Some weirdness about a 485
I am working on doing a restoration on a Tektronix 485 for the lab and I have been arguing with it for a little while. I am curious if anyone has run in to a scope that does not like to trigger at low frequencies? I am currently working on the 50 Ohm calibration and it seems that the scope in 50 Ohm mode REALLY does not like to trigger under 1.2Mhz. So it is struggling with 50 Khz cal signals. Vertical amplitude is good trigger is flakey. I have heard that some of these the TD¡¯s go kind of deaf at the high speed side of things but not the low side. Any ideas what might be causing this. I am continuing to investigate further.
Zen
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Re: -2465B - trace show gaps when turn on readout -requesting help
Not sure that this is much of a contribution, but the 24x5 scopes seem to use a more complex method of determining when a readout sweep occurs (than the 7k series). There are four "priorities" for the readout, depending on sweep speed (and other factors?). Summarizing the 2445A service manual (from pages 3-30 and 3-31):
Priority 1: ideally readout display should happen between traces, when the scope is not trying to display a waveform - before a trace starts, after a trace finishes, or between consecutive traces. Readout display in this mode causes no interference with the display of a waveform. This mode is only used when the sweep time is fast enough to display flicker-free readout, and slow enough to complete drawing the readout during the holdoff time.
Priority 2: the second most desirable time to display readout is between sweeps when the scope is waiting for a trigger event. This mode may cause slight interference with the leading edge of waveform display.
Priorities 3 and 4: the least desirable times are during a sweep. Here readout dots are "chopped" into the waveform display. The manual claims that "the waveform blanking associated with these displays is relatively random" and "is usually not noticeable."The manual says that priority 4 indicates a higher demand for display time.
There is specific circuitry (the "Refresh Pioritizer") that determines which mode is used and when readout dots are displayed. In the 2445A these are labeled U2850(A/B), U2950A, U2990A, and U2985. It's complicated, and it sounds like it can display fragments of readout at a time, maybe even just one dot at a time, all in an attempt to avoid blanking parts of a displayed waveform while maintaining a flicker-free readout image with proper intensity, regardless of sweep speed.
-- Jeff Dutky
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Re: -2465B - trace show gaps when turn on readout -requesting help
So true.? Sorry.
But they did manage to incorporate some more smarts.
I only have 3 "true" digital scopes, and generally (because of the CRT) treat the 2430A almost as if it were analog.
almost.........
maybe......
Thanks
Harvey
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On 3/26/2022 11:11 AM, Raymond Domp Frank wrote: On Sat, Mar 26, 2022 at 04:03 PM, Harvey White wrote:
They do it differently here?? I have a 2430A, and never noticed a problem
with mine.
I wasn't implying that: AFAIK, it's the same (chopping within or alternating between trace to access the readout) in the 24X5/7 'scopes, except work has been done to avoid needing a switch, like in the 7000's.
The 24X0's are very different beasts; being digital 'scopes, their display update rate is mostly independent from the signal (except maybe at very low frequencies, because the data just isn't there yet).
Raymond
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Re: 466 front panel lights, and early / late models
and if the voltage supply is variable, you get dimming LEDS.......
Harvey
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On 3/26/2022 11:27 AM, David Templeton wrote: Thank you, that clears most of it up.
I presume ¡°glow bulb¡± is Tek talk for neon in the manual.
In that case, it¡¯s the neon lights on the front that are very dim, probably fading with age.
Has anyone directly replaced neons with LEDs, at 140v replacing the series resistors with 15kohm should give a nice bright light , pity it would be dissipating 1.5W. May need to rethink that. There no reason why the switch can¡¯t come off 5v, same as the low voltage bulbs.
David
On 26 Mar 2022, at 14:41, Raymond Domp Frank <hewpatek@...> wrote:
?Hi David,
Please find my notes interleaved, after your text:
On Sat, Mar 26, 2022 at 02:34 PM, David Templeton wrote:
I find the front panel lights pretty dim, and was looking at updating them
with nice bright LEDs.
There is an early and late manual. The late manual says from serial number
B200000 and up. Serial number on the front is 700000+, so that should make it
a late or early?, there's no 'B' just a number starting '7'. I'm not sure how
the non-B numbers are dated. S/N's starting with "7" were made by Tektronix Heerenveen in the Netherlands. No direct correlation exists between numbers produced in different countries.
