Fluke 8600A Digital Multimeter Display Problem - UK Vintage Radio Repair and Restoration Discussion Forum

plati1945 · 10th Oct 2013, 8:44 pm

Hi, I've recently acquire an 8600A -01. I plugged it in to try it and it just came up with dots on the display. Upon opening the case I found the batteries leaking. I replaced them with 4 new Nimh batteries but this did not improve the operation of the meter. I then starting checking and found that the +/-15V rails were not working. The 5V rail was fine. I have removed the power supply board and checked all the transistors and diodes and they all seem to be fine. Can you give me any pointers as to where I should look next? I have downloaded the manual from Fluke. The one thing that I have noticed is that the resistor which is across the 2.8uF capacitor is 100k not 1M as stated on the circuit diagram. It does look original though with no signs of additional solder etc. to suggest it has been changed. Any help will be very welcome, thanks in advance.

David G4EBT · 10th Oct 2013, 11:26 pm

I have no personal experience with Fluke meters but over the years I've seen many references to display problems and suggestions as to how to cure them. This might be of help:

http://www.eham.net/reviews/detail/3057

Other forum members with direct experience might be able to advise better on this.

Best of luck!

David

PaulR · 11th Oct 2013, 9:15 am

This thread may be of some use

https://www.vintage-radio.net/forum/...ad.php?t=84157

PETERg0rsq · 11th Oct 2013, 9:25 am

Did you pull the resistor from the board before checking its value?
It could be the capacitor is leaking badly!
If I recall correctly it is a tantalum capacitor (I am away from home on holiday in France at moment, so cant check) and though never had a problem with one in a Fluke meter, they can prove troublesom in other devices.

As this is an inverter type PSU, the fact one side is OK eliminates the oscillator side of the PSU.

Look at the circuit and find a point after the regulator that can be lifted and check if the fault is with the PSU, or a fault elswhere in the circuit dragging the voltage down.

Batteries should be NiCad, not sure how the charging circuit will behave when confronted with NiMh. Will not cause the problems you have, but may damage the NiMh batteries. I think it uses a bulb as a current limiting device (maybe getting mixed up here with Fluke 8000 series, so check first!!!!), so not ideal for NiMh!!!

Peter

plati1945 · 11th Oct 2013, 10:00 am

The capacitor is not leaking, the resistor is colour coded to 100k and measures 100k. Should I change it? I have replaced NiCads with MiMh in several different pieces of equipment in the past and have never had any trouble, so I'm hoping this will be the same again. I think the problem is with the inverter circuit but I'm not sure how to check it. All the diodes, transistors and resistors seem to be OK. The transformer has no sign of any damage. It has continuity through the windings and isolation between primary and secondary.

Leon Crampin · 11th Oct 2013, 3:56 pm

The 8600A charging circuit is quite different from the 8000A and there is no lamp to act as ballast and as a visual charging indicator. The resistor across the "ballast" capacitor in the mains primary circuit is merely a discharge to prevent the mains plug pins being live on disconnection. 100k Ohms will do fine.

If you use cells other than NiCd, you must ensure that the battery voltage (4 cells) is within TTL tolerance limits. 4 x NiCd cells give 5V +/- 0.25 which is correct.

I've given my 8600A manual to another Forum member, so I can't check finer details. These meters are well worth restoring.

Leon.

plati1945 · 11th Oct 2013, 4:23 pm

NiMh batteries are well within TTL tolerance, so no problem there. If you want another copy of the manual I can send you one or you can download it yourself from Fluke. If I connect a 5V DC supply to the power supply board will that be all that is needed to test it and try and find out why the inverter is not working, It looks OK to do this to me but I don't want to damage anything that may be irreplaceable due to the age of the meter.

John_BS · 11th Oct 2013, 4:52 pm

If I've got the correct info, this power supply is mains in which charges a 5V battery, then a simple invertor to generate +/- higher voltages, followed by a linear regulator (U201) to give +/- 15V?
In which case, check for more than +/-15V on the output of the bridge rectifier CR203 to 206. If there's no volts there, it's the invertor (or an overload fault on the output). If there are volts, it could be U201 caput.

John

plati1945 · 6th Nov 2013, 5:12 pm

I have removed the power supply board and fed it from a 5V supply. The -15V regulator was faulty so I replaced it. The board then supplied steady + 15 and -15 voltages. Upon replacing it in the meter however, the voltages were pulled down by the rest of the circuitry. After I first replaced the P/S board, I did get some flashing of the 7 segment displays together with some clicking from the relay as it switched in and out. This only lasted a few seconds and then choke L2 started to smoke! A quick switch off was needed! Any suggestion as to likely cause would be very welcome!

