Date   

Tek 2445 - No Power

ElectroKid
 
Edited

Hi all,

My first post here :)
I got this 2445 and upon 1st examination the power supply was clicking - no power at all, no light on front panel.
Replaced all e-caps on the inverter board A3, The fan is the early version ('mouse wheel') and it was moving upon finger help...not enough current.
At one point some self test lights on the front panel came on for a second or two - but that's the only time it happened,
Not much later had another fault where a resistor with a wire wrapped on it LR1060 got burnt gave quite a smoke.
I replaced it with a new resistor and wrapped it with fine lacquered wire (taken from a small transformer) based on the number of turns of original burnt coil LR1060.
Along with it I also checked the power FETs attached to heatsinks, and one was faulty, so I replaced them all.
Power supply is till clicking, I noticed an overheating resistor R1071 gives up smoke and getting charred gradually as the power is on.
Note: I have the 2445 inverter version with two 18K resistors (R1073, R1069) 'standing' to form one 36K (unlike one 36K R1069 in the Tek 2465).
I decided to replace charred R1071, and near that point the clicking stopped and now there is no sign of life... I hope the x-formers are still ok though.
Worth noting is that I did my live tests without load connected which I now found is not the way to run these SMPS... I wonder what can go bad in that case.
I don't see any voltage to the Pre-Regulator section (13.2V)
Further details:
I have replaced the RIFA caps although they were intact.
I checked incoming voltage to the inverter board is twice 155V on the connecting pins so apparently the bridge is well.
The big reservoir caps were not replaced, I don't think they are bad.
I check the thermal cutout device is ok.

So basically what looked like a simple re-cap job turned into a more complicated fault finding.
Would like to hear your suggestions on how to proceed based on the above.


Re: Tek 7623A - Source of 151-0271-00 transistor (A5T4261) or a currently available equivalent.

tinkera123
 

Hi Fabio,
I appreciate your time taken for this response .... I have got the “gist” of this, although I will ponder a few of the issues further ... eg. I am assuming that the top part of the rise time response curve was being driven by the ‘troubled’ transistor .... and bottom section driven by the ‘good’ transistor ... Push Pull??
And I don’t yet understand the HF compensation circuitry.
Anyway, another brick in the wall ...
Thanks,
Ian

Hello Ian, in response to your message further down...

I've got busy in the past couple of days which prevented me from answering
you.

First of all, please don't expect too much... because I think that, in the
end, it had a 50% of plain luck...

