开云体育

Has anyone re-wound the HV transformer in the Tek 576 Curve Tracer?
Is there a link to show the number of turns on the windings?

Leave it alone. It does no harm like this. Not a problem IMO.

Usually, the pins should be neither bent asymmetrically, nor
straight (like they are in your other picture).

The vertical deflection plate wires coming out of the CRT neck
are very thin, soft, and bend easily... without being able to
break the seal.

This is as opposed to the ground pin, and the two horizontal
pins, which are thick, and may break the seal...

I would do the transient response, and if I found that I could
not correct a "munch" out of the edge back a division, I
would modify the bend to come together at the "knees" on the two
wires. The idea is to make the two wires sort of "knock knee'd",
with the degree of bend being whatever is necessary to correct
the "munch" just after the corner.

....-------..--------
...|.......\/........ <--transient response
...|.................
...|....... ^--"munch" (<0.2div)

Be careful to not let any deflection pin touch the mumetal shield,
that is instant death for the Vertical, or Horizontal hybrid.

Bear in mind that "perfect" from tektronix's point of view is less
than 0.2 divisions, so don't get carried away with trying to achieve
a different standard of perfection.

One should never discount the result of sloppy handling. But, this
pair of wires is pretty well protected. It is probably an intentional
bending. Sloppy handling usually results in the socket pins coming
loose from the deflection leads.

-Chuck Harris

Jean-Paul wrote:

While I'm not an expert on the 2465B AT ALL, I wouldn't worry about the bends and I wouldn't "fix" them.? While they probably could take an adjustment to realign them, they might have already been flexed a few times, and the last thing you want is a work hardened break.? A single bend shouldn't compromise the seal at all.? I have seen many bent CRT pins due to impacts, ham handed techs and ???, but even "normal" CRT leads tend to be random in my view.? Like you say, it lights up and seems normal,? I'd leave it at that.??
It's not like the 184 TMG, were the 2 fastest outputs seem to need magic to work at all!
-Dave

Hi again, I shot 4 better images:



first 2 suspect bernt pin uint, last 2 another normal unit.

Really hope the veteran 2465Bers can comment!

Bon journee,

Jon

Hello all:

Here is a photo of the CRT VERT plate and term in a newly received 2465B.

the area around the term is VERY delicate and affects Vert transient response. I have NEVER seen a CRT pin bent like this.

CRT light up and seems normal.



1/ Anyone seen this before?

2/ Will the bend compromise glass to metal seal and make it susceptible to future leaks?

3/ Could the pin angle be from adjustment of transient response or more likely inexperience and sloppy handling?

MANY THANKS

Jon

Ok. Thanks all. Confirmed 485 sucks. In at back?

Sent from kjo iPhone

Doesn’t that contradict post 1478-2b?

Sent from kjo iPhone

I wrote up a bunch of stuff about my TDS544A repair in the group, through several messages. This was maybe four or five years ago, before the move from yahoo, I think. I haven't had much luck searching here or there for old threads, so haven't been able to find any of it.

One thing I remember is that at least in the '544A, is there were two versions of the standby supply, and the big PS board in mine had a version using a TOP2xx-something IC, rather than a bipolar switching transistor or MOSFET circuit. There were either vestiges of the other version present, or maybe the board was laid out to support both versions, depending on jumpers and part population.

The TOP2xx part is a slick little deal - actually an IC with a built-in MOSFET switch, all in a TO-220 package. I found this one shorted out, and also its associated TVSS burned out. I found that I had the parts in my salvage stock (these are commonly used in small SMPS blocks like laptop supplies and such). I patched it enough to get it working, then on further study of the TOP2xx family and the PS circuit, I concluded there was a possible operating condition, event, or fault mode (can't recall which) that may allow momentary reversal of the drain voltage, and breakdown that could cause catastrophic failure. I modified the circuit a little bit, including adding a fast 1A rectifier like 1N4936 in series with the drain/feed terminal. It has worked just fine ever since.

