Date   
Re: REPAIRED : Tektronix 2465B with auto test stopped on "ADD" led lit

Siggi
 

On Fri, Jan 10, 2020, 1:59 AM Joseph <@jo6466> wrote:

My problem :
On power, the auto test start but stop when arrive at the "ADD" led
lighting ... Screen remain totally black

Fixing:
1) I measured the voltage on pins 14 and 15 of U2101 (DAC) and find them
near 0v .. it was not normal
Beg to differ, this IS normal. Pins 14/15 are the inputs of an opamp in
negative feedback. They should both be at zero volts, or very near. What's
important is the current into the DAC, which can't be directly measured.


2) I tested the R2010 to R2016 resistors value .. all was been ok
3) I tested the CONTINUITY of the tracks between them
bingo!! .. I discovered, under a little oxydation bubble on the track
near R2016, a break on it
4) after fixing it, the auto test gone until end and the screen lit
Congrats on your fix. Your image links seem to be mangled, I get 404s all
round.

Did you check and replace the electrolytic capacitors on the A5 board and
clean it? The most usual cause for this problem is electrolyte spillage
causing PCB and component corrosion.



Re: Tek 576 Curve Tracer USB port to a cpu ... ?

Michael A. Terrell
 

Rather than connecting to the deflection plates, why not pick off the
voltages at the input of the CRT drivers? They are closer to the range
needed for digitization, and less likely to damage the additional
circuitry. Have you seen these 6 channel USB ADC modules? PIC based, cheap
and 1mV resolution.

You could use two channels and convert them to a single level with software
as an alternative to adding a differential amp. It would also make it
easier to autozero.

https://www.ebay.com/itm/iCP12-1mV-usbStick-PC-USB-Oscilloscope-DAQ-Logger-PWM-Analog-IO-Board/122735062339

On Fri, Jan 10, 2020 at 2:12 AM Dennis Tillman W7PF <@Dennis_Tillman_W7PF>
wrote:

Hi Jim,
Yes. I was racing to get my thoughts down as fast as they were coming to
me so I had no time to go back and read what I was writing or to simplify
the requirements. It was more an explanation of the design principles Tek
engineers followed in the design of the amplifier / deflection signal
chain. Once you know that you will know what you can to do to keep the
circuitry of the A/D digitizers simple. It is simple to convert the
differential signals of each axis into a single ended signal. The bandwidth
requirement is very low so any OpAmp would work.

"The proof is left to the student" was what my professors would often say
sarcastically.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jim
Ford
Sent: Wednesday, January 08, 2020 6:17 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ?

