Date   
Re: Tek 2465 Problem

Panos
 

Hi,
this is well known to me, and the voltages seen more than good from the first moment.The subject is that I didn't give the proper attention initially in a low ripple at the + 5 volt line.

Now with the new replaced diodes, some things on screen changed for the better.

A small ripple on the beam during the cold start up disappeared. The same the beam from the cold start up appear immediately and not after 20 seconds. Even the thickness of the trace is now thinner after the warm up time of oscilloscope.

I'm just unfortunate who the diodes were failed by such a rare way. :-\

Re: Tek 485 short sweep

Reed Dickinson
 

I have had this problem with a few 485's I have refurbished and every time it was the X6 voltage multiplier U1600 located on the A15 Transformer Board.  It is supplied by Voltage Multiplier Inc., 8711 W. Roosevelt, Visalia CA  93291, their part number VM176 and sells for $175 in small quantities.  
You can test if U1600 is working but you must be very careful or you will burn out U660, the vertical output IC.  To test U1600 proceed as follows:
1)  Unsolder the connections from the A7 vertical board going from U660 to the CRT.  This removes part of the arcing path which might be present in the next few steps.2)  Pull out the connections to the horizontal plates present near the rear of the A11 Horizontal Amp board.3)  Unplug the two wires going from the hybrid board to the forward connections of the distributed vertical plates.
You have now isolated the CRT and eliminated any chance of damage to any semiconductor components due to a large current surge.  Now start your 485 up and run it for about a minute.  Turn the power off and immediately pull out the high voltage connector going from U1600 to the CRT.  If you get a nice fat spark as the connector clears the plastic socket then you know the X6 multiplier is working.  If you get a spark the problem is in the horizontal output circuit.  Replace all the CRT connections removed in the above numbered steps. If you get no spark replace U1600.  I always replace R1602, a 15K, 1/2W resistor but do not use a film resistor, use a carbon composition one.
Reed Dickinsonreed714@...

On Monday, December 23, 2019, 09:16:12 PM PST, Harvey White <madyn@...> wrote:

The horizontal input has a calibrated deflection factor.  Adjust the
vertical to the same factor, put a sinewave into both, and you should
get a 45 degree line.

If the amplifier is ok, and the problem is in the sweep, then you should
be able to center the horizontal dot (no sweep, x only). It should have
about the same travel (L and R) with the positioning control.

If you have another scope, you can check for linearity by borrowing a
ramp from it and using it for a horizontal sweep. Good function
generator will also work.

Harvey


On 12/23/2019 1:26 AM, stephen white wrote:
How can we narrow this short sweep to the sweep circuit or to the horizantal amp circuit ???  I am back at this problem child of mine again and am trying to figure which board to chase around on...I have a few more things to check per all the good inputs I have had here but seems like it would a good thing to  determine which board the problem is on..
Any thoughts on this??

Steve



Re: OT: measuring tiny distances

 

Hi snapdiode,
You probably know the density of the media that your drive reads and writes already but it is worth noting that the read/write head gap depends on the magnetic coercivity of the coating on the diskette, and that depends on the capacity of the diskette (360KB, 720KB, 1.44MB, 2.88MB, etc.).

The greater the storage capacity of the diskette the narrower the tracks have to be. Narrower tracks require magnetic material with higher coercivity to be coated on the diskette. In order to read and write these narrower tracks the magnetic field in the gap had to be higher which meant a thinner gap and the width of the gap had to be reduced to squeeze more tracks in.

In summary, the gap width depends on the data density of the floppy so your measurement and the reference may be referring to two different density heads.

Dennis Tillman W7PF

-----Original Message-----
From: snapdiode via Groups.Io
Sent: Monday, December 23, 2019 7:51 PM
To: TekScopes@groups.io
Subject: [TekScopes] OT: measuring tiny distances

Dear massed wisdom of this group, how would you measure the head gap of a floppy disk r/w head?
By counting pixels on a microscope pic I've arrived at the more or less believable 0.35 mils, or 0.009mm . One thing's for sure, it's tiny.
But that number is ten times smaller than the one reference I found that says it is 80 microns, or 0.08mm.





--
Dennis Tillman W7PF
TekScopes Moderator

Re: Tek 485 short sweep

Harvey White
 

The horizontal input has a calibrated deflection factor.  Adjust the vertical to the same factor, put a sinewave into both, and you should get a 45 degree line.

