开云体育

On Tue, 10 Jul 2012 15:35:51 -0000, "keithostertag"
<keitho@...> wrote:

TP1801 measures 5.69V (SM says should be 5.7V)
TP1805 measures 1.74V (SM says should be 1.8V)

So maybe, as David says, that sugggest the (main) problem is not earlier in the z-axis signal chain?

That is what your readings suggest to me. The problem appears to be
in the z-axis amplifier itself and not earlier.

Unfortunately the z-axis amplifier is pretty complicated. Fortunately
it should have relatively fast repetitive waveforms so it will be
easier to see on your non-storage oscilloscope.

TP1827 right in the middle of the z-axis amplifier divides it into two
sections and that test point is the output of a low impedance emitter
follower. I would check TP1801, TP1805, and TP1827 with an
oscilloscope and see if they match what is shown on the schematic.

After that I might start randomly looking for shorted or open
transistors in the second half of the circuit starting with Q1876 and
Q1854.

Hi Keith,

Hi Bill,

TP1801 measures 5.69V (SM says should be 5.7V)
TP1805 measures 1.74V (SM says should be 1.8V)

So maybe, as David says, that sugggest the (main) problem is not earlier in the z-axis signal chain?

Is the filament open or shorted to the cathode?

Measuring across the cathode (3KV TP) and one side of the heater I get about 100K.

Is the CRT filament drawing current?

Do you mean the heater?
Measuring across R1887 (the 16 ohm resistor in series with the heater) I get about 1.6V RMS.

Here is a photo of the signal at TP1876. Following the SM, I adjusted it's DC level to 9V (with intensity all the way down). In the photo it looks like 10V, but that's due to camera angle/tilt and difficult-to-read resolution.



I've added two additional horiz times so that you can see the actual shape of the waveform, in case that might be significant.

The photos were taken before adjusting the gain. I have to turn R1810 almost all the way CCW to reduce it down to the 74V peak the SM directs.

Is there a relatively easy but definitive way to test whether the CRT is good or not? I don't want to spend time tweaking things if the CRT isn't good.

BTW- access to the CRT on the R7903 is difficult, because the connections are below the z-axis board, and one needs to (evidently) unplug the connectors in order to remove the z-axis board. I haven't yet figured out the location of the deflection plates connectors.

Also, BTW- I'm using one of the military (grey) Fluke 27/FM's, which are reputedly true-RMS. Of course that doesn't mean I alway know how to use it properly.

Thanks,
Keith Ostertag

Last fall I sold a good one in the SF bay area (Silicon Valley) for $130 with one probe, no manual. Two buyers called, first one got it.
Bob

On Tue, Jul 10, 2012 at 9:00 AM, w6vy <w6vy@...> wrote:

What is a reasonable price to pay for a 465B in good condition - with probes and manual?

I'd say $75-150, depending on the details:

How good is the condition? Is there a warranty?
Are they Tek probes, or generic?
Is it an original service manual, or an operator's manual on a CD?

Anything over $100, and I'd also be considering a 2445 or 2465.

Oh, good call. That did not even occur to me but I routinely switch
my meter back and forth between average and RMS to check my sanity on
AC waveforms. Some meters may have problems with the high frequency
as well.

On Tue, 10 Jul 2012 10:44:31 -0000, "Albert" <aodiversen@...>
wrote:

Hi Keith,

As far as I know your Fluke 27 is average-based, not true RMS. Then the reading for square wave input will be higher than true RMS.

Albert

I also wanted to make sure the CRT heater voltage was present- measured about 8 VAC RMS at pins 8 & 9 on P1704. A little high, but I guess that's OK.

Keith Ostertag

The readout acquire uses the same ICs although it is encoded to binary
and processed by the microprocessor before being displayed.

I left out checking for the time slot pulse in my post. If it was
missing, then there could be short/open or U2320 (155-0017-00) which
is another custom Tektronix readout could be bad.

On Tue, 10 Jul 2012 13:13:23 -0000, "Albert" <aodiversen@...>
wrote:

Sure, though readout acquire, as viewed from the plugins, is still the old method. Missing units in readout could be caused by a fault during the corresponding time slot TS-9. I would first of all check for the presence of the -15V pulses at the main interface connectors, contacts B39. All 4 plugin positions have the B39 contacts in common so all should show the TS-9 pulse.
Albert

--- In TekScopes@..., "David C. Partridge" <david.partridge@...> wrote:

The readout in the 7854 is radically different - it is part of one of the logic boards.

Dave
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Rob
Sent: 10 July 2012 02:49
To: TekScopes@...
Subject: RE: [TekScopes] 7854: Excessive stored trace brightness.

P.S. All the numbers above are for a 7904. I assume they are the same in a 7854.