Regarding the first difficulty you brought up, Dennis, some ADCs have
differential inputs, so you may not need two. Or use a difference amp or
even an instrumentation amp or a transformer to convert from differential
to single-ended. Lots of options these days.Jim Ford sent from my Verizon,
Samsung Galaxy smartphone
-------- Original message --------From: Dennis Tillman W7PF <
@Dennis_Tillman_W7PF> Date: 1/8/20 5:37 PM (GMT-08:00) To:
TekScopes@groups.io Subject: Re: [TekScopes] Tek 576 Curve Tracer USB
port to a cpu ... ? Hi Ke-Fong Lin,Digitizing the deflection voltages is a
great idea because of its simplicity. It would be easy to capture the
deflection voltage for both axes with A/D converters and convert it into
X-Y data. A few issues that may make it a bit more difficult:* The
deflection signals are differential so the X axis would require two A/Ds
sampling the two vertical deflection plates and two A/Ds sampling the two
horizontal plates. Both of the vertical A/Ds would need to sample
simultaneously. The same is true for the two horizontal A/Ds.* There is no
information about what you are looking at. For a simple example of
measuring a bipolar transistor the data you capture has no information
about the Volts/Div of the horizontal axis or the Amps/Div of the vertical
axis, or what current step caused the trace to move vertically and by how
much. * You have no idea when to start and stop capturing the data. This
might be easy to fix if there is a start sync pulse you could use to
trigger the A/Ds. I'm not aware that there is a Stop pulse. It may be
possible to use a Z-axis output signal or un-blanking signal, if one is
available somewhere inside the curve tracer for this. The A/Ds would start
when the un-blanking signal went true and they wouldn't stop until the
un-blanking signal went false. Assuming there is a way to use the
un-blanking signal or equivalent this might work. The way this could work
is by pressing a momentary push button to tell your software to take a
sample of the next set of curves. It would then wait for the un-blanking
signal to go true. The software would automatically write the data
streaming from the four A/Ds to local memory. When the un-blanking goes
false, indicating the curve tracer is done displaying a complete set of
curves the A/Ds would be stopped and the software would automatically
send the sampled data to a display or back to the curve tracer's CRT so
the user could decide if they wanted to save it permanently or do this over
again. If you decide to save the data it would then ask you to enter the
settings of the curve tracer knobs or maybe what would be better would be
that you have the software generate a pattern on the CRt that could be as
simple as a diagonal line for example. By adjusting the line so it starts
in the lower left corner of the screen and ends in the upper right corner
of the screen you are providing a calibrated range that can then be used by
entering the settings of the vertical A/Div knob and the horizontal V/Div
knob. Finally you would include the base current steps and how many steps
there were.This actually might work!!!Dennis Tillman W7PF -----Original
Message-----From: TekScopes@groups.io [mailto:TekScopes@groups.io] On
Behalf Of Ke-Fong LinSent: Wednesday, January 08, 2020 2:00 PMTo:
TekScopes@...: Re: [TekScopes] Tek 576 Curve Tracer USB port
to a cpu ... ?> Would it not be a simple matter to somehow convert the 576
deflection > plate voltage signals to X-Y Data? Just thinking out loud
here.As mentioned already, the refresh is at 60Hz so a pen plotter cannot
go that fast.However. it should be possible to have the display "static"
and have the plotter slowly do it's work.But then you would have to design
a mechanism to "follow" the "beam" at the slow pen rate.That would be quite
complicated.In contrast, the spectrum analyzer is a single f(x) function to
plot. And in the case of my HP3580A which is a low frequency SA, the
sweeping speed is very slow (can be a few minutes).Indeed, what looks easy
for an Arduino, may not have been in the 70s!-- Dennis Tillman
W7PFTekScopes Moderator




--
Dennis Tillman W7PF
TekScopes Moderator



Re: Modifications to DC508 Frequency Counter

NigelP
 

I have the info for DC502 which can use option-7 and one of our members (Edgar) has been looking at doing PCB for it; not sure what progress he's made though.

Check out the threads for TM503 modifications and DC502.

Regards

Nigel G8AYM

Re: GPIB videos wanted?

Vintage Test
 

Hi Tam,

I have a Solartron 7081, a TDS744, various Datron multimeters and a bundle of TM5000 frames and modules that I’d love to be able to talk to with GPIB - I have an NI PCI adaptor in my PC. Your offer of information videos would be very gratefully accepted by all, I think!

Cheers,
Mel

--
you can never have enough oscilloscopes, DMMs, valve testers or soldering irons . . .

Re: Tek 576 Curve Tracer USB port to a cpu ... ?

Miguel Work
 

Hi, resistor X R680 and Y R580 is a good place to sample the analog signal in dierential. Is +7 to -7 volts for the spot goes side to side of de crt.


-----Mensaje original-----
De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Dennis Tillman W7PF
Enviado el: viernes, 10 de enero de 2020 8:12
Para: TekScopes@groups.io
Asunto: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ?

Hi Jim,
Yes. I was racing to get my thoughts down as fast as they were coming to me so I had no time to go back and read what I was writing or to simplify the requirements. It was more an explanation of the design principles Tek engineers followed in the design of the amplifier / deflection signal chain. Once you know that you will know what you can to do to keep the circuitry of the A/D digitizers simple. It is simple to convert the differential signals of each axis into a single ended signal. The bandwidth requirement is very low so any OpAmp would work.

