EDC/Krohn-Hite CR103 Current/Voltage Standard teardown (LARGE images)

[dc101]

Inspired by Dave's Krohn-Hite voltage standard review/teardown, I found a similar score on ebay.  Thought the group might be interested in seeing some pics.  This is an EDC current/voltage standard so it's similar to the one Dave reviewed, but has a few differences.  Here's a link to the schematic https://www.dropbox.com/s/gcvaueaggioyf9m/cr103%20schematics.pdf

Can anyone recommend a good lubricant for the switches?  I have contact cleaner, but haven't been able to find any switch lube on Mouser of DigiKey.

Thanks, and enjoy the pics.


Outside view of the case, with the top removed.


Overview of the inside.  The upper board (the one that is visible) is the voltage board.  Off to the right you can see the 100 ohm 1% power resistors.  To the left in-between the transformer and the main board, those cardboard tubes are covering some rather large caps, more on those later.


Close-up of the voltage board.  Lots of multi-turn trim pots which are used to calibrate the unit.  I'm assuming that the 801-A-225 is a packaged version of the chopper amp?  In the upper let, the metal cased IC is a RC4194 dual tracking voltage regulator


A look at the current board.  According to the schematic, the current board uses the same TSC7652 chopper amp as the voltage board.  The cardboard protective tubes are removed from the high voltage caps.


100-150 uF 500 Volt Caps


Another shot of the caps.  Part number TVLU-1775


Close up of the range selector switch.  The three trim pots on the right side (top of the picture) are the fine tune zero for the different voltage ranges.


Showing the various decades and the range selector switch as well.  The switches are kind of crusty looking.

[EEVblog]

Nice score. That's the unit I originally wanted, but I could only score the voltage only unit cheaply.

[TiN]

Lovely photos, thumbs up!

Actually thanks to CR103 schematics I was able to confirm trim resistors to calibrate my MV106.
Google did not find MV106 schematics, but this one is available.

[EEVblog]

Google did not find MV106 schematics, but this one is available.

Here you go:
http://www.eevblog.com/files/MV106%20Service%20Manual.pdf

[saturation]

Great unit and superb photos and schematic!  I have the MV106 for 2 years? now and its accurate and holding cal nicely too.  The EDC/KH units are great.  Use Dexoit for cleaning the contacts its oily enough to use as a lube if you must.

[Dr. Frank]

Thanks for sharing.
Congratulations for winning this nice instrument.

Becaused the schematic contains some obscure things, 2 questions, to check, please:

1. The 6-digit resistor decade, what values of resistor does it contain?
For example the MSD dial, should have 4-5 resistors, BCD coded.
What is the smallest for "1", the largest value, and  what is the total resistance if "10" is dialed in?

I assume, "10" equals 100 kOhm, and the smallest 10kOhm.
 
2. Would you please identify and photograph the assembly A3550, where the schematic is missing.
This should be mounted on the chassis, and I assume it to be a low ohmic resistor network, which divides the 10V down to 100mV, i.e. by 100:1.

Thank you

Frank

[dc101]

Frank,

No problem, I have a few pics for you.

Your question #2 is simple, they are the 100 ohm 1% power resistors on the right side of the case.


As for your first question.  Starting with MSD, they are 19990 ohms +/- .025%, 2K ohm +/- .005%, 200 ohms +/- .005%, 20 ohms +/- .025%, 2 ohms +/- .25% and the last, 0.2 ohms +/- 2%  The resistors are all Tel Labs brand.  Pictures below.  I also took a snap of the underside of the current board, I figured why not since I already had the bottom off.

Cheers,
-Tim

MSD


2K Ohm


200 Ohm


20 Ohm


2 Ohm


.2 Ohm


Underside of current board


Close-up of the sweet EDC logo on the current board

Thanks for sharing.
Congratulations for winning this nice instrument.

Becaused the schematic contains some obscure things, 2 questions, to check, please:

1. The 6-digit resistor decade, what values of resistor does it contain?
For example the MSD dial, should have 4-5 resistors, BCD coded.
What is the smallest for "1", the largest value, and  what is the total resistance if "10" is dialed in?

I assume, "10" equals 100 kOhm, and the smallest 10kOhm.
 
2. Would you please identify and photograph the assembly A3550, where the schematic is missing.
This should be mounted on the chassis, and I assume it to be a low ohmic resistor network, which divides the 10V down to 100mV, i.e. by 100:1.

Thank you

Frank

[dc101]

Frank,

I measured the resistance of the least significant decade switch and got values ranging from .100 to 1 ohm when going from 1-10 respectively on the rotary switch.  The rest of the switches all act the same, with the only difference being they just go up in range.  So the rotary switch with the 2 ohm resistors goes from 1-10 ohms in increments of 1 ohm, the next significant switch goes up by 10 ohms and so on.  This continues until the MSD, which seemed to give me some weird values so I think I was measuring it at the wrong spot.  I'll keep poking around at the MSD to figure out where I need to measure it at.

Cheers,
Tim

Thanks for sharing.
Congratulations for winning this nice instrument.