The diagram shows LEDs for all the front panel lights on the late model. Not
sure I believe that since they are white. And the early shows bulbs (running
off the 140v line!) Early models used low-voltage filament bulbs for the vertical scale indications and neon lamps with light pipes behind them for the other indications, hence the 140V supply. The neons are orange glowing through a matte colorless light pipe lens, leds are red, unless replaced by some enthusiast...
That all have light pipes going into little white housings. I cant find the
part number for the housing, I'd like to see what they are like first before
puling it all apart. Searching the light part number only gives a bare bulb The little white housing ("Lamp Holder" is Mechanical Part -176 in the manual, Tek Part 352-0331-00.
Qservice sells them @ $2.48 ea. ().
For example ch2 uncal is DS5038. The manual shows the light is on a connector
off board (page 265 in late pdf), but I can see it's soldered to board Vert
Mode BW SW, A3, but not listed in the A3 parts.
Yet, the early manual correctly shows the light, DS68, on the A3 board, and
switch is a flying lead from A2 board. (page 277 in early pdf)
So the questions are:
Is this a late manual 466 scope? With filament and neon lights, it's an early model most likely (not sure if "hybrids" were made in non-Beaverton factories).
What's with the LED symbols on the late manual? They are just what they seem to be: leds. originally red.
Where can I find the part number for the light housings?
You just did: "Lamp Holder" is Mechanical Part -176 in the manual, Tek Part 352-0331-00.
Raymond
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Re: 468 A15 Board Removal
The output high-voltage lead from the multiplier goes through a hole in the chassis and snakes under the CRT shield to a connection on the other side. Removing the multiplier, or freeing the A15 board, requires removing the CRT as shown in this video:
Before this can be done, both vertical boards and the attenuator must be removed as shown in this video:
Bob
--
Bob Haas
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Re: -2465B - trace show gaps when turn on readout -requesting help
On Fri, Mar 25, 2022 at 11:58 PM, Dr. Bernd Burfeindt wrote:
The blank out are about 1mm in length at the same horizontal position where
the text would appear. I can fix this issue when I replace the A5 board from
my second scope. So the issue must come from the A5 board.
I find this intriguing: Are the readout excursions timed at constant intervals from the trigger event and at the exact moment the horizontal dot position is just beneath the readout? I don't think that would be desirable; a random interruption largely hides the gap, so if I interpret Bernd's description correctly, it would indicate a malfunction. Raymond
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Re: -2465B - trace show gaps when turn on readout -requesting help
On Sat, Mar 26, 2022 at 04:03 PM, Harvey White wrote:
They do it differently here?? I have a 2430A, and never noticed a problem
with mine.
I wasn't implying that: AFAIK, it's the same (chopping within or alternating between trace to access the readout) in the 24X5/7 'scopes, except work has been done to avoid needing a switch, like in the 7000's. The 24X0's are very different beasts; being digital 'scopes, their display update rate is mostly independent from the signal (except maybe at very low frequencies, because the data just isn't there yet). Raymond
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Re: -2465B - trace show gaps when turn on readout -requesting help
If there's no switch, then they did it in circuitry.? I'm used to the 7000 series.
Harvey
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On 3/26/2022 10:47 AM, Siggi via groups.io wrote: On Sat, Mar 26, 2022 at 10:22 AM Harvey White <madyn@...>
wrote:
As others have said, the readout works in two modes. The beam (a single
one) is always shared. The readout circuitry can either wait for a
retrace (useful for high sweep speeds), or chop the beam at a given
rate. Chopping the beam produces those little blanks in the trace. A
little extra switching would have fixed that, but instead, Tek used a
slide switch on the readout board so you could pick the most convenient
setting. That's the "dual mode" I was talking about.
I've been through the readout schematics in a fair amount of detail before,
but I don't remember seeing a switch anywhere. I went back to look at the
readout schematics just now, and I still can't find a switch. Is it
possible you're confusing the 2465B with some other readout implementation?
According to the Theory of Operation, the 2465en have fairly elaborate
machinery that strives to maintain a flicker-free, uniform brightness
readout, no matter the sweep speed or trigger frequency.
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Re: -2465B - trace show gaps when turn on readout -requesting help
They do it differently here?? I have a 2430A, and never noticed a problem with mine.
Harvey
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On 3/26/2022 10:55 AM, Raymond Domp Frank wrote: On Sat, Mar 26, 2022 at 03:22 PM, Harvey White wrote:
Tek used a slide switch on the readout board so you could pick the most
convenient setting.? That's the "dual mode" I was talking about.
That's the way it was done in the 7000 series.
