Keithley DMM6500 teardown and comparison

2019-07-1211:38:14 评论 2,288 views


Common industry-known 6½-digit DMM from Keithley, Model 2000 just got refreshed with new blingy fancy design, as Tektronix/Keithley DMM6500. However this is not just a simple facelift, but actually meter redesigned from scratch. Tektronix released this DMM6500 in April 2018. Let’s see what makes it tick.

Other brand competitors for this meter would be old Fluke 8846A and Keysight 3446x series.

Image 1: Keithley DMM6500 front interface with touchscreen TFT LCD.


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As usual, all photos are clickable for high-resolution version.

Unfortunately, as with nearly all modern instruments, there is no more schematics or theory of operation information available in public manuals for Model DMM6500. Even service manual or calibration manual is not available at the time of writing this review.

Initial inspection and basic disassembly

Image 2: Rear view on the unit

Rear side quite busy with connector and option ports. Communication option feature GPIB card. Smaller populated card in center is scanner option. Old scan cards like 2001-TCSCAN and 2000-SCAN are fully supported.
There is no hardware power switch for mains power, so meter is always have stand-by power present.

Image 3: Bundled probes, decent quality with shrouded banana ports

Probes are typical for benchtop meter.

Image 4: Removed cover, top view

“We are in like Flynn”. Large mainboard with many slots and sections contain all the meter’s circuitry.

Image 5: Mainboard removed, mains transformer, option scanner card cage and wiring

Transformer is rigidly fixed to the chassis frame, which on early units caused some unwanted buzzing noise. Later units, according to Keithley, already addressed this.

Image 6: Bottom side of the mainboard

Not much components on this side, mostly passives with few chips.

Image 7: Input section

Input DCI function is protected by large fuse in holder. Mechanical front/rear switch also visible on the corner, with rest of input protection parts.

Image 8: Rear side of the front panel assembly

Front panel PCBA busy with BGA chips, as big fancy LCD need lot of juice to process and refresh the images quickly. Two Freescale/NXP chips in center are MPC5125 32-bit microprocessors with e300c4 Power Architecture® core, display interface, 10/100 MAC, USB and all usual interfaces.

Image 9: Another angle

Not sure why need two processors. Perhaps once is handling display/front panel functionality only, while the second actually runs meter firmware/functions? Lattice LFE5U is ECP5 FPGA, featuring 24K LUT elements and about a megabit of onboard memory. It supports lot of high-speed interfaces, and may be the one responsible of driving LVDS LCD.

Image 10: Mainboard layer count

Mainboard PCB is designed with six layer metal interconnect. This is clear, thanks to edge PCBA layer marker.

Image 11: Selected LM399AH voltage reference with Keithley marking on top

Image 12: Angle from the rear

Laser-trimmed hermetic film resistor visible on the left side. That is high-voltage divider for DCV/ACV ranges. Very common in Fluke meters and calibrators.

Image 13-15: Isolated sections

Si8631 and few opto’s take care of the insulation between outguard and inguard sides. Typical design for benchtop DMM, as these meters need to have front-end floating.

Image 16: Board

Image 17: Board

Image 18-19: Board

Image 20-21: Board

Image 22-25: Board

Image 26-27: Board

Image 28-29: Board

Image 30-31: View on the little fan

Small 40 × 40 mm DC fan located next to transformer. Hopefully this fan does not get too noisy after few years of use.

Image 32: Transformer assembly frame

Image 33-34: Second device next to transformer

Transformer shares same assembly block with inductor. Inductor is used for PFC correction for the mains input.

Image 35-36: Board

Image 37-39: Board

Image 40-41: Rear terminal jack

Rear terminal jack with IDC cable? That’s not really what we expected to see in 6½-digit meter with 10 µA current range.

Image 42-43: Board

Image 44-45: RJ45 MagJack and interface ports

Image 46-47: Few last internal photos

Performance results

Image 48: DMM measuring 50 mΩ shunt in 4-wire mode

To be updated.


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