"The proof is left to the student" was what my professors would often say sarcastically.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jim Ford
Sent: Wednesday, January 08, 2020 6:17 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ?

Regarding the first difficulty you brought up, Dennis, some ADCs have differential inputs, so you may not need two. Or use a difference amp or even an instrumentation amp or a transformer to convert from differential to single-ended. Lots of options these days.Jim Ford sent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: Dennis Tillman W7PF <@Dennis_Tillman_W7PF> Date: 1/8/20 5:37 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ? Hi Ke-Fong Lin,Digitizing the deflection voltages is a great idea because of its simplicity. It would be easy to capture the deflection voltage for both axes with A/D converters and convert it into X-Y data. A few issues that may make it a bit more difficult:* The deflection signals are differential so the X axis would require two A/Ds sampling the two vertical deflection plates and two A/Ds sampling the two horizontal plates. Both of the vertical A/Ds would need to sample simultaneously. The same is true for the two horizontal A/Ds.* There is no information about what you are looking at. For a simple example of measuring a bipolar transistor the data you capture has no information about the Volts/Div of the horizontal axis or the Amps/Div of the vertical axis, or what current step caused the trace to move vertically and by how much. * You have no idea when to start and stop capturing the data. This might be easy to fix if there is a start sync pulse you could use to trigger the A/Ds. I'm not aware that there is a Stop pulse. It may be possible to use a Z-axis output signal or un-blanking signal, if one is available somewhere inside the curve tracer for this. The A/Ds would start when the un-blanking signal went true and they wouldn't stop until the un-blanking signal went false. Assuming there is a way to use the un-blanking signal or equivalent this might work. The way this could work is by pressing a momentary push button to tell your software to take a sample of the next set of curves. It would then wait for the un-blanking signal to go true. The software would automatically write the data streaming from the four A/Ds to local memory. When the un-blanking goes false, indicating the curve tracer is done displaying a complete set of curves the A/Ds would be stopped and the software would automatically send the sampled data to a display or back to the curve tracer's CRT so the user could decide if they wanted to save it permanently or do this over again. If you decide to save the data it would then ask you to enter the settings of the curve tracer knobs or maybe what would be better would be that you have the software generate a pattern on the CRt that could be as simple as a diagonal line for example. By adjusting the line so it starts in the lower left corner of the screen and ends in the upper right corner of the screen you are providing a calibrated range that can then be used by entering the settings of the vertical A/Div knob and the horizontal V/Div knob. Finally you would include the base current steps and how many steps there were.This actually might work!!!Dennis Tillman W7PF -----Original Message-----From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Ke-Fong LinSent: Wednesday, January 08, 2020 2:00 PMTo: TekScopes@...: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ?> Would it not be a simple matter to somehow convert the 576 deflection > plate voltage signals to X-Y Data? Just thinking out loud here.As mentioned already, the refresh is at 60Hz so a pen plotter cannot go that fast.However. it should be possible to have the display "static" and have the plotter slowly do it's work.But then you would have to design a mechanism to "follow" the "beam" at the slow pen rate.That would be quite complicated.In contrast, the spectrum analyzer is a single f(x) function to plot. And in the case of my HP3580A which is a low frequency SA, the sweeping speed is very slow (can be a few minutes).Indeed, what looks easy for an Arduino, may not have been in the 70s!-- Dennis Tillman W7PFTekScopes Moderator




--
Dennis Tillman W7PF
TekScopes Moderator

Re: 577 Curve Tracer question

 

Hi David,
I'm not very good when it comes to following directions or asking others for help when I don't understand something so part of the fault is with me. I suggest you give the directions a try and form your own conclusion. I will be better off if others have greater success than me because then I can ask them for their help. As it is you are asking a blind person to lead you. How smart is that?

After I grew frustrated with the adjustment instructions in the service manual I just started turning trim pots until things seemed "better" than they were before I opened up the curve tracer. At that point I thought to myself you should stop because it is almost certain that you can only make it worse if you don't stop.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David Berlind
Sent: Wednesday, January 08, 2020 12:33 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 577 Curve Tracer question

Hi Dennis.