If the amplifier is ok, and the problem is in the sweep, then you should be able to center the horizontal dot (no sweep, x only). It should have about the same travel (L and R) with the positioning control.

If you have another scope, you can check for linearity by borrowing a ramp from it and using it for a horizontal sweep. Good function generator will also work.

Harvey

On 12/23/2019 1:26 AM, stephen white wrote:
How can we narrow this short sweep to the sweep circuit or to the horizantal amp circuit ??? I am back at this problem child of mine again and am trying to figure which board to chase around on...I have a few more things to check per all the good inputs I have had here but seems like it would a good thing to determine which board the problem is on..
Any thoughts on this??

Steve


Re: OT: measuring tiny distances

Chuck Harris
 

The usual way to measure such small distances is using
an optical microscope that has an eyepiece with micrometer
controlled moving reference lines. Zero the micrometer
with the reference lines at some known distance... usually
overlapping, and then adjust them to match the head gap.
The micrometer reading gets multiplied by the optics to
arrive at the actual gap.

Absent one of those special oculars, you can use a finely
ruled ruler, placed in the same frame as the gap, and
extrapolate the size of one of the lines to the gap.

If you have some fine wire, that you can measure with a
micrometer, you can compare it to the gap...

When the sizes get even smaller, a scanning electron microscope
can easily perform the same duty.

-Chuck Harris

snapdiode via Groups.Io wrote:

Dear massed wisdom of this group, how would you measure the head gap of a floppy disk r/w head?
By counting pixels on a microscope pic I've arrived at the more or less believable 0.35 mils, or 0.009mm . One thing's for sure, it's tiny.
But that number is ten times smaller than the one reference I found that says it is 80 microns, or 0.08mm.



Re: Tek 2235 Repair

guy232
 

Aye I read quite a few people having the high pitched whine in the 22xx. Usually they said it was due to one of the transformers. Forgive me if you've already found these links but I did a quick search here is a link that looked promising

https://groups.io/g/TekScopes/topic/2235_high_pitch_noise/23860566?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,1540,23860566

There were quite a few other good looking results down the list too
https://www.google.com/search?ie=UTF-8&client=ms-android-att-us&source=android-browser&q=2235+high+pitch+whine

OT: measuring tiny distances

snapdiode
 

Dear massed wisdom of this group, how would you measure the head gap of a floppy disk r/w head?
By counting pixels on a microscope pic I've arrived at the more or less believable 0.35 mils, or 0.009mm . One thing's for sure, it's tiny.
But that number is ten times smaller than the one reference I found that says it is 80 microns, or 0.08mm.

Re: tektronix 7S14 batteries and time base question

Carl Hallberg
 

Hi Dennis,
I don't have a problem gluing ground down LEDs together.  Don't know if the glue will turn translucent with age.  As far as what color to use, I'll give some examples:
Input voltage across LED at 20mA       to        Output voltage using 10Megohm input voltmeter

INFRARED   1.16V                                                 INFRARED  0.85V

RED   1.9V                                                            RED   1.3V

YELLOW  2.0V                                                      YELLOW  1.2V

BLUE    3.2V                                                          BLUE    2.3V

When I used wide angle LEDs, (manufactured with flat tops) the close proximity provides enough coupling to give good results.

Changing the drive current on the input side doesn't change the output side very much.  Voltages given are not exact.  Do we care about efficiency?  When I use to design digital circuit using transistors, Beta was selected for worse case of 10.  Very inefficient, but wouldn't fail over Military temperature range.  I don't know where we can get die upon die selected color LEDs.

Carl Hallberg

On Monday, December 23, 2019, 5:34:55 PM CST, Dennis Tillman W7PF <@Dennis_Tillman_W7pF> wrote:





Hi Chuck and John
I was surprised that several people ground the LED ends flat and glued them together. This seems counter intuitive to me for several reasons.

These are the reasons I think that grinding down the LED ends is not a good idea. I would appreciate it if you could explain the flaws in my thinking.
1) The polished surface of the LED lets the most light out. Wouldn’t a ground down (rough) surface scatter and block a portion of the emitted light.
2) The LED's dome shape focuses the light into a fairly narrow angle which increases the likelihood that the majority of the emitted light can be aimed right at the die of the LED that will convert the light to electricity.
3) Crazy Glue may appear clear to humans but what are its optical absorption characteristics? Does it absorb any of the wavelengths generated by the LED emitter?

