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Anyone know the trick to removing the Delay Time Position Vernier pot?

I have the fine adjustment knob off. Now what!?

Befuddled.

There is a nut inside the fixed part of the counter dial. It takes a 2-pin spanner
wrench made by Kilo, or you can make one, or if you have very strong fingers
you can use a round nose plier in the slots at peril of marring the dial. GL -J-

Ah! Great!

I have a pair of snap-ring pliers that kind of work. I gave it a bit of a tug, but didn't want to get aggressive with it not knowing that I was yanking on the right part or not.

I have the right idea then. Just needed to know what the right part to yank on was.

Thanks!
Dave

"You don't pay me to kick it. You pay me to know WHERE to kick it". (old repairman's joke).

On Wed, Nov 25, 2020 at 03:51 PM, Dave Peterson wrote:

I have a pair of snap-ring pliers that kind of work.

I do not have the factory tool, but I have a set of snap ring pliers that have round tips that work pretty well. I use masking tape over the outside of the vernier ring to prevent inadvertent damage if the pliers slip.
--
Michael Lynch
Dardanelle, AR

Your other problem is setting the Vernier where it is supposed to sit when you put it all together again! They don't all sit at 0.00, There is data about where they are supposed to read when the pot is at the extreme anticlockwise. If you have problems, just make them known here and you should get the right advice. Don't just adjust it to 0.00 - it is likely to be wrong.
Colin.

Ah, thank you Colin. I was wondering about that. My working scope isn't at 0.0, and this one wasn't either. And I have no recollection of what the Army scopes were set to. I can get close 'cuz I do remember that it was very close to 0 and like 1/4 turn ccw on the fine knob.
Long way to go before I'm back to setting this!
Dave

Colin Herbert wrote:

Your other problem is setting the Vernier where it is supposed to sit when you put it all
together again! They don't all sit at 0.00, There is data about where they are supposed
to read when the pot is at the extreme anticlockwise. If you have problems, just make
them known here and you should get the right advice. Don't just adjust it to 0.00 - it is
likely to be wrong.

Is this covered in the service manual? I would be interested in knowing how this needs to be set, as I am planning to move the guts of one 475 into the frame of another, and that would obviously involve disassembling and reassembling the delay vernier.

-- Jeff Dutky

Colin,

I've looked at five different scopes with a delay vernier and only one of them (a 2215) seems to be set at something other than 0.0 at the extreme CCW rotation. All three 475s and the 475A that I'm currently working on start the vernier at 0.0 when rotated fully counter clockwise. Now I certainly don't know about the two 475 parts scopes, or the 475A, but I'm certain that my father never disassembled the vernier or otherwise interfered with it (and, even if he had, he was the sort of person who would have restored it to exactly the condition he found it in). So now I'm doubly curious about how these things are set.

-- Jeff Dutky

I don't recall seeing it in any Service Manual, but our good friend H?kan has produced a document on the topic:



Colin.

Colin,

Oh, I had expected some kind of calibration process, but it's just a bunch of constant offsets for different models.

I see that I am lucky to only be concerned with a model that is always set to 0.0 (the 475 and 475A). Good to know, however, since I would surely have been led astray on my 2215.

Thanks

-- Jeff Dutky

I checked my working scope this morning. I wish we could do inline pictures. I reviewed my tear down pictures and found that I had a shot of the DTP knob before I took it off, and am 99% certain that it's in the full ccw position. The new (parts) one is SN 29XXXX, the "old" working one is 31XXXX. The 29XXXX is at 0.35, the 31XXXX is at 0.25. Interestingly the 29XXXX has the fine dial setscrew at the "1" position. The 31XXXX has the setscrew at the "3.5" position. That's funky, but not really relevant?

I also wonder about the history behind these "min" settings. There's got to be some engineering behind it.