I have my 577 and my Eico 667 Tube tester ready for the marriage according to your paper. It's in my project queue and I'm looking forward to the undertaking. First, I'm going to bring the tube tester up to snuff. Do you have a shortlist of things to do in order to get the storage into a good place on the 577 (rather than reading the confusing manual)?

Thanks.

David

On Wed, Jan 8, 2020 at 1:18 PM Dennis Tillman W7PF <@Dennis_Tillman_W7PF>
wrote:

Hi Jason,
Congratulations. You've got yourself a great curve tracer. If you ever
get the need to test vacuum tubes I designed an inexpensive adapter
that will let you do that on a 577. I wrote a paper on how I did it.

In my experience the only thing you will probably need to adjust is
the storage. My impression of all Tek storage tubes is that they are
particularly sensitive to their voltages being properly set. There is
a procedure in the Service Manual for doing this. I found it so
confusing (many of the adjustments seem to interact with each other)
that I eventually gave up and just settled for something that I could live with.
After a few minutes the scope has warmed up it the adjustments I made
seem to make the storage work OK. I'm sure that someone else could do
a better job than I did.

What part of the circuit are U520 and U530 used for? It seems odd that
they were missing. Do you have any idea why?

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Jason A. via Groups.Io
Sent: Wednesday, January 08, 2020 8:24 AM
To: TekScopes@groups.io
Subject: [TekScopes] 577 Curve Tracer question

Hello all! I've recently acquired a 577D1 curve tracer that was
missing a few components. I managed to find everything online that it
was missing (at least at first blush - time will tell on my
observation skills and glasses prescription). Replacement parts
156-0200-00 for U520 and U530 arrived yesterday. Before I plug in two
somewhat hard to find parts, is there anything I should be checking first?

Dennis Tillman W7PF
TekScopes Moderator



--
Dennis Tillman W7PF
TekScopes Moderator

Re: Tek 576 Curve Tracer USB port to a cpu ... ?

 

Hi Jim,
Yes. I was racing to get my thoughts down as fast as they were coming to me so I had no time to go back and read what I was writing or to simplify the requirements. It was more an explanation of the design principles Tek engineers followed in the design of the amplifier / deflection signal chain. Once you know that you will know what you can to do to keep the circuitry of the A/D digitizers simple. It is simple to convert the differential signals of each axis into a single ended signal. The bandwidth requirement is very low so any OpAmp would work.

"The proof is left to the student" was what my professors would often say sarcastically.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jim Ford
Sent: Wednesday, January 08, 2020 6:17 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ?

