Timebase Multiplier? - Page 1
Forum section: electronics / testgear

author: BeanerSA
author_rank: Newbie
timestamp: June 11, 2013, 10:26:11 am
content: Hi All,I recently picked up a cheap scope for dicking around with, and I tried to do a frequency measurement which just didn't seem to give the right result.I hooked up the probe to the 1KHz cal signal nope. Fed it a 1KHz audio tone, still no joy.I seem to be out by a factor of 10! 20uS/div * 5 divs = 100uS period. Inverse of that gives 10KHz.The manual mentions a timebase multiplier, but I can't find it on the panel. I checked the vernier and it is in the detent position. I'd accept that it was out of cal, but an even factor of 10.Model is BWD845http://bama.edebris.com/manuals/bwd/845Any ideas?

author: jpb
author_rank: Super Contributor
timestamp: June 11, 2013, 12:26:38 pm
content: Can't see anything wrong with your reasoning.Have you tried moving the green knob round a few divisions each way to see if they are all out by two positions? Maybe someone repaired the scope and put the knob back on wrong!

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: June 11, 2013, 06:08:05 pm
content: Quote from: jpb on June 11, 2013, 12:26:38 pmI like your theory! but three clicks is always x10 on that knob, so the test would be if it hits the stops in the wrong place.

author: manticore00
author_rank: Regular Contributor
timestamp: June 11, 2013, 06:29:23 pm
content: Is any input out by x10 on any timebase setting? If so perhaps the x10 magnification is stuck on? The button in the upper right of the picture doesn't appear to be depressed but there may be an issue behind the panel?

author: JackOfVA
author_rank: Unknown
timestamp: June 11, 2013, 06:42:52 pm
content: Take a look at page 2-1 of the instruction manual and verify that you do not have the time base vernier engaged. It allows you to vary the actual sweep speed from the timebase knob setting.The horizontal magnifier is a 5x, not the normal 10x, by the way.Whoever designed the front panel of that scope should be doing something they are more suited for, such as taking orders at a McDonald's hamburger shop. It's poorly labeled and grouped, let alone color coded.And a properly designed oscilloscope would have an indicator LED that illuminated when a time base vernier is engaged - it would be labeled "UNCAL" or the like. (Same with vertical gain vernier.)

author: BeanerSA
author_rank: Newbie
timestamp: June 12, 2013, 02:30:04 am
content: Quote from: jpb on June 11, 2013, 12:26:38 pmQuote from: Galaxyrise on June 11, 2013, 06:08:05 pmYou might be onto something, this is where the knob stopsAlthough it doesn't keep turning as you move clockwise, it stops at the smallest value.Quote from: manticore00 on June 11, 2013, 06:29:23 pmThe button at the top you are referring to is only an x1/x10 for the external trigger input. On page 3-4 is a section that reads, Delay Multiplier: Multiplies the TIME/DIV as selected by A time range switch over the range x0.5 to x10 providing a delay range from 200nSec to 20Sec.But I can't find any such control!Quote from: JackOfVA on June 11, 2013, 06:42:52 pmYes I was caught by the vernier control at first too. When you rotate the A timebase control, the vernier moves with it, must be dragging. Also, don't forget this is a 30 y/o scope!

author: vk6zgo
author_rank: Super Contributor
timestamp: June 12, 2013, 03:26:42 am
content: Quote from: JackOfVA on June 11, 2013, 06:42:52 pmWell,gee,it looks like Tektronix can't design Oscilloscopes,either.I've looked all over the 7B53A Dual time base on my Tek 7613---nary a sign of such a LED!The 7613/7B53A & the BWD were designed in a more robust time,when Technicians & Engineers who used such devices didn't need to be hand fed!

author: GK
author_rank: Super Contributor
timestamp: June 12, 2013, 03:29:49 am
content: That BWD control layout has nothing on, say, a Hameg 1507.Two more freebie scopes took up residency in my shed just last week; both BWD's and one an 845. Have only played with it a for a few minutes so far but can check out the timebase control operation this evening.

author: BeanerSA
author_rank: Newbie
timestamp: June 12, 2013, 03:37:00 am
content: Quote from: GK on June 12, 2013, 03:29:49 amI'd appreciate if you could let me know if you can find the x10 Delay Multiplier!

author: vk6zgo
author_rank: Super Contributor
timestamp: June 12, 2013, 03:40:57 am
content: For some strange reason,BWD explains the Delayed timebase in an unusual way,but it is exactly the same concept as the system used by Tektronix & HP.I've never used a BWD 845,though I have seen one,& read the Handbook.

author: BeanerSA
author_rank: Newbie
timestamp: June 12, 2013, 05:52:40 am
content: Quote from: vk6zgo on June 12, 2013, 03:40:57 amThe Delayed timebase seems to work fine on this, but that's different to Delay Multiplier.

author: JackOfVA
author_rank: Unknown
timestamp: June 12, 2013, 10:36:15 am
content: Quote from: vk6zgo on June 12, 2013, 03:26:42 amWell, I think you are mistaken about Tektronix.My 465 and 2246 both have an UNCAL LED on the horizontal time base, and the 465 pre-dates the 7K series by a good many years if I recall properly. Perhaps one of the bean counters found a way to save a few cents by omitting the indicator.Going back further, the 515 had an UNCAL indicator as well.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 12, 2013, 12:44:22 pm
content: I bet it wouldn't be a LED in the 515,though!I would have thought 465s & 7000 series were pretty much contemporaries.The first 7000 series I saw was in the early '70s---before that,we used 545Bs & the like.First 465 I saw was a few years later.I'm trying to remember if the 545 had an unlock light.It's pretty obvious if you have the variable time/div out of "CAL",so probably they left it out of the 7000 plugins to save space ---- originally they didn't light the pushbuttons,either.

author: GK
author_rank: Super Contributor
timestamp: June 12, 2013, 12:46:21 pm
content: Quote from: BeanerSA on June 12, 2013, 03:37:00 amThe delay multiplier (x0 to x10) for the B timebase trigger is the vernier/counter dial to the right of the Timebase sweep rate control. I think you are confusing that with the horizontal sweep multiplier though. The horizontal sweep multiplier however is only x5, not x10 and is turned on and off by pulling out and pushing in the horizontal position control knob (the knob to the immediate left of the external trigger-input BNC. So that is not your problem.As you can see in the attached photo, my timebase A sweep control knob goes right down to 2S. My actual sweep times on screen are verified as indicated on the timebase control. This is obviously where yours is askew. The knob is 3 positions out with respect to the switch wafer(s). The reason why your timebase A sweep knob still stops where it should at the end in the clockwise direction I suspect is due to the interlocking mechanism between the timebase A sweep time knob and the concentric outer collar that sets the sweep time for timebase B. I guess someone had had the mechanism apart and managed to put it back together wrong.

author: BeanerSA
author_rank: Newbie
timestamp: June 12, 2013, 02:09:59 pm
content: ^^Cheers, thanks for clearing that up. I'll take the top off and see if there is anything obvious wrong.

author: JackOfVA
author_rank: Unknown
timestamp: June 12, 2013, 02:13:12 pm
content: Quote from: vk6zgo on June 12, 2013, 12:44:22 pmI think the first of the 450/460/470 scopes came out a few years (3 or 4?) before the first 7000 series, but the higher performance 465/475 models might well have been around the same time the 7000 line was introduced.