On this 7623A, .as I got rid of the gross issues that it had, and could focus
on doing a careful HF step response, I noticed that no matter what I would do,
be it on the Vert. Output Amplifier, or on the Vertical Plugin, I couldn't get
a clean step response in the whereabouts of 3.5ns.
If I would push too much on the HF compensation adjustments, I would
eventually get 4.5ns at best, but with a lot of ringing on the step corner.
If I would adjust it to tame the ringing, the step response would worsen even
more to - say - 5.5 to 6ns (this is a 60MHz scope, not a 100).
But what was puzzling me was that the step was not really like a slow
transition, but it was really fast up to about 2/3rds of the amplitude, and
then it would turn into a really rounded shoulder... So, I thought there were
2 superimposed time constants at play and that maybe, only maybe, I would be
able to spot which stage was not keeping up, by probing the vert amplifier at
different nodes.
It crossed my mind, for instance, that local power supply decoupling could be
lacking at some spot and that the slower last third could be due to a
decoupling having depleted its stored charge during the first part of a hi
speed transition and then, the stage would be running on "lean" mixture and
dragging.
So I started looking at places where there should be a more or less steady
voltage value, either the power to each stage, or the biasing networks.
So I went on to probe the +15V (dcpl) that feeds the Q2405 and Q2505 (this is
the NPN pair that precedes the PNP 151-0271-00 tranny I found guilty) and also
the bias to the bases of the very stage where the 151-0271 trannies were. This
is a common base stage, that has about +8V bias, coming from the Thermal
balance adjustment voltage divider, and decoupled by a 1nF capacitor.
While probing the bases of the transistors looking for the base pin (I didn't
know it by heart), I eventually probed both emitters (of the two PNP
transistors) and noticed they were markedly different... much different than I
would expect from two complementary sides that were being driven with a nearly
symmetrical square wave, swinging in AC around the center point...
The signal at the base of one of the transistors had something like x mVpp,
while at the other emitter, if was like 4x.
Well, the bases are not tied together, but from the bias voltage, through 100R
resistors into each base, so I thought that the markedly different signals
would also be different from one base to another... but not... The bases had
pretty much the same signal (almost no signal in fact, since it's a decoupled
bias)... only the emitters were remarkably different.
So, I thought... well, either this is caused by the transistor themselves, or
it's the signal coming into them...
So I swapped the transistors, and the signal at the emitters swapped along...
So I knew the transistors were the cause for the difference... leaving only to
discover if they were just too different (un-matched) or if one of them was
faulty.
So I ran them through my AVR transistor tester, which is far from being a
curve tracer, but would be able to tell me of any gross differences they might
have...
While one of the transistors tested like a normal PNP transistor, with about
40 of gain (hfe), the other, despite showing an increased hfe of about 70
(almost double), tested like if it had an anti-parallel diode connected across
the emitter-collector, and this anti-parallel diode with a Vf of 3.5V... the
whole thing being completely unusual for a regular silicon transistor (not
being a mosfet, a darlington, or a power device).
Testing them with my DMM in diode test mode showed no differences between
them.
So, despite they test equal on the DMM, I concluded that transistor could only
be faulty.
To confirm my theory, I needed a pair of small signal transistors that were -
at least - reasonably fast and I was lucky enough to find a couple of BFQ241
in my parts bin, which are high voltage, 1GHz TO-92 transistors used as video
amplifiers of CRT computer monitors.
In the moment that I shuffled them in, not only the signals at the emitters
became similar (as they should), but I immediately got a strong overshoot on
the square wave...denoting that the HF response of that stage started
contributing a great deal to the overall response.
After readjusting the HF compensation trimmers, I managed to get a risetime
about 2ns faster than it was, with a nice top almost free of ringing or
aberrations.
At this point, it's almost at the performance we would expect from a 100MHz
amplifier but, I decided to bring the subject to the group, and see what could
come out.
A fellow member of the group contacted me off-list to tell he has one original
151-0271-00 in spare and was so kind of offering it to me... so I`m now
awaiting for it to arrive, which will still take a while, as I`m in Brazil.

Hope this illustrates well how I got there...

Rgrds,

Fabio


Re: Tektronix 2465. Odd wave pattern superimposed on waveforms.

John Osborne
 

Greetings from South East London.
My Thanks goes to Chuck Harris who very kindly took the time to reply to my plea for help. As he stated (I hadn’t noticed) the issue was only evident on inputs 1 and 2. I had incorectly assumed that the issue was on all. However channels 3 and 4 are actually perfect?

He stated
*****
“If this wave only travels on CH1 and CH2, but not on CH3 and CH4, it is probably a problem with the external garbage that Tektronix hung on the CH5+ and CH5- inputs of the U400 channel switch to handle the readout display. I had a 2465 that had this condition, and I was tearing my hair out, until it was suggested to me that the CA3049 transistor arraysU485, and U475, were put there to prevent this problem. The issue is that the channel switch doesn't have the internal hardware to disable the readout from being displayed... it can only select the vertical channel. So, Tektronix put the transistor arrays U475 and 480 on the CH5 input to select and deselect when the readout can be displayed. Note that the readout can only be displayed during CH1 and CH2.”
******
I am off on holiday so any further investigation will have to wait 3 weeks. My thanks to Chuck Harris who so very kindly pointed me in the right direction.
I will post a cure once the issue has been solved. If by chance any one can add any further info I would be grateful.

Many thanks

John.

-----Original Message-----
From: Chuck Harris <cfharris@...>
To: TekScopes <TekScopes@groups.io>
Sent: Tue, 12 Jun 2018 15:43
Subject: Re: [TekScopes] Tektronix 2465. Odd wave pattern superimposed on waveforms.

