Date   

Re: Tektronix 2230

satbeginner
 

Hi Saroj,

I was busy expanding the GridTied Solar panels we have here, hence again my later response.

In terms of temperature, my personal feeling is: The lower, the better.
In my 2215A('s) I have seen temperatures around 60 - 63 Celsius, a temperature I feel comfortable with.
But on the other hand, you have a 2230, so more electronics to power, so maybe higher temperatures in that scope...

In terms of electrical isolation you must keep using the Mica or more modern isolator, but I would add a TO-220 heatsink at both sides of the metal frame where the FET is mounted.
A bit like in this picture: https://groups.io/g/TekScopes/photo/64919/4?p=Name,,2215+repair,20,1,0,0
The addition of the two TO-220 heatsinks will improve lowering the FET's temperature, also with the FAN mounted in place.
Also, do put that little screw in the side panel back in when you close up the scope, that also helps cooling that part of the power supply.

This brings me to the Molex connector you still see in that picture: I never liked them.
They are very susceptible to corrosion, so it is easy to develop an extra serial resistance which will affect the operating settings of the FET, and might even rise the temperature.

So, in addition of what you see in the picture mentioned above, I would solder the wires directly to the FET after mounting it to the metal frame.

Have a nice weekend,

Leo


Re: 475 With a bowed display. . . .Ideas?

 

On Sat, Aug 8, 2020 at 04:40 PM, Michael W. Lynch wrote:


If it was just one minor division of deviation, I could live with this, but
the outermost vertical markers are about 6 minor divisions "leaned in" at the
top of the marker. It is almost like looking through a "fisheye" lens.

I'd think that's way out of range for the electrical Geometry adjustments that you mentioned earlier, so probably something is wrong of the sort that Chuck describes. It may be worthwhile to quickly check if the Geometry adjustment pot's range reaches the intended 0 to +110V. It's GND-related, so not dangerous to measure, unlike grid- and focus- voltage levels.

Re. the "fisheye" appearance: Is the distortion mostly (radially) symmetrical? In that case, I wouldn't think it could be just a moved magnet.

Trying another CRT seems to make sense. Not too much hassle with a 465/475. Just the usual care with the lingering anode voltage.


BTW, re. the first post, Michael wrote:

"Problem was C1442 was bad. High resistance and almost no capacitance, loading the +15V supply."

The high resistance and low capacitance resulted in your meter showing that the average or RMS voltage was too low so good regulation wasn't possible.
C1442 wasn't loading the +15V supply ("high resistance") but loading the 15V supply wasn't possible, since the regulation circuit received practically unbuffered rectified AC. It's probably what you meant.

Raymond


Re: AWG2021 Sample Waveform Library

Martin Hodge
 

Now if anyone ever comes across the "Check/Adjustment" disk (063-2171-XX) that came with the AWG2021 service manual you are expected to reciprocate! ;)


Re: 475 With a bowed display. . . .Ideas?

Michael W. Lynch
 

On Sat, Aug 8, 2020 at 08:22 AM, Chuck Harris wrote:


Typically, when a proper application of the Geometry,
Focus, Astigmatism, Trace Rotation, and other affiliated
adjustments results in a screen that just doesn't look
as pretty as we would like, it means that there has been
an outside physical influence on the CRT (READ: OOPS! BANG!
$%^! & #!!*^! Why Me???)
No signs of major trauma, but this is still a possibility. What confuses me in this regard is the fact the the unfocused spot on the CRT is beautiful and round, one of the best I have ever seen.

The Mumetal shield can get bent, or magnetized.
Not bent, but magnetized? VERY POSSIBLE. I am curious how such magnetization can occur as this issue has come up in other threads as well?

One of the steering magnets (held with Scotch tape) can fall off
of the CRT neck, causing the beam to partially strike one
many internal shield electrodes that looks like a hole in
a plate of metal.
I can look at this when I pull the CRT. Would this not distort the unfocused spot (mentioned above) somehow?