On the other hand I think there are advantages to grinding the ends flat:
1) The ground end combination takes up a fraction of the volume of two unground LEDs.
2) Mating the two LEDs flat against each makes it easier to align them to each other.

It seems to me that the greatest conversion efficiency will come when you can place a bare emitting LED die on top of the die of the receiving LED. At that point every emitted photon can kick out an electron in the receiving PN junction.

IR light is another issue I'm confused about. I think I must have misunderstood but it sounded like some people think IR LEDs would make a good choice for emitters. Wouldn't just the opposite be true since a photon's energy, E, is proportional to its frequency, v, as in E = hv.  Do IR LEDs emit more photons (greater brightness) and that is why they are a good choice? If so does the same thing apply for the receiving LED - which would have a high conversion efficiency resulting in the largest number of electrons being produced?

Dennis Tillman W7PF

-----Original Message-----
From: Chuck Harris
Sent: Monday, December 23, 2019 7:15 AM
Subject: Re: [TekScopes] tektronix 7S14 batteries and time base question

Hi John,
That has been my experience as well.  I did a long stint in a lab where we were doing IR spectroscopy, using lasers.
When I tried to make such a bias device, I ground both LED's ends flat, and welded them together with crazy glue.  I figured that it would reduce reflections at the red I was using.
I couldn't get spit out of them... measured with a 200M input impedance meter...  I guessed the older LED's just weren't bright enough.
Or, maybe the mechanism is not reciprocal?
-Chuck

John Griessen wrote:
On 12/22/19 11:30 PM, Chuck Harris wrote:
If I have been following correctly (always suspect), aren't we using
an LED illuminated by another LED to behave as a photo diode, and
produce the bias voltage for the switch?
One thing for sure from back when I worked with near IR LEDs and laser
diodes in a narrow beam system is that what absorbs IR or reflects or
not is not obvious from our visible light experience...  So, the
efficiency could be because the incoming IR light "gets in" instead of
reflecting.  They are both designed only to output, yet one is being used to receive...

Longer IR tends to go through more things that look black to us, and
probably go right through the plastic of LED lamps without much
refraction so angle and placement can be whatever.



--
Dennis Tillman W7PF
TekScopes Moderator

Re: tektronix 7S14 batteries and time base question

 

Professor Photon,
Well knock me over with a laser beam!
I believe you answered all of my questions very comprehensively.
Dennis Tillman W7PF

-----Original Message-----
From: Bruce Griffiths
Sent: Monday, December 23, 2019 4:17 PM
Subject: Re: [TekScopes] tektronix 7S14 batteries and time base question

LED encapsulation is clear epoxy. Clear epoxy is best suited to bonding LEDs end to end. Either mechanical preparation of the mating surfaces or priming is required. Done properly the roughened ends are thoroughly wet by the bonding epoxy and the joint is invisible.
The refractive index of cyanoacrylate adhesives is somewhat lower than that of epoxies.
For a Lambertian source like a LED, butt coupling is effective. Intervening optics doesn't improve the coupling. The dome lens on the LED doesn't collimate the light so that an intermediate lens is required to maximise coupling if this method is chosen.

For maximum coupling when butt coupling the separation of the 2 LED die should be comparable with the source diameter, However reflected light from the cupped lead frame of the LED may relax this requirement a little.

Optocouplers use butt coupling with a thin transparent insulating film between the emitter and the detector.

The peak response of a LED used as a photodetector occurs at a wavelength that differs slightly from its emission peak when used as an LED.

Most of this was covered in the HP optoelectronics Handbook around 1970-80.
Bruce

On 24 December 2019 at 12:34 Dennis Tillman W7PF <@Dennis_Tillman_W7pF> wrote:

Hi Chuck and John
I was surprised that several people ground the LED ends flat and glued them together. This seems counter intuitive to me for several reasons.

These are the reasons I think that grinding down the LED ends is not a good idea. I would appreciate it if you could explain the flaws in my thinking.
1) The polished surface of the LED lets the most light out. Wouldn’t a ground down (rough) surface scatter and block a portion of the emitted light.
2) The LED's dome shape focuses the light into a fairly narrow angle which increases the likelihood that the majority of the emitted light can be aimed right at the die of the LED that will convert the light to electricity.
3) Crazy Glue may appear clear to humans but what are its optical absorption characteristics? Does it absorb any of the wavelengths generated by the LED emitter?