Hi John,

If this wave only travels on CH1 and CH2, but not on CH3 and CH4,
it is probably a problem with the external garbage that Tektronix
hung on the CH5+ and CH5- inputs of the U400 channel switch to
handle the readout display.

I had a 2465 that had this condition, and I was tearing my hair
out, until it was suggested to me that the CA3049 transistor arrays
U485, and U475, were put there to prevent this problem.

The issue is that the channel switch doesn't have the internal
hardware to disable the readout from being displayed... it can only
select the vertical channel. So, tektronix put the transistor
arrays U475 and 480 on the CH5 input to select and deselect when
the readout can be displayed. Note that the readout can only be
displayed during CH1 and CH2.

I can't remember which array was bad, but they are cheap, and you
can test all of the transistors fairly easily in circuit.

-Chuck Harris

John Osborne via Groups.Io wrote:
Greetings to all.
I have recently purchased a non-working Tektronix 2465 (not A or B). Having carefully recapped the power supply which was blowing fuses due to leaky mains input filter capacitors I am left with an unusual fault.

The scope displays a good sine wave on all inputs. But superimposed on the perfect sine wave is a rippling wave that travels from right to left in quick succession. Perhaps 6 waves per second. It does not distort the sine wave in any way but travels along the wave on both the top and bottom edge of the trace. The wave is much lower in intensity than the sine wave displayed but is very noticeable.
Perhaps a common issue so please excuse me as I am new to this group.

Many thanks and best wishes to all.

John


Re: What removes sticker residue without hurting the blue paint?

Mark Mathis
 

Lemon Oil Furniture Treatment.

I have used Lemon Oil for over 30 years with great success on countless materials and finishes. With sufficient elbow power Lemon Oil always removes the adhesive without damage. Bear in mind, a slight difference in shading underneath the sticker can result from the difference in UV exposure. Exposed surfaces tend to darken over time, especially with older paints and plastics. This common also with woods such as Pine, Oak and White Ash.

Good day to all,
Mark

-----Original Message-----
From: Chris Elmquist
Sent: Tuesday, June 12, 2018 10:47 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] What removes sticker residue without hurting the blue paint?

This butyl cellosolve sounds like it can wreck more stuff than it fixes. I wanted proof that my beloved 409 should now be considered a member of the problem set and went searching. I found this NIH site that lists stuff with particular ingredients,

https://hpd.nlm.nih.gov/cgi-bin/household/search?tbl=TblChemicals&queryx=111-76-2

And it looks like it was “old” 409 that had it. But of note is that there are other things suggested in this thread that do still contain it that might be a risk. Simple Green (of several flavors) as one example.

Be careful out there...

Chris
--
Chris Elmquist N0JCF

On Jun 12, 2018, at 9:58 AM, Chuck Harris <cfharris@...> wrote:

Over the years, I have had a wide variety of
equipment with vinyl coated aluminum panels.

I used to cuss quite a bit when I got something
that was gorgeously pretty, but was sticky like
you were touching the sticky side of a piece of
tape. Virtually nothing would clean off the
sticky, and if you did, it would come back in a
little while... I wondered what had happened to
the vinyl.

Then I found it happening to equipment that I had
brought in my lab that was good, but dirty, then
cleaned with formula 409... my go to cleaner.

I read the ingredient list and saw the butyl
cellosolve... and stuck it away in my memory
somewhere.

Years passed, and more and more of my equipment
was getting sticky, when I bought a new truck.

The owner's manual had a warning about using window
cleaners containing butyl cellosolve, on the
instrument panel's windows. They said that it
would soften the plastic over time and make it fog.

A lightbulb went on, and I did some research on
butyl cellosolve, and found it was a super solvent
capable of soaking into almost all grease, dirt,
pitch, tar, and plastics. It cleaned by getting
inside of the dirt, expanding, and breaking it
apart so that it could be removed with a little
scrubbing... With plastics, it was to displace the
incredibly sticky stuff called plasticizer that is
used to make ridged PVC into flexible PVC... which
is what the stuff on the panels was.

A lot of pressure sensitive adhesives are very
similar chemically to plasticizer. And a lot of
the permanently affixed ID tags use a killer solvent
to bond them to plastic, vinyl, and painted panels.

