Date   

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

John Griessen
 

On 1/7/20 7:50 PM, cnc_joker via Groups.Io wrote:
I may be asking a dumb question, but why do you need a 576 if you want a curve tracer?
Not dumb at all. Someone already mentioned how to SMUs, (source measure units), could do it,
and those can be spendy, but a basic DAC that controls a power supply is not spendy and serves as
part of a modular system to characterize I-V devices like transistors and PV cells. All that's needed to make an instrument is a controller and a good reference and ADCs and that DAC connected to a 4 quadrant power amp,
and your favorite kind of code tools. I like micropython for this kind of thing -- it makes it easy to build
a standalone system that is $7 BOM for the microcontroller parts so you don't have to have a laptop attached to do things.


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

cnc_joker
 

I may be asking a dumb question, but why do you need a 576 if you want a curve tracer?
Could you not do the same thing with 2 computer controlled power supplies?
That and some software could characterize any 2 or 3 terminal DUT that a 576, 577 or even
a 570 can do. It is not as if the Tek curve tracers are fast, i.e. they plot at 60 Hz.

The computer controllable supplies would need to have programmable voltage and current
and be able to read the voltage and current. That does not seem to be too much of a
requirement.


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

Harvey White
 

Look at the inputs of the vertical and horizontal amplifier, assuming that they do not have an internal gain adjustment.  That means that the vertical and horizontal amp chains have a fixed amplification factor from the input to the plates, and that all of the scaling is done at the sweep circuitry.

At that point, the sweep settings have basically set up the inputs for a particular p-p input voltage regardless of the settings for the current or voltage settings for the part.

What that does not figure in, nor does it (at this point) allow you to do is understand the settings on the dials for current/voltage.  These are needed to reproduce the scale settings.  No idea where to get them, of course.

There's ways, but they get interesting and you may not be able to do them easily.  It depends on the circuitry inside, and all I'm working with is a "how it *should* work...."

Harvey

On 1/7/2020 4:29 PM, Matthew Hofmann wrote:
I have an old 575 like the one your brother has. I think I might do a little exploration into the circuitry to see how one might drive a pair of A/D converters to get the horiz & vert data.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Mlynch001
Sent: Tuesday, January 07, 2020 3:46 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ?

On Tue, Jan 7, 2020 at 02:29 PM, Matthew Hofmann wrote:

I assume that the 576 Curve Tracer doesn't have a USB interface and this guy
has somehow added one? Any idea how/where he tapped off of the 576 to
digitize the data on the CRT?
Matt,

Correct, No USB or other ports on the 576. It is from an age before USB was even a dream. There is a person who has accomplished this, yes. Where and How they tap in to get the data??? That is the $1 Million question, one we would like to discover the answer to. There must be some way to do it, but the cost of a commercial solution is steep. It is going to take some deep knowledge of the 576 and whatever method provides the interface. Some have suggested Arduino?


Re: 'Solder Rot'

Roy Thistle
 

On Tue, Jan 7, 2020 at 11:44 AM, DaveH52 wrote:


you will find a wealth of information, including
https://www.dfrsolutions.com/predicting-fatigue-of-solder-joints
Thanks for that link DaveH53 (Dave?).
From the paper (buried in the long introduction) , "The purpose of this paper is to provide a better understanding of the relevance of standard strain energy based models for low cycle fatigue of solder joints in predicting the behavior of standard SMT packages subjected to a very high number of power cycles.", where the paper leads me to believe "... a very high number of power cycles." is something like 250,000.
There is also some discussion about this being a significantly higher than room temperature phenomenon.
I have definitely experienced thermally induced strain in poorly designed laptops where heat/temperatures are a problem.
While very interesting... to me at least... and I'd like to hear more...I'd venture that for a lot of the stuff discussed on this list, failures due to the phenomena, discussed in the paper, are not an issue, for many of us?
Best regards, best wishes.
Roy


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

Mlynch001
 

Dennis,

I agree 100%. Below is the E-Bay Item, they have pictures of the USB port on the side of the 576. I believe this is the same product that you are talking about. I may not be the sharpest knife in the drawer, but the evidence is overwhelming that they are definitely picking off that switch data from somewhere inside the instrument.