Regarding the first difficulty you brought up, Dennis, some ADCs have differential inputs, so you may not need two. Or use a difference amp or even an instrumentation amp or a transformer to convert from differential to single-ended. Lots of options these days.Jim Ford sent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: Dennis Tillman W7PF <@Dennis_Tillman_W7PF> Date: 1/8/20 5:37 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ? Hi Ke-Fong Lin,Digitizing the deflection voltages is a great idea because of its simplicity. It would be easy to capture the deflection voltage for both axes with A/D converters and convert it into X-Y data. A few issues that may make it a bit more difficult:* The deflection signals are differential so the X axis would require two A/Ds sampling the two vertical deflection plates and two A/Ds sampling the two horizontal plates. Both of the vertical A/Ds would need to sample simultaneously. The same is true for the two horizontal A/Ds.* There is no information about what you are looking at. For a simple example of measuring a bipolar transistor the data you capture has no information about the Volts/Div of the horizontal axis or the Amps/Div of the vertical axis, or what current step caused the trace to move vertically and by how much. * You have no idea when to start and stop capturing the data. This might be easy to fix if there is a start sync pulse you could use to trigger the A/Ds. I'm not aware that there is a Stop pulse. It may be possible to use a Z-axis output signal or un-blanking signal, if one is available somewhere inside the curve tracer for this. The A/Ds would start when the un-blanking signal went true and they wouldn't stop until the un-blanking signal went false. Assuming there is a way to use the un-blanking signal or equivalent this might work. The way this could work is by pressing a momentary push button to tell your software to take a sample of the next set of curves. It would then wait for the un-blanking signal to go true. The software would automatically write the data streaming from the four A/Ds to local memory. When the un-blanking goes false, indicating the curve tracer is done displaying a complete set of curves the A/Ds would be stopped and the software would automatically send the sampled data to a display or back to the curve tracer's CRT so the user could decide if they wanted to save it permanently or do this over again. If you decide to save the data it would then ask you to enter the settings of the curve tracer knobs or maybe what would be better would be that you have the software generate a pattern on the CRt that could be as simple as a diagonal line for example. By adjusting the line so it starts in the lower left corner of the screen and ends in the upper right corner of the screen you are providing a calibrated range that can then be used by entering the settings of the vertical A/Div knob and the horizontal V/Div knob. Finally you would include the base current steps and how many steps there were.This actually might work!!!Dennis Tillman W7PF -----Original Message-----From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Ke-Fong LinSent: Wednesday, January 08, 2020 2:00 PMTo: TekScopes@...: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ?> Would it not be a simple matter to somehow convert the 576 deflection > plate voltage signals to X-Y Data? Just thinking out loud here.As mentioned already, the refresh is at 60Hz so a pen plotter cannot go that fast.However. it should be possible to have the display "static" and have the plotter slowly do it's work.But then you would have to design a mechanism to "follow" the "beam" at the slow pen rate.That would be quite complicated.In contrast, the spectrum analyzer is a single f(x) function to plot. And in the case of my HP3580A which is a low frequency SA, the sweeping speed is very slow (can be a few minutes).Indeed, what looks easy for an Arduino, may not have been in the 70s!-- Dennis Tillman W7PFTekScopes Moderator




--
Dennis Tillman W7PF
TekScopes Moderator

REPAIRED : Tektronix 2465B with auto test stopped on "ADD" led lit

Joseph
 

My problem :
On power, the auto test start but stop when arrive at the "ADD" led lighting ... Screen remain totally black

Fixing:
1) I measured the voltage on pins 14 and 15 of U2101 (DAC) and find them near 0v .. it was not normal
2) I tested the R2010 to R2016 resistors value .. all was been ok
3) I tested the CONTINUITY of the tracks between them
bingo!! .. I discovered, under a little oxydation bubble on the track near R2016, a break on it
4) after fixing it, the auto test gone until end and the screen lit

Start state :
[img]https://image.noelshack.com/fichiers/2020/02/4/1578575821-r0159787.jpg[/img]

Track break discover :
[img]https://image.noelshack.com/fichiers/2020/02/4/1578575799-capture-2020-01-09-a-13-44-58.jpg[/img]

Repair :
[img]https://image.noelshack.com/fichiers/2020/02/4/1578575821-r0159788.jpg[/img]

]Fix schema and verified voltages :
[img]https://image.noelshack.com/fichiers/2020/02/4/1578575799-capture-2020-01-09-a-13-38-29.jpg[/img]

Result :
[img]https://image.noelshack.com/fichiers/2020/02/4/1578575821-r0159789.jpg[/img]

Re: Tek 576 Curve Tracer USB port to a cpu ... ?

 

Hi Miguel,
There are many simple OpAmp circuits for converting differential input
signals to single ended signals so that problem is easy. By combining the
two differential signals per axis into one signal it would eliminate one D/A
converter from the vertical deflection amplifier and one from the horizontal
deflection amplifier.

Because this will be used with curve tracers which do not use high speed
circuits it will be possible to use ordinary OpAmps to do this. Their
bandwidth only needs to be a few MHz or less.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of John
Griessen
Sent: Wednesday, January 08, 2020 5:20 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ?

On 1/8/20 4:50 PM, Miguel Work wrote:
I think that the first step is to make single ended outputs, x y z. BNC
outputs in the rear panel for example, I have some drafts, schematics
designed to connect to deflection plates.

