Can anybody explain me really how do works the time base of HP scopes 1740A and - Page 1
Forum section: electronics / repair

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 27, 2016, 03:18:11 am
content: Tektronix 2220? I observed a sinewave of LG tv board that has 24 MHZ oscillatorand 24 mhz was enough to almost don't see well the signal it was very tight. I did need to use X10 resource on the HP and on the tektronix 2220.Seems the full range of these scopes are divided in two steps,or it is a mistake? pardon my ignorance.

author: tggzzz
author_rank: Super Contributor
timestamp: February 27, 2016, 09:58:44 am
content: Quote from: SAUL BRITTO on February 27, 2016, 03:18:11 amWhat do you mean "works"? Do you mean "use the timebase" or "internal operation of the tiembase"?If you mean "use the timebase", then you need to produce a better definition of your problem, including the position of all controls and preferable a picture of the trace.I have no idea what you might mean by "full range of these scopes are divided in two steps". My hp1740 has 23 steps (if I counted correctly).

author: rf+tech
author_rank: Frequent Contributor
timestamp: February 27, 2016, 07:32:58 pm
content: What Saul is referring to is the difference between main sweep and delayed sweep, that appear to him as two ranges. I no longer have an older scope with delayed sweep but seem to remember that there is a mechanical limit imposed upon main sweep when delayed sweep is lengthened. When delayed is set to 5 us/div then main sweep cannot be set faster.24 MHz sine wave has a period of 41.67 nanoseconds. The fastest sweep of 50 nanoseconds/div should display 12 full cycles without the need to use 10X magnification.@Saul, set the outer delayed sweep ring index mark to full clockwise stop (50 ns/div). It should now be possible to advance the inner main sweep to the full clockwise stop (50 ns/div).RF+ Tech

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 27, 2016, 10:37:50 pm
content: @Saul, set the outer delayed sweep ring index mark to full clockwise stop (50 ns/div). It should now be possible to advance the inner main sweep to the full clockwise stop (50 ns/div).Yes,I did it but, I just think that the 24 MHZ 1/4 of full scale of a 100 MHZ scope,be so tight...Thank you.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 27, 2016, 10:43:21 pm
content: That way when I measure 80MHz'll just have something using X10.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 27, 2016, 11:29:54 pm
content: rf+tech look at this:Is it normal? It is at full scale in main sweep, at 24mhz.

author: tggzzz
author_rank: Super Contributor
timestamp: February 28, 2016, 12:49:25 am
content: Quote from: SAUL BRITTO on February 27, 2016, 11:29:54 pmSince we don't know what you are probing, and since Chan1 and the timebase are both in the "uncalibrated" mode, who knows.I suggest you turn the chan1 LED off using the Chan1 cal pot, and the timebase LED off using the "sweep vernier" pot. If you are still having problems, post another picture and state what you would expect to be the displayed.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 01:43:15 am
content: Quote from: tggzzz on February 28, 2016, 12:49:25 amI noticed that a 100mhz scope at 1/4 of your capacity is showing a sinewave as if almost the end of it's main time base.This signal that you see is a sinewave at 24 mhz with the timebase at .05 uSeg.

author: rf+tech
author_rank: Frequent Contributor
timestamp: February 28, 2016, 01:54:05 am
content: Saul,When the timebase LED is on, the scope does not sweep at 50 ns/div. The sweep is slower and uncalibrated. I count 17.5 cycles of 24 MHz.1/24e6 = 41.67 ns/cycle17.5 x 41.67 = 729 ns total sweep time729 ns / 10 divisions = 72.9 ns/divCan you now see why the sweep is uncalibrated?The same applies to the vertical amplifiers.QuoteDoes full scale refer to horizontal scale or vertical scale? My interpretation is horizontal since the 10X magnifier is needed to see the individual cycles of 24 MHz.To display 80 MHz across 10 divisions:1/80e6 = 12.5e-9 = 12.5 ns per cycle50 ns per division = 500 ns per sweep500 ns per sweep / 12.5 ns per cycle = 40 cycles across 10 divisionsTo clearly see the individual cycles requires faster sweep.An important detail to consider: the stated bandwidth of a scope is that of theverticaldeflection system. Thehorizontaldeflection is less. For the HP1740A the horizontal deflection bandwidth is 5 MHz. At 50 ns/div x 10 divisions, the effective frequency is only 2 MHz.RF+ Tech

