Date   
Re: Tek 2467B Erratic Intensity controls

Jean-Paul
 

Hello all

Wonderful thread with Chuck and other super 2465 mavens giving us the benefits of long experience.

I would not assume replaced A5 board smd lytics exonérate the board of corrosion damage.

Reading the entire thread my gut instincts is A5 in the DAC and DAC référence area.

A careful inspection with strong light and magnifying glass might révèle the problem.

Try the DAC référence cal proceedure near the start of CAL.

Just the ramblings of an old retired EE

Jon

5103N Comments, advice

Harold Foster
 

All:

I just bought a 5103N with 5B12N, 5A20N and 5A22N plugins for a very good price, planning to use it for checking power supply PARD since it has the differential inputs. I have not really done anything with it other than turn it on - squiggles on screen - and plan to work with it further this weekend.

So: Is there anything in particular I should be on the lookout for when I start? Hints & Tips? This is the first Tek equipment I will be restoring and am not familiar with the Tektronix way of doing things and, as such, very much would appreciate any input anyone has.

Thank you,

Hal

Re: Tek 2467B Erratic Intensity controls

peter bunge
 

You are correct Chuck.
I never noticed that. I just let the 'scope cycle twice and it turned off
and now shows 'shutdown'.
Previously I noticed that on the first pass with a bright display (4
minutes) it turned the intensity down on the first pass but did not
shutdown.
Another thing is that the countdown is not precise nor regular. It hangs
at, say 27, then jumps to 24. Sometimes several seconds at a number other
times counting each second. On this test it actually went to 1 then showed
3, 2, 1, then blanked. The seconds starts up near 80. I don't know if the
irregular countdown is part of the delay fault but the countdown can now be
eliminated as a symptom.
Peter.

On Mon, Dec 2, 2019 at 1:21 PM Chuck Harris <cfharris@...> wrote:

Hi Peter,

About the display counter.

I think there is a bug in the software that makes the counter
count twice. If you wait long enough, the screen will blank.

I have seen this behavior on every 2467B that has come my way.

It counts 16M-->0, and then counts 16M-->0 and blanks.

You can determine the counter's behavior by looking at the
various EXER routines in the diagnostics menu. I don't recall
which routine it is, but it is listed in the manual.

-Chuck Harris

peter bunge wrote:
Thanks Chuck;
however I bought the U800 to repair a friend's 2465 scope that was
sitting
on a shelf with the feet overhanging so the cooling holes in the bottom
of
the 'scope were blocked. This may not have been the cause but the 'scope
failed suddenly.
My present problem with a 2467B S/N B051193 has nothing to do with U800
but
may be associated with U650. I mentioned the problems as general
interest.
The symptoms are that changes in either of the intensity pots takes
several, and up to many (30 or more), seconds to respond either in
intensity on the screen, or voltages at the sequencer pins. Without
touching anything on the 'scope the 'trace turn off' counts down from
minutes, to 59 seconds, down to 2 seconds, then starts again at (8)
minutes
without shutting off the display. So that feature is not working. At very
bright it did drop the intensity after 30 seconds but did not turn it off
so it may be partly working. I remember it turned the displays off until
a
knob was moved.
Delta v and delta t are erratic placing the dotted lines on the screen,
and
dt sometime shows dv lines or nothing. And they have the same sluggish
delay to doing anything.
The 5 capacitors have been professionally replaced before I got the
'scope
and they look good. There could still be corrosion somewhere but I don't
intend to replace them haphazardly without some evidence. I washed around
them by brushing Isopropyl Alcohol and letting it run down onto paper
towel. There is no evidence of a change. I don't think they are the
problem.
I re-soldered the legs of the coil and saw no change, not that I expected
to.
I was following the troubleshooting (page 458 in several pdfs) that asks
if
the LEDs respond to "A/B Trig" being pressed. This is confusing since
they
don't define 'respond'. Fortunately I have a 2465 with Tek manual which
asks the same thing. On the 2465 the displays are switched each
press/release but on my 2467B they change back when released. Is this
normal? Another problem is that if I go to 4 as directed it asks about
"signals conforming to guidelines at the left" and that page is missing
or
out of order in the pdf. My 2465 Tek manual shows the page I should see.
However with my new interpretation of 'respond' I was being led astray so
the answer should have been 'no' and I should not have gone to 4. The
next
step is "do scale factors appear with readout intensity full cw?" Yes
takes
me to "repair LED or front panel interconnect", unlikely, so this takes
me
nowhere.
I swapped sequencer U650 155-0244-01 with 155-0244-00 from the 2465 but
there was no change.
Still struggling but getting a better understanding. Time to 'scope
around
the circuits.
Peter