The 7854 readout is part of the display board. The inputs use the
same Tektronix custom ICs (analog multiplexor and analog to digital
converter) as the other 7000 series readouts but the output is
generated by the display board raster line generator as it is
processed by the microprocessor leading to the interesting display
antics during acquisition when interrupts are being continuously
processed.

Since the problem only affects specific character positions including
at least most if not all of row 4 on the character map, I suspect that
the readout problem occurs from the row decoder (U1220 155-0014-01) to
the binary encoder (U1230 74LS147). Possibly one bit in the data bus
driver (U830 81LS97) is bad.

Just reseating the chips could be enough to fix it if those icky TI
sockets were used, U1220 could be swapped with U1520 or replaced with
a decoder from another 7000 series readout board, or U1230 or U830 may
need replacing. A replacement 74LS147 should be easy to find for
U1230. U830 could be swapped with U930 and if bad, replaced with a
81LS97 or apparently the 74LS467 equivalent.

I do not see anything that would link this problem to the intensity
issue.

On Tue, 10 Jul 2012 08:54:11 +0100, "David C. Partridge"
<david.partridge@...> wrote:

The readout in the 7854 is radically different - it is part of one of the logic boards.

Dave
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Rob
Sent: 10 July 2012 02:49
To: TekScopes@...
Subject: RE: [TekScopes] 7854: Excessive stored trace brightness.

P.S. All the numbers above are for a 7904. I assume they are the same in a 7854.

What is a reasonable price to pay for a 465B in good condition - with probes and manual?

Thanks
Bob

On Tue, 10 Jul 2012 08:28:49 -0000, "magnustoelle"
<magnustoelle@...> wrote:

--- In TekScopes@..., David <davidwhess@...> wrote:
[..]

My 2440 has the rare video triggering option. The only time I have
used it was when looking at a VGA output and it worked great. In the
case of the 2440, it includes features like field and line selection.
Oddly enough, worked correctly with 1050 and 1200 line video.

[..]

Hi David,

no real surprise here - at least for the Horizontal Sync extraction, those comparator circuits work nicely with a lot of different video standard-signals.

Cheers,

Magnus

I was a little surprised that it worked correctly with HD video and
counted the lines correctly. I half expect it to roll over at 1024
lines although there was no good reason to expect it to do so.

In the case of the VGA signal I looked at to play with the video sync
on my 2440, I used sync on green instead of the separated horizontal
and vertical sync signals.

On Mon, 9 Jul 2012 22:39:06 -0700 (PDT), Denis <xyzzx_adv@...>
wrote:

? Having restarted this thread by mistake (I had intended my email to John directly but goofed) I will try to shed some light.? John' original comment on this thread (4 Mar 2011) did a good job of describing the NTSC signal and challenges of syncing a scope to the video stream with embedded V and H sync signals.
?
? Granted that VGA signals are similar in that they provide analog video signals, but they also provide H and V sync on the connector pins (not buried in the video stream).? So it is possible to setup the scope to trigger the 'A' Sweep with V sync and use the delayed sweep feature to effectively move down the computer screen and trigger the 'B' Sweep with H Sync and see an individual line of video.? Now, 'back in the old days' it was possible to connect a video monitor to the scope (524A) and see which line you were observing on the scope (it was brighter).? A trick I learned was to work my way down the monoscope resolution fan and adjust the focus by watching the HF amplitude increase as it got sharper (this was back in the days before computer generated images) when TV was Black and White.?
?
? While the Video option probably would do a good job of syncing the scope, the availability of the sync signals preclude the necessitity of the sync separator that the option provides.? Plus, since the VGA signal is progressive not interlaced all video fields are the same and there is not the need to identify them (NTSC on the other hand has four unique?fields, odd and even lines, 'A' frame and 'B' frame, which differ in burst phase polarity).? All of which is getting pretty deep into an antique video format (at least in some circles).? But, which leads me to answer Bob's question that I can't think of any other use for the video sync option.
Denis
________________________________
From: David <davidwhess@...>
To: TekScopes@...
Sent: Monday, July 9, 2012 12:13 PM
Subject: Re: [TekScopes] Re: Video triggering of 'scopes in general
?
I have a broken 7B53A with the video option that I may get around to
repairing some day. When I asked about it here, I was told that the
mixed sweep feature of the 7B53A is particularly useful for examining
video.

My 2440 has the rare video triggering option. The only time I have
used it was when looking at a VGA output and it worked great. In the
case of the 2440, it includes features like field and line selection.
Oddly enough, worked correctly with 1050 and 1200 line video.