-Chuck Harris

Kevin Oconnor wrote:
from Chuck:
"Goo gone is not aqueous. It is more like terpene,
made from the citrus, with mineral oil added to
prevent re-adhesion of the stickum."

Yes, oils seem to passivate the glue surface adhesion bond mechanism. Same as pouring Canola oil on a snake stuck in a glue trap. Slowly the glue is rendered ineffective and the snake squirms away none the worse for the experience! Not sure the atomic mechanism going on though.

I have seen some stickers on vinyl covered aluminum that seem to have modified the underlying vinyl by flattening out the orange peal surface. You can remove all trace of the adhesive, but you can do little regarding the latent outline of the sticker. The adhesive, when first applied, must react with the vinyl in some way. Any one else encounter this?


Re: Help with a TEK 502 scope

jrodriguezcsb@...
 

Sisi, thanks for the link. Pretty useful as I still do not navigate very well by the forum


Re: Help with a TEK 502 scope

jrodriguezcsb@...
 

Wow Dave,

just by looking at the pictures it seems both quite interesting and feasible!

Pease, give me a bit of time to read it carefully and undertand it and then I will come back here.

Thanks a million for that source!!

Anyway, any other source is still welcomed : )


Re: What removes sticker residue without hurting the blue paint?

Ed Breya
 

I too have a number of sticky-finish instrument cabinets (especially HP), and have tried without success over the years, to wash it off with some common solvents and detergents. Something that occurred to me, is instead of trying to remove the stuff, to maybe bind it with something, or to counteract the stickiness with an oil or wax finish. One possibility is to use a drying oil, like linseed, which would perhaps bind to the surface materials, and harden over time, to make a new finish (but slightly yellower than original). I have not tried this, so have no idea if it would work, or make things worse, but it may be worth looking at.

Ed


Re: What removes sticker residue without hurting the blue paint?

Chuck Harris
 

Do a search (CTRL "F") on 409, and you will discover
that the new and old 409 all contain it. I was quite
surprised to see that simple green is full of it too.

Great...

Thanks for the resource.

-Chuck Harris

Chris Elmquist wrote:

This butyl cellosolve sounds like it can wreck more stuff than it fixes. I wanted proof that my beloved 409 should now be considered a member of the problem set and went searching. I found this NIH site that lists stuff with particular ingredients,

https://hpd.nlm.nih.gov/cgi-bin/household/search?tbl=TblChemicals&queryx=111-76-2

And it looks like it was “old” 409 that had it. But of note is that there are other things suggested in this thread that do still contain it that might be a risk. Simple Green (of several flavors) as one example.

Be careful out there...

Chris
--
Chris Elmquist N0JCF


Re: What removes sticker residue without hurting the blue paint?

Chris Elmquist
 

This butyl cellosolve sounds like it can wreck more stuff than it fixes. I wanted proof that my beloved 409 should now be considered a member of the problem set and went searching. I found this NIH site that lists stuff with particular ingredients,

https://hpd.nlm.nih.gov/cgi-bin/household/search?tbl=TblChemicals&queryx=111-76-2

And it looks like it was “old” 409 that had it. But of note is that there are other things suggested in this thread that do still contain it that might be a risk. Simple Green (of several flavors) as one example.

Be careful out there...

Chris
--
Chris Elmquist N0JCF

On Jun 12, 2018, at 9:58 AM, Chuck Harris <cfharris@...> wrote:

Over the years, I have had a wide variety of
equipment with vinyl coated aluminum panels.

I used to cuss quite a bit when I got something
that was gorgeously pretty, but was sticky like
you were touching the sticky side of a piece of
tape. Virtually nothing would clean off the
sticky, and if you did, it would come back in a
little while... I wondered what had happened to
the vinyl.

Then I found it happening to equipment that I had
brought in my lab that was good, but dirty, then
cleaned with formula 409... my go to cleaner.

I read the ingredient list and saw the butyl
cellosolve... and stuck it away in my memory
somewhere.

Years passed, and more and more of my equipment
was getting sticky, when I bought a new truck.

