Author Topic: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown  (Read 22488 times)

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Offline EEVblog

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EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« on: January 28, 2015, 03:46:01 pm »
Dave does some performance checks and then tears down a Krohn Hite EDC 4601 0.05% 6 decade 1ppm resolution 0-1000V AC voltage standard.

Service Manual with schematics: http://www.eevblog.com/files/4601ServiceManual.pdf

User manual: http://www.krohn-hite.com/htm/ServiceSupport/PDF/Manuals/4601%20Manual.pdf

MV106 DC Voltage Standard:

Datasheets:
Vactrol: http://www.excelitas.com/downloads/dts_vtl5c3c4.pdf
XR2228 Multiplier/Decoder: http://html.alldatasheet.com/html-pdf/119347/EXAR/XR-2228/96/1/XR-2228.html
Epson SPG8640 oscillator/divider: http://www5.epsondevice.com/en/quartz/tech/discon/epsondiscon/2000catalog/spg_8640series_e.pdf

« Last Edit: January 29, 2015, 11:01:02 am by EEVblog »
 

Offline scopeman

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #1 on: January 28, 2015, 04:15:34 pm »
Hi Dave,

Nice teardown. Maybe you can get KH to send you a PDF of the manual with the schematics in them.
Anytime you get tired of this piece "old school" electronics I would be happy to take it off of your hands!

Sam
W3OHM
 

Offline pickle9000

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #2 on: January 28, 2015, 04:23:10 pm »
LM3914 is an awesome chip, super useful.
 

Offline coppice

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #3 on: January 28, 2015, 05:40:14 pm »
From the way the meter reading jumps around the output of this thing appears quite noisy. That's going the make the bandwidth of the meter a significant factor in the reading. Its not exactly the most sophisticated reference ever made.
 

Offline EEVblog

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #4 on: January 28, 2015, 06:14:00 pm »
From the way the meter reading jumps around the output of this thing appears quite noisy. That's going the make the bandwidth of the meter a significant factor in the reading. Its not exactly the most sophisticated reference ever made.

It's also not a DC reference.
I don't have another AC reference to compare noise performance to.
 

Offline electronics man

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #5 on: January 28, 2015, 07:17:56 pm »
it would have been nice if you could have hooked the scope across the output
follow me on twitter @get_your_byte
 

Online Dr. Frank

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #6 on: January 28, 2015, 07:30:33 pm »
Dave,

on all of these multi-dial calibrators, you better use full scale output, instead of 10% f.s. only.
Only then, you get full accuracy and stability out of it.
The 10V range (f.s.) is the most stable also.

You can easily see that in the datasheet:
accuracy, 10V: 0.05% of setting + 0.005% of range
stability, 8hrs.: 0.0075% of setting + 0.001% of range

That ..(x% of range) doubles your in-accuracy and instability, if you set these instruments to 10% only.

Therefore, always dial to "10" on the first digit:  .(10) 0 0 0 0 0 V  or to .9 9 9 9 9 (10) instead of 1. 0 0 0 0 0 V

If you repeat that A.C. stability (noise) measurement on your 34461A with 10V f.s., you would see a much better performance, about ten times better short term stability, I bet.


These AC standards usually convert a programmable D.C. reference to an A.C. output by comparing the D.C. setting to the precision rectified  A.C. signal..
 
Therefore, it's a pity, that the DC to AC comparator / rectifier is not explained in the manual, as the Theory of Operation chapter is missing.
Maybe, that's done by the XR-2228, although its squaring accuracy is normally too bad for that.

That means, that this instrument also contains a D.C. reference standard in first instance.
You may measure the DC reference of 0.. 10.00000V, or so, somewhere inside the circuit.

I bet this D.C. reference part of the circuitry is very similar to the DC standard you also own from KH /EDC.


Concerning the muddy corner of the instrument, that may be caused by high voltages present there.
If you open such HV calibrators, DC or AC, you will always find an accumulation of dust, something like carbon black, at and around all parts, which carry the HV, due to electrostatic  attraction.
This one looks a little bit odd, anyhow.

Frank
« Last Edit: January 28, 2015, 08:15:55 pm by Dr. Frank »
 

Online Fungus

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #7 on: January 28, 2015, 10:01:23 pm »
I've used LM3914s to get a simple constant current sink for LEDs. Just tie the 'input' pin high and you can connect 10 LEDs to it without worrying about resistor values. Using one for only 3 LEDs seems weird, but whatever...