On the other hand I think there are advantages to grinding the ends flat:
1) The ground end combination takes up a fraction of the volume of two unground LEDs.
2) Mating the two LEDs flat against each makes it easier to align them to each other.

It seems to me that the greatest conversion efficiency will come when you can place a bare emitting LED die on top of the die of the receiving LED. At that point every emitted photon can kick out an electron in the receiving PN junction.

IR light is another issue I'm confused about. I think I must have misunderstood but it sounded like some people think IR LEDs would make a good choice for emitters. Wouldn't just the opposite be true since a photon's energy, E, is proportional to its frequency, v, as in E = hv. Do IR LEDs emit more photons (greater brightness) and that is why they are a good choice? If so does the same thing apply for the receiving LED - which would have a high conversion efficiency resulting in the largest number of electrons being produced?

Dennis Tillman W7PF

-----Original Message-----
From: Chuck Harris
Sent: Monday, December 23, 2019 7:15 AM
Subject: Re: [TekScopes] tektronix 7S14 batteries and time base
question

Hi John,
That has been my experience as well. I did a long stint in a lab where we were doing IR spectroscopy, using lasers.
When I tried to make such a bias device, I ground both LED's ends flat, and welded them together with crazy glue. I figured that it would reduce reflections at the red I was using.
I couldn't get spit out of them... measured with a 200M input impedance meter... I guessed the older LED's just weren't bright enough.
Or, maybe the mechanism is not reciprocal?
-Chuck

John Griessen wrote:
On 12/22/19 11:30 PM, Chuck Harris wrote:
If I have been following correctly (always suspect), aren't we
using an LED illuminated by another LED to behave as a photo diode,
and produce the bias voltage for the switch?
One thing for sure from back when I worked with near IR LEDs and
laser diodes in a narrow beam system is that what absorbs IR or
reflects or not is not obvious from our visible light experience...
So, the efficiency could be because the incoming IR light "gets in"
instead of reflecting. They are both designed only to output, yet one is being used to receive...

Longer IR tends to go through more things that look black to us, and
probably go right through the plastic of LED lamps without much
refraction so angle and placement can be whatever.



--
Dennis Tillman W7PF
TekScopes Moderator






--
Dennis Tillman W7PF
TekScopes Moderator

Re: tektronix 7S14 batteries and time base question

Bruce Griffiths
 

LED encapsulation is clear epoxy. Clear epoxy is best suited to bonding LEDs end to end. Either mechanical preparation of the mating surfaces or priming is required. Done properly the roughened ends are thoroughly wet by the bonding epoxy and the joint is invisible.
The refractive index of cyanoacrylate adhesives is somewhat lower than that of epoxies.
For a Lambertian source like a LED, butt coupling is effective. Intervening optics doesn't improve the coupling. The dome lens on the LED doesn't collimate the light so that an intermediate lens is required to maximise coupling if this method is chosen.

For maximum coupling when butt coupling the separation of the 2 LED die should be comparable with the source diameter, However reflected light from the cupped lead frame of the LED may relax this requirement a little.

Optocouplers use butt coupling with a thin transparent insulating film between the emitter and the detector.

The peak response of a LED used as a photodetector occurs at a wavelength that differs slightly from its emission peak when used as an LED.

Most of this was covered in the HP optoelectronics Handbook around 1970-80.

Bruce

On 24 December 2019 at 12:34 Dennis Tillman W7PF <@Dennis_Tillman_W7pF> wrote:


Hi Chuck and John
I was surprised that several people ground the LED ends flat and glued them together. This seems counter intuitive to me for several reasons.

These are the reasons I think that grinding down the LED ends is not a good idea. I would appreciate it if you could explain the flaws in my thinking.
1) The polished surface of the LED lets the most light out. Wouldn’t a ground down (rough) surface scatter and block a portion of the emitted light.
2) The LED's dome shape focuses the light into a fairly narrow angle which increases the likelihood that the majority of the emitted light can be aimed right at the die of the LED that will convert the light to electricity.
3) Crazy Glue may appear clear to humans but what are its optical absorption characteristics? Does it absorb any of the wavelengths generated by the LED emitter?

On the other hand I think there are advantages to grinding the ends flat:
1) The ground end combination takes up a fraction of the volume of two unground LEDs.
2) Mating the two LEDs flat against each makes it easier to align them to each other.