On Sun, Dec 1, 2019 at 12:42 PM Chuck Harris <cfharris@...> wrote:


Re: Tek 2467B Erratic Intensity controls

Chuck Harris
 

Put a DVM on pin 13 of J119 to ground.

Turn the delta control slowly and watch how the voltage
changes. This voltage is generated by the DAC. It should
change smoothly from -1.25V through +1.25V as the delta
control is turned. It will stop moving past those extremes.

If your DAC is bad, nothing will work right.

Also, I forget, did you replace the smd capacitors on your
A5 board? You are in the right serial number range for them
to be a problem.

-Chuck Harris

peter bunge wrote:

Thanks Chuck, Bob Koller ruled out the battery for another reason; changing
the NVRAM did not fix his 'scope. So it is discounted for several reasons.
I have been using this 'scope for years. What I'm seeing is a sudden fault,
not normal trivial delays. These are 5 second delays.
The dV and dt switches don't get made analog so your suggestion, although
explaining some symptoms, does not explain the erratic selection of the
hor & vert dotted lines (and I don't know what draws them yet). I am
reading the manual to try and understand but all suggestions are welcome.
The analog signals (pots) are digitized and made analog again by the one
DAC U2101. The analog storage capacitors you are talking about are the ones
following the two Mux U2530 and U2521? U2530 does Vertical Position and
Intensity but U2521 does Hor Posn and I doubt both are bad. Besides the
levels, when they appear, are jumps not a gradual increase as seen on a
'scope and also by the sudden change of brightness of the displays.
I need to continue with the manual and understand the entire system. I wish
I had a spare A5 board to swap out and narrow down the search. There is a
big delay somewhere between reading the switches or pots and reaching the
Sequencer.
Peter


On Mon, Dec 2, 2019 at 11:50 AM Chuck Harris <cfharris@...> wrote:

Re: Tek 2467B Erratic Intensity controls

peter bunge
 

Thanks Chuck, Bob Koller ruled out the battery for another reason; changing
the NVRAM did not fix his 'scope. So it is discounted for several reasons.
I have been using this 'scope for years. What I'm seeing is a sudden fault,
not normal trivial delays. These are 5 second delays.
The dV and dt switches don't get made analog so your suggestion, although
explaining some symptoms, does not explain the erratic selection of the
hor & vert dotted lines (and I don't know what draws them yet). I am
reading the manual to try and understand but all suggestions are welcome.
The analog signals (pots) are digitized and made analog again by the one
DAC U2101. The analog storage capacitors you are talking about are the ones
following the two Mux U2530 and U2521? U2530 does Vertical Position and
Intensity but U2521 does Hor Posn and I doubt both are bad. Besides the
levels, when they appear, are jumps not a gradual increase as seen on a
'scope and also by the sudden change of brightness of the displays.
I need to continue with the manual and understand the entire system. I wish
I had a spare A5 board to swap out and narrow down the search. There is a
big delay somewhere between reading the switches or pots and reaching the
Sequencer.
Peter

On Mon, Dec 2, 2019 at 11:50 AM Chuck Harris <cfharris@...> wrote:

The processor has no knowledge of how fast the DAC is working.
It simply sends the DAC a value, and assumes it does its job.

I can think of a scenario that could be in play. All of the
controls are digitized, processed, made analog, and have their
analog value stored in a sample-and-hold gate.

Because the sample-and-hold gate is a capacitor that is holding
a charge, the CPU has to refresh that charge at regular intervals,
or it will leak down.

Suppose the MUX that charges the sample-and-hold capacitor is
broken so that it is high resistance, instead of its usual very
low resistance.

The CPU will set the DAC to the appropriate voltage, and the
broken MUX will charge it a little, then at each refresh interval,
the CPU will set the DAC to the same value, and the broken MUX
will charge it a little more... each refresh putting a little
more charge into the cap until it eventually reaches full charge.