Look for E-Bay Item #302445112576. You can also search for “576 Tektronix” as the search term. You will find it listed at $4500 plus $195 shipping. Supposedly a “refurbished and calibrated” 576 with the USB port and software.

When you find it and have a chance to look it over, I would like to hear your thoughts.

Sincerely,
--
Michael Lynch
Dardanelle, AR


Re: Hakko FR-301 alternatives?

Carsten Bormann
 

On 2020-01-08, at 01:25, John Crighton <john.crighton@...> wrote:

For hobbyists and enthusiasts, this cheap and cheerfull ZD-985 is probably a better investment than a Hakko.
Even cheaper is the ZD-915 — €80 (maybe add a €20 replacement handset if you want it more likely to be ready when you need it). Not a “quality tool”, but it really does the job if you need it once a month or so. Do heed the warning to let it heat up properly (say 4 minutes) before using it, or you might get some stuck solder in the handset.

It also helps if you know that when the solder is molten and you start the pump, you should wiggle the tip circularly around the pin for half a second so that is freed of solder on all sides and no longer sticks to the via. This is why a ZD-915 (or a FR-301, for that matter) is a whole class better than single pump action tools like the €24 ebay 283588229178, which is otherwise already a quite capable device (even if its safety is questionable: do not use without both an RCD/GFI and safety glasses, but I hope you have those in your lab anyway).

Grüße, Carsten


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

 

Hi Michael,
At some point in the video (I don't know where the eBay auction is) they say no modification is necessary to the 576. That has to be total BS. My definition of no modification is a little stricter: it means they never had to open the 576 up. Period.
If what you are saying is true about the port on the side then they did go inside the 576 and attach wires to the switches so they could set the gain or attenuation of their A/Ds properly and so they could pick off the readout information.

The little Vacuum Tube adapter I made for the Tek semiconductor curve tracers required no modification to the curve tracers at all. By that I mean you never open the curve tracer up for any reason. That's my definition of no modification.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Mlynch001
Sent: Tuesday, January 07, 2020 4:17 PM
Subject: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ?

Dennis,

Thanks for weighing in on this one. I was thinking the same thing, that it is easy to talk about it, but much more difficult to make it work, as you have already stated. They have added a USB port to the right side of the 576, This port appears in one of their promotional photos on E-Bay. They never indicate what the internal connections are, not sure why they ever would want to do this. However, it appears that they are at least partially tapping into the data from the existing readout to get the different voltage and current switch positions, since they display this same data on the laptop screen. Perhaps this is how they are getting the current/division and step currents? They are definitely using much of the existing 576 switch gear and circuitry then doing some sort of A/D conversion to deliver this by the USB Buss. The e-bay pictures show precious little of the interface, but they show that the resulting laptop display appears to be a partial clone of the original 576 display, with some added software in play as well, but again, the information is sparse at best. I am sure that some of the brilliant minds in the group could figure this out.

Michael Lynch
Dardanelle, AR




--
Dennis Tillman W7PF
TekScopes Moderator


Re: Hakko FR-301 alternatives?

Dale H. Cook
 

On 1/7/2020 4:37 PM, Arden wrote:

With all of the garbage I work on all sorts of stuff gets into the suction channel, shards of oxidized solder, charred wire insulation, and flux ash. Taking time and effort to clean out the suction channel and emptying
the collection cartridge was time wasted.
The filters in my Metcal SP440 catch all of the garbage and keep it from clogging things.
--
Dale H. Cook, Member, NEHGS, AGS, MA Soc. of Mayflower Descendants;
Plymouth Co. MA Coordinator for the USGenWeb Project
Administrator of https://plymouthcolony.net


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

JJ
 

Hi, Jim. I used many resources and tutorials - YouTube has many good
tutorials for beginners. There is Python and there is PYQT5. PYQT5 allows
you to build a Graphical User Interface (GUI) easily. - it uses Python.

It's a long road and takes time to become proficient - a few months at
least. I programmed in Java, C++, Javascript, and many other proprietary
languages over the past 50 years - so picking up a new language isn't all
that difficult for me.

