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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.

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.

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

On Sat, 23 Jun 2018 18:15:22 -0700, you wrote:

Hi all,

I made some measurements today of voltages in the LV test point area. The following are results measured with Fluke 189.

Tp1536 [+55] reads46.9
Tp1548 [+15] reads 0
Tp1558 [+5] reads 0.6
Tp1568 [-8] reads 0.48
Tp1518 [110] reads 106.6

The boards are clean with no burned parts. The only lights that turn on when the scope is turned on are 2 uncal indicators on the control panel. Any ideas of where to look first? This is my first scope to troubleshoot and it is bewilderingly complex for a new guy in town compared to the tube amps i am familiar with diagnosing. I REALLY appreciate the helpful camaraderie here..This is an amazing sharing of information here, not possible when this 465 was made.

Look for shorts on the +15 line to ground. I believe that others have
said that the reference for other supplies (say +5, and -8) depend on
the 15 volts being up and running. Not sure about the +55, but that
may clear up once the +15 is fixed.

Harvey

Russ

On Sat, 23 Jun 2018 18:13:46 -0700, you wrote:

Thank you all for suggestions - it worked! Indeed, after rotating both the outside (A) and the inside (B) timebase knobs a few times, and cranking up the intensity control, I did get something that resembles the sample trace: /g/TekScopes/photo/60634/0?p=Name,,,20,1,0,0

It seems though that the trace is bit blurry, jittery/jumpy, and with a significant amount of ghosting... The same symptoms (blurry, unstable and ghosting) are present on a simple trace as well: /g/TekScopes/photo/60634/1?p=Name,,,20,1,0,0

looking at the first trace, it seems as if the B timebase is not
triggering properly. You might try A only, and then B only (if you
can).

From the second trace, it looks as if B is not triggering properly,
but with the number of cycles of A, I'm not sure if A is ok, either.
That would be a reason to try A and B separately for one cycle or a
fraction of one.

Harvey

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

Hi all,

I made some measurements today of voltages in the LV test point area. The following are results measured with Fluke 189.

Tp1536 [+55] reads46.9
Tp1548 [+15] reads 0
Tp1558 [+5] reads 0.6
Tp1568 [-8] reads 0.48
Tp1518 [110] reads 106.6

The boards are clean with no burned parts. The only lights that turn on when the scope is turned on are 2 uncal indicators on the control panel. Any ideas of where to look first? This is my first scope to troubleshoot and it is bewilderingly complex for a new guy in town compared to the tube amps i am familiar with diagnosing. I REALLY appreciate the helpful camaraderie here..This is an amazing sharing of information here, not possible when this 465 was made.

Russ

Thank you all for suggestions - it worked! Indeed, after rotating both the outside (A) and the inside (B) timebase knobs a few times, and cranking up the intensity control, I did get something that resembles the sample trace: /g/TekScopes/photo/60634/0?p=Name,,,20,1,0,0

It seems though that the trace is bit blurry, jittery/jumpy, and with a significant amount of ghosting... The same symptoms (blurry, unstable and ghosting) are present on a simple trace as well: /g/TekScopes/photo/60634/1?p=Name,,,20,1,0,0

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

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.

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.

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 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.

Thank you for the link to the technical manual. I have a copy of the service manual, which says very little, and has no schematics. The technical manual looks like it will be a big help.

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

Gary Appel