The owner's manual had a warning about using window
cleaners containing butyl cellosolve, on the
instrument panel's windows. They said that it
would soften the plastic over time and make it fog.

A lightbulb went on, and I did some research on
butyl cellosolve, and found it was a super solvent
capable of soaking into almost all grease, dirt,
pitch, tar, and plastics. It cleaned by getting
inside of the dirt, expanding, and breaking it
apart so that it could be removed with a little
scrubbing... With plastics, it was to displace the
incredibly sticky stuff called plasticizer that is
used to make ridged PVC into flexible PVC... which
is what the stuff on the panels was.

A lot of pressure sensitive adhesives are very
similar chemically to plasticizer. And a lot of
the permanently affixed ID tags use a killer solvent
to bond them to plastic, vinyl, and painted panels.

-Chuck Harris

Kevin Oconnor wrote:
from Chuck:
"Goo gone is not aqueous. It is more like terpene,
made from the citrus, with mineral oil added to
prevent re-adhesion of the stickum."

Yes, oils seem to passivate the glue surface adhesion bond mechanism. Same as pouring Canola oil on a snake stuck in a glue trap. Slowly the glue is rendered ineffective and the snake squirms away none the worse for the experience! Not sure the atomic mechanism going on though.

I have seen some stickers on vinyl covered aluminum that seem to have modified the underlying vinyl by flattening out the orange peal surface. You can remove all trace of the adhesive, but you can do little regarding the latent outline of the sticker. The adhesive, when first applied, must react with the vinyl in some way. Any one else encounter this?


Re: Upgraded, stub tuned, Tektronix SG-504 leveling head back online for a last run

 

Hi Folks:
I am currently fulfilling a couple orders which exceeded my parts stock levels.
Based on the very positive response a few weeks ago, I decided to extend the offer on the Calibrated leveling heads at the 10% discount (119.50 shipped) off the EBAY prices as I have restocked a small quantity of components again for 10 units.
So If you need a discounted, built & calibrated leveling head with all factory new components> Please contact me : @Protofabtt
Worldwide snail mail as usual. Please note that Africa & S. America customers can take 8 weeks to get theirs. US is usually 3 weeks tops, Canada varies from 3 to 6 weeks depending on location.
I believe everyone got their units from the last batch so no lost items.

Ancel


Re: What removes vinyl plasticizer stickyness on cabinets?

Dave Seiter
 

I used to have a bag of small square section belts with the same issue- 2 or 3 of them turned into jelly, and the rest got "infected". I was never able to clean them, so the whole bag got tossed.
-Dave

From: John Ferguson via Groups.Io <jferg977=aol.com@groups.io>
To: TekScopes@groups.io
Sent: Tuesday, June 12, 2018 1:41 PM
Subject: Re: [TekScopes] What removes vinyl plasticizer stickyness on cabinets?

I sort of hope there isn't anything.

I've thrown out a lot of things because of this problem.  The saddest
was my IBM Thinkpad with the butterfly keyboard. I bought another on
ebay around 2004, but it had the same problem. I tried sanding it off
but made more of a mess.  Plasticizer coming out of belts on 3M 6150 QIC
tapes.  "Lifetime Warranty"  intended for archival storage.  Whee.

right now, I'm trying to clean a micro-usb jack on a microcontroller
that 'd dearly like to reprogram.  In its year in service flying around
in an R/C airplane it's apparently coroded enough to deny a good connection.


Re: What removes vinyl plasticizer stickyness on cabinets?

John Ferguson
 

I sort of hope there isn't anything.

I've thrown out a lot of things because of this problem.  The saddest was my IBM Thinkpad with the butterfly keyboard. I bought another on ebay around 2004, but it had the same problem. I tried sanding it off but made more of a mess.  Plasticizer coming out of belts on 3M 6150 QIC tapes.  "Lifetime Warranty"  intended for archival storage.  Whee.

right now, I'm trying to clean a micro-usb jack on a microcontroller that 'd dearly like to reprogram.  In its year in service flying around in an R/C airplane it's apparently coroded enough to deny a good connection.