I have also been an analog/digital circuit designer over that period as
well - so I'm with you. Using your hardware skills together with an Arduino
and coupled with Python allows you to bring the analog outside world into
your PC for data analysis and control.

I can send you a few books in PDF format that I used if you like.

But please note that you need to love this stuff - it takes time and
patience! But, once you get it, you can do virtually anything you want. The
best way to learn a new programming language is to jump in and practice.
Don't just read a book - you need to practice! Otherwise, it gets too
boring and overwhelming! It's good to have a project in mind - it's very
motivational.

Best,
John Justin


Re: Hakko FR-301 alternatives?

John Crighton
 

Hello Michael and the Group,

there is a review of this ZD-985 on youtube.
https://www.youtube.com/watch?v=Ft50m8UU5WQ
An old workmate of mine bought one and he is delighted with the performance
of the ZD-985 in removing large components from double sided boards.

I have an old Hakko 700 de-soldering station. It cannot remove large components as easily as the ZD-985
For me it seems to loose heat too quickly, from memory the element is around 40W. (For the ZD-985 a power of 80 Watts was mentioned in the video)
The parts are expensive for the Hakko 700. I have difficulty finding them.here in Sydney. The unit is 30 years old so once the heating element fails in the
gun, the unit is finished. Maybe I am expecting too much from Hakko in long term after sales service. The little rubber diaphragm in the vacuum pump is
not available from Hakko in Sydney. That tiny piece of thin rubber is a consummable and should be available. To me, Hakko is letting me down.

For hobbyists and enthusiasts, this cheap and cheerfull ZD-985 is probably a better investment than a Hakko.

Regards,
John Crighton
Sydney




I am cheap, so I took a chance on a CCC (Cheap Chinese Crap) ZD-985 Vacuum desolder station @ about $119.00 (about 2 years ago) delivered in 2 days. Amazon has a great return policy, so when I got it, I immediately started cleaning components off of old boards, for practice and as a "stress test". Figuring that this thing would throw craps in an hour or two, I was greatly surprised! The thing came through with flying colors. No return needed. That was almost two years ago, it still works great. I am not sure how much solder this thing has removed, but the gun has been cleaned many times with large globs of solder being removed from the gun each time. The ZD-985 also came with a bunch of extra parts, tips and filters. The only parts needed, so far, are the little filters that go inside the gun. For a cheap alternative, this thing is more than acceptable. It sure beats solder sick, manual solder suckers and the like. Much less likely to damage a precious board with this tool. Is it equal to a genuine HAKKO? I doubt it. Is it 90-95% of what a HAKKO is? I say it is for me and I have $200+ in my bank account as a result. The sad thing is that some HAKKO products or components are being sourced in China, and ruthlessly counterfeited there as well.

--
Michael Lynch
Dardanelle, AR


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

Mlynch001
 

Dennis,

Thanks for weighing in on this one. I was thinking the same thing, that it is easy to talk about it, but much more difficult to make it work, as you have already stated. They have added a USB port to the right side of the 576, This port appears in one of their promotional photos on E-Bay. They never indicate what the internal connections are, not sure why they ever would want to do this. However, it appears that they are at least partially tapping into the data from the existing readout to get the different voltage and current switch positions, since they display this same data on the laptop screen. Perhaps this is how they are getting the current/division and step currents? They are definitely using much of the existing 576 switch gear and circuitry then doing some sort of A/D conversion to deliver this by the USB Buss. The e-bay pictures show precious little of the interface, but they show that the resulting laptop display appears to be a partial clone of the original 576 display, with some added software in play as well, but again, the information is sparse at best. I am sure that some of the brilliant minds in the group could figure this out.

--
Michael Lynch
Dardanelle, AR


Re: Tektronix 2465 for sale ...

Roy Thistle
 

On Sun, Jan 5, 2020 at 03:26 PM, mosaicmerc wrote:


so I could maybe scrap out a m'board from 1
Hi mosaicmerc:
I'm interested. I have a couple of them that I need to fix.
Best regards and wishes.
Roy


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

Paul Amaranth
 

I've thought of making an LCD replacement for the 576 CRT. It would be
pretty neat, you could add a touch screen interface and calculate the
parameters on the fly (quite possible since you could get all of the
control settings as well as the X/Y data available). USB for data
download would be useful. I have a 576 with a double peaking CRT so
I'll probably get around toit one of these days.