Or, it can be that we are much more nit-picky than tektronix
was originally.
I'm just not that picky. I do not think I am asking too much for the markers to be vertical and consistent across the entire viewing area (or at least within one minor division). If it was just one minor division of deviation, I could live with this, but the outermost vertical markers are about 6 minor divisions "leaned in" at the top of the marker. It is almost like looking through a "fisheye" lens.

If you carefully read the specifications in the manual, you
will often find that we have been spoiled rotten by all of
the CRTs we get that are much better than the specifications
say they could be...
I totally agree. The CRT is one of those items that is a source of constant amazement for me. How they work and withstand decades of use and many times abuse. They are a marvel.

Bottom Line, sounds like I need to pull the CRT and inspect it for obvious damage. I can try another "known good" CRT, as I have one or two that produce very good and well aligned traces in other machines.
if a "Good CRT" shows the same symptoms in this chassis, then I need to look elsewhere.

I was thinking that I had missed some other related adjustment? I guess not?

Thanks for the valuable input.
--
Michael Lynch
Dardanelle, AR


Re: AWG2021 Sample Waveform Library

Tam Hanna
 

Also sending thanks!


Tam

--
With best regards
Tam HANNA

Enjoy electronics? Join 15k7 other followers by visiting the Crazy Electronics Lab at https://www.instagram.com/tam.hanna/


Re: 475 With a bowed display. . . .Ideas?

Stephen
 

On Fri, Aug 7, 2020 at 11:25 PM, Raymond Domp Frank wrote:

Possibly not:
In the paragraph immediately following your longish quote the OP writes:

"Y Align R1385 and Geometry R1390 will not bring the vertical markers
into proper vertical alignment even though they do have some effect on
the trace by making it less severe. Even though they never "Fix" the
problem."

Raymond
Ok.


Re: FG 504 problems

John Ferguson
 

the next step will be to discover the unobtanium part needed in one of the FG504's is also bad in the other.

john

On 8/8/20 9:06 AM, Chuck Harris wrote:
Tektronix never gets all of the information you need in
anything but the most trivial manuals.

Between what they withhold for proprietary reasons, what
they put in odd places, what they got plain wrong, and
what they simply didn't get around to documenting, there
is always something missing... something to wish for.

I needed access to the boards on a FG504 I am currently
repairing, and so I pulled the cables off of the floating
power supply board and removed it...

It took me an hour to trace all of the unlabeled connectors
back to their origin, so that I could figure out which one
went on which pin.

Yes, I know, I should have taken a picture... but I had another
FG504 in for repair so I figured I could just crib off of it...
except that someone had beaten me to it, and removed all of
the same connectors on that unit... OOPSIE!

Honestly, I am pretty happy that Tektronix did as good of a
job as they did on including pertinent information in their
manuals... I'll hold them to perfection when I can achieve
perfection myself.

-Chuck Harris

Colin Herbert via groups.io wrote:
Thanks for that info, Dan. Would you believe that when my wife brought me a mug of tea in bed this morning, I was reading the FG 504 Manual and noticed where the jumper is marked on the schematic. I think I was thrown as to its circuit location by the physical location on the circuit board. However, that revelation left me with the puzzle of which was the default (non-VCF) position and I was wondering as to how I might investigate that, when I looked at my email and your reply gave me the answer!

I still have some problems with the Function Generator (though I have fixed one) which relate to the symmetry adjustments.

An earlier problem involved the power-rails and one going bad after I'd measured it to be OK. That turned out to be a harmonica-type connector giving bad contact, so I re-seated all of those that I could locate, which solved that problem, but then left me with the question of whether I had put the W20 jumper back properly or not. You have now clarified that for me.

I wonder why this wasn't clearer in the Manual?

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dan G
Sent: 08 August 2020 01:15
To: TekScopes@groups.io
Subject: Re: [TekScopes] FG 504 problems

On Fri, Aug 7, 2020 at 03:41 PM, Colin Herbert wrote:

While its position is shown on
the Internal Adjustments section A3 Loop Board diagram, there appears to be no
indication of which is the default setting and which the VCF input setting. I
cannot locate the jumper on the schematics either.
Hi Colin,

The W20 jumper is shown on schematic <1> ("Triangle Wave Generator" in
post-B040000 service manuals, and "Main Loop" in early editions.) It
is shown in the upper left corner of the schematic, just above "VCF INPUT".