I don't recall them being non-zero back in my Army days. My experience, in general, is that there's not a lot of use for the B-delayed trigger. Perhaps more so in broadcast TV? (As another aside: in my profile picture I'm using the B-delayed function to examine a GHz radar transmit pulse triggered from a 20kHz system clock. Funny the things you remember). In any case, I don't recall the zero or values on the knob were of any interest. It was just a device to move the B-delayed signal under examination. This could be entirely my experience and use case only. I would be interested in learning what use cases in which values from this pot are needed.

Is this style of multi-turn pot just a means of obtaining fine delay control over a very large range? The ability to have nano-second resolution over a micro-second (or mili-second?) range. 1000-1 is a pretty large range.

Also interestingly, the other scope visible in my profile pic is a Tek 491 spectrum analyzer. I recall that it had a crank-knob on it. I was reviewing replacement knobs on the sphere site and came across that knob and all these memories came flooding back. I remember cranking on that thing to slew the spectrum analyzer across several orders of magnitude of frequency. So I wonder if these are just devices for handling fine control over a large range.

Dave

Dave,

I'd also be interested in people's practical experience using both the delayed timebase and the vernier control.

The oscilloscope operators instruction manuals for the 475 and 2213 (as well as The XYZs of Oscilloscopes) have some discussion of how to use the delayed timebase to perform different measurements, but I've had trouble wrapping my head around the discussions without concrete examples to try out myself. Here is the discussion on page 29 from The XYZs of Oscilloscopes (1981, for the 2213, which has neither a full dual timebase nor a vernier for the delay):

"Dual time base scopes offer you all the measurement capabilities of single time base instruments, plus:

? convenient comparisons of signals at two different sweep speeds
? jitter-free triggering of delayed sweeps
? and timing measurement accuracy of 1.5%

Most of this increase in measurement performance is available because you can separately control the two sweep speeds and use them in three horizontal operating modes. These modes — in a 2215 — are A sweep only, B sweep only, or A intensified by B as well as B delayed. The HORIZONTAL MODE switch controls the operating mode and two SEC/DIV switches — concentrically mounted on a 2215 — control the sweep speeds.

When you use the ALT (for alternate horizontal mode) position the HORIZONTAL MODE switch, the scope will display the A sweep intensified by the B sweep and the B sweep delayed. As you set faster sweeps with the B SEC/DIV switch, you'll see the intensified zone on the A trace get smaller and B sweep expanded by the new speed setting. As you move the B DELAY TIME POSITION dial and the change where the B sweep starts, you'll see the intensified zone move across the A trace and see the B waveform change."

My father replaced a 475 (which has a vernier) with a 2213 (which has merely has a blank knob) as his daily use scope in the early 80s, after having used the 475 for 6 or 7 years. He had the choice between the 2213 and the 2215 (which has a proper dual time base and a vernier to control the delay) so I can only conclude that he didn't feel that those features were useful in his work (he was a service technician working on laboratory mass analysis equipment — mass spectrometry, spectroscopy, chromatography — and the computers that were connected to that equipment).

-- Jeff Dutky

Hi Jeff,

I clearly recall using a brand new 475 at my work place some forty years ago, on which delay timer pot was not set to zero, it was set at 0.20. I don't exactly know why, but perhaps it represented the minimum inherent delay, that would always be there when using delayed sweep, due to circuit design.

My personal 465b also has this pot set at 0.20, but I am not sure whether it was set by the manufacturer, as this scope was a used, and possibly repaired one when I acquired it. Recently, I had to do some fixing on my personal 465b, and when I reassembled, I took care to set it to 0.20, whatever it means. I don't use the delayed sweep during my home use.

Hope this helps.

Shailendra

When I was a pup in the emerging field of digital data storage and field recorders, I was presented with a 465B for my bench. I remember staring at it for a minute or so, until the senior tech reached over and pulled on the power knob. I still hadn't found it...

Learned to love the 465, and still have the refurb one I bought with a loan from Grandma in the previous century, $2K

The data recorder (prefer not to say what it recorded...) used dynamic RAM with a 1mS refresh rate, and a 250 nS read cycle. Running the scope at 100 uS / Div on RAM clock the gave you a nice parade of closely spaced pulses at the left side of the screen, and over at the right side you might see the beginning of the next refresh cycle if the clock crystal in the recorder was off a bit. We would use the B-Delayed sweep to slowly scroll through the sequential addresses to the RAM, and thereby be able to see any desired address of the lower 8 bits of the bus as the address incremented.