You will see this as the control moving very slowly.

-Chuck Harris

peter bunge wrote:
Yes they are 'sticky' especially if I move ch2 then ch1. Also the digital
display of the DC trigger point is sluggish and often does not change
with
the +/- level knob. It acts like a delay to the ADC which is not a
component but a complex group.
It could be a sluggish DAC U2101 sending to the sequencer via U2530 and U
2630 but I can't understand how (Analog Control tab 2). I am about to
'scope them. It is interesting that there is signs of work done around
the
DAC, perhaps a broken trace but it is difficult to tell hence 'scoping to
look for a suspicious signal to follow. It could be an address line
floating but I would expect more problems. They look clean. pins 19 & 18
look messy but they are current O/P so look at U2630 pins 3 and 12. The
voltage here does not follow the intensity pots but is delayed. It jumps
suddenly but is clean. Moving on......
Peter.

On Sun, Dec 1, 2019 at 3:35 PM Bob Koller via Groups.Io <testtech=
yahoo.com@groups.io> wrote:


Re: Tek 2467B Erratic Intensity controls

Chuck Harris
 

Hi Peter,

About the display counter.

I think there is a bug in the software that makes the counter
count twice. If you wait long enough, the screen will blank.

I have seen this behavior on every 2467B that has come my way.

It counts 16M-->0, and then counts 16M-->0 and blanks.

You can determine the counter's behavior by looking at the
various EXER routines in the diagnostics menu. I don't recall
which routine it is, but it is listed in the manual.

-Chuck Harris

peter bunge wrote:

Thanks Chuck;
however I bought the U800 to repair a friend's 2465 scope that was sitting
on a shelf with the feet overhanging so the cooling holes in the bottom of
the 'scope were blocked. This may not have been the cause but the 'scope
failed suddenly.
My present problem with a 2467B S/N B051193 has nothing to do with U800 but
may be associated with U650. I mentioned the problems as general interest.
The symptoms are that changes in either of the intensity pots takes
several, and up to many (30 or more), seconds to respond either in
intensity on the screen, or voltages at the sequencer pins. Without
touching anything on the 'scope the 'trace turn off' counts down from
minutes, to 59 seconds, down to 2 seconds, then starts again at (8) minutes
without shutting off the display. So that feature is not working. At very
bright it did drop the intensity after 30 seconds but did not turn it off
so it may be partly working. I remember it turned the displays off until a
knob was moved.
Delta v and delta t are erratic placing the dotted lines on the screen, and
dt sometime shows dv lines or nothing. And they have the same sluggish
delay to doing anything.
The 5 capacitors have been professionally replaced before I got the 'scope
and they look good. There could still be corrosion somewhere but I don't
intend to replace them haphazardly without some evidence. I washed around
them by brushing Isopropyl Alcohol and letting it run down onto paper
towel. There is no evidence of a change. I don't think they are the problem.
I re-soldered the legs of the coil and saw no change, not that I expected
to.
I was following the troubleshooting (page 458 in several pdfs) that asks if
the LEDs respond to "A/B Trig" being pressed. This is confusing since they
don't define 'respond'. Fortunately I have a 2465 with Tek manual which
asks the same thing. On the 2465 the displays are switched each
press/release but on my 2467B they change back when released. Is this
normal? Another problem is that if I go to 4 as directed it asks about
"signals conforming to guidelines at the left" and that page is missing or
out of order in the pdf. My 2465 Tek manual shows the page I should see.
However with my new interpretation of 'respond' I was being led astray so
the answer should have been 'no' and I should not have gone to 4. The next
step is "do scale factors appear with readout intensity full cw?" Yes takes
me to "repair LED or front panel interconnect", unlikely, so this takes me
nowhere.
I swapped sequencer U650 155-0244-01 with 155-0244-00 from the 2465 but
there was no change.
Still struggling but getting a better understanding. Time to 'scope around
the circuits.
Peter

On Sun, Dec 1, 2019 at 12:42 PM Chuck Harris <cfharris@...> wrote:

Re: Tek 2467B Erratic Intensity controls

Bob Koller
 

Peter,

I need to put this instrument back on the bench to investigate further. It has been shelved for awhile.
U950 is the the Z-Axis hybrid, these can be defective, I have replaced a few over the years, but I haven't seen one that caused the uP to act up.
I guess anything is possible..