Yes! That's how to divide and conquer. This seems to have some interest.
Maybe there are volunteers for gruuuuunt work needed...

I have examples of volt divider layout that works for 2 kV to record traces
with micropython on a STM32f401CEU6, various FETs, diodes, R's, C's. If the
pickoff point is higher, then it needs more work, but I think there has to
be some under 2kV analog to digitize in there somewhere. (I have not even
looked at schematic.)





--
Dennis Tillman W7PF
TekScopes Moderator

Re: GPIB videos wanted?

KeepIt SimpleStupid
 

The first attempt at that was SCPI and later VISA.`
With LabView, the manufacturer wrote an instrument driver for you.  Versions of Labview can be a real problem.  Upgrading usually possible, downgrading no.

On Thursday, January 9, 2020, 6:58:26 PM EST, Greg via Groups.Io <wa6kno=aol.com@groups.io> wrote:

I too have an Agilent(?) 82357B USB/GPIB interface.  Not sure if it's the real deal though.  I too would like to use it to talk to my TDS 620A, TDS 640A and TDS 644A scopes.  I have tried to connect it to them and I think  they have responded to the ISN?  command  Any other command and I get a timeout error. Don't know why.  I have the Agilent I/O suite.  I would especially like to learn how to read and back up my NVRAM contents on these scopes.  Would like some one to show me how to do that.  I have very little experience with GPIB.  I built a console port connector for these scopes and can't get it to work.  Would also like some help with that.  Any and all help will be greatly appreciated.  Thank you.  Greg
 


-----Original Message-----
From: David Kuhn <Daveyk021@...>
To: TekScopes <TekScopes@groups.io>
Sent: Thu, Jan 9, 2020 9:30 am
Subject: Re: [TekScopes] GPIB videos wanted?

P.S. - I forgot.  I used the Agilent USB/GPIB adaptor, both the real 32357B
and the Chinese $99 version (works fine) and both Tek and Agilent VISA.  I
think the agilent VISA, must be install as secondary so that the Tek
OpenChoice desktop utility works.

P.S.S. - If anyone has a VB module to do a TEK TDS3000 series Scope screen
capture, I would love to see that,

On Wed, Jan 8, 2020 at 6:09 AM Tam Hanna <tamhan@...> wrote:

Hello Folks,

sorry for annoying you - but I have seen a lot of discussion of GPIB
programming recently on this and a few other mailing lists I am
subscribed to.


Given that I have a NI GPIB card and did a lot of work with Visual
Studio and C#, I wanted to ask if there is anyone who would be
interested in a few tutorial videos? I just ask because making these
clips is hard work and I do not want it to be made with no interest...


Tam

--
- - - - -
With best regards
Tam HANNA

Enjoy electronics? Join 13500 followers by visiting the Crazy Electronics
Lab at https://www.instagram.com/tam.hanna/




Re: 454 HV regulation off

Jack Ohme
 

I was going to inspect the resistor chain individually, but that would
involve desoldering of the entire HV section. As much as I love the rest of
this unit, hiding a bunch of stuff under a panel of soldered components
seems like a poor move on Tek's part.

On Thu, Jan 9, 2020 at 9:17 PM Jack Ohme via Groups.Io <machinamancerjack=
gmail.com@groups.io> wrote:

Ok Roger, I've been meter checking around the transistors on the Z axis
board, like you said may be bad, as well as checking points mentioned by
Arden, and I've discovered something interesting. Z axis board output P
(connected to emitter of Q1423) is supposed to be at around -4.35v, when
really its at about -3.9v. It goes up to about -4.5v when I adjust the HV
adjustment pot, remember what I said earlier about the screen going to an
acceptable level when I tweaked that pot? But anyway, after a glorious
second, it returns back to around -3.9v. :(
The ohmmeter measures between point L (at the top of the chain of 3M
resistors), and TP1349 (the -1960v test point) at around 1.2Mohm, but
across C1408 its 10M so I'm fairly sure it ain't a leaky cap. Strangely
enough, there are 1.2Mohms worth of resistors between point L and +75...
but I think this is all beyond the point. Measuring large resistances in
such a complex circuit is worthless. I could pull the string and measure,
but frankly I'm not so sure that's the issue. I feel like the strange
behavior would be more appropriate of a bad cap or transistor. I will keep
looking for any bad transistors on the board, but so far, measurements seem
alright besides the bad one on Q1423. I could of course replace it, but I'd
like to be sure before suspending my work for 5 days for an eBay order,
haha.