Raymond
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Re: -2465B - trace show gaps when turn on readout -requesting help
On Sat, Mar 26, 2022 at 03:22 PM, Harvey White wrote:
Tek used a slide switch on the readout board so you could pick the most
convenient setting.? That's the "dual mode" I was talking about.
That's the way it was done in the 7000 series. Raymond
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Re: -2465B - trace show gaps when turn on readout -requesting help
On Sat, Mar 26, 2022 at 10:22 AM Harvey White <madyn@...> wrote: As others have said, the readout works in two modes. The beam (a single
one) is always shared. The readout circuitry can either wait for a
retrace (useful for high sweep speeds), or chop the beam at a given
rate. Chopping the beam produces those little blanks in the trace. A
little extra switching would have fixed that, but instead, Tek used a
slide switch on the readout board so you could pick the most convenient
setting. That's the "dual mode" I was talking about.
I've been through the readout schematics in a fair amount of detail before, but I don't remember seeing a switch anywhere. I went back to look at the readout schematics just now, and I still can't find a switch. Is it possible you're confusing the 2465B with some other readout implementation? According to the Theory of Operation, the 2465en have fairly elaborate machinery that strives to maintain a flicker-free, uniform brightness readout, no matter the sweep speed or trigger frequency.
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Re: 466 front panel lights, and early / late models
Hi David, Please find my notes interleaved, after your text: On Sat, Mar 26, 2022 at 02:34 PM, David Templeton wrote:
I find the front panel lights pretty dim, and was looking at updating them
with nice bright LEDs.
There is an early and late manual. The late manual says from serial number
B200000 and up. Serial number on the front is 700000+, so that should make it
a late or early?, there's no 'B' just a number starting '7'. I'm not sure how
the non-B numbers are dated.
S/N's starting with "7" were made by Tektronix Heerenveen in the Netherlands. No direct correlation exists between numbers produced in different countries.
The diagram shows LEDs for all the front panel lights on the late model. Not
sure I believe that since they are white. And the early shows bulbs (running
off the 140v line!)
Early models used low-voltage filament bulbs for the vertical scale indications and neon lamps with light pipes behind them for the other indications, hence the 140V supply. The neons are orange glowing through a matte colorless light pipe lens, leds are red, unless replaced by some enthusiast...
That all have light pipes going into little white housings. I cant find the
part number for the housing, I'd like to see what they are like first before
puling it all apart. Searching the light part number only gives a bare bulb
The little white housing ("Lamp Holder" is Mechanical Part -176 in the manual, Tek Part 352-0331-00. Qservice sells them @ $2.48 ea. ().
For example ch2 uncal is DS5038. The manual shows the light is on a connector
off board (page 265 in late pdf), but I can see it's soldered to board Vert
Mode BW SW, A3, but not listed in the A3 parts.
Yet, the early manual correctly shows the light, DS68, on the A3 board, and
switch is a flying lead from A2 board. (page 277 in early pdf)
So the questions are:
Is this a late manual 466 scope?
With filament and neon lights, it's an early model most likely (not sure if "hybrids" were made in non-Beaverton factories). What's with the LED symbols on the late manual? They are just what they seem to be: leds. originally red. Where can I find the part number for the light housings?
You just did: "Lamp Holder" is Mechanical Part -176 in the manual, Tek Part 352-0331-00. Raymond
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Re: -2465B - trace show gaps when turn on readout -requesting help
As others have said, the readout works in two modes.? The beam (a single one) is always shared.? The readout circuitry can either wait for a retrace (useful for high sweep speeds), or chop the beam at a given rate.? Chopping the beam produces those little blanks in the trace.? A little extra switching would have fixed that, but instead, Tek used a slide switch on the readout board so you could pick the most convenient setting.? That's the "dual mode" I was talking about.
Harvey
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On 3/25/2022 8:01 PM, Harvey White wrote: Are there dual modes for readout refresh on the board, and is the old board set up the same way as the new one?
Harvey
On 3/25/2022 6:58 PM, Dr. Bernd Burfeindt via groups.io wrote:
Hi,
with the time-base equal or slower than 1ms/scale I noticed "blank outs" on the trace when I turned on the readout. The blank out are about 1mm in length? at the same horizontal position where the text would appear. I can fix this issue when I replace the A5 board from my second scope. So the issue must come from the A5 board.
I am requesting help to repair the A5 board - which I had fixed for leaky capacitor. PCB traced looks Ok and I replaced corroded resistor etc. Calibration was done as well. I read the theory of operation but I could not come up with a good trouble shooting plan. Maybe some does not switch fast enough.