It seems to me that the greatest conversion efficiency will come when you can place a bare emitting LED die on top of the die of the receiving LED. At that point every emitted photon can kick out an electron in the receiving PN junction.

IR light is another issue I'm confused about. I think I must have misunderstood but it sounded like some people think IR LEDs would make a good choice for emitters. Wouldn't just the opposite be true since a photon's energy, E, is proportional to its frequency, v, as in E = hv. Do IR LEDs emit more photons (greater brightness) and that is why they are a good choice? If so does the same thing apply for the receiving LED - which would have a high conversion efficiency resulting in the largest number of electrons being produced?

Dennis Tillman W7PF

-----Original Message-----
From: Chuck Harris
Sent: Monday, December 23, 2019 7:15 AM
Subject: Re: [TekScopes] tektronix 7S14 batteries and time base question

Hi John,
That has been my experience as well. I did a long stint in a lab where we were doing IR spectroscopy, using lasers.
When I tried to make such a bias device, I ground both LED's ends flat, and welded them together with crazy glue. I figured that it would reduce reflections at the red I was using.
I couldn't get spit out of them... measured with a 200M input impedance meter... I guessed the older LED's just weren't bright enough.
Or, maybe the mechanism is not reciprocal?
-Chuck

John Griessen wrote:
On 12/22/19 11:30 PM, Chuck Harris wrote:
If I have been following correctly (always suspect), aren't we using
an LED illuminated by another LED to behave as a photo diode, and
produce the bias voltage for the switch?
One thing for sure from back when I worked with near IR LEDs and laser
diodes in a narrow beam system is that what absorbs IR or reflects or
not is not obvious from our visible light experience... So, the
efficiency could be because the incoming IR light "gets in" instead of
reflecting. They are both designed only to output, yet one is being used to receive...

Longer IR tends to go through more things that look black to us, and
probably go right through the plastic of LED lamps without much
refraction so angle and placement can be whatever.



--
Dennis Tillman W7PF
TekScopes Moderator


Re: tektronix 7S14 batteries and time base question

 

Hi Chuck and John
I was surprised that several people ground the LED ends flat and glued them together. This seems counter intuitive to me for several reasons.

These are the reasons I think that grinding down the LED ends is not a good idea. I would appreciate it if you could explain the flaws in my thinking.
1) The polished surface of the LED lets the most light out. Wouldn’t a ground down (rough) surface scatter and block a portion of the emitted light.
2) The LED's dome shape focuses the light into a fairly narrow angle which increases the likelihood that the majority of the emitted light can be aimed right at the die of the LED that will convert the light to electricity.
3) Crazy Glue may appear clear to humans but what are its optical absorption characteristics? Does it absorb any of the wavelengths generated by the LED emitter?

On the other hand I think there are advantages to grinding the ends flat:
1) The ground end combination takes up a fraction of the volume of two unground LEDs.
2) Mating the two LEDs flat against each makes it easier to align them to each other.

It seems to me that the greatest conversion efficiency will come when you can place a bare emitting LED die on top of the die of the receiving LED. At that point every emitted photon can kick out an electron in the receiving PN junction.

IR light is another issue I'm confused about. I think I must have misunderstood but it sounded like some people think IR LEDs would make a good choice for emitters. Wouldn't just the opposite be true since a photon's energy, E, is proportional to its frequency, v, as in E = hv. Do IR LEDs emit more photons (greater brightness) and that is why they are a good choice? If so does the same thing apply for the receiving LED - which would have a high conversion efficiency resulting in the largest number of electrons being produced?

Dennis Tillman W7PF

-----Original Message-----
From: Chuck Harris
Sent: Monday, December 23, 2019 7:15 AM
Subject: Re: [TekScopes] tektronix 7S14 batteries and time base question

Hi John,
That has been my experience as well. I did a long stint in a lab where we were doing IR spectroscopy, using lasers.
When I tried to make such a bias device, I ground both LED's ends flat, and welded them together with crazy glue. I figured that it would reduce reflections at the red I was using.
I couldn't get spit out of them... measured with a 200M input impedance meter... I guessed the older LED's just weren't bright enough.
Or, maybe the mechanism is not reciprocal?
-Chuck

John Griessen wrote:
On 12/22/19 11:30 PM, Chuck Harris wrote:
If I have been following correctly (always suspect), aren't we using
an LED illuminated by another LED to behave as a photo diode, and
produce the bias voltage for the switch?
One thing for sure from back when I worked with near IR LEDs and laser
diodes in a narrow beam system is that what absorbs IR or reflects or
not is not obvious from our visible light experience... So, the
efficiency could be because the incoming IR light "gets in" instead of
reflecting. They are both designed only to output, yet one is being used to receive...

