fluke 73 series III slow to gt to reading - Page 1
Forum section: electronics / repair

author: ddwilson
author_rank: Contributor
timestamp: March 18, 2018, 03:09:29 am
content: This meter I just was given the varistors and Cap C9 were blown, replaced them. Everything now works and matches what my calibrator is set for.Problem is it takes about 20 seconds for it to slowly get to the reading. Any suggestions?ThanksDoug

author: retiredcaps
author_rank: Super Contributor
timestamp: March 18, 2018, 03:21:31 am
content: Quote from: ddwilson on March 18, 2018, 03:09:29 amWhat reading are you trying to get? DCV, ohms?Please give an example of how it gets to the reading. For example, when measuring 10.0V DC reference, Fluke 73 starts at 10.50, 10.45, 10.40, 10.35, 10.30, 10.25, 10.20, 10.15, 10.10, 10.05 and finally 10.00. At each reading, it pauses 2 seconds for a total of 20 seconds.

author: ddwilson
author_rank: Contributor
timestamp: March 18, 2018, 05:12:07 am
content: Resistance and diode, both start out at OL and counts its way down through M Ohms, K ohms, ohms and tenths, thousandths. Volts and mA will both start at zero and count their way up. Each step is barely long enough to see it on the display so maybe .5 sec per step. Each step usually is in 0.1 to 0.3 increments until it gets to where it is reading and holds constant.

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 18, 2018, 11:49:37 pm
content: Interesting that it slowly counts up on Voltage and down on Ohms. I don't really know what's wrong with your meter but I'll throw out some suggestions for your consideration.Start with a good cleaning. Take off the LCD and dunk the board in IPA. Use a brush to scrub the board. Pay particular attention to the areas in-between the leads of the analog processor chip U1. Allow to dry thoroughly, a fan and/or gentle heat is good. This procedure very often fixes or at least improves weirdness in the front end. It only takes miniscule leakage currents to cause symptoms.If you haven't already, check the PTC thermistor RT1 and the big fail-safe resistor R1 for correct values. The thermistor should be around 1.1K. In voltage mode the input goes IN through these series components. In Ohms/Diode/Cont modes, the test current comes OUT through these components. I don't have a schematic for this particular model so I'm not sure what R1 is on yours, but it is probably either a 3.5K or 2.0K wirewound, or maybe a 1K film.Check to see if the ADC input can actually respond at normal speed if driven directly. Find pin 2 of the voltage divider resistor network Z1. (Pin 1 is on the lower end and has a square pad.) Set the unit for DCV. Apply200mVbetween the COM jack and Z1 pin 2. (Careful, do not overload this input.) The meter should respond by quickly displaying "2.000".

author: ddwilson
author_rank: Contributor
timestamp: April 01, 2018, 07:38:13 pm
content: Cleaned and scrubbed the board a couple of times, voltage and current work the way they should and are dead on with my calibrated tester. Resistanceis a little better but still slowly steps to where it should be reading , usually takes about 15-20 sec to get to the value.Thanks for the suggestion of cleaning with ISP

author: coromonadalix
author_rank: Super Contributor
timestamp: April 01, 2018, 11:10:03 pm
content: please dont start multiple threads about the same unit

author: ddwilson
author_rank: Contributor
timestamp: April 02, 2018, 01:17:06 am
content: Sorry but I am working on two meters with different problems.

author: ddwilson
author_rank: Contributor
timestamp: April 10, 2018, 03:33:52 am
content: update found that someone had replaced the surge protector ds which is part number 655134 which is now obsolete. tried one from a dead meter i had but it is not good. the resistance and voltage measurements now work but until i find a substitute for the surge protector the current reading does not work. Any suggestions what to try or where to find the part?

author: retiredcaps
author_rank: Super Contributor
timestamp: April 10, 2018, 04:00:48 am
content: Quote from: ddwilson on April 10, 2018, 03:33:52 amCan you post a picture of this component from the Fluke 73 III?Seehttps://www.eevblog.com/forum/repair/fluke-77-repair-teardown/

author: ddwilson
author_rank: Contributor
timestamp: April 12, 2018, 11:19:42 am
content: The yellow component with the cut in it is the spark gap that I am looking for. May try cleaning the one I pulled out of my parts meter and see if it will work. Do not seethem online anywhere at the moment.

author: ddwilson
author_rank: Contributor
timestamp: April 16, 2018, 02:29:44 am
content: Cleaned the spark gap that I removed from a meter with a bad processor and installed it. The meter is working perfect now and according to my calibrated multi-meter testeris very accurate.Doug