The jumper is in the N/C position when it is placed toward the back of the
plug-in. Moving it to the front of the plug-in routes the VCF Input signal
to P1275.


dan








Re: 475 With a bowed display. . . .Ideas?

Chuck Harris
 

Typically, when a proper application of the Geometry,
Focus, Astigmatism, Trace Rotation, and other affiliated
adjustments results in a screen that just doesn't look
as pretty as we would like, it means that there has been
an outside physical influence on the CRT (READ: OOPS! BANG!
$%^! & #!!*^! Why Me???)

The Mumetal shield can get bent, or magnetized. One of
the steering magnets (held with Scotch tape) can fall off
of the CRT neck, causing the beam to partially strike one
many internal shield electrodes that looks like a hole in
a plate of metal.

Or, it can be that we are much more nit-picky than tektronix
was originally.

If you carefully read the specifications in the manual, you
will often find that we have been spoiled rotten by all of
the CRTs we get that are much better than the specifications
say they could be...

-Chuck Harris

Raymond Domp Frank wrote:

On Sat, Aug 8, 2020 at 01:26 AM, Stephen wrote:


I’m not sure, but that makes me think « geometry »? Maybe??
Possibly not:
In the paragraph immediately following your longish quote the OP writes:

"Y Align R1385 and Geometry R1390 will not bring the vertical markers
into proper vertical alignment even though they do have some effect on
the trace by making it less severe. Even though they never "Fix" the problem."

Raymond




Re: FG 504 problems

Chuck Harris
 

Tektronix never gets all of the information you need in
anything but the most trivial manuals.

Between what they withhold for proprietary reasons, what
they put in odd places, what they got plain wrong, and
what they simply didn't get around to documenting, there
is always something missing... something to wish for.

I needed access to the boards on a FG504 I am currently
repairing, and so I pulled the cables off of the floating
power supply board and removed it...

It took me an hour to trace all of the unlabeled connectors
back to their origin, so that I could figure out which one
went on which pin.

Yes, I know, I should have taken a picture... but I had another
FG504 in for repair so I figured I could just crib off of it...
except that someone had beaten me to it, and removed all of
the same connectors on that unit... OOPSIE!

Honestly, I am pretty happy that Tektronix did as good of a
job as they did on including pertinent information in their
manuals... I'll hold them to perfection when I can achieve
perfection myself.

-Chuck Harris

Colin Herbert via groups.io wrote:

Thanks for that info, Dan. Would you believe that when my wife brought me a mug of tea in bed this morning, I was reading the FG 504 Manual and noticed where the jumper is marked on the schematic. I think I was thrown as to its circuit location by the physical location on the circuit board. However, that revelation left me with the puzzle of which was the default (non-VCF) position and I was wondering as to how I might investigate that, when I looked at my email and your reply gave me the answer!

I still have some problems with the Function Generator (though I have fixed one) which relate to the symmetry adjustments.

An earlier problem involved the power-rails and one going bad after I'd measured it to be OK. That turned out to be a harmonica-type connector giving bad contact, so I re-seated all of those that I could locate, which solved that problem, but then left me with the question of whether I had put the W20 jumper back properly or not. You have now clarified that for me.

I wonder why this wasn't clearer in the Manual?

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dan G
Sent: 08 August 2020 01:15
To: TekScopes@groups.io
Subject: Re: [TekScopes] FG 504 problems

On Fri, Aug 7, 2020 at 03:41 PM, Colin Herbert wrote:

While its position is shown on
the Internal Adjustments section A3 Loop Board diagram, there appears to be no
indication of which is the default setting and which the VCF input setting. I
cannot locate the jumper on the schematics either.
Hi Colin,

The W20 jumper is shown on schematic <1> ("Triangle Wave Generator" in
post-B040000 service manuals, and "Main Loop" in early editions.) It
is shown in the upper left corner of the schematic, just above "VCF INPUT".