I do development with arduinos and they are pretty amazing.
I don't think I'd use it for this though, the code space is
not that huge and it would be very easy to fill it up.
Maybe you could do it, but that doesn't fit my idea of
proper software. The finite state machine you have to use
for anything of complexity tends to get out of hand in
order to use the event loop paradigm embedded in them.

A multi threaded application would probably be a better
architecture.

I also do not like the idea of having to use a PC for data
display. Software programs like that have a tendency to
wander away from the instrument. An since developers always
use the latest/neatest/etc package to build the UI it becomes
impossible to build after a few revisions down the road (IF
code is available - try building some of the Non-GNU SDR
software if you don't believe me). I've lost track of the
number of revisions of Qt I've had to use for various
packages.

It took me months to track down the TekMate software that interfaced
to the 24xx scopes.

My two cents.
Paul

--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix & Windows


Re: Hakko FR-301 alternatives?

Thomas Garson
 

Hello Jean-Paul,

Not to dissuade you from getting a good desoldering tool, but before you do that, get yourself some Chip Quik.

Chip Quik is very low temperature solder that readily alloys with normal solder when the two are melted together, thus drastically reducing the melting temperature of the resulting amalgam.

Once treated with Chip Quik, solder in a plated through hole, even in a 6 layer board, will stay molten long enough to suck it out or wick it at a temperature low enough to preclude significant damage to a quality PCB. It is often possible to gently remove a many legged through hole IC from a PCB using ChiQuick just by melting it into the solders and using a Wiha Ausheber.

My work includes rework DSP products that make extensive use of multi layer PCBs that mix through hole and SMD components. Chip Quik can be melted into those tiny flat pins on 100+ lead SMD LSI chips, again, allowing them to be removed, without physically damaging chip or pads, as all pin connections can be melted simultaneously as not destructive temperatures.

Once parts are removed, holes and pads can be easily cleaned with wick and retinned with regular alloy solder.

If I had to choose between a directed hot air desoldering station and Chip Quik, I would take the Chip Quik.

Thomas Garson
Aural Technology, Ashland, OR
By my calculation, the dynamic range of the universe is roughly 679dB,
which is approximately 225 bits, collected at a rate 1.714287514x10^23 sps.

On 1/7/20 4:49 AM, Jean-Paul wrote:
Hello all, this old EE has used solder wick and various spring loaded solder suckers, all are slow, and damage delicate PCBs. Due to maintenance, cost and bench space, I never got a rework station like the Pace. Now am restoring a number of TEK 2465/7B and 7000 plugins, so easily unsoldering components and ICs without board damage is a must.
Seems the Hakko FR-301 is highly regarded and gun style, needs no separate power supply/vacuum. (USA 120V model) But rather costly $250-350.
I have several other Hakko 926 (ancient analog control) irons quality and longevity is super.
I ask the Forums feedback on the Hakko, as well as lower cost alternatives.
Most of my work is thru hole, not SMD, perhaps 3-10 jobs in a year.
MANY THANKS
Jon


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

 

Hi Rick,
Thanks for pointing out this video. It is interesting for many reasons.
* How many people would tack on an additional $2,000 on top of $2,000 that this company sells a used 576 for. There is
* It is a very amateurish demonstration of something they want a lot of money for. The You Tube demo and an asking price of ~$2,000 are very inconsistent.
* At one point in the video he unplugs a USB cable but you can't see what it is being unplugged from. They appear to be very careful to not show the "black box" the USB cable plugs into that would be the hardware interface between the 576 and the Windows program.
* Does the "black box" have to be connected to points inside the 576?
* I went to their web site. They sell used electronic equipment like, among other things 576 curve tracers. I could not find anywhere on their site where I could learn more about it.

It would be possible to capture some of the information without opening the 576 up and connecting to points inside it. An A/D connected between the emitter and collector would capture the voltage being applied between those two terminals. The current steps flowing through the base are harder to digitize unless you insert a small resistor in the base current generator to measure them.

