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One thing that wasn't said on this thread ( unless I missed it) is that these scopes can be LETHAL !!! If you get "stung" by CRT high voltage (-1450) if it doesn't kill you, you'll be one hurtin buckaroo getting up off the floor over there in the corner of the room. That said, it sounds ( from reading ) you've got a low voltage failure for openers (15v most likely) and once that is corrected, things will probably come to life.
My main warning is that when one is around the filament of a CRT one must REMEMBER !!!

The filament low voltage AC ' is actual "riding" on Cathode (-1450) voltage SO extreme care is needed in any measurements in this area. ( high voltage probe).. perhaps the easiest and safest way to check CRT filament ( not glowing) is to simply remove the CRT connector ( after any high voltage has "bled off" and measure the resistance between pins 1 and 14 on the CRT neck....should be a very low ( <1ohm) resistance.
Anyway main purpose in writing here was to make sure you don't get electrocuted
Good Luck !

On Sun, 24 Jun 2018 11:43:29 -0700, you wrote:

Hi Harvey,

I think you (and Dave before) forget here that the supplies are protected by foldback current limiting. In case of a nearly dead short the current will be much smaller than in normal circumstances, and I guess that also the power dissipation in the series pass transistor will be smaller (the reduced current "wins" from the increased Vce so to speak). The bulk cap voltage will be higher than normal.

True, and I've made some of them. However, as I remember it, the
voltage across the sense resistors should be the VBE drop of the
trigger transistor. I'm also going on general theory without looking
at the specific schematic as well.

I prefer (if possible and reasonable) to talk about the theory, and
let the owner apply it. Maybe a little more difficult, but once
that's done, then the theory and practice are both in hand.

For the theory, the "standard" current limiting says that if the
supply is a 1 amp supply, it will try to deliver 1 amp into the load,
even if shorted. The pass transistor has to get rid of all the power
(say for an 18 volt bulk supply running at 1 amp, 18 watts).

Foldback current limiting triggers at the current limit (say for both
supplies, 1.5 amps), but effectively reduces the short circuit current
to, (say), 300 ma. Thus the pass transistor has to dump .3 * 1.8, or
5.4 watts into a dead short.

Harvey

Albert

On Sun, Jun 24, 2018 at 08:11 am, Harvey White wrote:

So, look for the bulk voltage, you'll find it to be a bit low. Now
look at the voltage drop on the pass transistor (that's the variable
resistor function). If there's a short on the output (I'd suspect
one), then the transistor drops the whole bulk supply voltage and
should be rather warm. There's a current sense resistor in there, say
0.1 to 2 ohms or so, generally with a transistor base/emitter junction
across it. Look for .5 to .7 volts across this resistor. If so, then
the supply is trying to current limit to protect itself.

Hello Dimitri,
To you and all, first of all, apologies if my answer is maybe mission the
history (your previous messages) but I'm writing from my phone and couldn't
let this go.
Itseems no one mentioned or asked you about the following, and it may
explain (or not) this - so called -ghosting.
To which function the DM44 multimeter on the top is set.
If it's on function Time, or 1/time, the ghost you are seeing can be,
maybe, the alternate delay controlled the the DM's 44 delta time control.
To rule that out, just make sure the DM44 is set to function Volts, Ohms or
Temperature an tell us if the ghosting disappears.
Or else, keep the Time or 1/time selected and check if the ghosting changes
or moves, as you turn the delta time knob on the DM 44, while keeping
everything else constant.
If the ghosting moves, then what you're seeing maybe nothing more than the
DM44's differential delay time measurement, which when activated in
conjunction with the MIX function can turn the display quite confusing, as
they (the time and 1/time measurement functions) are meant to be used in
conjunction with the "A Intense" and the "B Delayed" horizontal modes.
In that case, I suggest you download and read the manual of the DM44 option
itself, and understand how this ingenious function is meant to work.
Brgrds,
Fabio

On Sat, Jun 23, 2018 at 06:13 pm, Dmitri Shuev wrote:

I suppose that I will start by trying to clean both A and B Volts/Div
Attenuator Switch contacts...

Should help, but that jitter might be settings. If B sweep has an auto trigger, turn it off. Also switch it to DC coupling and turn off any low or high filters. Adjust the trigger level slowly and at some point it should be stable. Hopefully. If not, it is probably some caps somewhere.

Nice scope, a coworker used to have one like it. He didn't use it all that much, I used my old trusty 422 much more. In consumer electronics even on the 20V/div scale you can tell 5V, 12V, -12V and all that. I let it freerun and literally used it that way, then when I got to switchers and whatever like the HOT, HVOT or LOPT then it is triggered. And the 422 has a good enough trigger circuit to lock to almost anything. I don't know if yours has tunnel diode triggering but as far as I have seen it is the best. A 422 will lock onto noise, I shit you not. Put music to it and you'll see things you have never seen.