The jumper is in the N/C position when it is placed toward the back of the
plug-in. Moving it to the front of the plug-in routes the VCF Input signal
to P1275.


dan








Re: 2465 Fan Collet Thingy

 

On Fri, Aug 7, 2020 at 01:55 PM, DaveC wrote:
Can you please provide a link to he location of these files? I looked in the group files and there aren’t many. I didn’t see anything relating to a collet.
Hi Dave,

it was explained somewhere in this thread: go into the files section and search for "collet".

cheers
Martin


Re: 475 With a bowed display. . . .Ideas?

 

On Sat, Aug 8, 2020 at 01:26 AM, Stephen wrote:


I’m not sure, but that makes me think « geometry »? Maybe??
Possibly not:
In the paragraph immediately following your longish quote the OP writes:

"Y Align R1385 and Geometry R1390 will not bring the vertical markers
into proper vertical alignment even though they do have some effect on
the trace by making it less severe. Even though they never "Fix" the problem."

Raymond


Re: FG 504 problems

Colin Herbert
 

Thanks for that info, Dan. Would you believe that when my wife brought me a mug of tea in bed this morning, I was reading the FG 504 Manual and noticed where the jumper is marked on the schematic. I think I was thrown as to its circuit location by the physical location on the circuit board. However, that revelation left me with the puzzle of which was the default (non-VCF) position and I was wondering as to how I might investigate that, when I looked at my email and your reply gave me the answer!

I still have some problems with the Function Generator (though I have fixed one) which relate to the symmetry adjustments.

An earlier problem involved the power-rails and one going bad after I'd measured it to be OK. That turned out to be a harmonica-type connector giving bad contact, so I re-seated all of those that I could locate, which solved that problem, but then left me with the question of whether I had put the W20 jumper back properly or not. You have now clarified that for me.

I wonder why this wasn't clearer in the Manual?

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dan G
Sent: 08 August 2020 01:15
To: TekScopes@groups.io
Subject: Re: [TekScopes] FG 504 problems

On Fri, Aug 7, 2020 at 03:41 PM, Colin Herbert wrote:

While its position is shown on
the Internal Adjustments section A3 Loop Board diagram, there appears to be no
indication of which is the default setting and which the VCF input setting. I
cannot locate the jumper on the schematics either.
Hi Colin,

The W20 jumper is shown on schematic <1> ("Triangle Wave Generator" in
post-B040000 service manuals, and "Main Loop" in early editions.) It
is shown in the upper left corner of the schematic, just above "VCF INPUT".

The jumper is in the N/C position when it is placed toward the back of the
plug-in. Moving it to the front of the plug-in routes the VCF Input signal
to P1275.


dan


Re: 7834 Missing Trace

Roger Evans
 

I was going to suggest that the brightness controls would get less noisy with use but you got there first. You can try to get a little cleaning fluid such as IPA into switches and variable controls that are interittent or noisy, but usually they improve a lot with use. Similarly have you tried selecting each of the calibrator voltages in turn, several times, to try and clean the switches. Again the horizontal (A, B, Alt, Chop) and vertical mode buttons and the small trigger selector buttons usually benefit from repeated use.

There may be a variable control on the calibrator which is also noisy, I can't find the calibrator in my manual! If you just move the trace up and down with no vertical signal does that also get noisy?

What about the left vertical slot, is that working?

Congratulations on finding the misaligned board, it was probably only just touching the contacts when you received the scope and removing the plugin just gave it a tiny jolt.

Regards,

Roger


Re: looking for internal photos of Input RC Normalizer (067-0537-00)

Greg Muir
 

With respect to modifying an item of this type I suspect that whomever does it has no need for the intended function and, instead looks at the usefulness of the enclosure. If the more-or-less nonstandard value normalizers seem to be more prey to modification, it is unknown as to why except for the possibility that a large number of them may have been dumped by a large user (military?) and then they were found on the surplus market by others.