On Thu, Jan 9, 2020 at 5:45 PM KB6NAX <gumbear@...> wrote:

To be precise, the circuits on the Z axis board provide intensity control
and unblanking. There is no provision for intensity modulation such as
TV
video via that circuit. The rear panel AC coupled Z axis input to the
CRT
cathode provides intensity modulation from an external source. OK,
picky,
picky.... -Arden





Re: 2465B Buying advice

John Williams
 

David: I did not say they were “disguised.” I said they were sold as 2465b. They were listed as 2465B and when they arrived they were 2465. I have purchased for my store 2465b scopes that worked fine until they warmed up, and then the u800 would fail. This could take anywhere from a few minutes to an hour. After they cooled the cycle would repeat itself. This is a classic well known failure mode. Nothing “disremembered.”

Re: 454 HV regulation off

Jack Ohme
 

Ok Roger, I've been meter checking around the transistors on the Z axis
board, like you said may be bad, as well as checking points mentioned by
Arden, and I've discovered something interesting. Z axis board output P
(connected to emitter of Q1423) is supposed to be at around -4.35v, when
really its at about -3.9v. It goes up to about -4.5v when I adjust the HV
adjustment pot, remember what I said earlier about the screen going to an
acceptable level when I tweaked that pot? But anyway, after a glorious
second, it returns back to around -3.9v. :(
The ohmmeter measures between point L (at the top of the chain of 3M
resistors), and TP1349 (the -1960v test point) at around 1.2Mohm, but
across C1408 its 10M so I'm fairly sure it ain't a leaky cap. Strangely
enough, there are 1.2Mohms worth of resistors between point L and +75...
but I think this is all beyond the point. Measuring large resistances in
such a complex circuit is worthless. I could pull the string and measure,
but frankly I'm not so sure that's the issue. I feel like the strange
behavior would be more appropriate of a bad cap or transistor. I will keep
looking for any bad transistors on the board, but so far, measurements seem
alright besides the bad one on Q1423. I could of course replace it, but I'd
like to be sure before suspending my work for 5 days for an eBay order,
haha.

On Thu, Jan 9, 2020 at 5:45 PM KB6NAX <gumbear@...> wrote:

To be precise, the circuits on the Z axis board provide intensity control
and unblanking. There is no provision for intensity modulation such as TV
video via that circuit. The rear panel AC coupled Z axis input to the CRT
cathode provides intensity modulation from an external source. OK, picky,
picky.... -Arden



Re: 2465B Buying advice

David DiGiacomo
 

On Thu, Jan 9, 2020 at 7:40 PM John Williams <books4you@...> wrote:

Very true. I have seen rebadged 2465 units sold as 2465B. I would never buy a 2465B from eBay or anywhere I could not test it.
I think you are misremembering... there's no way you can disguise a
2465 as a 2465B.

The eBay issue is the seller "2465b", who sells modified 2445Bs as 2465Bs.

It is very difficult to identify one of these units without looking inside.

The U800 failure can take hours to show up, not just minutes. There is no way to tell if that defect is present without testing. Just saying.
I have not seen an intermittent U800 failure. In my experience, once
it fails, it stays that way (unless you remove and "rebake" the part).