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 02:26:18 am
content: Oh thank you guys. But how to put off this led? I understand many concepts about scopes and anothers I need help.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 02:30:28 am
content: OK I did it, Is like V CAL.by tggzzz commentary I figured out that the vernier sweep of this scope is not working.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 02:52:23 am
content: Does full scale refer to horizontal scale or vertical scale? My interpretation is horizontal since the 10X magnifier is needed to see the individual cycles of 24 MHz.Yes rf+tech, is horizontal.And my question is: it's normal a 100mHZ oscilloscope don't show a individual cycle of a 24 mHZsinewave,since it is at 1/4 of your capacity?

author: rf+tech
author_rank: Frequent Contributor
timestamp: February 28, 2016, 03:05:27 am
content: Saul,QuoteNow that the sweep is "calibrated", 24 MHz should show 12 cycles across at 50 ns/div. Is this correct? If not correct and the error is large, then the vernier not working may be the cause for the large error.RF+ Tech

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 03:18:42 am
content: Ok sweep vernier working,was just a bad contact in a eight pins connector. A bit of würth spray solved the problem!

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 03:20:13 am
content: Rf+tech I will count the cycles.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 03:35:13 am
content: Image after sweep vernier fix.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 04:25:31 am
content: rf+tech this is a signal of 1.5 KHZ 2Vpp T/DIV .2 ms.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 05:52:11 am
content: Looking this same signal at the tek 2220 at 0.5 ms it fits exactly inside each graticule on the gridd of screen,how can I adjust the 1740A to the same condiction? I see that it is not right.

author: rf+tech
author_rank: Frequent Contributor
timestamp: February 28, 2016, 02:00:50 pm
content: Saul,Please do this simple calculation:Period = 1 / FrequencyHow much error exists between the measurement and the calculation?RF+ Tech

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 08:51:36 pm
content: I did it= 0,000666667 In this image I am at 1,5 KHZ if period = 1/1500= 0.000666667 Sorry I AM HORRIBLE WITH MATH.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 09:14:26 pm
content: On my super donkey vision are 6 errors. Maybe 7.

author: tggzzz
author_rank: Super Contributor
timestamp: February 28, 2016, 09:14:59 pm
content: Not "having" arithmetic is a problem.And it is time (seconds, s) not conductance (Siemens, S) .

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 09:30:18 pm
content: Thank you tggzzz

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 28, 2016, 11:29:35 pm
content: rf+tech I count at 24 MHZ .05us 12 cycles but I will to post a new photo.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 29, 2016, 03:28:05 am
content: F= 1/T = 1/0.00005=200001/20000= 0.00005us

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 29, 2016, 03:58:18 am
content: New photo that I think has 12 cycles:

author: rf+tech
author_rank: Frequent Contributor
timestamp: February 29, 2016, 04:10:51 am
content: Saul,The photo actually shows 12.5 cycles across 10 divisions.Look at the time marks at the arrows added to your photo.RF+ Tech

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 29, 2016, 04:11:41 am
content: rf+tech about that your equation I did P= V.tP= 24000000 x 0.00005= 1200 is it right? IF IT IS NOT RIGHT I see at least a 12 ratio,then on the anterior image there is an error of 5 cycles to more. Right?

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 29, 2016, 04:15:15 am
content: Quote from: rf+tech on February 29, 2016, 04:10:51 amThen I have to count that half cycle on the begin and on the end,how can I fix this rf+tech?

