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454a questions

bob
 

Hello, just picked up a tek 454a, my first scope, so I am new to them but I do understand the concept and getting to know it, I have a couple of questions, first, channel one does not work, it shows a trace but no adjustment, no signal, nothing, but channel two works good, anything I should look for, and second, I was playing around with a dead lcd tv, I was testing resistors, power supplies, etc, I was picking up a signal from different components on the board, which I believe are energized, and some parts no signal, most likely no power, being the dead part does not produce a signal, can I come to the conclusion that the part of the board that is dead could be the problem with the tv?

Thanks


Re: 2440 noise

Dennis S.
 

The noise subsided as I did another self calibration, duh.

Sorry for the "noise" :-D

Dennis


2440 noise

Dennis S.
 

Dear group members,
I am seeking advise for a recently bought Tektronix 2440 oscilloscope.

It shows a 125 MHz noise in the 2-100 ns/div deflection ranges, as seen here:
http://img17.imageshack.us/img17/2064/img1079ed.jpg
The upper trace is channel 1, the lower channel 2. Both are connected to ground by external 50 Ohm terminators (same picture with both inputs internally grounded or open). Acquire is set to AVG mode, 256 samples, REPET off, trigger so that it just triggers on the top edge of the noise.
What I found out so far is this:
- The noise does not change its scale by setting CAL PATH ON.
- The noise disappears if I enable the BW limit (either 20 or 100 MHz works).
- The noise disappears if the deflection is set to 200 ns/div and slower (maybe since the signal is then only sampled with 250 MS/s?).
- The noise is much higher on channel 1 than on channel 2
- I can trigger on the noise.

So far, I'm quite puzzled where to search for the cause of this behaviour. :-(

What I have done so far:

First, I fixed the dead batteries inside the DS1235 by cutting them out and wiring them to a fresh Lithium cell. Works well if you cut carefully with a Dremel or so, the cells are located on the bottom of the package, their ground contact point to the side where pin 1 is (pictures on request).
Then I did an external calibration, everything succeeded, all self tests pass.
Every voltage present on the right side board is well within specs, including noise.
Besides this noise on CH 1, it works well.
BTW, it is a model from the Netherlands, H7002xx.

Well, any Idea what I could look for now?

Dennis


Re: Tek CFC250 CMC250 Freq counters

faustian.spirit <faustian.spirit@...>
 

In case you have any 7k series oscilloscope, have a look at the 7D14 and 7D15 plugins. Very convenient (all in one probe tip), and in practice rather accurate.

--- In TekScopes@..., "dehav7" <yachadm@...> wrote:

Hi all
Does anyone have any experience or comments regarding these 2 freq counters - reliability, ease of service, etc?

Looking to buy a FC, just not sure where I should focus my efforts.

Thanks
Menahem Yachad


Re: Tek CFC250 CMC250 Freq counters

David DiGiacomo
 

On Thu, May 19, 2011 at 2:22 PM, dehav7 <yachadm@...> wrote:
Hi all
Does anyone have any experience or comments regarding these 2 freq counters - reliability, ease of service, etc?
They are undistinguished Taiwanese models - quite overpriced because
of the Tek label. You would be better off getting a good reciprocal
counter such as an HP5315A, HP5316A, Keithley 776, Philips PM6654,
Racal-Dana 1992, etc.


Re: 2465B fan voltage

 

Thanks guys - that makes sense - now I know, so I guess mine is running cool.

Menahem


Tek CFC250 CMC250 Freq counters

 

Hi all
Does anyone have any experience or comments regarding these 2 freq counters - reliability, ease of service, etc?

Looking to buy a FC, just not sure where I should focus my efforts.

Thanks
Menahem Yachad


.... How do you manage getting THAT kind of a screen burn?

faustian.spirit <faustian.spirit@...>
 

130521489871

speechless.


Re: Pease help diagnosing my 2235

Greg
 

"lagunablue94c" <bryanlow70@...> wrote:

1. Intensity knob only adjusts from bright to really bright
2. Vertical line on left hand side of screen
3. Line running through waveform - looks like the electron gun
moving to start position
4. Waveform is noisy
5. When measuring a low voltage signal, the signal is added to a
phantom 24v sine wave
6. Delay trace shows up as a vertical line on the left side of
the screen

Thanks,
Bryan
In part make sure you understand all the controls.
There are two brightness controls. The delay controls
are some what confusing (to me) and take some prctice,
but I am not saying your don't have an issue. What
I am saying when I first got mine I though something
was wrong, but it was OK and I just did not understand
the operation of the 2235a.

Bryan I have a 2235a and love it. I had a few issues.
I can't address your specifics, but all my problems
were with the two vertical attenuator's X1 and X10 (per
channel). They are very delicate and subject go failure.
Some times you can unplug them, pop off the snap-on
plastic cover and re-solder some connection.

Obviously your issues sound more in-depth, but I thought
I share that with you.


Re: 2465B fan voltage

gwangju3 <gwangju3@...>
 

Menahem,

The 12V regulator circuit includes a thermister that varies the output voltage depending on the temperature inside the power supply.