Re: What removes vinyl plasticizer stickyness on cabinets?

Dave Seiter
 

I'd be interested in solutions as well.  I've had cabinets from HP and other mfrs suffer from this, as well as my old Ryobi power tools (I replaced them with better ones because of this, even though they still work (or did...)).  From tacky to down right gooey!
I had some luck with Shackley's Basic I (it seemed to reduce stickiness, but is no longer made), but nothing has worked well.  It seemed that anything that removed the stickiness completely also attacked the plastic.  I tried many cleaners, iso, goof-off, goo gone, gas, everything on the solvent shelf including stuff like MEK.  Also tried caustics.  Note that the tests were all done on sections of a panel that was really gooey.  
-Dave

From: Kevin Oconnor <@KO3Y>
To: TekScopes@groups.io
Sent: Tuesday, June 12, 2018 7:46 AM
Subject: [TekScopes] What removes vinyl plasticizer stickyness on cabinets?

This topic is related to the thread on stickers, but is generally over the entire cabinet of the instrument. My humble understanding is that the plasticizers used to make the vinyl supple and stretchy so it can be bonded to the metal sheet prior to stamping and bending slowly separates from the PVC matrix. This makes the surface tacky.
Soap & water cleaning are ineffective. I have usually resorted to some kind of solvent. Something that reacts with the plasticizer but not PVC.  Goof-off works but does soften PVC.  mineral spirits does not soften the PVC, but also doesn't remove all the tackiness.
I'd be interested in other experiences.....

Kjo


Re: Tek 7623A - Source of 151-0271-00 transistor (A5T4261) or a currently available equivalent.

Fabio Trevisan
 

Hello Ian, in response to your message further down...

I've got busy in the past couple of days which prevented me from answering you.

First of all, please don't expect too much... because I think that, in the end, it had a 50% of plain luck...

On this 7623A, .as I got rid of the gross issues that it had, and could focus on doing a careful HF step response, I noticed that no matter what I would do, be it on the Vert. Output Amplifier, or on the Vertical Plugin, I couldn't get a clean step response in the whereabouts of 3.5ns.
If I would push too much on the HF compensation adjustments, I would eventually get 4.5ns at best, but with a lot of ringing on the step corner.
If I would adjust it to tame the ringing, the step response would worsen even more to - say - 5.5 to 6ns (this is a 60MHz scope, not a 100).
But what was puzzling me was that the step was not really like a slow transition, but it was really fast up to about 2/3rds of the amplitude, and then it would turn into a really rounded shoulder... So, I thought there were 2 superimposed time constants at play and that maybe, only maybe, I would be able to spot which stage was not keeping up, by probing the vert amplifier at different nodes.
It crossed my mind, for instance, that local power supply decoupling could be lacking at some spot and that the slower last third could be due to a decoupling having depleted its stored charge during the first part of a hi speed transition and then, the stage would be running on "lean" mixture and dragging.
So I started looking at places where there should be a more or less steady voltage value, either the power to each stage, or the biasing networks.
So I went on to probe the +15V (dcpl) that feeds the Q2405 and Q2505 (this is the NPN pair that precedes the PNP 151-0271-00 tranny I found guilty) and also the bias to the bases of the very stage where the 151-0271 trannies were. This is a common base stage, that has about +8V bias, coming from the Thermal balance adjustment voltage divider, and decoupled by a 1nF capacitor.
While probing the bases of the transistors looking for the base pin (I didn't know it by heart), I eventually probed both emitters (of the two PNP transistors) and noticed they were markedly different... much different than I would expect from two complementary sides that were being driven with a nearly symmetrical square wave, swinging in AC around the center point...
The signal at the base of one of the transistors had something like x mVpp, while at the other emitter, if was like 4x.
Well, the bases are not tied together, but from the bias voltage, through 100R resistors into each base, so I thought that the markedly different signals would also be different from one base to another... but not... The bases had pretty much the same signal (almost no signal in fact, since it's a decoupled bias)... only the emitters were remarkably different.
So, I thought... well, either this is caused by the transistor themselves, or it's the signal coming into them...
So I swapped the transistors, and the signal at the emitters swapped along...
So I knew the transistors were the cause for the difference... leaving only to discover if they were just too different (un-matched) or if one of them was faulty.
So I ran them through my AVR transistor tester, which is far from being a curve tracer, but would be able to tell me of any gross differences they might have...
While one of the transistors tested like a normal PNP transistor, with about 40 of gain (hfe), the other, despite showing an increased hfe of about 70 (almost double), tested like if it had an anti-parallel diode connected across the emitter-collector, and this anti-parallel diode with a Vf of 3.5V... the whole thing being completely unusual for a regular silicon transistor (not being a mosfet, a darlington, or a power device).
Testing them with my DMM in diode test mode showed no differences between them.
So, despite they test equal on the DMM, I concluded that transistor could only be faulty.
To confirm my theory, I needed a pair of small signal transistors that were - at least - reasonably fast and I was lucky enough to find a couple of BFQ241 in my parts bin, which are high voltage, 1GHz TO-92 transistors used as video amplifiers of CRT computer monitors.
In the moment that I shuffled them in, not only the signals at the emitters became similar (as they should), but I immediately got a strong overshoot on the square wave...denoting that the HF response of that stage started contributing a great deal to the overall response.
After readjusting the HF compensation trimmers, I managed to get a risetime about 2ns faster than it was, with a nice top almost free of ringing or aberrations.
At this point, it's almost at the performance we would expect from a 100MHz amplifier but, I decided to bring the subject to the group, and see what could come out.
A fellow member of the group contacted me off-list to tell he has one original 151-0271-00 in spare and was so kind of offering it to me... so I`m now awaiting for it to arrive, which will still take a while, as I`m in Brazil.