Becaused the schematic contains some obscure things, 2 questions, to check, please:

1. The 6-digit resistor decade, what values of resistor does it contain?
For example the MSD dial, should have 4-5 resistors, BCD coded.
What is the smallest for "1", the largest value, and  what is the total resistance if "10" is dialed in?

I assume, "10" equals 100 kOhm, and the smallest 10kOhm.
 
2. Would you please identify and photograph the assembly A3550, where the schematic is missing.
This should be mounted on the chassis, and I assume it to be a low ohmic resistor network, which divides the 10V down to 100mV, i.e. by 100:1.

Thank you

Frank

[dacman]

I use LPS-1 for a switch lube, and for a CR103 type switch, I'd blow it off with compressed air.

The A3550 module is shown in the fourth picture in the first set of pictures.  It's the black module in the lower right next to the standoff.  It's on the bottom board.  (It's not on the chassis.  The Schematic is incorrect in this regard.)

All the dials get their odd steps by placing the first resistance in parallel with the second.  The rest are used in series.  One advantage (but not the only) is that this allows the use of six same value resistors for a zero to ten dial.

[ollopa]

Apparently the switch contacts have a special low resistance coating that can easily be wiped off by using the incorrect cleaner or lubricant or by not using any lubricant.


http://www.krohn-hite.com/htm/technotes/technical_note.htm#Technical%20Note%20#012


Switch Maintenance for Models: 330, 1030, 4032, 4600, 4601, CR series, E100RC, MV series.

    The decade and range switches of the Models referred to above are lubricated at the factory. It is recommended that these switches DO NOT receive any service during the first year of operation.  If you feel there is a problem, consult the factory.

    Note:
    Over-zealous, arbitrary, or unnecessary cleaning may damage the switch contacts, which should be maintained below 10 milliohms.

    Cleaning:
    Do not arbitrarily clean the switches. In many instances, lubrication may be all that is required.

    Relubricate After Cleaning!
    Lubricating - DO NOT USE OIL!
    The use of a cleaner without lubricating could shorten the life of the switches to about two months.

    Contamination From Silicone Based Lubricants:
    Silicone based cleaners/lubricants should not be used where electrical contacts and other electrical components are used. Silicone will react with plastics and atmospheric contamination to form insulating films and silicone carbide compounds. Over time, silicone will react with plastics, softening them, thereby breaking down the integrity of the component (switch, relay, etc.). Silicone-based lubricants may also have been used as a mold release agent or as a general cleaner for housings. Since silicone can migrate great distances, it is recommended to clean the silicone off the surfaces. DeoxIT and PreservIT will displace the silicone.

    Do Not Use Pencil Erasers:
    Do not use an eraser - any type of eraser - to clean contacts. Erasers are highly abrasive and will remove the precious metal plating. Further, the glue in erasers leave behind a film that is extremely difficult to remove which can later cause intermittent operation. Rubbing an eraser back and forth across the contacts can be a potential static generator.

    General Information & Precautions
    When using any aerosol, the unit should be de-energized (turned off) and used in well ventilated areas.

    Switch Contacts cleaner. DeoxIT is a fast-acting, deoxidizing solution that cleans, preserves, lubricates and improves conductivity on metal connectors and contacts.

    Switch Contacts lubrication. PreservIT seals, lubricates and preserves metal surfaces for protection from oxidation and contamination. For use on clean/new surfaces or those pre-cleaned with DeoxIT. PreservIT contains no cleaners or de-oxidizers. It provides long-lasting protection for newly manufactured components or those cleaned by ultrasonics, DeoxIT or other procedures. PreservIT is recommended as a final treatment for surfaces that are in constant motion and/or subject to higher degrees of atmospheric contamination.

    Spray Products Directions

    DeoxIT Cleaner:
    Ideal for general purpose applications. Contains petroleum naphtha as the carrier solvent. It is flammable but non-aggressive to almost all materials. Apply a short burst to metal surface and operate device to assist breaking up of oxide layers. For severely oxidized surfaces, wait a few minutes before operating. Then use lint-free applicators on accessible surfaces and wipe until surface appears clean. In inaccessible areas flush away oxides with DeoxIT D5. As a final step, spray a short burst of DeoxIT for protection. Includes precise, three-way adjustable valve for controlled dispensing with minimal waste and over-spray.

    PreservIT P5 Lubricant:
    Ideal for general purpose applications. Contains petroleum naphtha as the carrier solvent. It is flammable but non-aggressive to almost all materials. After cleaning metal surface, apply a short burst of PreservIT. If accessible, wipe with a lint- free applicator. If discoloration appears, the metal surface is not clean - use DeoxIT first. As a final step, spray a short burst of PreservIT for protection. PreservIT P5 includes precise, three-way adjustable valve for controlled dispensing with minimal waste and over-spray.

[saturation]

US users should use the right Deoxit not just on the the EDC, but for any device requiring contact cleaning, then you can't go wrong.  You only need needle size droplets per application.  Its history and details are on forum archives, or sift facts from marketing hype from the caig website:

http://www.caig.com/

There is an equivalent version not made by Caig for EU users but other nations, you have access to both, choose what is cost effective.