Re: Tek 2467B Erratic Intensity controls

Chuck Harris
 

The processor has no knowledge of how fast the DAC is working.
It simply sends the DAC a value, and assumes it does its job.

I can think of a scenario that could be in play. All of the
controls are digitized, processed, made analog, and have their
analog value stored in a sample-and-hold gate.

Because the sample-and-hold gate is a capacitor that is holding
a charge, the CPU has to refresh that charge at regular intervals,
or it will leak down.

Suppose the MUX that charges the sample-and-hold capacitor is
broken so that it is high resistance, instead of its usual very
low resistance.

The CPU will set the DAC to the appropriate voltage, and the
broken MUX will charge it a little, then at each refresh interval,
the CPU will set the DAC to the same value, and the broken MUX
will charge it a little more... each refresh putting a little
more charge into the cap until it eventually reaches full charge.

You will see this as the control moving very slowly.

-Chuck Harris

peter bunge wrote:

Yes they are 'sticky' especially if I move ch2 then ch1. Also the digital
display of the DC trigger point is sluggish and often does not change with
the +/- level knob. It acts like a delay to the ADC which is not a
component but a complex group.
It could be a sluggish DAC U2101 sending to the sequencer via U2530 and U
2630 but I can't understand how (Analog Control tab 2). I am about to
'scope them. It is interesting that there is signs of work done around the
DAC, perhaps a broken trace but it is difficult to tell hence 'scoping to
look for a suspicious signal to follow. It could be an address line
floating but I would expect more problems. They look clean. pins 19 & 18
look messy but they are current O/P so look at U2630 pins 3 and 12. The
voltage here does not follow the intensity pots but is delayed. It jumps
suddenly but is clean. Moving on......
Peter.

On Sun, Dec 1, 2019 at 3:35 PM Bob Koller via Groups.Io <testtech=
yahoo.com@groups.io> wrote:

Changing Color

Karin Johnson
 

Is there any way in Groups.io to change the color of the header test in the messages?

Karin

Re: Tek 2467B Erratic Intensity controls

Chuck Harris
 

Hi Peter,

The battery has nothing to do with read or write speed.
The NVRAM *is* the CPU's general purpose RAM. The battery
only takes effect when the 5V logic power is turned off.

If the NVRAM were slow to read or write, the CPU would simply
fail to work. It would be executing garbage data, and would
jump off the end of the world, so to speak.

The CPU in the 2465B family is greatly overtaxed by the
addition of all knobs being fly-by-wire. Because of this,
it sometimes misses your starting to turn the knob for a bit,
and then catches up later.

AutoLVL is particularly bad. You might try the knobs in
both AutoLVL and Auto triggering positions.

It also has two speed knobs on the position controls, that
move large distances if you turn the knob fast, and flips
into fine mode when you move the knob slowly. This will seem
to be a lag.

Because the processor is overtaxed, if its clock crystal
were to operate at a subharmonic, like 1/2 speed, or less,
it would seem like the knobs never gets serviced.

-Chuck Harris

peter bunge wrote:

My reasoning that the NOVRAM is causing the delayed response to the pots is
that maybe it is marginal at writing but OK at reading with low battery.
Anyway it should be replaced.
What is a good replacement?
Are the ones listed from China and Hong Kong OK to use?
How do I know if the battery is good in a "new" one?
What programmer is good to use?

On Sun, Dec 1, 2019 at 7:48 PM peter bunge via Groups.Io <bunge.pjp=
gmail.com@groups.io> wrote:

The Trig Level goes through a different Mux to the Intensity and position
controls. The three Mux O/Ps are joined and feed comparator LM311 U2510
(all on Tab 2 schematic) The Mux O/Ps (TP9) are clean and jump when a pot
is suddenly turned, the same for the comparator O/P. I am trying to find
something common to the Position, Trig Level, and Intensity Pots. The
comparator O/P goes through U2220 and it seems to respond immediately to
pot changes. Then there is the dv and dt switches that seldom work and when
they do the dotted lines are jumpy when moved with the pots below the
switches.
I assume the various positions are saved in RAM (the NOVRAM). Could it be
getting slow because of a low battery?
Is there a quick check I can make?