Pretty much a similar use case as with analog TV, the variable delay allowing you to scroll to a particular line, or portion of a line, in the video scan...

_Dave KC6UPS

And the value of the DTP Vernier was irrelevant, right?

So far we have that it appears there was an initial setting by model, but no definition to the reason or significance of that value.

Does anyone have a working setup in which the value of the Vernier can be checked? Does it indicate time values? If so, wouldn't it have to be scaled according to the time/div setting?

Now that I think about it, isn't that all this dial can do? Indicate decimal values from 0.00 to 9.99? I don't think I've ever tested it turned it fully CW. Does the pot stop at 10 turns? That's kind of a rhetorical question. I'll try myself when I get in the shop. I also need to do my own homework and review the calibration procedure in the manual.

Dave

On Fri, Nov 27, 2020 at 05:08 PM, Dave Peterson wrote:

Does anyone have a working setup in which the value of the Vernier can be
checked? Does it indicate time values? If so, wouldn't it have to be scaled
according to the time/div setting?

The dial shows the delay from the start of the A time base to the start of the B time base in time units selected by the number on the A time base selector (if in the cal. position). Usually, this is observed using the B trace. So, with the A time base set at e.g. 1 us/div, when changing the value on the dial from e.g. 3.61 to 4.61, the B trace moves by 1 us (if B is set to "Run after Delay"), *whatever* the setting of the B time base. The fact that the number relates to the A, and not the B time base may seem counter-intuitive at first.
Although the "delay time multiplier" knob, as it's called, is almost always used differentially, I guess the "offset" mentioned by some compensates for the absolute minimum delay (for the start of the B time base), achievable when setting the delay time multiplier knob CCW.

Raymond

Thanks for the excellent description Raymond!

Two things: I checked my working scope, and the range is precisely 10.00 turns. Mine starts at 0.25(5) (5 is estimated as midway between the 5 and 6 tick marks), and ends at 0.25(5).

There is a calibration procedure in the service manual:?. I don't fully understand the procedure yet - I don't have a Time Mark Generator nor experience with one. But as Raymond described, it seems to be differential, not absolute. And I don't see (yet) an initial setting calibration. See page 5-57, item 77 through 79.

Besides twirling knobs to check functionality, I haven't had the chance to really dig back into the B timing. I'm only going off my memory of 35 years ago. So thanks again for the concise description Raymond.

Dave

Just thought I'd mention that you don't need to let the lack of a time mark generator hold you back. TMGs are convenient for what they do, but all you really need is a source of accurate enough square waves or pulses, with edges sharp enough relative to the sweep rate. You just use the edges as the references to align with the graticule marks. For instance, a 1 MHz square wave is equivalent to 1 uSec markers. If it comes from something that's crystal-controlled, it will be way more accurate than the scope timebase anyway.

Ed

Cheapo function generator is in the mail - somewhere between Chicago and here now I believe. Building up my bench, so running a bit lean on things like this. But I figured a cheapo purpose built generator is better than the cell phone app I used to rough in the eBay 465 I got to start with! :P

Once I have that in hand, and this parts scope back up - assuming I can get it back to working - I'll do just that - use a square wave in place of the TMG. There's some decent output images of the TMG on the TekWiki (or from the TekWiki, or just the web, I don't recall) that made me realize a square wave is a decent enough equivalent. But I wonder what features of the TMG a hack like myself might be missing.

Dave

Remember that a common FG will not be all that accurate in frequency, or have great edge speed. There are types that do, but not so common. The easy way is if you happen to have any kind of digital signal generators or sources that are accurate. You can also slap together simple DIY sources, with basic parts like a XO clock module, followed by various dividers. Use 74HC logic for up to about 20 MHz. Beyond that it gets a little more complicated.

Ed