PS: You can also do it with AN6884s if you only need 5 LEDs. They're dirt cheap if you buy packs of 50. They're also SIP packages and don't take up much space on a PCB.  :)

Edit: "SIP packages" as defined by the department of redundancy department...
« Last Edit: January 28, 2015, 10:35:17 pm by Fungus »
 

Offline EEVblog

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #8 on: January 28, 2015, 11:21:14 pm »
That means, that this instrument also contains a D.C. reference standard in first instance.
You may measure the DC reference of 0.. 10.00000V, or so, somewhere inside the circuit.
I bet this D.C. reference part of the circuitry is very similar to the DC standard you also own from KH /EDC.

Yes, I mentioned that, almost certainly the same zener reference and circuit as in the MV106 DC standard.

Quote
Concerning the muddy corner of the instrument, that may be caused by high voltages present there.
If you open such HV calibrators, DC or AC, you will always find an accumulation of dust, something like carbon black, at and around all parts, which carry the HV, due to electrostatic  attraction.
This one looks a little bit odd, anyhow.

Yes, but in this case that's not the high voltage side, it's just the mains side, the high voltage is right over on the other side of the chassis.
 

Offline max_torque

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #9 on: January 29, 2015, 02:30:08 am »
That means, that this instrument also contains a D.C. reference standard in first instance.
You may measure the DC reference of 0.. 10.00000V, or so, somewhere inside the circuit.
I bet this D.C. reference part of the circuitry is very similar to the DC standard you also own from KH /EDC.

Yes, I mentioned that, almost certainly the same zener reference and circuit as in the MV106 DC standard.

Quote
Concerning the muddy corner of the instrument, that may be caused by high voltages present there.
If you open such HV calibrators, DC or AC, you will always find an accumulation of dust, something like carbon black, at and around all parts, which carry the HV, due to electrostatic  attraction.
This one looks a little bit odd, anyhow.

Yes, but in this case that's not the high voltage side, it's just the mains side, the high voltage is right over on the other side of the chassis.

It does look to me that some time ago, rather like something has "gone bang" in that back LHS of the device and left some sooty remnants!

 

Offline station240

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #10 on: January 29, 2015, 03:25:34 am »
Yes, but in this case that's not the high voltage side, it's just the mains side, the high voltage is right over on the other side of the chassis.

It does look to me that some time ago, rather like something has "gone bang" in that back LHS of the device and left some sooty remnants!

Maybe there was a MOV or filter capacitor across the mains input, that exploded and was removed. Might explain why that area has heatshink on it, if the wiring had to be renewed anyway.
 

Offline JackOfVA

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #11 on: January 29, 2015, 04:13:46 am »
Looks like the power transformer has been roughly handled as well - look at the lamination stack near the front by the trim pot module -- laminations are bent out, almost like someone forced a screwdriver into the corner.  How that passed QC is interesting as well.
 

Offline cj555

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #12 on: January 29, 2015, 04:51:04 am »
Dave, you find the most interesting stuff to tear down!  Thanks, learned something again.

But.......was I the only one who noticed that 18 kg is not 50 lb??  It's more like 40 (OK, closer to 39 lb 10 oz).  No matter what the manual says!

...also, every time you say "that's a bit how ya doin!"...now I think of "that crazy Kiwi" Doug Jones  :D.

 

Offline dentaku

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #13 on: January 29, 2015, 05:28:03 am »
Vactrols are mostly being used in audio applications these days. You can still buy modern ones for things like analog synths and effects boxes.

I once built one with an LED and an LDR taped together.
 

Offline SeanB

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #14 on: January 29, 2015, 05:39:34 am »
A few thoughts. The main board likely dates from the late 1970's, probably they made a batch of them, partially populated them with the reference soldered in, and probably they originally used SFC2741 opamps as original spec, as they have been selected for low offset and low popcorn noise. They then just put them in storage until needed. Shows in the composition resistors on the board, and the 1970's style capacitors and the precision resistors ( the Vishay glass film resistor has been around since the 1970's, it just was a very expensive part then) along with the roller tinned board. When needed they likely unsoldered the original IC's and installed sockets to use more modern parts with a better spec, but left the original reference untouched ( and probably were careful not to solder near it to keep the tempco stable) as an aged reference.

The relay being used without a base is simple, you cannot bolt the base down with the single bolt, but have to use 2 bolts at the ends of the socket, then use a spring clip to hold the relay down. No room on the board for that, and likely the original relay type was no longer available, so they used the best that fitted the restricted space.

The output stage was also likely an upgrade, as the original probably used 2 TO3 power transistors and the driver stage on the main board, the mosfet upgrade being easy to do with a bias change ( some of those new resistors and cut traces and new holes) and a protection/mounting board for the leads.

