- Manual references
- Initial inspection and basic disassembly
- Transformer hum
- Update from reader on newer DMM6500
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.
|±10mV, ±100mV, ±1V, ±10V, ±100V
|Best 1 Year Specification: ±25 ppm + 2
|±100mV, ±1V, ±10V
|Best 1 Year Specification: ±25 ppm + 2
|DC Noise spec
|6 nV & 25s NPLC5, FILT, 10mV, 2.5µV & 1s NPLC1, FILT, 10V
|1 Ω – 100 MΩ
|10, 100 µA, 1,10,100 mA, 1,3,10 A
|100 µA, 1,10,100 mA, 1,3,10 A
|1,10,100 nF, 1,10,100 µF
|Up to 1 MSPS for V/I
|10V clamp (10,100 µA, 1,10 mA)
|-200°C to +1820°C, Type J,K,N,T,E,R,S,B
|Accuracy: ±0.2 °C, 0.001°C resolution
|±0.8ppm of reading + 0.5ppm of range
|>10 GΩ for 10mV-10V ranges
Table 1: Model DMM6500 measurement functions
Let’s also look on other market competitors:
|Half-rack 2U 19” instrument
Table 1: Comparison summary to other popular meters on market
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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
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.
Probes are typical for benchtop meter.
“We are in like Flynn”. Large mainboard with many slots and sections contain all the meter’s circuitry.
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.
Not much components on this side, mostly passives with few chips.
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.
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.
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.
Mainboard PCB is designed with six layer metal interconnect. This is clear, thanks to edge PCBA layer marker.
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.
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.
Small 40 × 40 mm DC fan located next to transformer. Hopefully this fan does not get too noisy after few years of use.
Transformer shares same assembly block with inductor. Inductor is used for PFC correction for the mains input.
Rear terminal jack with IDC cable? That’s not really what we expected to see in 6½-digit meter with 10 µA current range.
Early DMM6500 units had quite pronounced transformer 50/60Hz audible hum. This was reported as solved for later production units.
One of our readers, Vit S. suggested a mitigation for affected units humming. His unit came set to 220V (for EU geo). EU spec is 230V, ±10%. It was suggested that transformer might be saturated from bit overvoltage, as we generally have overvoltaged mains a bit. He measured mains and it read at 245 VAC, so switching input on DMM6500 to 240V reduced audible humming.
Update from a reader on his DMM6500
Robert S. sent us some more photos of Keithley DMM6500 inner workings. Thank you for contribution.
This DMM was purchased new in March 2021 and have few differences inside:
There is a mod wire soldered from U32.3 to K7.2-3. Also Keithley put a silkscreen labels on board to specify when K5 will be populated or not, depends on option model.
This DMM was assembled around 46th week of 2020. LM399A reference with special partnumber for Keithley was cooked around 10th week of 2020.
Sadly we can learn that transformer still makes the same horrible hum, no enhancements only the label has been styled. Transformer hum issues were supposed to be fixed since original DMM6500 release to market.
To be updated.
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