Longer IR tends to go through more things that look black to us, and
probably go right through the plastic of LED lamps without much
refraction so angle and placement can be whatever.



--
Dennis Tillman W7PF
TekScopes Moderator

Re: tektronix 7S14 batteries and time base question

Chuck Harris
 

Hi Carl,

I did this experiment long, long ago, so any modern LED
is very much brighter than those I used.

I will give it a try with more modern LEDs.

-Chuck Harris

Carl Hallberg via Groups.Io wrote:

Hi Chuck,
I used 8 Red, 5mm size, clear plastic, 15,000 mcd, dome type LEDs glued together in pairs after grinding the domes flat. Also used heat shrink over each pair. This produced approximately 1.4V output while supplying 20 mA to the driver LED. I later added a 15uF TANT (might be too big, but had lots of them) to the output LED per Ed Breya. This worked ok. I later experimented with flat top (wide angle) LEDs with white driver (20,000 mcd) to red output. Not too much difference. I first use duco cement, but found 'Crazy Glue' was a better choice. Dennis Tillman now has this 7S14 and was happy it worked after he replace the 'time' knob. I did take picture before the caps and after.
Carl Hallberg (W9CJH)




On Monday, December 23, 2019, 9:15:07 AM CST, Chuck Harris <cfharris@...> wrote:





Hi John,

That has been my experience as well. I did a long stint
in a lab where we were doing IR spectroscopy, using lasers.

When I tried to make such a bias device, I ground both LED's
ends flat, and welded them together with crazy glue. I figured
that it would reduce reflections at the red I was using.

I couldn't get spit out of them... measured with a 200M input
impedance meter... I guessed the older LED's just weren't
bright enough.

Or, maybe the mechanism is not reciprocal?

-Chuck

Re: tektronix 7S14 batteries and time base question

Chuck Harris
 

Back in the day, IR LED's were the first developed, and
always made more power, more efficiently than any other
variety.

I suspect that the same is still true, though blue probably
gives them a run for the money...

-Chuck Harris

Miguel Work wrote:

For my experience, semiconductors are more sensible for IR wavelengths, is not casual that optocouplers works with IR.

https://www.facebook.com/search/top/?q=optical%20communication%20using%20leds%20alone&epa=SEARCH_BOX

CCD for exemple is more sensible for red light.

Regards

Miguel

Re: Tek 2235 Repair

Oscar Anderson
 

Alright, looks like a bad connection. I reseated a bunch of connectors inside the scope, pushed some buttons a few more times and it seems to be working.

New thing (that I hear is a common issue with these) is an a high-frequency audible whine from the SMPS. I assume it's probably about time for the 35-year-old capacitors to be replaced. I also have read something about it being a failing inductor

There a "recommended" procedure for solving this? It's slightly annoying, but I mostly want to deal with it so it doesn't cause other problems in the future.

Re: Tek 485 short sweep

Abc Xyz
 

My 465B has Traces that are too Short and also they will not Position
correctly.

On Mon, Dec 23, 2019, 12:41 PM DaveH52 <@DaveH52> wrote:

The 90V supply was at about 70V, and the trace was folded over upon
itself. I removed it with a pair of pliers and substituted a film cap (that
I ultimately mounted inside the HV cover) and the problem was gone.



Re: Tek 2465 Problem

 

Diagnosing a 2465 starts with J119 voltage check.  If all the voltages on J119 are correct (value and ripple) then your power supply is good enough for everything else.  Don't bother with power supply investigations if J119 has the right voltages.  The proper readings are in the Service Manual near trouble shooting flow chart step 11.

On Sunday, December 22, 2019, 03:55:18 PM CST, Panos <sadosp@...> wrote:

On Sun, Dec 22, 2019 at 04:31 PM, Panos wrote:


because they have very low in ohm resistance (about 130 ohm) when I measure
these with forward polarity. Conversely they have a complete cut.
Sorry I must to said forward 80 ohm and conversely 2 kohm.