Unlike stand-alone MOSFETs that usually have the intrinsic body diode taking any reverse currents, I think in the TOP2xx IC, there is quite a lot circuitry around its MOSFET, making it susceptible to reversal. The external TVSS only protects against over-voltage, not reversal, so a blocking diode added at the drain was the way to go.

The only thing I recall about the other version (from the schematic), is it may have been a fairly simple flyback/blocking oscillator circuit to accomplish the same thing. There was even a blank spot on one of the heatsink structures, surrounded by unpopulated board circuitry.

Ed

On 8/21/2019 6:26 PM, John wrote:

I have looked at other Tektronix groups but they are extremely small (one had 71 members). While I agree those 71 might be experts it is unlikely. So here goes an off topic question for those with abundant Tektronix experience just not scope related.

I am considering a purchase of a used Arbitrary Function Generator (AFG) or an Arbitrary Waveform Generator (AWG). I do know the difference between these two classes of instruments. Tektronix has quite a large selection of possible candidates. I don't need very high frequency capability and up to 20 MHz would be sufficient. However I am looking for good square waves (rise times in the range <=8 nS) with very low overshoot. Good quality sine waves. Plus the ability to upload arbitrary waveforms to the instrument either via RS-232 or GPIB. I am comfortable in repairing instruments having just nearly completed an HP 8662A restoration with only calibration left to do. So there are the AFG300 series, AWG202x series, AWG700 series, AWG400 series and probably others I don't know about. Some of these instrument families come from the dreaded leaking electrolytic capacitor age and may be irreparable due to PCB damage. eBay at present has really, in my estimation, looney tune pricing for some of these instruments so I am in no hurry to purchase. What I am looking for is any advice of models which are problematic and should be avoided and other such advice. Sorry for the off topic post but there didn't seem to be anywhere else with so much Tektronix experience.

On an AFG5101, I had a display problem.? I replaced it with another that did not have an electroluminescent backlight.? In the process, I lost the ability to control the backlight.? The new display was a negative (black background) display with an LED backlight.

It still works, though.

oh, and BTW: do NOT clean the front panel with any solvents, there's a coating that can be removed that you don't want to remove.

Harvey

John Proctor
VK2DLP

Hi John,
If it has a Tek logo on it this is not off topic at all. We collect, support, fix, and recommend anything made by Tek.
Dennis Tillman W7PF

OK that was a mix up. I accidentally posted to the Tek576 curve
tracer thread.
I am repeating it here in the correct thread so it can be found.

Hi Ed; I sent you my repair log and in it you will find that the reason
the first transistor blew a year ago was high ESR in C17.
I had replaced the Q9 and both TVR (VR4 & VR5) and Q9 immediately
blew again. When C17 was replaced (you have to read my notes) Q9 survived
for a year.
I just removed C17 and the ESR is 7 ohms (was less than 1 when replaced).
I should not have installed a used capacitor and obviously need to choose
a NEW replacement more carefully. Any suggestions? Perhaps a tantalum? It
is 47 uF and the voltage cannot go above (CR10 + VR1 + CR11 + CR9 = about >
7.8v). So 20 to 35 v.
To check with the boost converter disabled disconnect one end of CR8.
References to the schematic of the TDS 544A with MJE8501 and
MJE1320 pencilled in besides Q9.
The TVS are Littlefuse 1.5KE 220CA and 1.5KE250CA available from
DigiKey, BU508AW also available from DigiKey.

On Wed, Aug 21, 2019 at 4:08 PM Ed Breya via Groups.Io <edbreya=
[email protected]> wrote:

Peter,

On Wed, Aug 21, 2019 at 11:50 AM Siggi <siggi@...> wrote:

Hey Peter,

I repaired one of those from a TDS684A which had failed in an interesting
mode. The TVSes had become uni-directional, and so current was flowing
through the TVSes, T3 and Q9 continuously. Out of circuit they measured as
a diode in one direction, but as an open in the other (I didn't have any
way to measure their threshold voltage). It seems only RT4/5 were limiting
the current/damage at that point. I couldn't figure out why the TVSes had
failed, but apparently it's not uncommon for them to do so.
I suspect you'll find a very close schematic on H?kan's download page:
. Looking at the schematic, it occurs to
me that CR7 & C15 make a snubber, whereas the TVSen are clamps. If the
snubber fails, I'd expect the TVSes and the switching transistor to suffer
higher transients, so maybe that's one place to look. R21 is also perhaps
suspect, as it will presumably discharge C15 between cycles.