When one looks at the price for a comparable Pomona Electronics box complete with BNC connectors attached and the $40 price tag, some old item that they found (probably in their junk box) looks pretty attractive cost-wise. And this type of thing is not only found for a Tek product. I have seen many other manufacturers products built in similar enclosures (especially the Pomona products) apparently being repurposed for the immediate need of the user.

Greg


Re: Cut wiring harness

kim.herron@sbcglobal.net
 

I wouldn't worry about the wire color or the tracers.  Funny thing about the electrons.  They don't have any idea what color the wire is.  :-O.

Kim Herron W8ZV kim.herron@... 1-616-677-3706

On Friday, August 7, 2020, 8:11:18 PM EDT, Jamie Ostrowski <jamie.ostrowski@...> wrote:

Thanks everyone for the tips. I'll try experimenting with my splicing
technique using these ideas and see if I can come up with a satisfactory
joint. It sure would be nice if I can find wire with matching tracers but
so far I haven't had any luck, which is unfortunate.

On Fri, Aug 7, 2020 at 2:08 PM Dwayne Reid <dwayner@...> wrote:

Hi there, Jamie.

One possible alternative is to use 30 AWG wire to hold the lap joints
together before soldering.  However, this requires more room to work.

This type of connection is required for some levels high-reliability
work (IPC Level 3S).  Strip the conductors, wrap the lap joint with
thin tinned wire, solder.  Use the minimum amount of solder
necessary, don't let the solder wick under the conductor
insulation.  We purchase 30 AWG tinned wire from Belden in multi-pound
spools.

The downside of this technique is that you have to be able to
separate the conductors far enough for your fingers (or round-nose
tweezers) to fish the wrapping wire around the conductor.  But it
makes extremely reliable connections that don't exceed the insulation
diameter.

dwayne


At 10:50 AM 8/7/2020, Leon Robinson wrote:

In these conditions I would suggest that the splices be lap soldered and
shrink tube to minimize the size of the splices.
I know lap splices are frowned upon but here I think it is the
better solution.

Leon Robinson    K5JLR

Political Correctness is a Political Disease.

Politicians and Diapers should be changed
often and for the same reasons.

    On Friday, August 7, 2020, 11:18:30 AM CDT,
kim.herron@... <kim.herron@...> wrote:

  Yes I have done this before, in several arenas.  Cars, AM
transmitters, linear amplifiers, custom built test
equipment, etc.  IF you have BOTH
pieces that have been cut, you can match up the wire
colors and splice them together.  You will want to cut the
looms back on both ends so that your repairs don't
become so large that you can't get the loom back in
place.  You'll need to stagger your repair splices so that
you can get it back together.  That will require some
replacement wire, and lots of shrink tube.  Doing this will
be much easier that trying to recreate the harness.  I've
done that too, but the work involved here would be
excessive.  The splice route is the way to go.

If you have the original manual with all the wiring info, it
makes it easier to ID what goes where.

On 7 Aug 2020 at 8:58, Jamie Ostrowski wrote:


I bought a pair of 556 oscilloscopes from an electronics scrapper
that I am restoring. I think I'm able to get the rest of the parts
that were harvested from the person who sold them to the scrapper,
but unfortunately, they sliced through a couple of wire harnesses.
The point where they were sliced the harnesses are made up of what
looks like 24 gauge tinned wire and others look like maybe 20 gauge.
I'm trying to weigh whether I should splice the looms back together
or if I should re-wire. Re-wiring looks like it's going to be an
incredibly painful process that will take me literally probably 100
hours of work per scope. Just hunting down originally correct color
coding wires is going to be a nightmare, and then routing them
correctly and re-tying the looms......whew.

It's unbelievable how much work one snip of a wire cutter can
generate.

Has anyone gone down a path like this before in a restoration and do
you have any tips?

Fortunately I do have a third complete 556 that I can use as a model
to compare with.