The A/D attached to the collector lead would have to handle a huge voltage range. I'm not sure how you would do that except by the user manually selecting what the range would be in advance so a resistive divider of the right attenuation could be inserted between the 576 and the A/D inside their interface box. The same would be true for the base current. You would have to specify what the step range is going to be so the gain of the trans-impedance amplifier (or whatever they use) to drive the base current A/D could be set to a range it could handle.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of garp66
Sent: Monday, January 06, 2020 2:11 PM
To: TekScopes@groups.io
Subject: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ?

hi,

Has anyone thought of interfacing a Tek 576 Curve Tracer (Or any of the other Tek Curve Tracers) to a laptop via USB ?

I have been thinking of putting an Arduino or Rasp Pi inside a Tek 576, with a few A/D & D I/O shields to get the data out for comparisons and automated measurements.

I just saw this YouTube Demo of a "pricy" USB conversion :
(dated Jan 30, 2019)

https://www.youtube.com/watch?v=LSMqD5iwj4U

done by Tuntien of
https://equiptek.com/000.htm

rick







--
Dennis Tillman W7PF
TekScopes Moderator


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

Jim Ford
 

Hi, John.With your experience writing Python code, maybe you could point me in the right direction.  I'm trying to learn Python so I can control my test equipment over GPIB and USB.  I downloaded a Python tutorial, but it was more like an overview and told me way more than I wanted to know and none of what I needed to know!  Maybe good for a software engineer but useless for a hardware guy like me.I was going to private message you but then I figured that others on TekScopes could benefit as well.Thanks in advance for your help.Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: JJ <jajustin@...> Date: 1/7/20 3:22 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ? I think the voltages need to be picked off before they get to thedeflection plates. If you digitize the signals and send them across theserial interface using an Arduino, all you need to do on the PC side is toplot the stored samples of each voltage against each other - Ic isessentially derived from a voltage across a 1 ohm resistor. You can use theMatlib library to plot. the samples against each other - Ic vs Ib, Ic vsVce, etc. I don't think that you need access to any of the 576 controlssince the samples themselves get scaled automatically and dynamically byMatlib when plotting.I just finished writing a program using Python /PYQT5 to drill holes in aPCB using an inexpensive GRBL based CNC machine - 3018 Pro (I paid $170).GRBL based CNCs all use Arduinos. The program uses an affine matrixtransformation - so you don't need to line up the PCB to drill the holesafter etching.I don't believe that it's all that difficult to do!Best,John Justin


Re: Hakko FR-301 alternatives?

guy232
 

I bought the fr301 new on the bay for around 250. Works great, tons of vids on youtube too showing operation & disassembly (fr300 is similar to 301)

The best part about the 301 compared to the cheaper alternatives is that it maintains resale value quite well. When the Fr-301 came out there were quite a few guys selling their old fr-300s for $180-200 and they actually sold.

The 301 is also handy because it can be stored away in the case and put on the shelf or in a drawer to free up real estate it you dont use it much.


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

JJ
 

I think the voltages need to be picked off before they get to the
deflection plates. If you digitize the signals and send them across the
serial interface using an Arduino, all you need to do on the PC side is to
plot the stored samples of each voltage against each other - Ic is
essentially derived from a voltage across a 1 ohm resistor. You can use the
Matlib library to plot. the samples against each other - Ic vs Ib, Ic vs
Vce, etc. I don't think that you need access to any of the 576 controls
since the samples themselves get scaled automatically and dynamically by
Matlib when plotting.

I just finished writing a program using Python /PYQT5 to drill holes in a
PCB using an inexpensive GRBL based CNC machine - 3018 Pro (I paid $170).
GRBL based CNCs all use Arduinos. The program uses an affine matrix
transformation - so you don't need to line up the PCB to drill the holes
after etching.

I don't believe that it's all that difficult to do!