Does anyone has a good idea to look for?
Bernd
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Re: -2465B - trace show gaps when turn on readout -requesting help
I¡¯ve never looked at these signals, but to my understanding, the readout
board asserts /ROR when it wants to display dots. The display sequencer,
however, gates access to the trace through the /ROA signal. I¡¯d start by
looking at those two, comparing between good and bad boards. Note that the
readout is stealing the trace, and if this is not random to the sweep, you
may be able to observe the stealing as it occurs at the same spot during
consecutive sweeps.
If this is happening in auto trigger mode without trigger, try whether you
still see it during triggered sweeps. See if holdoff changes the problem at
all.
?ann f?s., 25. mar. 2022 kl. 18:58 skrifa?i Dr. Bernd Burfeindt via
groups.io <femtocam@...>:
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Hi,
with the time-base equal or slower than 1ms/scale I noticed "blank outs"
on the trace when I turned on the readout. The blank out are about 1mm in
length at the same horizontal position where the text would appear. I can
fix this issue when I replace the A5 board from my second scope. So the
issue must come from the A5 board.
I am requesting help to repair the A5 board - which I had fixed for leaky
capacitor. PCB traced looks Ok and I replaced corroded resistor etc.
Calibration was done as well. I read the theory of operation but I could
not come up with a good trouble shooting plan. Maybe some does not switch
fast enough.
Does anyone has a good idea to look for?
Bernd
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Re: -2465B - trace show gaps when turn on readout -requesting help
Hi Harvey,
what do you mean with dual refresh mode and how can I check this on the A5 board?
Bernd
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Re: -2465B - trace show gaps when turn on readout -requesting help
Are there dual modes for readout refresh on the board, and is the old board set up the same way as the new one?
Harvey
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Show quoted text
On 3/25/2022 6:58 PM, Dr. Bernd Burfeindt via groups.io wrote: Hi,
with the time-base equal or slower than 1ms/scale I noticed "blank outs" on the trace when I turned on the readout. The blank out are about 1mm in length at the same horizontal position where the text would appear. I can fix this issue when I replace the A5 board from my second scope. So the issue must come from the A5 board.
I am requesting help to repair the A5 board - which I had fixed for leaky capacitor. PCB traced looks Ok and I replaced corroded resistor etc. Calibration was done as well. I read the theory of operation but I could not come up with a good trouble shooting plan. Maybe some does not switch fast enough.
Does anyone has a good idea to look for?
Bernd
|
-2465B - trace show gaps when turn on readout -requesting help
Hi,
with the time-base equal or slower than 1ms/scale I noticed "blank outs" on the trace when I turned on the readout. The blank out are about 1mm in length at the same horizontal position where the text would appear. I can fix this issue when I replace the A5 board from my second scope. So the issue must come from the A5 board.
I am requesting help to repair the A5 board - which I had fixed for leaky capacitor. PCB traced looks Ok and I replaced corroded resistor etc. Calibration was done as well. I read the theory of operation but I could not come up with a good trouble shooting plan. Maybe some does not switch fast enough.
Does anyone has a good idea to look for?
Bernd
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How NOT to diagnose no traces on a 2467
Hey y'all,
I found this old video, which I believe is the first time I powered up my
2467: . This is a great example of what NOT to
do :). This was recorded on a potato, so please excuse the audio and video
quality.
I messed up plenty after this, but if I'd read the service manual before
popping the covers and around, twiddling pots, etc, it would have saved me
SO much time. It was all good times though, so I don't have any regrets (to
mention), and it taught me a lot.
The critical fault with this 2467 was a single bad zener on the A5 board
that clamped the +1.36, -1.25V references to zero. This led to no traces,
no OSD. Also notice how the attenuators won't stay in 50 Ohm coupling. The
scope though they were frying, again due to that one A5 board fault.
Other than that one Zener on the A5 board, it just needed a bunch of pot
and contact cleaning. Of course after I'd poked and prodded it, it also
needed a full calibration - but then it probably wanted to be calibrated
anyway.
So, if you're poking at your 2465/2465A/2467/2465A/2465B/2467B for the
first time after a fault, don't be like me. Check out the service manual,
or ask here what the front panel is trying to tell you.
Siggi
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I ordered 2 MC68A02s to replace my MC68A08. They were only $3.11 each with free shipping, so I thought I might as well order a couple. The MC68A08 is already socketed on my board. That is convenient. Is that original or has somebody already worked on my 2465?
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Re: Type 106 Saga (Again)
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Bob Haas
Raymond Domp Frank