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.

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

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)

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@erols.com> 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@erols.com>

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@concepts.nl>

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

On Tue, Jan 7, 2020 at 04:40 PM, Ke-Fong Lin wrote:

I find it very surprising that the 576 doesn't have an X-Y output for a
plotter.

Maybe that's because Tek doesn't have a plotter offering (contrary to HP).
And there are various add-on to take photos of scope's screen.

Lin,

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.

I would guess that you are 100% correct in your thinking about the lack of a TEKTRONIX plotter. Not much motivation to put an X-Y output and then give your customer a motivation to buy an HP or other brand of plotter? On the other hand, TEKTRONIX was pushing Scope Cameras, big time. They had considerable experience with scope cameras, so it was natural that they went that direction.

--
Michael Lynch
Dardanelle, AR

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@erols.com> 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@erols.com>

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@concepts.nl>

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

You don't really need to worry a lot about it.

Use the arduino serial write to get the data to the PC.

Then in whatever program you use, be it pascal, visual basic, or what, open a com port for the data

You'll then get a data stream of what you've written.  I'd recommend ascii of the form

X= nnnn.nnnn; Y=nnnn.nnnn;

C has parse routines, other languages might.  There may be some nice tutorials out there.

For graphics, you can use things like write line, and then set pixel (mythical functions, depends on the language).

Short story is that it is possible to do.

Graphics are fairly easy once you see that you can write text anywhere on the screen, draw a line from point A to point B, and then plot a point (or draw a line from point A to B, depending on style).

The reason for doing it yourself is that you'll learn a lot, and that you can customize it to do exactly what you want.


Harvey

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.

I find it very surprising that the 576 doesn't have an X-Y output for a plotter.
These were common in the 60s-70s and I guess even in the 80s, before GPIB became common place.
For instance, my HP3580A spectrum analyzer has a 0-5V X-Y output with the related pen on-off outputs.
So you can have a nice spectrum plot on paper!
Maybe that's because Tek doesn't have a plotter offering (contrary to HP).
And there are various add-on to take photos of scope's screen.

The big advantage of the 576 is that it is solid state and the logic is TTL, so it may be easier to work directly with the ARDUINO than it might prove with the 575, just taking a guess on that . The one interface that I have seen not only exports the CRT Traces, but also the knob positions and voltages as well (on the 576 at least). The fact that the 576 contains that wonderful and complex readout card, might actually make the job easier to interface. I would be interested in such a project. I have a few ARDUINO boards lying around, looking for something to do. I think the ARDUINO code would be the hardest part, but what do I know.

--
Michael Lynch
Dardanelle, AR

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

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

Arduinos can dump serial stream data direct in to a pc the micro can handle
all the pc interconnect as well.

On Tue, Jan 7, 2020 at 11:00 PM, walter shawlee wrote:

replace any bad switching rectifiers if needed.

Hello Mr Walter,
can you be more specific with the bad rectifiers please. If I understand correctly you mean that in some cases someone can find a partially bad rectifier?

Panos.

Getting the data digitized is the easy part. Can someone write the software
interface between the USB and the computer screen?
Arduinos and PICs probably have USB driver functions, its the graphics that
is the problem for me. I wish I had the skills.
I use a camera but the shutter speed needs to be long enough to avoid
bright patches of trace.
Tektronix at one time produced a digital camera to replace the Polaroid
ones but they went obsolete as fast as computers.

On Tue, Jan 7, 2020 at 4:29 PM Matthew Hofmann <mhofmann@sbcglobal.net>
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?
--
Michael Lynch
Dardanelle, AR

Bert, my drum beats hail and hearty for anyone who can do a job with el-cheapo tools and the results are no different than using the super expensive "I wanna have one too" tools. I jest a bit but over the years I gave up on the idea of owning a de-soldering gun for one simple reason: 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. If I constantly worked on circuit boards alone a gun would be great to have. So it's solder wick, hand desoldering pump, poking through clogged plated through holes, draining solder off of overloaded terminals, etc. So to have a big clunker taking up space on my work bench is a non option. Repairing and replacing damaged pads, often from previous rework, is all part of the job. -Arden

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.

The 2mV vertical range on the 2235 is a triumph of marketing over technology, as it really pushes the performance of the scope to a place where it doesn't willingly want to go. virtually all 2235's exhibit increasing noise on this range as they age, and sometimes the displayed noise is huge (when the psu caps deteriorate in the secondary of the switching supply).

I have had to fix many of these, and generally follow this plan:
----------------------------------------------------------------------------------
1. replace all LV psu secondary caps with modern low ESR versions (820uf becomes 1000uf).
check for ripple after the change at the psu test points, and replace any bad switching rectifiers if needed.
2. tighten all ground hardware all over the scope, especially around the vertical assembly. make sure all case ground screws (2) are there too.

Recently I had one stubborn unit that just wouldn't behave even after re-capping (which it desperately needed), and I traced the fault to a very unusual area. all of the switching supplies are slaved the the adjustment of the -8.6V level. my unit measured -8.42V, which I initially ignored as it seemed to be within spec. BUT, the manual specifies a tighter adjustment range, and incredibly, as I raised the voltage to just over -8.6V with the rear edge trimpot on the motherboard, the displayed ripple almost vanished. I have never seen this interaction before, so I thought I would pass it on, as it may prove useful to anybody re-capping one of these nice little 100MHz scopes.

the difference between good and bad ripple display is a very narrow -8.6V adjustment range, about 150mV, which I found amazing, as I cannot see how this has such a dramatic effect, but it does. no adjustment or parts replacement can totally remove ALL ripple from the 2mV range display, but you can certainly improve it down to about one minor division. bad scopes with poor caps can be 5-10 minor divisions, making it unusable on the 2, 5 and 10mV ranges.

I hope this proves useful to others working on 2235's.
all the best,
walter (walter2@sphere.bc.ca)
sphere research corp.
https://www.sphere.bc.ca/test/index.html

Hi Jack,

I had my leads wrong, the grid is actually around
150 volts ABOVE the cathode, which explains everything. Thank God it isn't
a broken grid, but... the Z axis board is certainly messed up if something
like this is going on.

Now that you confirm that you made a sign mistake (question in my previous response) the fault is certainly not in the Z-axis board, diagram <16>, or in the CRT itself. In y opinion it must be a fault in the CRT supply circuitry diagram <17>. Probably in the grid supply. Probably an open "bottom" end of the grid bias pot R1447. Did you measure the resistance between wiper and joint of R1447/D1440? Does it go to zero in one detend of the wiper?

Albert

On 07/01/20 19:17, Panos wrote:

On Tue, Jan 7, 2020 at 08:27 PM, Tom Gardner wrote:

As a fallback, take a video.....

Yes Tom I know, but unfortunately is useful only if you have a GPIB option on your oscilloscope and very very patience to work with this.

If you have the information, you can find a way of using an external programmer to put the info into the new ic.

The GPIB is not necessary.

But even then, if/when the earom lost a constant, this is a sign that it has come its end of life and need to replace.

You have to proactively capture the contents before any part of it is lost!