John Goller, K9UWA & Jean Goller, N9PXF
Antique Radio Restorations
k9uwa@...
Visit our Web Site at:
http://www.JohnJeanAntiqueRadio.com
4836 Ranch Road
Leo, IN 46765
USA
1-260-637-6426






--
Dwayne Reid  <dwayner@...>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
780-489-3199 voice  780-487-6397 fax  888-489-3199 Toll Free
www.trinity-electronics.com
Custom Electronics Design and Manufacturing





Re: FG 504 problems

Dan G
 

On Fri, Aug 7, 2020 at 03:41 PM, Colin Herbert wrote:

While its position is shown on
the Internal Adjustments section A3 Loop Board diagram, there appears to be no
indication of which is the default setting and which the VCF input setting. I
cannot locate the jumper on the schematics either.
Hi Colin,

The W20 jumper is shown on schematic <1> ("Triangle Wave Generator" in
post-B040000 service manuals, and "Main Loop" in early editions.) It
is shown in the upper left corner of the schematic, just above "VCF INPUT".

The jumper is in the N/C position when it is placed toward the back of the
plug-in. Moving it to the front of the plug-in routes the VCF Input signal
to P1275.


dan


Re: Cut wiring harness

Jamie Ostrowski
 

Thanks everyone for the tips. I'll try experimenting with my splicing
technique using these ideas and see if I can come up with a satisfactory
joint. It sure would be nice if I can find wire with matching tracers but
so far I haven't had any luck, which is unfortunate.

On Fri, Aug 7, 2020 at 2:08 PM Dwayne Reid <dwayner@...> wrote:

Hi there, Jamie.

One possible alternative is to use 30 AWG wire to hold the lap joints
together before soldering. However, this requires more room to work.

This type of connection is required for some levels high-reliability
work (IPC Level 3S). Strip the conductors, wrap the lap joint with
thin tinned wire, solder. Use the minimum amount of solder
necessary, don't let the solder wick under the conductor
insulation. We purchase 30 AWG tinned wire from Belden in multi-pound
spools.

The downside of this technique is that you have to be able to
separate the conductors far enough for your fingers (or round-nose
tweezers) to fish the wrapping wire around the conductor. But it
makes extremely reliable connections that don't exceed the insulation
diameter.

dwayne


At 10:50 AM 8/7/2020, Leon Robinson wrote:

In these conditions I would suggest that the splices be lap soldered and
shrink tube to minimize the size of the splices.
I know lap splices are frowned upon but here I think it is the
better solution.

Leon Robinson K5JLR

Political Correctness is a Political Disease.

Politicians and Diapers should be changed
often and for the same reasons.

On Friday, August 7, 2020, 11:18:30 AM CDT,
kim.herron@... <kim.herron@...> wrote:

Yes I have done this before, in several arenas. Cars, AM
transmitters, linear amplifiers, custom built test
equipment, etc. IF you have BOTH
pieces that have been cut, you can match up the wire
colors and splice them together. You will want to cut the
looms back on both ends so that your repairs don't
become so large that you can't get the loom back in
place. You'll need to stagger your repair splices so that
you can get it back together. That will require some
replacement wire, and lots of shrink tube. Doing this will
be much easier that trying to recreate the harness. I've
done that too, but the work involved here would be
excessive. The splice route is the way to go.

If you have the original manual with all the wiring info, it
makes it easier to ID what goes where.

On 7 Aug 2020 at 8:58, Jamie Ostrowski wrote:


I bought a pair of 556 oscilloscopes from an electronics scrapper
that I am restoring. I think I'm able to get the rest of the parts
that were harvested from the person who sold them to the scrapper,
but unfortunately, they sliced through a couple of wire harnesses.
The point where they were sliced the harnesses are made up of what
looks like 24 gauge tinned wire and others look like maybe 20 gauge.
I'm trying to weigh whether I should splice the looms back together
or if I should re-wire. Re-wiring looks like it's going to be an
incredibly painful process that will take me literally probably 100
hours of work per scope. Just hunting down originally correct color
coding wires is going to be a nightmare, and then routing them
correctly and re-tying the looms......whew.

It's unbelievable how much work one snip of a wire cutter can
generate.

Has anyone gone down a path like this before in a restoration and do
you have any tips?

Fortunately I do have a third complete 556 that I can use as a model
to compare with.