Re: Troubleshooting tips for a Tek 485 scope

Mlynch001
 

Reed,

Thanks for the advice! I just finished the repair of a very nice 465. I had wondered if this was a simple matter of cleaning switches on the 485. The 465 had a beam finder that seemed to be working, but it had uncontrollable intensity. It turned out that the beam finder was not actually releasing, but was making some sort of intermediate connections and causing that issue. I cleaned the switches and used some DeOxit on them. This fixed that intensity problem and everything else as well. I have fixed many scopes as simply as cleaning their filth or stuck switches. I trust that this 485 repair is as simple as you have suggested. Your work speaks for itself, and I value your generous advice greatly. I’m sure that the capacitor replacement will take much more time than cleaning the switches. This particular scope is a beauty, I have been looking for a nice one for some time, and I have almost nothing in it. Since I have little experience inside the 485, I was not wanting to go poking around inside and cause inadvertent and most unnecessary damage. Thanks again.

Sincerely,
--
Michael Lynch
Dardanelle, AR

576 Curve tracer Digitizer/Screen replacement

ykochcal
 

I followed the other threads on 576’s

Its clear that there are a few people thinking about a Digitizer/Screen replacement for the 576

I acquired a 576 that I have not dug into and don’t know the condition of the screen.
So getting a bit ahead of my self, I too have done some thinking.

I looked at different ways to do things many of which were mentioned in the other thread.

My conclusion was that an Analog Discovery USB Oscilloscope might be good choice.
At the time Digilent was selling them to students for what must have been close to cost. I believe Digilent sold to National Instruments and now the cost has gone up to $279.

Any way it has two 25V differential channels with 14 bits of resolution at 100MS/s.
Also has 16 I/O lines and a bit of power with a USB interface.

Step 1 would be to just connect it in X/Y mode possibly with 4 op amps to buffer the signals. I think that could be done with a modification that could be removed without much evidence.

Step 2 would be to use the I/O to get connected to an initial pulse and then a pulse from each step.

Step 3 would be to connect Opto Couplers to each light and run those into the I/O
Most likely through a matrix, I think that would be a major permanent modification unless there is a connector that can be tapped into.

Step 4 would be to use the SDK to write some software to create a proper interface.

The claim is that it can run on windows or Linux and now run it can run on a raspberry pi, which would make a screen replacement with out a windows PC possible.

And then Step 5 would be to add a tube tester adapter.

And then Step 6 would be to digitize the tube manufactures graphs and properly scale them to display in the background of the display.

So far more thinking then doing.

I have a 576 condition unknown, a Analog Discovery and a tube tester with the right switches.
John

Re: 2465B Buying advice

John Williams
 

Very true. I have seen rebadged 2465 units sold as 2465B. I would never buy a 2465B from eBay or anywhere I could not test it. The U800 failure can take hours to show up, not just minutes. There is no way to tell if that defect is present without testing. Just saying.

Modifications to DC508 Frequency Counter

Gary Robert Bosworth
 

Does anyone have the original application note that describes exactly how to modify a DC508 1GHz Frequency Counter to include Option 1 and Option 7? I believe the modifications are extremely simple. These modifications allow the Frequency Counter to interface directly with the 492/494 spectrum analyzer and its tracking generator.

Gary

Re: 454 HV regulation off

KB6NAX
 

To be precise, the circuits on the Z axis board provide intensity control and unblanking. There is no provision for intensity modulation such as TV video via that circuit. The rear panel AC coupled Z axis input to the CRT cathode provides intensity modulation from an external source. OK, picky, picky.... -Arden

Re: 2465B Buying advice

Gary Robert Bosworth
 

Be very careful when it comes to 2465B. MANY on the market are modified
units with a new handle that says 2465B but they did not start out as one.
I have been told that these modified units are fast, but they are not
authentic and you might have a difficult time reselling it in the future.

Gary

On Thu, Jan 9, 2020 at 5:03 AM Harold Foster <@HalFoster> wrote:

All:

I'm looking for a very good, fast analog scope and so far the 2465B seems
to be the best choice; I would very much welcome any tips and advice before
I go shopping. Options that are worth holding out for? Certain
manufacturing dates/serial numbers? Fair prices? Different models?

TIA,

Hal



--
Gary Robert Bosworth
@grbosworth
Tel: 310-317-2247