I have never seen the fan receive a full twelve volts. I suppose if you operate the 2465B at the 50C ambient for extended time it might send 12V to the fan.

--Victor

--- In TekScopes@..., "Gerald, VK3GJM" <vk3gjm@...> wrote:

Hi Menahem,

20 minutes after powerup, 9.3V. Same room temp.

Regards

Gerald
VK3GJM

--- In TekScopes@..., "Gerald, VK3GJM" <vk3gjm@> wrote:

Hi Menahem,

Initial start up from cold room temp 7.08V, slowly increasing to 8.0V after 3 minutes of operation with a room temp of 18 degrees C

Regards


Gerald

VK3GJM

--- In TekScopes@..., "dehav7" <yachadm@> wrote:

Hi all,
On mine, I measure 7.8VDC at the solder mounting post on the rear chassis, adjacent to the actual fan.
The SM does not specify an output voltage after the LM317.
The TA300DC Fan is rated at 12VDC....

Can anyone concur whether this 7.8VDC is the correct voltage?
Thanks

Menahem


Re: 1.2 ohm 1/2 watt carbon comp resistor source?

gwangju3 <gwangju3@...>
 

--- In TekScopes@..., "Frank C" <fc911c@...> wrote:

Thanks Victor

That might be an better option if I cant locate some.

Frank


----- Original Message -----
From: gwangju3
To: TekScopes@...
Sent: Monday, May 16, 2011 4:43 PM
Subject: [TekScopes] Re: 1.2 ohm 1/2 watt carbon comp resistor source?



Do you have room for two 1/4W? Use two 1/4W in parallel to get the 1/2W 1.2ohm.

--Victor

--- In TekScopes@..., "Frank C" <fc911c@> wrote:
>
> Hi Victor
>
> thanks for the source, I might not have room for two.
>
> Thanks
> Frank
>
>
> ----- Original Message -----
> From: gwangju3
> To: TekScopes@...
> Sent: Monday, May 16, 2011 4:15 PM
> Subject: [TekScopes] Re: 1.2 ohm 1/2 watt carbon comp resistor source?
>
>
>
> Put two of these in parallel: OD24GJE-ND
>
> --- In TekScopes@..., "gwangju3" <gwangju3@> wrote:
> >
> > They don't have 1.2 Ohms, but they do have 2.4 Ohms.
> > Get two and parallel.
> >
> > --Victor
> >
>


Re: 2236 DMM issue - Now fixed :-)

Jim Popwell Jr <jpopwell@...>
 

enjoy!
jim



On May 19, 2011, at 1:30 AM, Kevin Wood wrote:

 

Well, I found the problem. U1909 had what appeared to be an internal short
from the +7.5V supply rail to some of the output pins.

Everything was fine until the range changes started to switch in the AC
compensation networks. Then the 7.5v rail got dragged down and, if the
input level was high enough, the device would latch-up and short both
rails.

New 4053 substituted and it's working fine.

Many thanks to Jim for his ideas in troubleshooting this.

Kevin



Re: 2465B fan voltage

Gerald
 

Hi Menahem,

20 minutes after powerup, 9.3V. Same room temp.

Regards

Gerald
VK3GJM

--- In TekScopes@..., "Gerald, VK3GJM" <vk3gjm@...> wrote:

Hi Menahem,

Initial start up from cold room temp 7.08V, slowly increasing to 8.0V after 3 minutes of operation with a room temp of 18 degrees C

Regards


Gerald

VK3GJM

--- In TekScopes@..., "dehav7" <yachadm@> wrote:

Hi all,
On mine, I measure 7.8VDC at the solder mounting post on the rear chassis, adjacent to the actual fan.
The SM does not specify an output voltage after the LM317.
The TA300DC Fan is rated at 12VDC....

Can anyone concur whether this 7.8VDC is the correct voltage?
Thanks

Menahem


Re: 2465B fan voltage

Gerald
 

Hi Menahem,

Initial start up from cold room temp 7.08V, slowly increasing to 8.0V after 3 minutes of operation with a room temp of 18 degrees C

Regards


Gerald

VK3GJM

--- In TekScopes@..., "dehav7" <yachadm@...> wrote:

Hi all,
On mine, I measure 7.8VDC at the solder mounting post on the rear chassis, adjacent to the actual fan.
The SM does not specify an output voltage after the LM317.
The TA300DC Fan is rated at 12VDC....

Can anyone concur whether this 7.8VDC is the correct voltage?
Thanks

Menahem


Re: Pease help diagnosing my 2235

Kevin Wood G7BCS
 

Hi Bryan,

In addition to the excellent suggestions already made, if the cathode is
OK at about -2KV I would have a careful look at the DC restorer circuit
that drives the control grid of the tube.

I.E. C855, CR851, 853, 854, 855 and associated components

This circuit takes the Z axis signal from the intensity control
incorporating the blanking pulse when the timebase retraces (a few tens of
volts at a guess) and references it to the cathode voltage (-2KV if all is
well) so it can control the grid of the tube relative to the cathode.