Best,
John Justin


Re: 2235 2mV vertical range noise and surprising fixes

 

regarding the 2235 secondary psu rectifiers:

YES, it is possible to see leaky, shorted or open secondary supply rectifiers,
which results in big ripple.  this is FAR less common than bad caps (over 90% of the problems) but it does happen after many years. if I cannot get the bus voltage ripple low enough (just compare to other supplies), that's the next item to replace. I've only had to do it a few times, but that's more than never.

one more thing, I always use a floating device to measure DC volts and ripple, the Fluke 867B graphical multimeter works great for me, I can see everything at once, and no ground interactions.

regards,
walter

--
Walter Shawlee 2
Sphere Research Corp. 3394 Sunnyside Rd.
West Kelowna, BC, V1Z 2V4 CANADA
Phone: +1 (250-769-1834 -:- http://www.sphere.bc.ca
+We're all in one boat, no matter how it looks to you. (WS2)
+All you need is love. (John Lennon)
+But, that doesn't mean other things don't come in handy. (WS2)
+Nature is trying very hard to make us succeed, but nature does not depend on us.
We are not the only experiment. (R. Buckminster Fuller)


Re: 454 screen brightness issues?

Jack Ohme
 

and sorry, but i dont have access to a VTVM :(

surely if my meter cant measure across it, then there at least isnt a
catastrophic short?

On Tue, Jan 7, 2020 at 2:49 PM Jack Ohme via Groups.Io <machinamancerjack=
gmail.com@groups.io> wrote:

also anyone know where B1473-75 are? looks like tek added some neon bulbs
there to make sure the grid didnt go above K, but i dont know what theyre
doing now...

On Tue, Jan 7, 2020 at 2:40 PM Jack Ohme via Groups.Io <machinamancerjack=
gmail.com@groups.io> wrote:

I am fairly certain its the HV by this point, mike, since my -1960v is
only
around 1800v. I meant the front panel intensity control with the touchy
wiper. I'm currently trying to ascertain the best way of getting a look
inside the HV circuitry, the 12KV multiplier for the anode seems to be on
top of the -2kv section for cathode and grid. I'm awful with loose parts
so
I'd rather not tear the whole thing down, currently scouring the manual
for
test points I could use to point out which diode or cap is bad in the
bias
supply.

On Tue, Jan 7, 2020 at 2:36 PM Mike Dinolfo <@mdinolfo> wrote:

Jack, in response to your email of 1:33 pm:

I think it's possible that your "excessive trace brightness" problem
could be an issue with HV circuit component failure (as others have
suggested), and/or Z-axis circuitry or adjustment. I should also add
"and/or something else that I don't know". It's good that you've
managed to get +12V at TP1349, because I think this pretty much
indicates that the Z-axis circuitry is OK. But more on that below...

Regarding your resistance measurement: I believe that probably the
majority of "garden variety" multimeters in use today do not allow for
measurement of resistances in the 50 megohm range (they only indicate
"open circuit" or the equivalent of "no measurement possible"), but I
also believe most of the VTVM's of 50 or 60 years ago would do so.
Although a VTVM's accuracy and resolution for those measurements is
only
fair, it would be sufficient for the measurement that I tried to
describe; that's why I suggested a VTVM. So your multimeter/ohmmeter
might be indicating "open circuit." But look at the schematic for the
454 CRT circuit and the Z-axis board and you will see the resistors
(R1442 thru R1449) that I mentioned; measuring from TP1349 (on the
Z-axis board) to CRT pin 3 is effectively a measurement of the
resistance across the terminals of C1449. Or you could do a "deep
dive"
into the HV compartment (removing a few layers of components) and
measure the resistances individually. Note that I've never done such a
"deep dive"measurement, but I think I've seen emails from other
Tekscopes group members saying that a "power down" measurement of these
resistances might not be valid because the resistances could change
under applied voltages during "power up" conditions. It's also a lot
of
work (my opinion) to do such a "deep dive" measurement, and even more
work to replace these components in a shotgun approach. So I've been
trying to encourage you to verify the Z-axis circuitry is OK before you
zero in on the HV circuitry as the culprit.

Regarding your "12V at the point" measurement: When doing the "Adjust
CRT Grid Bias" adjustment on page 6-11 of the manual, you have adjusted
INTENSITY to get +12 volts at TP1349, correct? When you then go to the
next step, to adjust CRT Grid Bias R1447, can you then reduce the
visible dot or trace on the screen to get it "turned down" to a
reasonable level of brightness? When you talk about "the pot" and "the
dial" and "8-10% of the pot's wiper", I admit that I'm confused as to
whether you are talking about the INTENSITY control (front panel) or
grid bias trimmer pot R1447.