If switching to manual DC not auto trigger doesn't take care of it let us know. I'll RTFM and see if I get any ideas.

On Fri, Jun 22, 2018 at 10:56 am, Mike Merigliano wrote:

The Tek 475 is analog, with a CRT screen, so the tools for LCD screens will
probably not work.

I meant Bob's computer monitor. If LCD which most are these days, some are not quite perfect. My 23" on my good old PC, I think it is an Acer has great viewing angle, about like a CRT. But my laptop which has an edge (bottom) lit LCD is not so good.

There were people on here recently looking for donations for the cost of scanning a bunch of manuals and making PDFs out if them. I would have kicked in a few bucks but I do not have a credit card, so someone told me to just spread the word about this site...OK.

Look back a couple of pages of posts and you'll probably find it, if not maybe they'll find you. If you got something they don't, and are willing, let them have it. In fact they probably only need to borrow it. Get them back and actual paper manuals still have intrinsic value, and I have worked with them and liked it. Sometimes I print sections and tape them together into the bedsheet they resemble.

It's up to you, I would at least scan them or let others scan them. I have a couple of old ones which don't seem to be on the net, once they get it together I will send them what I have, either scans or the paper itself.

I will do everything in my power (which ain't much really) to keep good technology out of the dumpster.

i find myself with a Duraprobe 123 100 mHz probe, which is very nice but doesn't say tektronix on it anywhere.

It has H and L adjustments which i assume are intended to get rid of the spikes using the self-compensation routine.? My other probes each have only a single adjustment.

How do you adjust this thing?? Is it really a Tek product?

Hi Harvey,

I think you (and Dave before) forget here that the supplies are protected by foldback current limiting. In case of a nearly dead short the current will be much smaller than in normal circumstances, and I guess that also the power dissipation in the series pass transistor will be smaller (the reduced current "wins" from the increased Vce so to speak). The bulk cap voltage will be higher than normal.

Albert

Thanks everyone I just must have missed it or typed it in wrong

--
Richard Knoppow
dickburk@...
WB6KBL

On Sat, 23 Jun 2018 at 20:45 Gary Appel <garyappel@...> wrote:

Thank you Siggi.

The gentleman on EEVBlog has a 'scope that reported exactly the same
errors
as I have, so it sounds like it may very well be the same problem. I tried
squirting a little freeze mist on the acquisition memory. It didn't "fix"
the problem, but the trace certainly responded. With a little freeze mist
it
tried to come back to the same value as when the trace was rolling.

After spending some more time looking at the 'scope today, it does appear
to
be triggering. I'm not sure if that has changed since last night, or if I
was not setting the trigger correctly last night. As you suggested, I set
the trigger to AC and with the level at the center line it triggered on
Ch1,
Ch2, Ext, and line.

Cool - it all sounds consistent with RAM failure then.

At low sweep speed, where the trace rolls across the screen, the 'scope is
displaying a waveform, and it makes sense that they wouldn't be using the
acquisition memory for that, although there is an substantial offset and
calibration error in that mode. With a 0 offset and 0 position ground lies
about two divisions above the center line. Using the measure menu to
measure
the level, it does not agree with the volts / division. So there is likely
a
second problem.

If you've tried to run signal path compensation after the acquisition
system wonked out, this could be working as intended. The acquisition
system will have been used to measure the DC offset to compensate, and it
could have measured a large "ghost" offset.

Most of the IC's have a '95 date code. The Dallas chip has a '96 date code.

It is certainly on borrowed time. I have seen a number of references to
replacing the Dallas chip, after first copying the contents. It's probably
time for that as well.

I'm not sure it's worth the effort to preserve the memory contents of the
NVRAM, as the calibration procedure for this scope looks like a piece of
cake.
All you need is some DC and a "fast rise" (<10ns) pulse generator. This is
pretty typical for the CCD-based scopes, it was easy as pie to calibrate my
2430 using what I already had around the lab, plus some spit and bubblegum.

I do have an analog 'scope as well - a 2465A, that is also likely on
borrowed time. I suspect the Dallas chip in that 'scope is probably just
about as old.

Piffle - my 2467 has a keeper with an '85 date code in it, and it's still
going strong :). Of course I'm set to calibrate it, should the keeper give
up the ghost, so I'm not too bothered - I'm quite curious to see how long
the battery will last.

It sounds like my first task should be to replace that acquisition memory.

Yups, sounds like.

Meanwhile, in my impatience, I just ordered a replacement 'scope. It's
only
100 MHz, but now that I'm not earning a living with my equipment, I'm not
sure I need a 400 MHz digital 'scope any more.

