Fluke 1653 repair - RCD test

[miele]

Here, I share a repair report, hoping the it might help in case of similar issures.
During my initial research, I found several reports of Fluke 165x having unreliable RCD measurement, this might be the same issue.

I recently bought a defective Fluke 1653 for a good price, mainly to check my own house installation after renovation.
The description mentioned "All tests working but calibration not possible". I was also provided an email from Fluke, stating that RCD measurement needed repair in order to proceed with the calibration.

When I got the instrument, I tested it for a while, trying out all settings and ranges. Indeed everything was working fine, except for the RCD tests.
I realized, that using the low current range (e.g. 30mA), I was not able to trip my 30mA RCD, but with higher current ranges (e.g. 300mA) the RCD tripped. However the measured tripping current was way off (90mA)

Next step was to measure the AC current while RCD tripping using the different current ranges, to find out what really happened.
Catching the right moment with my HP34401 turned out not be be easy, as the device sets a fast current ramp (especially if your multimeter is powered by the RCD you are tripping... )

Still, I was able to observe some kind of linearly increasing AC current ... but serveral orders of magniture to low.
At least, this explains, why the RCD was not tripping.
For the higher ranges, the AC currents started very low as well, then jumped suddenly. At this point the RCD tripped.
Smells like range switching, with one range broken ....

Serching for "fluke 165x service information", you will find an extensive service manual, which helped me a lot, as it provided schematics and explanations.
As I don't think, it is legal, I don't provide a link here.

This instrument provides two differnt RCD measurements: it can measure the trip current and the trip time.
For that purpose, it has an active load consisting of 4 MOSFET, operated in linear region.
The load is controlled by a µC and the current is measured by a shunt.

Indeed, there are two measurement ranges using a 1\$\Omega\$ shunt (R36) and a 10\$\Omega\$ resistor (R62).
The 1 Ohm shunt can be switched off by MOSFET Q19 for low current ranges.

The rest was easy: I took the meter appart and measured R62 - and yes, it was serveral kOhm. 
As I did neither observe cracks in the resistor nor burn marks, I can't say why it failed.
Could have been overload or a small fracture due to thermomechanical stress or shock.

Replaced, reassambled and everything worked perfectly. 

One additional hint: the ribbon cable connectors are rather fragile. Care has to be taken to connect them correctly.
I had the issue, the after reassembly, the meter showed Err 1 without leads. The L connector was dead for current measurements.
It turned out, the the ribbon was a little bend inside the connector resulting in the L-Line relay not to switch.

BTW: I would be very much interested in the detailed description of the communication protocol, including the calibration commands. In the service information it is referred to as "165X Serial Interface Specification document"

[EHT]

The rest was easy: I took the meter appart and measured R62 - and yes, it was serveral kOhm.

Excellent tip. I seem to have the same problem; R62 is 15 Ohms. I'm going to replace it with one of these which is 10 Ohm 2.5W 0.1% rather than 1W 1%. There is no visible heat damage. I think this part is just a bit underrated.

A few of the solder joints on the larger components are a bit poorly done. Couple of dry joints on the MOVs.

[miele]

Glad, that I could help 

There was no visible damage on mine as well.
It should not see much more than 100mA before the 1 Ohm shunt takes over, but if there are SW bugs, who knows, what happens.
There are also reliability issues with these big resistors ...

Anyway, the one you chose looks much more appropriate. Probably too expensive for Fluke.

My THT solder joints do not look very nice as well. I think, they use handsoldering in production. But no problems so far.

[broketest]

Hello,
Found this post. I have the RCD measurement tripping on ground. I tested all resistor around R36 and all are good. All other measurements are ok. Any idea?
Many thanks

[EHT]

Not sure quite what you mean, but there is the rest of the circuit around Q15-18. The svc manual describes the design, presume you have that.

[miele]

Hi Broketest, I can try to help but I need more details.
-Which Fluke unit?
-How are you measururing
 - what do you mean by "tripping on ground" ?
 - Any difference depending on the selected range?
 - How long does it take for the RCD to trip after you start the measurement?
Regards
Ralph.

[broketest]

Hello,
After a research, i've replaced Q15 to Q18, and now have a "Err1". Tried to retrofit but still "Err1". A Fluke classic... . I hear the relay cliking when i put it on.
Thank you for any info

[miele]

Hi broketest,
sorry to hear, that you get Err1.
To my understanding, this Error signals, that the main µC (U101) can't communicate with the secondary µC (U301)
As there are many units on ebay with this Error, I think, this µC easily looses its flash memory or gets damaged.
Would be nice to have an image of this flash, but I couldn't find it nowhere.

You should also check, if the ribbon cable are properly connected. A loose ribbon cable can also interrupt the communication between the two µC.
I had this already.

Regards,
Ralph.

[Navid]

Hi Guys
i buy fluke 1653b multi function tester.every thing is working good except RCD test.in RCD mode the tester doesn't show RCD time.i could change the RCD current range and its trip the RCD but time doesn't show any thing just on LCD showing 000ms. when want to test RCD , i think tester suddenly trip the RCD with no delay as i push test button suddenly RCD is tripping.
please help me to solve this problem.
thanks

[DanEdwards]

I picked up a Fluke 1653 as well, it went in for calibration but failed the RCD 10mA trip current  1/2, A part of the test.

The test result was 9.42mA with an upper limit of 3.5mA. Other than that the test results are flawless.

Probed all around the RCD portion of the PCB but everything seemed fine. Can't pick out anything specific part of the schematic that could be suspect.

A 10mA RCD is something that I wouldn't normally test, but still it's something that would be nice to get fixed.