On Mon, 09 Jul 2012 17:52:43 -0000, "Robert"
<mailto:go_boating_fast%40yahoo.com> wrote:

Some 7B53As have video sync. I have two. Don't really use that feature but they work fine anyway. Might check those manuals as well.
Also, Is that feature good for anything else?
Bob

--- In mailto:TekScopes%40yahoogroups.com, Denis <xyzzx_adv@...> wrote:

John,
?? I would like to request a copy of the 453 Mod 127C Schematic.?? I still have some NTSC gear around and want to see how Tek implemented sync separation, for possible inclusion into a 453A.
??Thanks,
Denis


________________________________
From: John S <John@...>
To: mailto:TekScopes%40yahoogroups.com
Sent: Friday, March 4, 2011 9:21 AM
Subject: [TekScopes] Video triggering of 'scopes in general


??
- All the old TV standards adopted around the world have an odd numbers of lines in a "complete" picture, which is defined as a TV Frame. (25Hz Europe, c.30Hz USA)
- To conserve RF bandwidth, the signal is transmitted in sequential Fields, each of which contains half the lines (odd lines Field 1, even lines Filed 2 etc), as required to assemble the full TV Frame.
- This is known as interlace scanning, and gives rise to display artefacts such as line-twitter on strong horizontal black-white transitions.
- As the odd number of lines is clearly not divisible by 2, odd fields terminate (theoretically) half way through a line, and even fields commence similarly.
- The problem confronted by TV engineers is to get the 'scope to trigger stably (ideally) at the FRAME rate, which is half the field rate. This allows a 'scope with a good dual-time-base delayed sweep to select a particular line. (The line can be a bit dim, as the 'scope is only writing for c. 60uS in every c. 40mS).
- I have a 453 with TV triggering ( MOD127C ): Tek used to supply special graticules (which I also have) based around standardised TV test & measurement waveforms.
- broadcasters use a few of the "blank" lines in the field blanking area* to transmit the test waveforms so an entire transmission chain can be quality monitored

I can supply a copy of the MOD127C 453 handbook description to anyone who's interested.

John

* the "field blanking" lines contain synchronising pulses which are "broader" than on normal video lines, and the shift in DC level is used by the sync separators in the TV to lock the frame oscillator to field rate. They were kept free of video in order to allow the CRT scan time to return to the top of the screen without losing active picture content.

--- In mailto:TekScopes%40yahoogroups.com, Gala Dragos <gala_dragos@> wrote:

Hi!

I've worked with a TD2002B recently. It had a trigger mode named "Video". It was used to display PAL/SECAM/NTSC video signals and lines. How do I do that with Tektronix 475 or 465 ?

Thanks.

--- In TekScopes@..., KeepIt SimpleStupid <keepitsimplestupid@...> wrote:

It should be the same as the 211, 212 scope I think.

No - not even close. 21x and 221 use 10 'A' NiCd cells. 222 and 224 use a "gel-cell" lead acid battery which consists of two cells. It was made custom for Tek, and even the individual cell dimensions don't match anything I have found in vendor's data sheets.

Best regards,
Steve

Sure, though readout acquire, as viewed from the plugins, is still the old method. Missing units in readout could be caused by a fault during the corresponding time slot TS-9. I would first of all check for the presence of the -15V pulses at the main interface connectors, contacts B39. All 4 plugin positions have the B39 contacts in common so all should show the TS-9 pulse.
Albert

Hi Keith,

As far as I know your Fluke 27 is average-based, not true RMS. Then the reading for square wave input will be higher than true RMS.

Albert

Hi,
I have a Tek 468 analogue with digital display and storage. The problem: the scope works fine in analogue mode, however when digital mode is selected, the trace appears to be modulated at a higher frequency causing a blurred display. If the timebase x10 is used to expand the trace, it appears to be composed of a semi sinusoidal waveform.(Its not possible to determine the frequency as in the digital mode the timebase control doesnt seem to have much effect)and its not possible to re-create this effect in analogue mode. I have checked grounding connections, re-seated the i/cs etc all to no effect. My next step is to check the digital psu for excess ripple.
Has anyone come across this problem before or can anyone point me in the right direction?
Note: The digital functions seem to work ok,save, store etc.
Very often the 'scope will not 'POST (power on self test,) but will come on in analogue mode.
The digital LED display does work, and so do the cursors and they do measure, but the cursors are modulated in the same way as the trace.

Bill

--- In TekScopes@..., "photo692002" <photo692002@...> wrote:

Is anyone aware of a supplier for the battery pack or the cells within? I want to sell this scope and would like to suggest to the buyer where a pack might be obtained.

Larry

Check this then Google on LCS-214

/H?kan

--- In TekScopes@..., David <davidwhess@...> wrote:
[..]

My 2440 has the rare video triggering option. The only time I have
used it was when looking at a VGA output and it worked great. In the
case of the 2440, it includes features like field and line selection.
Oddly enough, worked correctly with 1050 and 1200 line video.

[..]

Hi David,

no real surprise here - at least for the Horizontal Sync extraction, those comparator circuits work nicely with a lot of different video standard-signals.

Cheers,

Magnus

Is the CRT filament drawing current?

Regards,
David Partridge