Hope this illustrates well how I got there...

Rgrds,

Fabio

On Thu, Jun 7, 2018 at 05:14 pm, tinkera123 wrote:


Hi Fabio,
This stuff is still above my 'expertise' level .... but for my education ....
could you outline for me how you got to this point ... from a circuit analysis
perspective??
Cheers, Ian

On Wed, Jun 6, 2018 at 03:06 pm, Fabio Trevisan wrote:
On my 7623A, the Vertical Output amplifier fails to give me that last
nanosecond of step response.
The best I was being able to get from it was about 4.5ns risetime and even
though, at the expense of a decent flat-top.
After some chasing I narrowed down the problem to the PNP transistors of the
pair Q2441 / Q2451.



Re: Help with a TEK 502 scope

Dave Wise
 

Thanks for the URL, Siggi. The last picture in the album is my assistant performing a thermal stress test. :)

DW
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Siggi <siggi@...>
Sent: Tuesday, June 12, 2018 9:52 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help with a TEK 502 scope

On Tue, 12 Jun 2018 at 12:07 Dave Wise <david_wise@...> wrote:

I saved detailed notes and photos in topic and photo album titled "453 HV
Transformer Rewind".
See <https://groups.io/g/TekScopes/album?id=12876>.


Re: What removes sticker residue without hurting the blue paint?

Bob Albert
 

Don't use brake fluid; it takes the paint off.
Bob

On Tuesday, June 12, 2018, 9:51:05 AM PDT, Stan Corbett <stantooga@...> wrote:

bug spray works well for removing ink markers

Stan VE6SWC


________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of walter shawlee <@walter2>
Sent: June 12, 2018 8:42 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] What removes sticker residue without hurting the blue paint?

for me, the most reliable "sticker" remover has consistently been goo-gone.
this is especially true with government asset labels and old cal stockers.
I also use alcohol sometimes, but it is just not as effective.

generally for cleaning, I use windex, scotch-brite pads and sometimes
the chemicals above
to get the cases clean.  I find the hardest things to remove are not
labels, but those idiotic big permanent marker notations scribbled at
random on equipment. they are truly hard to eliminate, especially from
plastic finishes.

I sometimes use a solder-flux safety wash spray chemical to remove them,
but it can be a problem for the case finish, so real care is required.
generally alcohol and other chemicals merely remove the topmost layer of
the marking, and leave the finish-soaked remains intact. very frustrating.