Thanks for your assistance, I will post if I make some progress.

Good luck!

;_ylc=X3oDMTJmYjg3amVpBF9TAzk3MzU5NzE0BGdycElkAzEwOTI5MzMzBGdycHNwSWQDMTcwNTA4MzY2MwRzZWMDdnRsBHNsawN2Z2hwBHN0aW1lAzE1Mjk4NTY0NTI-

This one?

Does anybody know the fate of the Yahoo Agilent keysight HP group ?

I can't seem to find it anymore

On Sat, 23 Jun 2018 20:52:35 -0700, you wrote:

Harvey, Thanks for your reply. I referred to the manual suggested here by other members, 465 Late, as my sn is the later model. On pg 215 and for the next several pages it explains (to someone with more savy than I have re these circuits) troubleshooting the lv circuits. All voltages seems dependent on the 55v working properly. I wonder if I need to first bump the 55v up from its out of spec 46.9v first? I have very limited experience with transistors and their proper function in this circuit. But i did notice most seem to be plug and play connections instead of soldered like l am familiar with in old tube amps. That makes the plug in 40ish yr old connections throughout this scope suspect imho. I hope I'm wrong.

You'll find that plug and play is a good thing. In old tube amps, you
could removed the individual tubes (which generally fail with low
emission), to make sure that the tubes are not shorted (that's
something I personally have not seen).

With the plug connections, you'll find that they may fail with a
higher resistance, but that is not generally going to lower the power
supply voltage at the supply itself. So you can unplug several
sections to see what is going on.

It is possible for a power supply to be dragged down by another
supply. One way is a reference problem. If the 55 volt supply is
used as a direct reference (no zeners in another supply), then
changing it changes the other supply. If there's a reference in that
second supply and all the 55 volt supply does is power the reference,
then the 55 volt supply has to change significantly to affect the
other supply. (9-10 volts is significant, but not here).

A second way is that whatever is supplying the bulk voltage to both
supplies (an inverter, a power transformer, or a common winding)
simply has too much current drawn from it and resistive losses do the
dirty deed.

Now, what I remember on the 15 volt supply readings you've provided is
that the voltage is zero. Zero is a pretty significant number here.

I'd start at the bulk supply input for the 15 volt supply, that's the
unregulated input. (you may want to look for some of my other posts
on power supply theory, if you are interested, they may help a bit.)

Generally, in these supplies, there's a large transistor used as a
variable resistor. The supply is effectively a high power voltage
divider with the transistor being the top resistor and the rest of the
circuitry being the lower resistor.

These supplies are frequently current limited as well.

So, look for the bulk voltage, you'll find it to be a bit low. Now
look at the voltage drop on the pass transistor (that's the variable
resistor function). If there's a short on the output (I'd suspect
one), then the transistor drops the whole bulk supply voltage and
should be rather warm. There's a current sense resistor in there, say
0.1 to 2 ohms or so, generally with a transistor base/emitter junction
across it. Look for .5 to .7 volts across this resistor. If so, then
the supply is trying to current limit to protect itself. Again, look
at power supply theory and then look to current limited supplies,
series regulator style.

Now, for power off tests, which you can do first. Unplug as many
leads as possible from the power supply, you're interested in the
lines going to the various boards. Make sure the power supply
capacitors are discharged, then measure the resistance from ground to
each of the power supply output leads. Those should be within spec.

If they are not, then at least one possible fault lies on the power
supply board itself.

If those readings are ok, then measure the resistance at each of the
power supply inputs to each board, those should be within spec.
Remember that a 1 ohm reading on the 15 volt line will try to draw 15
amps, so that's completely unreasonable. (I'd guess that the
resistance would be at least 15 ohms and perhaps 30 or more). Don't
worry about the low resistance due to capacitor charging, the final
value is important here.

Some people will power up the scope with the supply disconnected
(check to see if Tek says that's ok), and then check voltages. Then
power off, and plug in boards one by one until something fails. That
works, too, but I'd suggest resistance readings first.

Generally, you're likely to find one of those little epoxy drop
tantalum capacitors shorted. Also, with the boards as exposed as
possible, look for evidence of overheated parts, darkened paint,
discolored PC board, or ashes in what's left of a resistor (which, if
open, disconnects the short. Look anyway....)

Hopefully, this gives you a start. We've all been where you are, but
for some of us, it's a little longer ago.

Harvey

Any coaching with specific instructions for a guy with a pretty well equipped lab but limited sources here in Mexico for technical help. In the late 60's I was able to fix a Perkin Elemer Atomic Absorption Spectrophotometer in a lab I ran in Alaska with phone coaching from PE saving perhaps months of down time during a very short productive prospecting season. I have much better repair tools than I did then, so l am confident with the diagnostic veterans here helping, that i can get this otherwise clean old scope working again.