10th Oct 2013, 8:44 pm	#1
plati1945 Retired Dormant Member Join Date: Oct 2013 Location: Lowestoft, Suffolk, UK. Posts: 4	Fluke 8600A Digital Multimeter Display Problem Hi, I've recently acquire an 8600A -01. I plugged it in to try it and it just came up with dots on the display. Upon opening the case I found the batteries leaking. I replaced them with 4 new Nimh batteries but this did not improve the operation of the meter. I then starting checking and found that the +/-15V rails were not working. The 5V rail was fine. I have removed the power supply board and checked all the transistors and diodes and they all seem to be fine. Can you give me any pointers as to where I should look next? I have downloaded the manual from Fluke. The one thing that I have noticed is that the resistor which is across the 2.8uF capacitor is 100k not 1M as stated on the circuit diagram. It does look original though with no signs of additional solder etc. to suggest it has been changed. Any help will be very welcome, thanks in advance. Last edited by AC/HL; 10th Oct 2013 at 8:53 pm. Reason: Moved to new thread

10th Oct 2013, 11:26 pm	#2
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,761	Re: Fluke 8600A Digital Multimeter Display Problem I have no personal experience with Fluke meters but over the years I've seen many references to display problems and suggestions as to how to cure them. This might be of help: http://www.eham.net/reviews/detail/3057 Other forum members with direct experience might be able to advise better on this. Best of luck! David

11th Oct 2013, 9:15 am	#3
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,233	Re: Fluke 8600A Digital Multimeter Display Problem This thread may be of some use https://www.vintage-radio.net/forum/...ad.php?t=84157

11th Oct 2013, 9:25 am	#4
PETERg0rsq Heptode Join Date: Jun 2009 Location: St Helens, Lancashire, UK. Posts: 641	Re: Fluke 8600A Digital Multimeter Display Problem Did you pull the resistor from the board before checking its value? It could be the capacitor is leaking badly! If I recall correctly it is a tantalum capacitor (I am away from home on holiday in France at moment, so cant check) and though never had a problem with one in a Fluke meter, they can prove troublesom in other devices. As this is an inverter type PSU, the fact one side is OK eliminates the oscillator side of the PSU. Look at the circuit and find a point after the regulator that can be lifted and check if the fault is with the PSU, or a fault elswhere in the circuit dragging the voltage down. Batteries should be NiCad, not sure how the charging circuit will behave when confronted with NiMh. Will not cause the problems you have, but may damage the NiMh batteries. I think it uses a bulb as a current limiting device (maybe getting mixed up here with Fluke 8000 series, so check first!!!!), so not ideal for NiMh!!! Peter __________________ SPECIALIST.....Knows everything about nothing EXPERT..........Knows nothing about everything Last edited by PETERg0rsq; 11th Oct 2013 at 9:28 am. Reason: maybe getting mixed up with Fluke 8000 series!!!

11th Oct 2013, 10:00 am	#5
plati1945 Retired Dormant Member Join Date: Oct 2013 Location: Lowestoft, Suffolk, UK. Posts: 4	Re: Fluke 8600A Digital Multimeter Display Problem The capacitor is not leaking, the resistor is colour coded to 100k and measures 100k. Should I change it? I have replaced NiCads with MiMh in several different pieces of equipment in the past and have never had any trouble, so I'm hoping this will be the same again. I think the problem is with the inverter circuit but I'm not sure how to check it. All the diodes, transistors and resistors seem to be OK. The transformer has no sign of any damage. It has continuity through the windings and isolation between primary and secondary.

11th Oct 2013, 3:56 pm	#6
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,870	Re: Fluke 8600A Digital Multimeter Display Problem The 8600A charging circuit is quite different from the 8000A and there is no lamp to act as ballast and as a visual charging indicator. The resistor across the "ballast" capacitor in the mains primary circuit is merely a discharge to prevent the mains plug pins being live on disconnection. 100k Ohms will do fine. If you use cells other than NiCd, you must ensure that the battery voltage (4 cells) is within TTL tolerance limits. 4 x NiCd cells give 5V +/- 0.25 which is correct. I've given my 8600A manual to another Forum member, so I can't check finer details. These meters are well worth restoring. Leon.

11th Oct 2013, 4:23 pm	#7
plati1945 Retired Dormant Member Join Date: Oct 2013 Location: Lowestoft, Suffolk, UK. Posts: 4	Re: Fluke 8600A Digital Multimeter Display Problem NiMh batteries are well within TTL tolerance, so no problem there. If you want another copy of the manual I can send you one or you can download it yourself from Fluke. If I connect a 5V DC supply to the power supply board will that be all that is needed to test it and try and find out why the inverter is not working, It looks OK to do this to me but I don't want to damage anything that may be irreplaceable due to the age of the meter.

11th Oct 2013, 4:52 pm	#8
John_BS Octode Join Date: Dec 2008 Location: Wincanton, Somerset, UK. Posts: 1,780	Re: Fluke 8600A Digital Multimeter Display Problem If I've got the correct info, this power supply is mains in which charges a 5V battery, then a simple invertor to generate +/- higher voltages, followed by a linear regulator (U201) to give +/- 15V? In which case, check for more than +/-15V on the output of the bridge rectifier CR203 to 206. If there's no volts there, it's the invertor (or an overload fault on the output). If there are volts, it could be U201 caput. John

6th Nov 2013, 5:12 pm	#9
plati1945 Retired Dormant Member Join Date: Oct 2013 Location: Lowestoft, Suffolk, UK. Posts: 4	Re: Fluke 8600A Digital Multimeter Display Problem I have removed the power supply board and fed it from a 5V supply. The -15V regulator was faulty so I replaced it. The board then supplied steady + 15 and -15 voltages. Upon replacing it in the meter however, the voltages were pulled down by the rest of the circuitry. After I first replaced the P/S board, I did get some flashing of the 7 segment displays together with some clicking from the relay as it switched in and out. This only lasted a few seconds and then choke L2 started to smoke! A quick switch off was needed! Any suggestion as to likely cause would be very welcome!