I keep Tek blue paint in stock to re-do covers, but it is only truly
successful once the case is thoroughly cleaned and the old finish
roughened for good adhesion, and scratches smoothed with scotch-brite. A
bit of effort can restore the finish to as-new. I used to have the
olive-gray HP paint as well, but it was only useful on older items.

-all the best,
walter

--
Walter Shawlee 2
Sphere Research Corp.
Phone: +1 (250-769-1834 -:- http://www.sphere.bc.ca
Sphere Research Corporation - Used Electronic Test ...<http://www.sphere.bc.ca/>
www.sphere.bc.ca
Sphere's site contains an original e-library, including quotes, business practices and ethics, short stories and columns. Plus, an Electronic Test Equipment and Slide Rule on-line warehouse with engineering resources



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)


Re: Help with a TEK 502 scope

Siggi
 

On Tue, 12 Jun 2018 at 12:07 Dave Wise <david_wise@...> wrote:

I saved detailed notes and photos in topic and photo album titled "453 HV
Transformer Rewind".
See <https://groups.io/g/TekScopes/album?id=12876>.


Re: What removes sticker residue without hurting the blue paint?

Stan Corbett
 

bug spray works well for removing ink markers

Stan VE6SWC


________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of walter shawlee <@walter2>
Sent: June 12, 2018 8:42 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] What removes sticker residue without hurting the blue paint?

for me, the most reliable "sticker" remover has consistently been goo-gone.
this is especially true with government asset labels and old cal stockers.
I also use alcohol sometimes, but it is just not as effective.

generally for cleaning, I use windex, scotch-brite pads and sometimes
the chemicals above
to get the cases clean. I find the hardest things to remove are not
labels, but those idiotic big permanent marker notations scribbled at
random on equipment. they are truly hard to eliminate, especially from
plastic finishes.

I sometimes use a solder-flux safety wash spray chemical to remove them,
but it can be a problem for the case finish, so real care is required.
generally alcohol and other chemicals merely remove the topmost layer of
the marking, and leave the finish-soaked remains intact. very frustrating.

I keep Tek blue paint in stock to re-do covers, but it is only truly
successful once the case is thoroughly cleaned and the old finish
roughened for good adhesion, and scratches smoothed with scotch-brite. A
bit of effort can restore the finish to as-new. I used to have the
olive-gray HP paint as well, but it was only useful on older items.

-all the best,
walter

--
Walter Shawlee 2
Sphere Research Corp.
Phone: +1 (250-769-1834 -:- http://www.sphere.bc.ca
Sphere Research Corporation - Used Electronic Test ...<http://www.sphere.bc.ca/>
www.sphere.bc.ca
Sphere's site contains an original e-library, including quotes, business practices and ethics, short stories and columns. Plus, an Electronic Test Equipment and Slide Rule on-line warehouse with engineering resources



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)


Re: Help with a TEK 502 scope

Dave Wise
 

I saved detailed notes and photos in topic and photo album titled "453 HV Transformer Rewind". Maybe it will be useful, but you will have to figure out your turns counts unless someone else here knows.

HTH,
Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of jrodriguezcsb@... <jrodriguezcsb@...>
Sent: Tuesday, June 12, 2018 2:18 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help with a TEK 502 scope

Hi Albert,

I have been reading in both the forum and the internet and I found quite interesting info like this page:
https://ludens.cl/Electron/tek310/tek310.html
Unfortunately, I do not have 2 HV windings, in fact I have 3. I have 3 diode tubes in the secondary...

In this forum however I have not found a clear procedure, I found several links to a previous Yahoo group but I can not access.

I will try to upload photos in that way - thanks for the advice : )

I looked in Ebay and only found a 300USD with another 250USD of shippings, as in the programming fiel, it is out of range... and in bad shape

Anyway, any idea about:
1. Anyone who sell one for parts or just the parts
2. Rewinding it

Thanks for all this support, you are such a nice guys!


Re: 575 - advice sought from owners

John
 

On Tue, Jun 12, 2018 at 05:36 am, David Holland wrote:


They made a noise when going in
Was that cries of "Oh please don't throw us in the trash, we're perfectly healthy!" ? :>)