Fluke 335D

[psykok]

Hi,

I recently scored a Fluke 335D and picked it up last week.


At the first look, the unit looks in very good condition ... near mint.
I was also surprised  to get the original user/service manual.

[psykok]

Sorry I broke the rule  : I tuned  it on first.

The first test was not bad at all for unit calibrated back in the 93.


After a bit of adjustment it became almost perfect

[coromonadalix]

 

Dont want to brag, but the 34401a was calibrated  recently ?

[psykok]

The 34401a is my most recently calibrated device, calibration was done for 5years ago from what I know.

Anyway  it was more kind of exercise  for me to know if I could tweak the Fluke.
Of course  everything should be redone by following the exact procedure described  in the manual  and with freshly calibrated  devices.

I opened the device to check the inside and to have a look more specifically  to the caps.
The inside looks like the outside: very clean


The first board I pooled  out :


I'm pretty  sure that this resistor as not working correctly

[Dr. Frank]

Your 335D looks like heavily used, but otherwise in mint condition, even the extension PCB is in place. 

Always a pleasure to see the guts of these instruments.

Thanks for sharing,

Frank

[psykok]

Yesterday I check all the electrolytic caps  and the usual small Sprague in metal packages are gone.

[psykok]

So I changed all the electrolytic caps and the burned resistor.

And surprise now  it doesn't work anymore.
I still get something at the output but completely out of range and specially for the 10v range which gives me something about 17-19v with the decade set to 10v.

The small relay on the board A8 (protection ?) is constantly switching.

I cannot believe that changing a couple of cabs did that.

[Dr. Frank]

reseat all PCBs and check for bent pins.
If you have replaced all caps, including the big ones with > 2 pins on the motherboard, pay attention that the metal base pins (3 or 4EA) may have been used as bridges, which now are lacking, if you replaced them by 2 pin types only.

Frank

[psykok]

I have replaced all the caps expected the big ones but I will check all the pcb connection ... Good idea

[psykok]

Finally after putting out and in 2 time carefully everything is working again.

[psykok]

was playing yesterday night with the 335.
After around 2h of warmup  the instrument looks quite stable and I was able to tune the 0 reading for all the ranges (it was not possible before, I had always something  like 50 to 100uv residues)

10v range is definitely more accurate now. Apparently  the rotary  decade needs a little adjustment, apart from that it looks very good.
Now I need to found someone  with a recently calibrated multimeter to check if everything is ok.

I also found a reference to this chopper upgrade: http://friedrich-messtechnik.de/index.php/2012-11-20-02-38-33/chopper-fluke-335-332
Has someone  already tested this circuit ? does it bring really  noticeable  improvement ?

[Dr. Frank]

was playing yesterday night with the 335.
After around 2h of warmup  the instrument looks quite stable and I was able to tune the 0 reading for all the ranges (it was not possible before, I had always something  like 50 to 100uv residues)

10v range is definitely more accurate now. Apparently  the rotary  decade needs a little adjustment, apart from that it looks very good.
Now I need to found someone  with a recently calibrated multimeter to check if everything is ok.

I also found a reference to this chopper upgrade: http://friedrich-messtechnik.de/index.php/2012-11-20-02-38-33/chopper-fluke-335-332
Has someone  already tested this circuit ? does it bring really  noticeable  improvement ?

Your instrument looks just fine. Judging from the pictures you have the more modern 'reference amplifier' and the MOSFET chopper type PCBs inside.

This chopper upgrade was intended to replace the old mechanical chopper in first place.
Your MOSFET chopper is really good enough, so I strongly recommend not to replace it.

You need to check/adjust the 3 ranges, but also the linearity, which can be made better than 0.5 ppm, therefore a 3458A would be great for that job.

Does its differential amplifier work properly, and w/o excessive noise in its 10µV range?
There is an interesting thread about the Fluke 845AR/AB, how to exchange the neon bulbs with working modern ones from Barthelme.
https://www.eevblog.com/forum/metrology/teardown-fluke-845aabar-tweaks-and-mods-(and-repairs)/msg2595273/#msg2595273

I would always try to maintain the original design in first instance, whenever you have the chance to get spare parts.

Frank
 

[psykok]

Hi,

Thanks for the feedback.

Unfortunately I do not have access to a 3458A or similar.
I have to look for a voltnut event somewhere to get my device checked and maybe adjusted.

I played yesterday again with the 335d and I was able to get the same results as the day before. The only annoying thing is that I need at least 2h for the device to get stable.



Alex