I had a scope with exactly the same symptoms of excessive brightness and a
couple of the diodes in the restorer circuit were to blame.

While you're in the area, check the values of all the resistors. The 510k
resistors in the focus chain are particularly prone to going high in
value, although this doesn't appear to be your main problem there may be
other resistors going faulty.

As for the AC signal that's superimposed on the trace, can you estimate
its' frequency? I agree that this is probably down to ripple on one of the
power supply rails. Checking its' frequency relative to the two supply
choppers might give you some clues - in addition to just checking the
rails for ripple, of course.

Kevin


2465B fan voltage

 

Hi all,
On mine, I measure 7.8VDC at the solder mounting post on the rear chassis, adjacent to the actual fan.
The SM does not specify an output voltage after the LM317.
The TA300DC Fan is rated at 12VDC....

Can anyone concur whether this 7.8VDC is the correct voltage?
Thanks

Menahem


Re: 2236 DMM issue - Now fixed :-)

Kevin Wood G7BCS
 

Well, I found the problem. U1909 had what appeared to be an internal short
from the +7.5V supply rail to some of the output pins.

Everything was fine until the range changes started to switch in the AC
compensation networks. Then the 7.5v rail got dragged down and, if the
input level was high enough, the device would latch-up and short both
rails.

New 4053 substituted and it's working fine.

Many thanks to Jim for his ideas in troubleshooting this.

Kevin


Re: Pease help diagnosing my 2235

magnustoelle
 

G'd Day Bryan,

and welcome to the group.

Just to amend to Tom Miller's excellent advice: Do not compromise on any safety aspects when doing high voltage probing.

You might want to check the usual online-auctions for a SIMPSON High Voltage probe or similar. I am using a SIMPSON 00509 probe for some time now and I am happy with it.

Good Luck with your troubleshooting.

Magnus


Re: Some stupid 7k history questions... Power Measurement using the 7854

Egge Siert <eggeja@...>
 

Another plugin that would be useful was written up as a very detailed design example anyone could build using the customizable 7A17 plugin. It was an XY Multiplier. It had two inputs and it multiplied the two inputs together. For example, if you measured the voltage at a test point and fed it into one input, and you measured current through that point with a current probe the resulting display was the power in watts being consumed by your circuit.This would be handy for lots of things and flexible enough that there would be lots of other uses as well.

Hi Dennis,

In Section 2 of the 7854 Application Note 42W-5700 this application is described, using a the 7A13 (+ two P5055's), 7A18A and A6302/AM503 and a small program for the 7854.

Egge Siert


Re: Pease help diagnosing my 2235

Tom Miller <tmiller@...>
 

Ok, here is what you need to do first.
 
Go to section five of the service manual, "Adjustment Procedures" and start doing steps 1 to 6. Look at the AC ripple on each of the low voltage DC test points. Record each of the levels. Be vary careful doing this as a slip of a probe can make things much worse, On page 6-8, the voltages and ripple limits are given.
 
Tell us what the results are. You will need a high voltage probe for your DC meter to measure the cathode voltage correctly. It will be about 2000 volts negative.
 
At first glance, it looks like the grid bias is up too high.
 
Regards,
Tom
 
 

----- Original Message -----
Sent: Wednesday, May 18, 2011 3:59 PM
Subject: [TekScopes] Pease help diagnosing my 2235

 

Hello everyone,
First off I'd like to thank you for having a group like this who might help a poor chump like me. 
I'm an electronics novice trying to learn more so I bought a 2235 for $70 with the understanding that one channel works.  Well, upon initial startup only one trace showed up.  After making some quick adjustments I was delighted to find traces for both channels.  Unfortunately after further investigation it seems neither channel works correctly.
I've searched through the Textronics troubleshooting manual, service manual, operators manual and schematic trying to understand my problems but I'm not knowledgeable enough to make a diagnosis.  I'm hoping someone here could give me a little insight so here's what's wrong:

  1. Intensity knob only adjusts from bright to really bright
  2. Vertical line on left hand side of screen
  3. Line running through waveform - looks like the electron gun moving to start positio n
  4. Waveform is noisy
  5. When measuring a low voltage signal, the signal is added to a phantom 24v sine wave
  6. Delay trace shows up as a vertical line on the left side of the screen
Here of some pictures of this scope in action:
From tektronix">pic1
Both channels measuring 500mA internal reference signal.  Seems ok.

From tektronix">pic2
120vac signal. Note vertical line on left side & lighter line running through middle of trace.

From tektronix">pic3
Other end of 120vac signal.  Note light horizontal line coming from end of trace.

From tektronix">pic4
Upper trace is the line-in to an audio amplifier.  Lower trace is the amplified output.  It's difficult to see it here, but the real signal is added to a 24v sine wave.

From tektronix">pic5
Lower trace is measuring the 500mA internal reference signal.  Vertical line in upper left corner is the delay trace.

I can't see anything obviously wrong under the cover.  There is some discoloration of the mainboard around some of the big power resistors but that's probably to be expected.

If anyone has any ideas I'd really appreciate it.

Thanks,
Bryan

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