On Sun, Dec 1, 2019 at 5:39 PM peter bunge via Groups.Io <bunge.pjp=
gmail.com@groups.io> wrote:

Yes they are 'sticky' especially if I move ch2 then ch1. Also the digital
display of the DC trigger point is sluggish and often does not change
with
the +/- level knob. It acts like a delay to the ADC which is not a
component but a complex group.
It could be a sluggish DAC U2101 sending to the sequencer via U2530 and U
2630 but I can't understand how (Analog Control tab 2). I am about to
'scope them. It is interesting that there is signs of work done around
the
DAC, perhaps a broken trace but it is difficult to tell hence 'scoping to
look for a suspicious signal to follow. It could be an address line
floating but I would expect more problems. They look clean. pins 19 & 18
look messy but they are current O/P so look at U2630 pins 3 and 12. The
voltage here does not follow the intensity pots but is delayed. It jumps
suddenly but is clean. Moving on......
Peter.

On Sun, Dec 1, 2019 at 3:35 PM Bob Koller via Groups.Io <testtech=
yahoo.com@groups.io> wrote:

On Sun, Dec 1, 2019 at 12:01 PM, peter bunge wrote:


"The symptoms are that changes in either of the intensity pots takes
several, and up to many (30 or more), seconds to respond either in
intensity on the screen, or voltages at the sequencer pins. Without
touching anything on the 'scope the 'trace turn off' counts down from
minutes, to 59 seconds, down to 2 seconds, then starts again at (8)
minutes
without shutting off the display. So that feature is not working. At
very
bright it did drop the intensity after 30 seconds but did not turn it
off
so it may be partly working. I remember it turned the displays off
until
a
knob was moved.
Delta v and delta t are erratic placing the dotted lines on the
screen,
and
dt sometime shows dv lines or nothing. And they have the same
sluggish
delay to doing anything."
This is interesting, do the Position controls exhibit similar laggy
behavior?

I have a 2465B control board that does something similar; all the
analog
controls are much slower to respond than a normally operating
instrument.
It passes self test, and works normally other that the very laggy and
jumpy response to control changes.









Re: Tek 2467B Erratic Intensity controls

peter bunge
 

Thanks Bob, that eliminates another potential cause. It seemed like a
reasonable cause that the new values were not being saved and old values
were being used. What do you think of the " Did you try cleaning the
contacts on the old U950 and re-insert it?" suggestion from Siggi? I hate
to disturb it. Have you tried this? I wonder where it fits in? It does not
seem to be in the ADC or CPU loop to be able to delay any signal updates
like the Trig Level display. Is your Trig Level digital display delayed?
My 2467B was fine one day then started acting up.
Delayed Trig Level display. However the trigger point responds immediately
as I move up the leading edge of the calibrator signal (20nS/div). It just
does not get updated on the CRT readout, or takes seconds to update.
Delayed Intensity adjustments. Time-out no longer works properly.
Posn response sluggish, horiz and all vertical.
My dV and dt switches often remember the last one pressed (dV gives the two
horizintal dotted lines, then dV to turn them off. Now dt brings them back
instead of two vertical dotted lines. Right now I can only get the
horizontal ones. I just pressed both and now I can't get either. Vertical
line suddenly appeared after many seconds. How are yours working?
These delayed dV and dt switch selections suggest the problem is not in the
ADC loop but just the digital values being delayed. Just thinking aloud on
the keyboard.
I will go away to read the manual for a bit.
Peter

On Mon, Dec 2, 2019 at 9:40 AM Bob Koller via Groups.Io <testtech=
yahoo.com@groups.io> wrote:

My instrument has a new NVRAM, I routinely replace the Maxim/Dallas part
with the less expensive ST M48Z08 part.
The new, or the old, NVRAM make no difference with the sluggish or sticky
control action.

It seems to me that the uP is busy with something else, but what?
This instrument is a B05+ s/n, with the readout integrated on the control
board. I wonder if there is some problem there, perhaps causing extra uP
load?



