Fluke 341 DC Voltage calibrator - restoration - Page 1
Forum section: electronics / general

author: tekfan
author_rank: Frequent Contributor
timestamp: March 15, 2012, 12:33:59 am
content: Several weeks ago I got another beat up piece of test equipment. This time a Fluke 341 DC Voltage calibrator. This calibrator came from England. By the looks of the stickers I would say from the Solartron company that makes precision mulimeters.It was probably used a lot to about the mid 90's. It's actually made in 1972 so that makes it 40 years old. Despite the condition I think it has aged pretty well.Some specs:Output Voltage: 0 to 1111.110 volts dcVoltage Range:10V: 0 to 11.11100 (10 uv steps)100V: 0 to 111.1110 (100 uv steps)1000V: 0 to 1111.110 (1 mv steps)Resolution: 1 ppm of range (10 uv max)Accuracy of Output:10V Range: +/-0.01% of setting or +/-0.0003% of range100V Range +/-0.01% of setting or +/-0.0002% of range1000V Range +/-0.01% of setting or +/-0.0002% of rangeRipple and Noise:60 Hz Line - Less than 100 uv rms or 1 mv p-p400 Hz Line - Less than 100 uv rms or 2 mv p-pIt's pretty amazing what they could accomplish with just discrete components (well almost).I've seen many people on the forum try to build their own precision voltage source but you just can't beat one of these.And it's cheaper too.This is the condition in which it arrivedMissing knobs,feet and screws, bent chassis, lables all over, extremely dustyVery dusty. There were even a few cobwebs around the HV outputs on the transformer.Mains and HV fuse. Again, it doesn't look all that well with all the dust.Opening the covers reveals more and more interesting things.Gold plated wire wound trimpots, gold plated switches,and the infamous Fluke crumbling switch spacers

author: retiredcaps
author_rank: Super Contributor
timestamp: March 15, 2012, 05:10:42 am
content: I love following your restoration stories and pictures. It certainly a refreshing contrast to the current "I must have the latest ipad/iphone because it is cool" and throw away the "old generation" attitude that most people seem to have.I look forward to see your progress and the finished product.

author: saturation
author_rank: Super Contributor
timestamp: March 15, 2012, 01:06:56 pm
content: Ah yes! A wonderful calibrator.I'm in the market for one of these myself for the same reason I bolded, its cheaper to find and fix old metrology grade devices. Even after you build a DIY you'll still not have the well known performance capability of a working unit, if the repairs are done right.Looking forward to your progress.My only concern in obtaining one, is having to calibrate it once it works. In the USA, I have no choice but to pay a formal calibration rate of $100-250 to do it, it will cost >= to the 341!Quote from: tekfan on March 15, 2012, 12:33:59 am

author: robrenz
author_rank: Super Contributor
timestamp: March 15, 2012, 01:15:08 pm
content: Quote from: saturation on March 15, 2012, 01:06:56 pmSame situation with a IET microOhm meter I got off Ebay for $350.00 in Mint condition. $469.00 for full calibration by IET Ouch

author: muvideo
author_rank: Frequent Contributor
timestamp: March 15, 2012, 01:25:03 pm
content: Wonderful piece of equipment, thank oyu for the pics.Did you find online (ebay etc...) or locally?Fabio.

author: tekfan
author_rank: Frequent Contributor
timestamp: March 16, 2012, 01:02:17 am
content: More precision wirewound resistorsPrecision, ultra stable, low drift, bla bla bla voltage reference. It's not even heated like the newer LM199 and similar.Very unimpressive but it works. This provides 15 volts that is divided by the resistors.This has a standard voltage divider and not a Kelvin - Varley divider.Calibrator with boards and front panel removed for cleaning.Looks like some genious tried to clean the meter with paint thinnerFront panel. Just shows how dirty this thing really is.

author: tekfan
author_rank: Frequent Contributor
timestamp: March 28, 2012, 08:33:04 pm
content: With the boards cleaned I reassembled the thing and started looking for shorted componentsI found that transistor Q13 was shorted. It's a standard 2N3906. One more reason why I like old test equipment.If it's a small signal transistor it's probably a 2N3904, 2N3906 or 2n2222Zener diode CR48 was open. The original one was a 13 volt diode but I didn't have them so I paralleled two 6.2 volt ones.It's not a part of the reference supply so the exact value isn't important.That was all that was wrong with the calibrator. Once connected to a multimeter the output voltage could be set.It isn't always this stable. You can upset the last digits on the multimeter by just walking past it or wiggle the leads a bit.More pictures to come.

author: T4P
author_rank: Super Contributor
timestamp: March 29, 2012, 03:14:21 pm
content: Man , 3906 is a PNP device not a NPN like the 3904

author: tekfan
author_rank: Frequent Contributor
timestamp: March 29, 2012, 04:34:07 pm
content: Quote from: Dave.S on March 29, 2012, 03:14:21 pmYes I know a 2N3906 is a PNP device.I was just talking about the types of transistors that are often found in test equipment from this era.Of course you couldn't substitute a PNP with an NPN transistor.

