copper and vias during soldering) and cracking and "tearing" of aged through-hole solder joints.

--Eric

On Jan 6, 2020 6:32 AM, Tim Phillips <timexucl@gmail.com> wrote:




from Tim P (UK)
The posts re '465M junker' remind me of a post I sent a couple of years
ago. I had a 1S1 plug-in that was intermittent, sometimes OK, sometimes
just would not sample.
Did the usual things, re-seat transistors, clean switches, check sampling
bridge etc. Finally, I lifted the PCBs, thinking maybe a wire-clipping or
solder blob had got between the PCB and the chassis. Close examination
with
a jewellers loupe and bright light showed a  bad joint, where the solder
seemed to have parted from a transistor socket - there was a visible gap
between the solder fillet and the pin, not broken but as if the solder had

'shrunk'. Found a few other cases also. I guess solder ages like most
things, or sort-of-crystallises.
Tim






Re: 454 screen brightness issues?

EB4APL
 

My experience with this symptom has been always a DC restorer problem, even I bought a defective R&S scope with this symptom and the problem was the DC restorer diodes as I was figuring out.

Also I had a problem with a non operating focus control and the cause was the focus DC restorer diodes also. I think that these diodes are stressed in some way and with time they develop leaks that make the circuit to fail. I tried to measure these leaks, but it happens when they are subjected to HV and I don't have the right equipment to test them, so I replaced all the diodes in the failing DC restorer (3 or 4, depending on the circuit) and the problem solved. Since most of the work is to reach this part of the scope, changing all of them is a good advice.

The problem could be elsewhere, of course, but if you have right voltages in the CRT the DC restorer is a good candidate.

Regards,

Ignacio

El 06/01/2020 a las 0:29, Jack Ohme escribió:
I received a verified-working Tek 454 scope from eBay, and it seems to now,
after shipping, have an issue where the CRT is incredibly bright, like
we're talking burn-a-hole-in-your-vision bright. Naturally I immediately
powered it off, fearing damage to the CRT, and upon turning it back on to
test it, dialing the trace way off the screen, there is still a sizeable,
though not dangerous, glow from electron splash. The grid appears to be at
-150 to -190 volts depending on the brightness setting, and the grid bias
trimmer does essentially nothing, moving the grid bias by around 8 volts
only (not sure if this is a fault or just the design). I checked for a G-K
short, but its about 25 megaohm between (in-circuit), so looks good. I'm
wondering if maybe the grid assembly was knocked loose during shipping
maybe? I'm not intimately familiar with the CRT construction, so maybe
someone more well-acquainted with Tek's CRTs could give me some idea of
what may be going on...


Re: My email address was changed by Groups.io my request for contributions

magnustoelle
 

Good Day,

Dennis, a word of thanks for looking after this group and for all the time you have spent in order to keep this a friendly and informative place!

I was happy to contribute 20. Sent per paypal today; the 1€-fee was well spent.

Cheers,

Magnus

On 01/01/2020 19:02, Dennis Tillman W7PF wrote:
HI Albert,
Groups.io changed my real email address without my knowing it so non-members could not search our posts and harvest our email addresses. I didn't know this is what groups.io did. The only wat I can tell you what the correct email address is if I spell it out like this:
dennis at ridesoft dot com.
You can figure out from this what my email address really is.
Dennis

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Albert Otten
Sent: Wednesday, January 01, 2020 3:29 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] My email address was changed by Groups.io my request for contributions

There is one more issue Dennis. I use the website. There @Dennis... is a link which points to https://groups.io/profile/Dennis_Tillman_W7PF . This is not your profile at Tekscopes since /g/Tekscopes is missing from the path. I can read your Tekscopes profile, but I get a "404 not found" error on that link.

Albert




'Solder Rot'

Tim Phillips
 

from Tim P (UK)
The posts re '465M junker' remind me of a post I sent a couple of years
ago. I had a 1S1 plug-in that was intermittent, sometimes OK, sometimes
just would not sample.
Did the usual things, re-seat transistors, clean switches, check sampling
bridge etc. Finally, I lifted the PCBs, thinking maybe a wire-clipping or
solder blob had got between the PCB and the chassis. Close examination with
a jewellers loupe and bright light showed a bad joint, where the solder
seemed to have parted from a transistor socket - there was a visible gap
between the solder fillet and the pin, not broken but as if the solder had
'shrunk'. Found a few other cases also. I guess solder ages like most
things, or sort-of-crystallises.
Tim


Re: 454 screen brightness issues?

John
 

PS: also the 7M5 in parallel with that pot.


Re: 454 screen brightness issues?

John
 

I assume your -1960V is checked ok. Ditto all three LV supplies. Have a look at the chain of 10M resistors R1442-6 : ohms law suggests you should have a much larger grid swing from the bias pot?

John

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