Fluke 510A - AC voltage reference - Page 1
Forum section: electronics / general

author: branadic
author_rank: Super Contributor
timestamp: July 12, 2025, 06:29:16 pm
content: I've noticed that Fluke 510A has no own thread so far, time to change that.For a side project I'm in the need of some AC voltages at different frequencies in the near future. While I don't have a MFC at hand, I've decided to try to get some Fluke 510A AC voltage references and change them to the desired frequencies I'm interested in. An overview of how to set the frequencies in these units is given in this articlehttps://xdevs.com/article/f510a_p1/Yesterday, 4x Fluke 510A arrived from the US, all set to 2400 Hz (for convenience 2.4 kHz). They were very well packaged and thus showed no signs of damage during transport, brilliant, though some binding posts on the back are slightly damaged.First thing to do was to switch them to 230 V (switch on the back). Step 2 was to remove the covers for a brief overall inspection. In 3 units the electrolytic caps were already replaced at some point in their life, one unit still has the factory ones. Eventually, I found some components burnt into ashes in one unit. Furthermore, underneath them two traces were vaporized too and the board also slightly turned into carbon. So, that needs fixing.While the covers were already off, it was time to give them a thoroughly cleaning in order to remove the signs of previous usage and users, stickers and sticker residue, because working on a unit that is clean and beautiful is way more convenient than working on a unit you permanently stick to, right?All units had the feet missing, so it was time to start the printer. While the first set of feet was printing from PETG, I removed the burnt components, scratched off the carbon, fixed the FR4 with some epoxy, restored the traces and looked for the values of the resistors. Turned out to be R102 = 5.6 Ω, R103 = 10 Ω, R104 = 5.6 Ω, R105 = 100 Ω and R106 = 84.5 Ω. Sounds like they are related to one another, right? They are and they are part of the overload indicator, thus I need to check that area for more broken components. The LED at the front must have been bright like the sun, when the previous owner abused the output.I already started a list with components to order and to replace. And since we all know how ugly used test equipment can look like, I have not taken pictures before cleaning. I spare you that and we can all appreciate their look after they were completely refurbished.-branadic-

author: p-wave
author_rank: Newbie
timestamp: July 12, 2025, 08:01:35 pm
content: Hi Branadic nice post,I have a Fluke 510a sn.2418xxx 400Hz also, in good working condition, if you need some comparison check.p-wave

author: branadic
author_rank: Super Contributor
timestamp: July 12, 2025, 09:13:11 pm
content: At the moment I only need to identify all the components I need to replace and find the proper screws for attaching the feet and for the missing screw of one of the covers. They are not listed in the manual, but are imperial.-branadic-

author: Kleinstein
author_rank: Super Contributor
timestamp: July 12, 2025, 09:27:22 pm
content: With the resistors burned there may well be a shorted transistor in the amplifier that caused the issue.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: July 12, 2025, 10:30:39 pm
content: Quote from: branadic on July 12, 2025, 09:13:11 pmI pulled one of the screws out of my 510, it is a 6/32, and thread is about 10mm long so probably 3/8" long, but that might change depending upon your 3D printed foot depth.

author: 1audio
author_rank: Frequent Contributor
timestamp: July 14, 2025, 06:00:17 pm
content: It looks like someone confused it for a voltmeter and tried to measure the AC line. There are several transistors that would be toasts as well. And possibly the +18V supply. A major oops.I did some tweaking on my 510 years ago and got its distortion down to .00057% or less depending on how you measure. Its also due for new supply caps. Details follow.https://www.diyaudio.com/archive/blogs/1audio/904-upgrade-fluke-510a-ac-voltage-reference.html

author: branadic
author_rank: Super Contributor
timestamp: July 14, 2025, 07:03:46 pm
content: QuoteLooks like you went for AN67 "An Ultralow Distortion, 10kHz Sine Wave Source for Calibration of 16-Bit or Higher A/D Converters", "EDN -- 11.10.94 Oscillator keeps THD below 1 ppm" and "Test 18-bit ADCs with an ultrapure sine-wave oscillator" ...QuoteWould you mind sharing the marked up schematic here? The link doesn't seem to work anymore.-branadic-

author: 1audio
author_rank: Frequent Contributor
timestamp: July 15, 2025, 04:05:39 am
content: I'm marking up a schematic with the changes after confirming them. I did this 13+ years ago and my notes are long gone. I also rescanned the schematic since all the on line manuals are really hard to follow. I'll post very soon. Let me know if I should scan the complete manual I have.This is a great rundown on calibrating the 510:https://xdevs.com/article/f510a_p1/#motivI did mine with a Fluke 540 and DC calibrator but this process is simpler.

author: 1audio
author_rank: Frequent Contributor
timestamp: July 16, 2025, 07:00:35 pm
content: I have attached a better scan of the schematic and a marked up version (my markup tools are primitive but the information is there). Its pretty straightforward stuff.

author: branadic
author_rank: Super Contributor
timestamp: July 19, 2025, 02:51:19 pm
content: Partial repair of the section in question.EDIT: For everyone metric, the covers need 6-32 3/8" (0.375") Self Sealing screws and the feet 6-32 5/8" (0.625") Pan Head screws.-branadic-

author: 1audio
author_rank: Frequent Contributor
timestamp: July 20, 2025, 05:25:59 am
content: Looks good. Mine is the same rev (G). Photo of the same area on mine with the mods attached.

author: branadic
author_rank: Super Contributor
timestamp: July 22, 2025, 07:54:01 pm
content: Turned out almost all transistors at the output were shorted. I also found at least one shorted tantalum cap. They will all have to go.Order of replacement components was already placed and I'm waiting for them to arrive to proceed.Edit: The units have rev. G, J and L here.-branadic-

author: branadic
author_rank: Super Contributor
timestamp: July 27, 2025, 02:58:36 pm
content: Replaced all caps in all units and a bunch of semiconductors in the burnt unit. While the three are already up and running, the burnt unit is still unhappy and uncal indicator is lighting up. Need to dig in a bit deeper.-branadic-

author: branadic
author_rank: Super Contributor
timestamp: July 30, 2025, 08:04:05 pm
content: I'm happy to report that the first unit is up and running too. Turned out it was C38, that was causing me trouble. C20 was used as a donor and populated with 100 nF foil cap instead.-branadic-