Good luck,
Siggi

On Tue, Aug 20, 2019 at 3:33 AM peter bunge <bunge.pjp@...> wrote:

A year ago I repaired a TDS 644A power supply.with overheated VR4 and VR5
snubbers and blown Q9 switch transistor. Q9 was replaced with an MJE8501
which was pencilled in on the schematic. The transistor that I removed

was

a BU508A but replacements I ordered from China tested about 500v on a

curve

tracer so the MJE8501 was left in.
I also found that C17 was defective and replaced it.
A year later the new VR4 and VR5 show signs of overheating and Q9 is

blown

again.
VR4 and VR5 should never handle any current, only clip transients. Q9
should not experience excessive voltages because the regulator and all

lock

out circuits were tested and are working. I had adjusted R18 (A19 power
factor control) slightly to set the bulk voltage at 408v as it was a bit
high.
Does anyone have any experience with suggestions to repair this power
supply.

Anyone looking to buy a MDO3054 scope. I have a spare unit with all accessories. It is a really nice scope. Check Tektronix site for specs.
Contact electronixtoolbox@....
Craig

OK that was a mix up. Two threads crossed and this was meant for the
TDS644A thread. And of course the capacitor was 47 uF not 47 ohms although
the ESR is 7 ohms on the one removed.

On Wed, Aug 21, 2019 at 8:09 PM peter bunge via Groups.Io <bunge.pjp=
[email protected]> wrote:

Hi Ed; I sent you my repair log and in it you will find that the reason the
first transistor blew a year ago was high ESR in C17.
I had replaced the Q9 and both TVR (VR4 & VR5) and Q9 immediately blew
again. When C17 was replaced (you have to read my notes) Q9 survived for a
year.
I just removed C17 and the ESR is 7 ohms (was less than 1 when replaced). I
should not have installed a used capacitor and obviously need to choose a
NEW replacement more carefully. Any suggestions? Perhaps a tantalum? It is
47 ohms and the voltage cannot go above (CR10 + VR1 + CR11 + CR9 = about
7.8v). So 20 to 35 v.
To check with the boost converter disabled disconnect one end of CR8.
References to the schematic of the TDS 544A with MJE8501 and MJE1320
pencilled in besides Q9.
The TVS are Littlefuse 1.5KE 220CA and 1.5KE250CA available from DigiKey.
BU508AW also available from DigiKey.

On Wed, Aug 21, 2019 at 4:08 PM Ed Breya via Groups.Io <edbreya=
[email protected]> wrote:

Peter,

Here are some comments regarding the 576, 577, and TDS644A.

Yes, the brown HV transformer is the bad kind, so it will likely crap out
soon. The symptoms are about right.

The 576 v. 577 discussion will likely never end, because they each have
their pluses and minuses, and either is a fine CT for most uses. There is
no consensus, except that it's nice to have both.

The TDS series scopes, as far as I can tell, all use a similar PS
topology, but unfortunately not identical in the details. I had to fix

the

standby PS in a TDS544A a while back. As I recall, the main
supply/preregulator is a power factor correction (PFC) type. In its

common

form, it is a boost converter, so it is set up to make preregulated DC
somewhat above the highest expected peak voltage of the power line -
typically 350-375 V for 240 V operation, or doubled 120 V in a dual-range
configuration. In a full-range, continuous coverage design, the input

line

can be anything between the lowest and highest line possible, in any
country. I think the ones I have (TDS 544A, 754A, and 820) are

full-range,

but there may be some that use dual-range. Regardless of this detail, the
highest expected rectified raw DC should be somewhat less than 400 V, so
somewhere around there is what the PFC converter is designed to put out,
and still provide regulation. All lower voltages are simply boosted up to
this level, giving very wide coverage.