John Goller, K9UWA & Jean Goller, N9PXF
Antique Radio Restorations
k9uwa@...
Visit our Web Site at:
http://www.JohnJeanAntiqueRadio.com
4836 Ranch Road
Leo, IN 46765
USA
1-260-637-6426






--
Dwayne Reid <dwayner@...>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
780-489-3199 voice 780-487-6397 fax 888-489-3199 Toll Free
www.trinity-electronics.com
Custom Electronics Design and Manufacturing





Re: 475 With a bowed display. . . .Ideas?

Stephen
 

On Fri, Aug 7, 2020 at 09:38 AM, Michael W. Lynch wrote

Nice find Michael. Congrats.

Problem is when I put my marker signal from my marker generator into the unit
and set Volts/Div knob for 6-8 division vertical markers then I center the
middle marker to align with the center vertical graticule line, as you move
away from the center, the markers become more and more "leaned in" in at the
top. Left and right of center, the tops of the markers lean progressively
more and more toward the center as you move farther from the centerline. The
bottom trace line is barely, but ever so slightly bowed. The vertical markers
are straight but just leaning in toward the centerline. The bottom trace
bowing is not nearly as profound as the "leaning" of the markers. Trace can
be adjusted to about 1/2 trace width of bow, checking at top middle and bottom
of the display.
I’m not sure, but that makes me think « geometry »? Maybe??


475 With a bowed display. . . .Ideas?

Michael W. Lynch
 

I recently found a nice 475. Upon receiving the unit, I fired it up, the scope presented a strange garbled trace. Checking the various LV supplies, I found the +15V and the +15V Unregulated to be very low at about 12.2 and 16.5 respectively. Lifted the +15V jumper and there was no change, indicating that the problem was in the power supply, not the scope circuitry. Otherwise the scope looks almost new inside, no signs of tampering or repairs. All other supply voltages are spot on.

Problem was C1442 was bad. High resistance and almost no capacitance, loading the +15V supply. Replaced that cap with a new modern cap and both voltages are now spot on. Ripple checked on all supplies and we are within specs.

Cleaned and exercised all the push button switches.

Trace is bright and fairly clear for a mesh CRT.

Horz and Vert Position controls work as expected.

Focus works well

Trace Rotation R1386 controls rotation either side of horizontal equally.

Set the scope in X-Y and defocus the dot, the resulting spot is nice and round. Astig control R1397 produces the expected change in the spot. The Spot will go "oblong" in both X and Y directions in response to turning R1397.

Horizontal timing is close to right as the timing marker setting generally agrees with the Time/Div switch setting, some adjustment is needed, but the horizontal is only off about 5-7% or so.

Problem is when I put my marker signal from my marker generator into the unit and set Volts/Div knob for 6-8 division vertical markers then I center the middle marker to align with the center vertical graticule line, as you move away from the center, the markers become more and more "leaned in" in at the top. Left and right of center, the tops of the markers lean progressively more and more toward the center as you move farther from the centerline. The bottom trace line is barely, but ever so slightly bowed. The vertical markers are straight but just leaning in toward the centerline. The bottom trace bowing is not nearly as profound as the "leaning" of the markers. Trace can be adjusted to about 1/2 trace width of bow, checking at top middle and bottom of the display.

Y Align R1385 and Geometry R1390 will not bring the vertical markers into proper vertical alignment even though they do have some effect on the trace by making it less severe. Even though they never "Fix" the problem.

I have fixed several of these scopes and never encountered this issue before, where it could not be adjusted out of the instrument.

Ideas or suggestions?

Thanks in Advance.
--
Michael Lynch
Dardanelle, AR


Re: 7834 Missing Trace

sdferg7@...
 

For clarity, the image I took was at the same intensity setting on the knob, but now that I just turned it on after sitting for a while, the issue with the brightness seems to have corrected itself. The traces also no longer exhibit the popping in and out as I described before. They now come on smoothly with the intensity knobs. The problem with the upper peaks seems to come and go a little bit, but is much better now. However, when I try chop mode I get two dots, one for each time base.

Shane