Re: Tek 2467B Erratic Intensity controls

Bob Koller
 

My instrument has a new NVRAM, I routinely replace the Maxim/Dallas part with the less expensive ST M48Z08 part.
The new, or the old, NVRAM make no difference with the sluggish or sticky control action.

It seems to me that the uP is busy with something else, but what?
This instrument is a B05+ s/n, with the readout integrated on the control board. I wonder if there is some problem there, perhaps causing extra uP load?

Re: Tek 485 can not switch to 50 Ohm input impedance: U80 faulty?

Yeun-Jung Wu
 

Hello Tom:

Thank you for pointing me things to be checked and a possible work around. I will try your suggestion a few later when I got spare time.

Yeun-Jung Wu

Re: Tek 2467B Erratic Intensity controls

peter bunge
 

My reasoning that the NOVRAM is causing the delayed response to the pots is
that maybe it is marginal at writing but OK at reading with low battery.
Anyway it should be replaced.
What is a good replacement?
Are the ones listed from China and Hong Kong OK to use?
How do I know if the battery is good in a "new" one?
What programmer is good to use?

On Sun, Dec 1, 2019 at 7:48 PM peter bunge via Groups.Io <bunge.pjp=
gmail.com@groups.io> wrote:

The Trig Level goes through a different Mux to the Intensity and position
controls. The three Mux O/Ps are joined and feed comparator LM311 U2510
(all on Tab 2 schematic) The Mux O/Ps (TP9) are clean and jump when a pot
is suddenly turned, the same for the comparator O/P. I am trying to find
something common to the Position, Trig Level, and Intensity Pots. The
comparator O/P goes through U2220 and it seems to respond immediately to
pot changes. Then there is the dv and dt switches that seldom work and when
they do the dotted lines are jumpy when moved with the pots below the
switches.
I assume the various positions are saved in RAM (the NOVRAM). Could it be
getting slow because of a low battery?
Is there a quick check I can make?

On Sun, Dec 1, 2019 at 5:39 PM peter bunge via Groups.Io <bunge.pjp=
gmail.com@groups.io> wrote:

Yes they are 'sticky' especially if I move ch2 then ch1. Also the digital
display of the DC trigger point is sluggish and often does not change
with
the +/- level knob. It acts like a delay to the ADC which is not a
component but a complex group.
It could be a sluggish DAC U2101 sending to the sequencer via U2530 and U
2630 but I can't understand how (Analog Control tab 2). I am about to
'scope them. It is interesting that there is signs of work done around
the
DAC, perhaps a broken trace but it is difficult to tell hence 'scoping to
look for a suspicious signal to follow. It could be an address line
floating but I would expect more problems. They look clean. pins 19 & 18
look messy but they are current O/P so look at U2630 pins 3 and 12. The
voltage here does not follow the intensity pots but is delayed. It jumps
suddenly but is clean. Moving on......
Peter.

On Sun, Dec 1, 2019 at 3:35 PM Bob Koller via Groups.Io <testtech=
yahoo.com@groups.io> wrote:

On Sun, Dec 1, 2019 at 12:01 PM, peter bunge wrote:


"The symptoms are that changes in either of the intensity pots takes
several, and up to many (30 or more), seconds to respond either in
intensity on the screen, or voltages at the sequencer pins. Without
touching anything on the 'scope the 'trace turn off' counts down from
minutes, to 59 seconds, down to 2 seconds, then starts again at (8)
minutes
without shutting off the display. So that feature is not working. At
very
bright it did drop the intensity after 30 seconds but did not turn it
off
so it may be partly working. I remember it turned the displays off
until
a
knob was moved.
Delta v and delta t are erratic placing the dotted lines on the
screen,
and
dt sometime shows dv lines or nothing. And they have the same
sluggish
delay to doing anything."
This is interesting, do the Position controls exhibit similar laggy
behavior?

I have a 2465B control board that does something similar; all the
analog
controls are much slower to respond than a normally operating
instrument.
It passes self test, and works normally other that the very laggy and
jumpy response to control changes.







OT: floppy disk head

snapdiode
 

Just wondering if in the collected knowledge pool here if anyone has any information on how floppy drive heads were manufactured?
Specifically the 5.25" drives. It's very similar to a P6042 head I guess, there's awfully fine wire, a core, some potting compound, polished surfaces, and built-in self-destruct mechanisms.
For example, the Newtronics D500 mechanism used in Commodore floppy drives has a failure mode where a winding for the read coil goes open circuit.
How can you fix that? It's not very likely to be repairable.