It's been a while since I studied it, but I think that in standby, the

PFC

is actually running all the time too, and the standby supply runs from

the

PFC output. It isn't necessary for the PFC to be running all the time,
since when it's off, the rectified DC from the line passes through, but
would not be boosted or regulated. This would be OK too, since the

standby

supply should be able to operate over a wide input range too. Either
arrangement can work, but controlling the on and off states would be
different.

The standby supply keeps it ready to go, and supplies power for

scope-side

circuits, including the one-bit memory (I think it's a latching relay) of
its last power state. When the power button is pushed, the state is
switched to the opposite of whatever it was. In the case of turning the
scope on, the PFC converter is activated - if it's not always on anyway -
then the main output chopper fires up, converting the 400 VDC to the low
voltage secondaries.

Anyway, in standby, you may see the input voltage to the standby

converter

be something similar to the peak of the input AC, or fixed near 400 V,
depending on the implementation details. In the scope on state, this
voltage should be around 400 V.

Ed

Hi Ed; I sent you my repair log and in it you will find that the reason the
first transistor blew a year ago was high ESR in C17.
I had replaced the Q9 and both TVR (VR4 & VR5) and Q9 immediately blew
again. When C17 was replaced (you have to read my notes) Q9 survived for a
year.
I just removed C17 and the ESR is 7 ohms (was less than 1 when replaced). I
should not have installed a used capacitor and obviously need to choose a
NEW replacement more carefully. Any suggestions? Perhaps a tantalum? It is
47 ohms and the voltage cannot go above (CR10 + VR1 + CR11 + CR9 = about
7.8v). So 20 to 35 v.
To check with the boost converter disabled disconnect one end of CR8.
References to the schematic of the TDS 544A with MJE8501 and MJE1320
pencilled in besides Q9.
The TVS are Littlefuse 1.5KE 220CA and 1.5KE250CA available from DigiKey.
BU508AW also available from DigiKey.

On Wed, Aug 21, 2019 at 4:08 PM Ed Breya via Groups.Io <edbreya=
[email protected]> wrote:

Peter,

Here are some comments regarding the 576, 577, and TDS644A.

Yes, the brown HV transformer is the bad kind, so it will likely crap out
soon. The symptoms are about right.

The 576 v. 577 discussion will likely never end, because they each have
their pluses and minuses, and either is a fine CT for most uses. There is
no consensus, except that it's nice to have both.

The TDS series scopes, as far as I can tell, all use a similar PS
topology, but unfortunately not identical in the details. I had to fix the
standby PS in a TDS544A a while back. As I recall, the main
supply/preregulator is a power factor correction (PFC) type. In its common
form, it is a boost converter, so it is set up to make preregulated DC
somewhat above the highest expected peak voltage of the power line -
typically 350-375 V for 240 V operation, or doubled 120 V in a dual-range
configuration. In a full-range, continuous coverage design, the input line
can be anything between the lowest and highest line possible, in any
country. I think the ones I have (TDS 544A, 754A, and 820) are full-range,
but there may be some that use dual-range. Regardless of this detail, the
highest expected rectified raw DC should be somewhat less than 400 V, so
somewhere around there is what the PFC converter is designed to put out,
and still provide regulation. All lower voltages are simply boosted up to
this level, giving very wide coverage.

It's been a while since I studied it, but I think that in standby, the PFC
is actually running all the time too, and the standby supply runs from the
PFC output. It isn't necessary for the PFC to be running all the time,
since when it's off, the rectified DC from the line passes through, but
would not be boosted or regulated. This would be OK too, since the standby
supply should be able to operate over a wide input range too. Either
arrangement can work, but controlling the on and off states would be
different.

The standby supply keeps it ready to go, and supplies power for scope-side
circuits, including the one-bit memory (I think it's a latching relay) of
its last power state. When the power button is pushed, the state is
switched to the opposite of whatever it was. In the case of turning the
scope on, the PFC converter is activated - if it's not always on anyway -
then the main output chopper fires up, converting the 400 VDC to the low
voltage secondaries.