Dirt on the mains side is easy, they used a Schaeffner mains filter, and it did the usual flaming exit after a few years. Clean up the board a little with a brush, new inlet ( unfiltered) and away it went.

the oscillator board is likely the only new design, as the original board would have used all discrete parts in the most case, and some specialist IC's that went obsolete in the 1980's, like so many small low volume specialist semiconductors do. So a new board design to do the same job, using as many of the original parts as possible. Thus the Vactrol, and on the main board is likely an even older one, that uses an incandescent lamp inside as a light source instead of the new fangled LED, though it will be run at a current that at best warms the filament to a dull red.
 

Online Dr. Frank

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #15 on: January 29, 2015, 07:27:29 am »
Comparing to the MV106 video, the 1N829 reference diode again is soldered onto these standoffs, in this muddy compartment.
These diodes where Dave was pointing at in this actual video, were simply the anti-parallel diodes to protect the inverting inputs of the three/four OpAmps nearby.
I assume, that reference diodes were mostly housed in plastic or painted glass cases, as if they were housed in simple glass diode case, any light onto the chip would affect the zener voltage.

The trim pots around probably set the offsets of the OpAmps only.

As there's all that dirt around, which looks like it would be conducting stuff, (the idea of an exploded AC filter cap seems to be striking), I'd like to propose to clean that compartment thoroughly, to maintain the accuracy.

Frank
« Last Edit: January 29, 2015, 07:55:00 am by Dr. Frank »
 

Offline EEVblog

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #16 on: January 29, 2015, 11:08:11 am »
 

Offline EEVblog

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #17 on: January 29, 2015, 11:10:04 am »
Interesting stuff as always. Video quality is definitely worse than older videos though. Seems like lower bitrate and more digital encoding noise.

Technically, a lower bitrate per frame. 28Mbps 50fps (maximum of camera) vs 17Mbps 25fps (not maximum of camera, I could have 28Mbps 25fps).
But I don't see the difference.
 

Offline EEVblog

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #18 on: January 29, 2015, 11:11:29 am »
A few thoughts. The main board likely dates from the late 1970's

Service manual schematic dates the design to 1986.
 

Offline plexus

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #19 on: January 29, 2015, 12:50:20 pm »
Im watching as I type so you may have addressed this: What does THAT smell like??? I can almost smell it from here (Canada). want to know if Im right?

Just so y'all know, if you question Dave's apparent obsession with gear smell, I totally get it. For example some years ago a friend gave me a roadcase for a music synthesizer. I am an electronic musician. I opened the case and said, "Was a Roland in here?".  Sure enough it was! I explained that different synth manufacturers have different smells especially the older synths from the 70s and 80s which were made more.from organic compounds .

That  AC standard LOOKS like its pungent??
 

Offline boffin

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #20 on: January 29, 2015, 03:33:53 pm »
Dave; when you were trying to date the thing, you missed the fact that all of those multi-turn trimmers (and the relays) also had date codes on them
Boffin at play https://snafu.ca/
 

Offline IshtarTor

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #21 on: January 29, 2015, 03:56:31 pm »
I think the effect of the blowing was interesting, and I would like to see how it looks like with the FLIR, and what is the stability effect of using a hair drier or something like that on different areas of the instrument. Maybe there is something to learn here on the design of precision instruments ?
 

Offline EEVblog

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #22 on: January 29, 2015, 04:22:39 pm »
Dave; when you were trying to date the thing, you missed the fact that all of those multi-turn trimmers (and the relays) also had date codes on them

Yep. When you are yapping into a camera whilst trying to subconsciously think what to say, and what to say next, and looking at the LCD screen, and thinking about the shot etc, it's surprisingly easy to miss stuff.
 

Offline boffin

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #23 on: January 29, 2015, 04:47:00 pm »
Dave; when you were trying to date the thing, you missed the fact that all of those multi-turn trimmers (and the relays) also had date codes on them

Yep. When you are yapping into a camera whilst trying to subconsciously think what to say, and what to say next, and looking at the LCD screen, and thinking about the shot etc, it's surprisingly easy to miss stuff.

Wasn't trying to criticize, just help.  Not everyone looks for date codes on the passives.
Boffin at play https://snafu.ca/
 

Offline ludek

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Re: EEVblog #709 - EDC 4601 AC Voltage Standard Teardown
« Reply #24 on: January 30, 2015, 02:04:39 am »
Dave said "...sort of "HP 200" oldschool, used in a light bulb, as the main stability element in your oscillator." - what device do you mean?
I'm very interested in unusual sollutions. Please more info about this stability elemnt (which EEV Blog number(?) or something).
Very nice video BTW I like "rare" gear tearing down.?
.
 


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