TEK DMM252 Multimeter wrong voltage and current measurement - Page 1
Forum section: electronics / repair

author: Pauldg1
author_rank: Newbie
timestamp: April 13, 2020, 11:10:27 am
content: Hello,I bought a TEK DMM252 but it doesn't work well.- Resistance can be measured like 10R 10K 1M, works fine.- Voltage DC: Between 3Vdc and 30Vdc the meter indicates around 200mV.- Voltage AC: At 230VAC the meter indicates 0,787V- mA range DC: At 400mA the meter indicates 32mA- A range DC: At 1A the meter indicates 0,07AWhat could be wrong.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 13, 2020, 02:47:59 pm
content: HIBlown input fuses, over current, overvoltage, high voltage spark .......... an human error, damaged input parts like voltages divider, switching ic's etc ...Share photos of your inside unit ..There a thread here, it may help youhttps://www.eevblog.com/forum/testgear/tektronix-dmm-252/

author: Pauldg1
author_rank: Newbie
timestamp: April 13, 2020, 06:43:11 pm
content: I have already checked the 3 power resistors R35, R36, R37 and all measures 470R.Also checked spark gaps Sg1, Sg2, Sg3 and all high impedance.Both two fuses are ok.

author: retiredcaps
author_rank: Super Contributor
timestamp: April 14, 2020, 12:35:29 am
content: Quote from: Pauldg1 on April 13, 2020, 06:43:11 pmWhat is "high impedance"? Is it 10M? Is it 0L?What reading do you get for the two PTCs? They should be around 500 to 1500 ohms?

author: retiredcaps
author_rank: Super Contributor
timestamp: April 14, 2020, 12:37:54 am
content: Quote from: Pauldg1 on April 13, 2020, 11:10:27 amDid you buy it "as is" or is it supposed to be in working condition?

author: coromonadalix
author_rank: Super Contributor
timestamp: April 14, 2020, 04:43:58 am
content: Thats an huge difference ...as istested or not testedtested with best of my knowledge ....Sometimes thats why they sell it, made a mistake ... etc ..Hope you repair it.

author: Pauldg1
author_rank: Newbie
timestamp: April 14, 2020, 07:37:41 am
content: Hello, find below the measurement results:SG1: 17,4Mohm or 18,5Mohm depending +/- or -/+ measurement (in circuit).SG2: 17,5Mohm or 18,6Mohm depending +/- or -/+ measurement (in circuit).SG3: 17,3Mohm or 18,4Mohm depending +/- or -/+ measurement (in circuit). SG3 itself measure O.L. when soldered out.PTC1: 1,62 Kohm (in circuit).PTC2: 1,51 Kohm (in circuit).By the way, it was not so convenient from buyer and seller:- The seller sold it as "it works" and she sold it for a deceased family member. She could have told better "working unknown".- I should have asked more in detail what works and what was tested.No problem, learn process for seller and buyerAnd hopefully it can be fixed.

author: retiredcaps
author_rank: Super Contributor
timestamp: April 14, 2020, 06:38:27 pm
content: Quote from: Pauldg1 on April 14, 2020, 07:37:41 amI would remove SG1 and SG2 and verify they read 0L out of circuit.

author: Pauldg1
author_rank: Newbie
timestamp: April 15, 2020, 02:18:47 pm
content: SG1, SG2, SG3 read all 0.L out of circuit.

author: retiredcaps
author_rank: Super Contributor
timestamp: April 15, 2020, 07:22:29 pm
content: All your input protection seems fine. These are the ones that would affect your voltage readings, but not the incorrect amperage readings.Right now, I'm out of ideas.

author: giosif
author_rank: Frequent Contributor
timestamp: April 15, 2020, 11:13:06 pm
content: Maybecorrupt(this is analog calibration, so no corruption possible here) or wrong/incomplete calibration?How about those VRx trim pots?Any signs of corrosion or damage on them?

author: Pauldg1
author_rank: Newbie
timestamp: April 16, 2020, 08:02:56 am
content: The VRx trims are as new. Everything looks very nice, no dust, no corrosion, no rework (before I measure the GSx’s.)It seems not a calibration issue because it is very far away from what is expected.Also the relationship between actual values and measured values are non linear.Are there schematics available of the Tek Dmm252 or Appa 105 or Appa 105R equivalent?

author: coromonadalix
author_rank: Super Contributor
timestamp: April 16, 2020, 12:27:21 pm
content: Jrc nju9210 meter chipset

author: Pauldg1
author_rank: Newbie
timestamp: April 17, 2020, 08:04:58 am
content: Thanks for the datasheet of the chip which is used in the multimeter.The datasheet describes circuit examples, but the implementation inthe Tek multimeter is different and more extensive.Is there a schematic available of Tek or Appa?I found great info and schematics of fluke multimeters, but not of Tek and Appa.Thanks in advance to share info.

author: barijan
author_rank: Contributor
timestamp: June 26, 2020, 05:20:54 pm
content: Check the four studs attaching the two boards together, and if its screws are clean and well tight on both boards.These are not only structural, but provides important electrical contact betweeen the boards as well.Also, check the 2-board connector and pins for bad contact or looseneess.All these itens are crucial for the correct working and are prone to oxidize or get loose with age.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: June 26, 2020, 06:05:55 pm
content: Is it just me or do some circular tracks that go to the selector switch look somehow corroded? Maybe someone spilled something on the thing a long time ago.