Re: Tek 485 short sweep

DaveH52
 

The 90V supply was at about 70V, and the trace was folded over upon itself. I removed it with a pair of pliers and substituted a film cap (that I ultimately mounted inside the HV cover) and the problem was gone.

Re: Tektronix ORS2488/ORS622 SDH/SONET Reference Receiver

Roy Thistle
 

Hi Melvin:
There is,
https://www.artisantg.com/info/ATG0yxxv.pdf
and
https://groups.io/g/ManualExchange/topics
You have an optical fiber based digital network to test/quantify?
Best wishes and regards.
Roy

Re: tektronix 7S14 batteries and time base question

Carl Hallberg
 

Hi Chuck,
I used 8 Red, 5mm size, clear plastic, 15,000 mcd, dome type LEDs glued together in pairs after grinding the domes flat.  Also used heat shrink over each pair.  This produced approximately 1.4V output while supplying 20 mA to the driver LED.  I later added a 15uF TANT (might be too big, but had lots of them) to the output LED per Ed Breya.  This worked ok.  I later experimented with flat top (wide angle) LEDs  with white driver (20,000 mcd) to red output.  Not too much difference.  I first use duco cement, but found 'Crazy Glue' was a better choice.  Dennis Tillman now has this 7S14 and was happy it worked after he replace the 'time' knob.  I did take picture before the caps and after. 
Carl Hallberg (W9CJH)

On Monday, December 23, 2019, 9:15:07 AM CST, Chuck Harris <cfharris@...> wrote:





Hi John,

That has been my experience as well.  I did a long stint
in a lab where we were doing IR spectroscopy, using lasers.

When I tried to make such a bias device, I ground both LED's
ends flat, and welded them together with crazy glue.  I figured
that it would reduce reflections at the red I was using.

I couldn't get spit out of them... measured with a 200M input
impedance meter...  I guessed the older LED's just weren't
bright enough.

Or, maybe the mechanism is not reciprocal?

-Chuck

John Griessen wrote:
On 12/22/19 11:30 PM, Chuck Harris wrote:
If I have been following correctly (always suspect), aren't
we using an LED illuminated by another LED to behave as a
photo diode, and produce the bias voltage for the switch?
One thing for sure from back when I worked with near IR LEDs and laser diodes
in a narrow beam system is that what absorbs IR or reflects or not is
not obvious from our visible light experience...  So, the efficiency could be because
the incoming IR light "gets in" instead of reflecting.  They are both designed only to
output, yet one is being used to receive...

Longer IR tends to go through more things that look black to us, and probably go
right through
the plastic of LED lamps without much refraction so angle and placement can be whatever.

Re: tektronix 7S14 batteries and time base question

Miguel Work
 

For my experience, semiconductors are more sensible for IR wavelengths, is not casual that optocouplers works with IR.

https://www.facebook.com/search/top/?q=optical%20communication%20using%20leds%20alone&epa=SEARCH_BOX

CCD for exemple is more sensible for red light.

Regards

Miguel





-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Chuck Harris
Enviado el: lunes, 23 de diciembre de 2019 16:15
Para: TekScopes@groups.io
Asunto: Re: [TekScopes] tektronix 7S14 batteries and time base question

Hi John,

That has been my experience as well. I did a long stint in a lab where we were doing IR spectroscopy, using lasers.

When I tried to make such a bias device, I ground both LED's ends flat, and welded them together with crazy glue. I figured that it would reduce reflections at the red I was using.

I couldn't get spit out of them... measured with a 200M input impedance meter... I guessed the older LED's just weren't bright enough.

Or, maybe the mechanism is not reciprocal?

-Chuck

John Griessen wrote:

On 12/22/19 11:30 PM, Chuck Harris wrote:
If I have been following correctly (always suspect), aren't we using
an LED illuminated by another LED to behave as a photo diode, and
produce the bias voltage for the switch?
One thing for sure from back when I worked with near IR LEDs and laser
diodes in a narrow beam system is that what absorbs IR or reflects or
not is not obvious from our visible light experience... So, the
efficiency could be because the incoming IR light "gets in" instead of
reflecting. They are both designed only to output, yet one is being used to receive...

Longer IR tends to go through more things that look black to us, and
probably go right through the plastic of LED lamps without much
refraction so angle and placement can be whatever.