Anyway, in standby, you may see the input voltage to the standby converter
be something similar to the peak of the input AC, or fixed near 400 V,
depending on the implementation details. In the scope on state, this
voltage should be around 400 V.

Ed

John,

I am no expert here, but i have bought two AWG20xx series one 2040 and one 2020. Both were sold as "good, working" both had serious issues when they arrived. I paid top dollar for both and was able to get a full refund on both because of non-functionality of the units. They were not DOA, but one had some sort of wacky signal issues and the other had been modified for some sort of proprietary serial port on the side, in place of the disc drive. I could not use it either. Be careful, these things are loaded with special ICs and microprocessors. Like most digital gear, there are no schematics, so they are not for the faint of heart to repair. I want another one, but I am not going to pay these "looney tunes" prices that folks are asking.

--
Michael Lynch
Dardanelle, AR

I have looked at other Tektronix groups but they are extremely small (one had 71 members). While I agree those 71 might be experts it is unlikely. So here goes an off topic question for those with abundant Tektronix experience just not scope related.

I am considering a purchase of a used Arbitrary Function Generator (AFG) or an Arbitrary Waveform Generator (AWG). I do know the difference between these two classes of instruments. Tektronix has quite a large selection of possible candidates. I don't need very high frequency capability and up to 20 MHz would be sufficient. However I am looking for good square waves (rise times in the range <=8 nS) with very low overshoot. Good quality sine waves. Plus the ability to upload arbitrary waveforms to the instrument either via RS-232 or GPIB. I am comfortable in repairing instruments having just nearly completed an HP 8662A restoration with only calibration left to do. So there are the AFG300 series, AWG202x series, AWG700 series, AWG400 series and probably others I don't know about. Some of these instrument families come from the dreaded leaking electrolytic capacitor age and may be irreparable due to PCB damage. eBay at present has really, in my estimation, looney tune pricing for some of these instruments so I am in no hurry to purchase. What I am looking for is any advice of models which are problematic and should be avoided and other such advice. Sorry for the off topic post but there didn't seem to be anywhere else with so much Tektronix experience.

John Proctor
VK2DLP

The manual says to check the DAC but does not say where it is.
I am about to start again. Any suggestions?
PeterB

Peter,

The DAC is Described in the manual on 3-9, it is built from discrete components. My 576 had numerous Axial Electrolytic caps bad as well as the Power Supply filter caps Some of the caps replaced: C759, C294, C698, C 696. The 5 V supply was only putting out 3.6V or so when I got the thing. Of course, nothing worked. I also had several bad transistors as well as a couple of bad J-FETS. In other words, mine was a wreck. Mine suddenly quit working one day due to failed Q800 in the +12.5LVPS. I outlined the numerous repairs on my unit in the "Repairs" section of the 576 page of TEKWiki.


--
Michael Lynch
Dardanelle, AR

Hi everyone,
The "Limited Viewing" light, like everything else in a Tek scope has to be calibrated properly to do its job. I seem to remember that Walter S. at Sphere Research had a 7104 that was barely usable since the light came on even in the lowest setting of the intensity control. That was a case where it needed to be adjusted properly. In a brightly lit lab it will be annoying to keep that light off. In my home lab it is never a problem since the room doesn't need to be that bright.

The smartest way you can test a 7104 for screen burn-in before you buy it is to put a timebase in a vertical slot and another one in a horizontal slot. Set both to auto mode so they free run. Set the one in the Horiz to run at a fast time/Div (10uSec/Div to 1uSec/Div for example) and set the one in the vertical slot to run slower (10mSec/div to 2 mSec/Div for example). This will create a raster on the CRT. If you turn the brightness up the raster will reveal every imperfection or burned-in image on the screen if there are any.

Dennis Tillman W7PF

Outstanding! I will definitely take a look!

Thank you Roy and best regards!
Jason