Fluke 337 repair - Page 1
Forum section: electronics / repair

author: agamero
author_rank: Newbie
timestamp: September 22, 2023, 11:52:58 pm
content: Today my Fluke 337 had a power failure, batteries was dead but one of them was leaking a little bit, I cleaned it but it begins to beep and zero button did not work. I open it and there was some residual of the alkaline solution so I clean it up using some vinegar and isopropyl alcohol, and all begins to work almost perfectly, but there was some random beeping so I open again a couple of times UNTIL negative wire was cutter because the movement and some corrosion. I try to clean the soldering to reinstall the wire but this board has asleeved hole and that bloody wire tip was really hard to remove so I make a big mistake by pulling it out and the sleeve went out. I use a little piece of sandpaper to clean the copper around the hole and I was able to solder the wire, unfortunately, the Fluke 337 did not wake up again, I saw that the board is a multilayered one, so likely there is a lost connection inside. I was thanking to use an external wire to connect this point to where the wire is supposed to go, but I have no diagram. Since I was moving a lot the board, the positive wire got cut also but, leason lernt, y solder a new wire to the other side of the board. I could test that there was voltage present on the board when I installed the battery, so I don't really know if there are a missing o wrong connection or I kill my beloved meter. Any chance of help from you guys?

author: Paceguy
author_rank: Regular Contributor
timestamp: September 24, 2023, 07:01:00 pm
content: Hi, I wish you luck fixing it. If it can't be revived, I would be interested in purchasing the selector knob from you. My 336 needs a knob. Thanks!

author: agamero
author_rank: Newbie
timestamp: September 24, 2023, 11:52:48 pm
content: I will have it in mind,but considering a mail from Chile to Canada (?) this knob will turn into the expensive one ever . By the way, today I was thinking about usin a powerful light to see through the board if is there any hiden connection and where is going to. So I guess that soon I will know if this device is going to live again

author: canadaboy25
author_rank: Regular Contributor
timestamp: September 26, 2023, 06:11:27 pm
content: Shouldn't be a terribly difficult repair given you have an adequate soldering iron. In the background of the image I can see some small diameter solder which is a good start.Post a couple close-up pictures of the damaged area from both sides of the PCB so we can get a better idea what's going on.

author: agamero
author_rank: Newbie
timestamp: October 02, 2023, 07:13:35 pm
content: I used the data of the voltage regulator LTER e3 and of the multiplexer 70HC4053, both visible on the board to check connections to the battery incoming wires and detect that the output pin was connected to ground! So I check the wire soldering that I did initially and cleanit with a fine sandpaper and test it with an external 3 volts power supply and it worked intermittently because a bad contact, but confirmed that the meter is in good shape. Just 5 minutes ago I installed a new wire, this time I put a lot of soldering on the wire first, then I passed through the hole, and then used the hot air gun and it worked wonderfully well!!!. I did a test and the meter worked fine, at least turned on and selection knob was doing its job. Now I will begin to normalize everything to close it and I hope it keep working, but I am happy to see that it was possible to do the soldering. The main lesson is that indeed the negative connection is going inside the board and, in case of an emergency, you could use the negative contact near the voltage regulator or other line connected to that point.

author: canadaboy25
author_rank: Regular Contributor
timestamp: October 02, 2023, 08:50:33 pm
content: Congrats on getting it fixed!In cases where you can't repair the connection and you have no idea where the trace is going, there is the option of grinding down the PCB until the internal layers are exposed and making a connection that way. Glad you didn't have to go through that here.

author: agamero
author_rank: Newbie
timestamp: October 02, 2023, 09:54:41 pm
content: Thank you. I also found the reason of the random beeping, when I finally turn it on, I select dc amps, where is normal to see a little offset that has to be nullify using the zero button, but this time it went to zero by itself as if the zero button was been press, so I check again and found that the board was elevated of normal position pushed by the new wires of the batteries, so I short them a little bit and run them with a lot of care to avoid this extra pressure, install the board again making sure that position was the rigth one, tie up the screws, close everything and tested, again, this time was perfect. On the picture you can see my "x100" coil that sometimes I use to measure small dc currents. It never crossed my mind that this lack of position was the cause of the random beeping.

author: Ugur
author_rank: Regular Contributor
timestamp: October 05, 2023, 12:10:49 pm
content: Another reason for random beeps.The copper surfaces where the commutator pins touch the board may short circuit to each other over time. If so, you need to scrape the short circuit with a scalpel tip.

author: agamero
author_rank: Newbie
timestamp: October 05, 2023, 06:52:46 pm
content: Thank you, I will check it