Fluke 335D - Page 1
Forum section: electronics / testgear

author: psykok
author_rank: Frequent Contributor
timestamp: August 16, 2020, 08:22:32 pm
content: 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.

author: psykok
author_rank: Frequent Contributor
timestamp: August 16, 2020, 08:27:22 pm
content: 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

author: coromonadalix
author_rank: Super Contributor
timestamp: August 17, 2020, 08:59:45 am
content: Dont want to brag, but the 34401a was calibrated recently ?

author: psykok
author_rank: Frequent Contributor
timestamp: August 17, 2020, 12:01:53 pm
content: 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 cleanThe first board I pooled out :I'm pretty sure that this resistor as not working correctly

author: Dr. Frank
author_rank: Super Contributor
timestamp: August 17, 2020, 12:22:53 pm
content: 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

author: psykok
author_rank: Frequent Contributor
timestamp: August 17, 2020, 12:25:58 pm
content: Yesterday I check all the electrolytic caps and the usual small Sprague in metal packages are gone.

author: psykok
author_rank: Frequent Contributor
timestamp: August 20, 2020, 06:15:47 pm
content: 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.

author: Dr. Frank
author_rank: Super Contributor
timestamp: August 20, 2020, 06:50:29 pm
content: 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

author: psykok
author_rank: Frequent Contributor
timestamp: August 20, 2020, 07:12:24 pm
content: I have replaced all the caps expected the big ones but I will check all the pcb connection ... Good idea

author: psykok
author_rank: Frequent Contributor
timestamp: August 20, 2020, 08:14:42 pm
content: Finally after putting out and in 2 time carefully everything is working again.

author: psykok
author_rank: Frequent Contributor
timestamp: August 21, 2020, 07:28:34 am
content: 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-335-332Has someone already tested this circuit ? does it bring really noticeable improvement ?

author: Dr. Frank
author_rank: Super Contributor
timestamp: August 21, 2020, 08:42:39 am
content: Quote from: psykok on August 21, 2020, 07:28:34 amYour 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/#msg2595273I would always try to maintain the original design in first instance, whenever you have the chance to get spare parts.Frank

author: psykok
author_rank: Frequent Contributor
timestamp: August 22, 2020, 11:31:29 am
content: 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