Re: 577 AC collector supply not reading zero on display

 

Hi DW,
If the 577 is showing 2 horizontal divisions at 50mV/Div that implies there should be 100mV p-p between emitter and collector banana jacks. If that voltage is a really there then we can measure a current using a 100 ohm resistor.

Put the resistor between the emitter and collector in the left set of banana jacks and flip the left / right switch to the left. Set the series resistor to its smallest value of 0.12 ohms. You should get 1ma of current from 100mV through a 100 ohm resistor. If you set the vertical knob to 0.2ma/ Div you should get a DIAGONAL LINE that goes from 0V and 0ma (the lower left corner) to 2 divisions (100mV) horizontal and 5 divisions (1mA) vertical. If you switch the collector supply from NPN to PNP the diagonal line will move to the upper right corner.

Dennis Tillman W7PF

-----Original Message-----
From: DW
Sent: Sunday, December 01, 2019 6:17 PM
Subject: Re: [TekScopes] 577 AC collector supply not reading zero on display

<SNIP>
With the collector in AC on 6.5V with 2k series resistor, horizontal devision set to 50mV...
A flickering line appears 2 divisions in length I find if I increase the D1 brightness (Turn the D1 brightness fully clockwise) the flickering pattern goes away into a solid green light which is interesting to note I plugged a voltmeter into the Emitter and collector terminals and observe 38mV of AC voltage I short the emitter and collector terminals and find the 2 division line shrinks to a dot and the voltmeter reads about 0mV AC Obviously some small amount of AC power is getting through and measured on the display and voltmeter




--
Dennis Tillman W7PF
TekScopes Moderator

Re: 577 AC collector supply not reading zero on display

DW
 

Thanks for the reply

With the collector in AC on 6.5V with 2k series resistor, horizontal devision set to 50mV...
A flickering line appears 2 divisions in length
I find if I increase the D1 brightness (Turn the D1 brightness fully clockwise) the flickering pattern goes away into a solid green light which is interesting to note
I plugged a voltmeter into the Emitter and collector terminals and observe 38mV of AC voltage
I short the emitter and collector terminals and find the 2 division line shrinks to a dot and the voltmeter reads about 0mV AC
Obviously some small amount of AC power is getting through and measured on the display and voltmeter

When I put the collector in DC- PNP the line shifts to the upper right corner of the display as a dot with the voltmeter measuring about 9mV AC, barely visible on the display
When the LEFT RIGHT selector switch is switched to neutral position I observe 500mV AC, strange
When I put the collector in DC+ NPN the line shifts to the lower left corner of the display as a dot with the voltmeter measuring about 9mV AC, again barely visible on the display

I find if I select any position other than AC on the collector the display shots a dot.

In the following test I put the collector to 25 volts 2kohm in DC- and DC+ at 0 collector voltage 50mV Division and measure the emitter to collector voltage of any slight DC voltage
(DC+ -0.4mV) (DC- 0.3mV)
Interestingly when performing this test I found if I move the series resistor control above 2kohm the dot starts to become the flickering line I observe before in AC but now it is in DC+ or DC-, If I set the series resistance lower about 2k or below the flickering line becomes the dot.

In AC 25V 50mV Division, changing the series resistance has no effect other than just displaying a line that is 7 divisions long which is pretty bad!

Re: 577 AC collector supply not reading zero on display

 

Hi DW,
Unfortunately I don't know if that is good or bad.
<SNIP>
I connected a voltmeter to E Sense and Base and got -95mV at 0.0 on the offset multi When I turned the offset multi so I got -595mV it seems the manual indicates the spot is supposed to move somewhat but I didn't notice any movement of the spot, I believe this is a good indication?

QUESTION:
What happens if you turn the collector voltage to zero and then switch the Collector Supply Polarity from NPN to +DC (or from PNP to -DC)? Does the beam stay at 2 divisions? It will no longer be a line since you are not sweeping the collector voltage. Instead it will be a dot. The question is does it stay at the 2 division point or does it return to zero when you do this. The answer may provide a clue to what is causing this.