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 29, 2016, 04:18:08 am
content: Looks like after the sweep vernier fix it is a bit better.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 29, 2016, 05:35:10 am
content: I am reading about this calibration but I still don't have a time marker,can I fix this problem with frequency counter and a good function generator?

author: rf+tech
author_rank: Frequent Contributor
timestamp: March 01, 2016, 03:31:43 pm
content: Saul,Before jumping into sweep calibration, it is best to know some details about the accuracy of available signals.What is the source of the 24 MHz signal? How accurate is this signal? Is it crystal controlled?And the same about your function generator - how accurate is this? Is it synthesized or free running? Do you have a frequency counter?Also, I see from your posts that you are having difficulty measuring time with an oscilloscope. What is to the left of the first vertical line is not counted.Go back to the 24 MHz signal as shown in the photo with red arrows.Position the bottom peak of the first cycle exactly on the first vertical display line.Move the vertical position up so the bottom peaks are on the center line.Count 12 bottom peaks and read the scale.From the photo, this looks like 9.5 or 9.6 divisions.How many divisions do you measure?Now turn the sweep vernier from right to left.Do you see many more cycles?Turn the sweep vernier to the right (CAL position).Does bottom peak 12 return to the same position?RF+ Tech

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 01, 2016, 10:47:55 pm
content: Ok I will do it.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 12:24:54 am
content: Quote from: rf+tech on March 01, 2016, 03:31:43 pmYes it is a crystal controlled oscillator.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 12:30:01 am
content: I have done these adjustments and got it better,but when a change the sweep time see small differences:http://i65.tinypic.com/2z80vp3.jpg

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 12:36:37 am
content: 1uSEC I use 1mhz, 10uSEC 100KHZ and so on but,when I change the time to a near time I see that it does not keep completely stable there is a small difference

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 01:13:08 am
content: I'm dabbing ice with this FG.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 03:15:54 am
content: I figure out my FG is deffective,seems a PS problem.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 03:45:11 am
content: Bingo! A cap in leackage and that a leakage wow!!!

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 03:55:14 am
content: rf+tech what is the nomenclature for trigger offset on the HP scopes?

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 09:13:27 am
content: rf+tech I have new photos and show you later.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 09:17:59 am
content: I have done some comparisons with a tek 2220 that I have on the bench and they are very very near.

author: tggzzz
author_rank: Super Contributor
timestamp: March 02, 2016, 09:23:18 am
content: Saul, you might findhttps://entertaininghacks.wordpress.com/library-2/good-questions-pique-our-interest-and-dont-waste-our-time-2/helps you in the long term. Not all of the points apply to you, of course!Dokeep askinggoodquestions. But this forum isn'ttwitter (as inhttps://www.google.co.uk/search?q=define:twit).

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 10:36:44 am
content: I apologize if I made a mistake or bothered in any way but, I'm new in the forum and really need some warnings. But, how to discuss an issue?

author: tggzzz
author_rank: Super Contributor
timestamp: March 02, 2016, 11:04:53 am
content: Quote from: SAUL BRITTO on March 02, 2016, 10:36:44 amNo problem at all; no apologies necessary. You are honestly trying to learn, and that is good. The reason for pointing to that link is to helpyouget betteranswers.Minor point: learn how to use the "quote" button, so people can understand what you are replying to.More important point: think before posting, and where appropriate follow some of the guidelines noted on that page. Note that I don't always follow them!

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 11:25:06 am
content: Quote from: tggzzz on March 02, 2016, 11:04:53 amThank you for your advice, was not my intention to cause this kind of event. I will be ever grateful when you advice me about my fails. I confess that I am still a little confused about the right way to act in the forum, will try to improve every day.

author: tggzzz
author_rank: Super Contributor
timestamp: March 02, 2016, 03:54:31 pm
content: Quote from: SAUL BRITTO on March 02, 2016, 11:25:06 amAs I told my daughter, "let's makenewmistakes".Do continue posting and asking questions!

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: March 02, 2016, 11:36:30 pm
content: Quote from: tggzzz on March 02, 2016, 03:54:31 pmOk thx.