author: muvideo
author_rank: Frequent Contributor
timestamp: March 29, 2012, 05:16:03 pm
content: Last photo is art, it's fascinating to imagine the knowledge and work needed to line up all that zeros.Fabio.

author: SeanB
author_rank: Super Contributor
timestamp: March 29, 2012, 06:16:04 pm
content: Looks like new, compared to how it looked at arrival. Nice to see it is so accurate even after 40 years of hard use.

author: wkb
author_rank: Super Contributor
timestamp: March 30, 2012, 06:13:40 am
content: Quote from: tekfan on March 28, 2012, 08:33:04 pmParalleled??

author: tekfan
author_rank: Frequent Contributor
timestamp: March 30, 2012, 10:38:13 am
content: Quote from: wkb on March 30, 2012, 06:13:40 amPut them in series.It was late when I was writing this.

author: Frangible
author_rank: Regular Contributor
timestamp: April 01, 2012, 12:26:43 am
content: Nice job on the meter cover - how did you return it to transparency?

author: SeanB
author_rank: Super Contributor
timestamp: April 01, 2012, 06:33:01 am
content: I would hazard a guess that acrylic polish was involved, along with a lot of elbow grease.

author: muvideo
author_rank: Frequent Contributor
timestamp: June 05, 2012, 05:08:05 pm
content: Quote from: Frangible on April 01, 2012, 12:26:43 amSorry to revive an old thread, but maybe this can be of interest.Tekfan, I repaired a 343 and I have the meter transparent plasticdamaged from what seem solder splashes.What did you use to restore the trasparency?Thank you,Fabio.

author: tekfan
author_rank: Frequent Contributor
timestamp: June 05, 2012, 05:40:05 pm
content: Quote from: muvideo on June 05, 2012, 05:08:05 pmFirst I used an old rag soaked in nitro thinner to try and get the meter face as flat as possible.Then some very fine sand paper and then even finer sand paper. I was pretty pleased with the result but my arm hurt the whole next day. I guess you could get an even nicer finish if you use a plastic polish.There should also be a red scale for monitoring the current. It's barely visible since it faded away after all these years.

author: muvideo
author_rank: Frequent Contributor
timestamp: June 05, 2012, 09:21:09 pm
content: Quote from: tekfan on June 05, 2012, 05:40:05 pmThis is the status of the mine, I dont remember if the plate can be extracted, but in caseI can make a scan of it so you can try to restore the original look.P.S. How were your lamps? I had half of the lamps broken, I put in yellow/orange leds and the effect is almost identicalto the original onesFabio.

author: tekfan
author_rank: Frequent Contributor
timestamp: June 07, 2012, 09:06:32 pm
content: Quote from: muvideo on June 05, 2012, 09:21:09 pmNo worries. I can always shine a light into the meter to see the current.One of the lamps in my calibrator was out. Following the service manual I got some very strange resistance readings in many parts of the circuit, because the lamp was burned out. In the end I just moved the defective bulb to the holder below the function switch. I don't need that lamp anyway.I should probably replace it since they look so nice. Almost like LEDs but....warmer.

author: muvideo
author_rank: Frequent Contributor
timestamp: June 07, 2012, 09:15:32 pm
content: Quote from: tekfan on June 07, 2012, 09:06:32 pmNo problem, the dropper resistors for the leds will be keep them warm(that's 28V there... )Fabio.

author: casinada
author_rank: Frequent Contributor
timestamp: November 06, 2012, 06:43:37 am
content: Did anybody measure the hfe of Q48, Q46, Q44, and Q42 transistors? (2N3739)I measured mine with a Component tester and they show 1, 4, 74, and 0. The Vbe is around 660mv for all of them.The 343A works but is not stable at the micro volt level.Thank you

author: muvideo
author_rank: Frequent Contributor
timestamp: November 06, 2012, 10:05:05 am
content: Hello, what do you intend for :Quote from: casinada on November 06, 2012, 06:43:37 amIn my unit there were only two of the four 2N2739 still working, and many other problems,but it was still fairly stable, as far as I can go with my meters.I swapped the 2N2739 transistors with low cost switching ones, I had many of these, 13007if I remeber correctly, I just performed a quick selection for beta.I was waiting to find the correct ones at reasonable cost, but it works well now and it stilluses the switching ones.I just measured the old parts with a cheap transistor meter:#HfeVbe153687mV246697mV30697mV4na97ohmFor the first 3 Vbe measured with a better meter at 1mA is 605-610mV at 15°CAs a side note I dont know what are the problems one can have using switchingtransistors instead of 2N2739, or if there will be regulations problems,if anybody can explain the difference is welcome.Fabio.