Finally, my earlier emails did not correctly state the process
described
on page 6-11 of the manual, and for that I apologize. But I'm kind of
at
a dead end as far as any further suggestions.

Mike D N4MWP

On 1/7/20 1:33 PM, Jack Ohme wrote:
Mike-

My meter measures an open circuit from pin 3 to point 1349, I think
the
resistance is more than it can measure. I was able to get 12v at the
point,
but its VERY touchy, about half of the pot does next to nothing, then
the
middle changes so fast you have to brush the dial with your finger to
dial
in past 2 or 3 volts difference, then it becomes very slow again. So
about
20 volts of the 6.8v -> 32v transit occur on about 8-10% of the pot's
wiper
surface. Seems unusual to me, not the source of the problem at least,
but
perhaps a clue. It just seems very odd to me that the CRT grid
measures
within spec for the datasheet... actually about 25 volts more
negative
than
its listed typical operating values at intensity pot centre. To the
best
of
my understanding, a higher negative bias makes the screen darker, so
this
is quite confusing indeed, and what led me to believe there may be a
busted
grid.

On Mon, Jan 6, 2020 at 8:10 PM Mike Dinolfo <@mdinolfo>
wrote:

Jack:

In my previous email, I unsuccessfully tried to transcribe the
procedure
for CRT grid bias adjustment described on page 6-11 of the manual.
Grid
bias adjustment control R1447 does not directly affect the voltage
at
TP1349. Refer to the manual (page 6-11) for the exact process; my
apologies for my error. I suggest the following:

1. Setup the scope's controls as described on page 6-8 and 6-9
"Preliminary Procedure".
2. Try to adjust the INTENSITY control to get +12V at TP1349, as
per
page 6-11 "Adjust CRT Grid Bias." If this cannot be done, there
might
be a Z-axis problem. If you can get +12 volts, then go to step 3
below:
3. Adjust CRT Grid Bias potentiometer R1447 per paragraph 6.d on
page
6-11.
4. Let us know what the results are. Although at this point I might
be
at a loss as to further ideas.

It's also possible that there might be an issue with the grid bias
resistors/potentiometer (R1442 thru R1449) as others have suggested.
If
you have access to a ohmmeter (such as a VTVM) that can detect
variations of about 1.8 megohms in a total resistance of about 52
megohms, then you can check this by measuring the resistance (with
power
down) from the CRT pin 3 to TP1349 while varying grid bias
potentiometer
R1447 from fully CCW to fully CW. You might get one measured value
with
the ohm meter's leads in one position, and another with the meter
leads
"reversed"; if so then go with the higher set of measurements, as
the
lower set of measurements would be due to forward bias of D1440.

Mike D N4MWP

On 1/6/20 7:37 PM, Jack Ohme wrote:
Mike,

I have a copy of the manual in PDF and on paper. The intensity dial
correctly changes the voltage (although the screen brightness shows
no
change), but the grid biasing potentiometer does not change the
voltage
at
TP1349, which stays at around 6.8v. I'm not sure whats happening
here,
if
this is the grid biasing pot that is broken or something nearby on
the
Z
axis board, but I will inspect the schematics. Let me know if you
think
of
anything to look for.

-Jack

On Mon, Jan 6, 2020 at 2:15 PM Albert Otten <
aodiversen@...>
wrote:
Hi Jack,
Where should I be looking for those DC restorers, in the -1920v?
The 454 has no DC restorers. The HV transformer has separate
windings
for
the grid and the cathode circuit. The rectified voltage for the
grid
can be
reduced somewhat by the grid bias pot R1447 (in the divider chain
with
R1442-R1446) and is stacked on the voltage supplied by the Z-axis
amplifier.
When you follow Mike's suggestion and use a pdf of the manual, you
will
note that the waveform at TP1349 is almost invisible. The blue
picture
in
the paper manual is also very faint. The voltage switches between
the
2
written values 17.7 V and 6.75 V.

Albert