Thx, Russ

Not to discount the possibility of a short on +15v, there are other possibilities that may be easier to check out. First, are the rectified un-regulated voltages present and sufficient for the regulators to function? What are the DC voltages and AC ripple across the rectifier filters, C1512, C1513, C1542, C1552, and C1562? Each of these should be a volt or more greater (DC) than their respective regulated outputs. For example, C1542 should be 16v or more. If a short exists on the +15v rail, this may be less than 16 volts, but it should not be zero.
Now, with +15v at zero, +5v & -8v regulators cannot function, as the error amplifiers, U1554a&b will have no Vcc bias on pin 8, so no or little output is expected.
Next, I would check the +22v error amplifier bias, U1524b. It needs to be +19v or so for the +15 regulator to operate. If OK, move on to Q1544 AND Q1546. What are the collector, base and emitter voltages of these? What about the voltage across R1549? What are the input and output voltages on U1524b, that is, pins 5,6, and 7?
With the above information in hand, we should be able to give a much better idea as to the source of the problem.

Dave

Hi Gudjon,

Certainly interesting! At present my CSA803 is the only equipment with a serial interface and I don't have plugins yet. So testing those Python scripts has to wait. (And I'm not yet familiar with Python.)
Those FTDI products might be a better choice, at least better documented. I simply ordered an available converter from a local webshop and it appeared to be that Prolific PL2303 type.
BTW my interest in using GPIB and Serial started because the touch panel produced errors. With GPIB the command TEST XTND immediately closes the GPIB connection when an error is detected while with Serial you can continue, IIRC.

Albert

maybe this will help you - I just fixed (sort of) a 465 that was dead. it was dead because the filter cap (the big huge filter cap) on the +5V supply was a dead short, and a prior person had removed the bridge rectifier (so it wasn't blowing a fuse) - I went around in circles for about 3 hours before I realized that I had misread the designation on the schematic and was looking at the wrong part of the circuit (which oddly enough also had a weak, but not dead short) filter capacitor. After getting that scope working I looked at a 475 that had an erratic trigger and found a shorted 2.2 microfarad dipped capacitor that was a dead short.


So, something to check is that you have all the voltages (on my 465 the 5V was about 1.8V), on mine at least the test points are pretty clearly labeled. I see from above that both the 15 and the 5V are zero - check the voltages at the bridge rectifier, if the filter caps are shorted, that voltage will be way off. and if you are lucky it will be the rectifier that has failed and not the transformer. once you get the voltages to be present, feeling the little dipped caps with the power on (stay away from the HV section) can tell you a cap is going bad, it will be warm/hot. also feel any other electrolytic, none should be warm. And, wiggle all the transistors while you are near them (with power off) to clean any oxide off their leads.

Any of those voltages that are absent will probably cause a no-trace condition. Oh, and one more thing that messed me up, the indicator light by the power switch is not a power-on light, it is a power-low light, I spent time troubleshooting why it didn't come on before I read more carefully how it was labeled.


so maybe my two mistakes can help you find your problem faster. Good luck

Hi Albert

I connect to my CSA803 with an FTDI USB to Serial converter that I
soldered a DB-25 connector to.
I have rewritten the example programs from the programmers manual to
Python and tested on both
Linux and Windows.
Joel Koltners screen capture program is rewritten as a command line
utility. The GUI application depends
on a too old version of WX-Python.




Hope it is of any interest.

Regards
Gudjon

On Sat, Jun 23, 2018 at 05:32 pm, Raymond Domp Frank wrote:

On Fri, Jun 22, 2018 at 11:20 pm, lop pol wrote:

I would be satisfied with that trace.

In real circuits, poor probing techniques will introduce more serious
errors
than shown on that trace.

Thank you. Wish I could say It was done, but this scope is full of problems.
Now time to figure out why single sweep is not working.

The rising edge and first few tens of ns after it look fine now but the dip
just before its start doesn't. It's not serious but not nice either. From what
I can see of the waveform, it probably indicates some (remaining)
frequency-dependent phase shift but again, I wouldn't worry too much.
During all your work improving the first few ns after the step, did you keep
an eye on the low(er) frequency response? You would expect a mostly flat and
horizontal top and bottom line at square wave frequencies of 100 kHz and
below, down to 1 kHz.
Good luck with your further efforts on this 'scope!

Raymond

Thank you (everyone) for taking the time to share your knowledge with me. I know most of you have worked really hard to learn what you have. I am humbled daily by visiting with you all. Tomorrow is another day and I will use it to apply what you are teaching me.