Dennis Tillman W7PF

-----Original Message-----
From: DW
Sent: Sunday, December 01, 2019 3:24 PM
Subject: Re: [TekScopes] 577 AC collector supply not reading zero on display

I took a look at the service manual on page 5-6
On step 6, check horizontal gain.
I connected a voltmeter to E Sense and Base and got -95mV at 0.0 on the offset multi When I turned the offset multi so I got -595mV it seems the manual indicates the spot is supposed to move somewhat but I didn't notice any movement of the spot, I believe this is a good indication?

I should note I did not see no spot but a flickering line 2 divisions long, I thought I could tell if there is a deviation by looking at the ends of the line and noting the new relative location, I noted no change of position.




--
Dennis Tillman W7PF
TekScopes Moderator

Re: Tek 2467B Erratic Intensity controls

peter bunge
 

The Trig Level goes through a different Mux to the Intensity and position
controls. The three Mux O/Ps are joined and feed comparator LM311 U2510
(all on Tab 2 schematic) The Mux O/Ps (TP9) are clean and jump when a pot
is suddenly turned, the same for the comparator O/P. I am trying to find
something common to the Position, Trig Level, and Intensity Pots. The
comparator O/P goes through U2220 and it seems to respond immediately to
pot changes. Then there is the dv and dt switches that seldom work and when
they do the dotted lines are jumpy when moved with the pots below the
switches.
I assume the various positions are saved in RAM (the NOVRAM). Could it be
getting slow because of a low battery?
Is there a quick check I can make?

On Sun, Dec 1, 2019 at 5:39 PM peter bunge via Groups.Io <bunge.pjp=
gmail.com@groups.io> wrote:

Yes they are 'sticky' especially if I move ch2 then ch1. Also the digital
display of the DC trigger point is sluggish and often does not change with
the +/- level knob. It acts like a delay to the ADC which is not a
component but a complex group.
It could be a sluggish DAC U2101 sending to the sequencer via U2530 and U
2630 but I can't understand how (Analog Control tab 2). I am about to
'scope them. It is interesting that there is signs of work done around the
DAC, perhaps a broken trace but it is difficult to tell hence 'scoping to
look for a suspicious signal to follow. It could be an address line
floating but I would expect more problems. They look clean. pins 19 & 18
look messy but they are current O/P so look at U2630 pins 3 and 12. The
voltage here does not follow the intensity pots but is delayed. It jumps
suddenly but is clean. Moving on......
Peter.

On Sun, Dec 1, 2019 at 3:35 PM Bob Koller via Groups.Io <testtech=
yahoo.com@groups.io> wrote:

On Sun, Dec 1, 2019 at 12:01 PM, peter bunge wrote:


"The symptoms are that changes in either of the intensity pots takes
several, and up to many (30 or more), seconds to respond either in
intensity on the screen, or voltages at the sequencer pins. Without
touching anything on the 'scope the 'trace turn off' counts down from
minutes, to 59 seconds, down to 2 seconds, then starts again at (8)
minutes
without shutting off the display. So that feature is not working. At
very
bright it did drop the intensity after 30 seconds but did not turn it
off
so it may be partly working. I remember it turned the displays off
until
a
knob was moved.
Delta v and delta t are erratic placing the dotted lines on the screen,
and
dt sometime shows dv lines or nothing. And they have the same sluggish
delay to doing anything."
This is interesting, do the Position controls exhibit similar laggy
behavior?

I have a 2465B control board that does something similar; all the analog
controls are much slower to respond than a normally operating instrument.
It passes self test, and works normally other that the very laggy and
jumpy response to control changes.





Re: 577 AC collector supply not reading zero on display

DW
 

I took a look at the service manual on page 5-6

On step 6, check horizontal gain.

I connected a voltmeter to E Sense and Base and got -95mV at 0.0 on the offset multi
When I turned the offset multi so I got -595mV it seems the manual indicates the spot is supposed to move somewhat but I didn't notice any movement of the spot, I believe this is a good indication?

I should note I did not see no spot but a flickering line 2 divisions long, I thought I could tell if there is a deviation by looking at the ends of the line and noting the new relative location, I noted no change of position.