Uni-T UT505A Teardown - Page 1
Forum section: electronics / testgear

author: threephase
author_rank: Regular Contributor
timestamp: September 15, 2019, 08:39:13 pm
content: Some pictures of the internals of a Uni-T UT505A Insulation multimeter that I have been looking at for a while. The build is actually quite nice, with some good features found on more expensive insulation testers.Kit contents are quite basic, but adequate for insulation testing on installations and motors. Test leads are PVC insulated and breakdown when tested at 1000V, so could affect readings at high insulation values, but they are not the worst I have tested.With the back cover removed the battery back leads are secured into the rear case to reduce stress on the connections and plug into the main PCB allowing the whole rear case to be separated from the front.Input jacks are embedded within the front case and connect to the PCB via connection strips held in with a machine screw. The remote probe connections are clip on around stubs moulded into the front case. The meter is stamped as CAT IV rated, an isolation slot is visible around the voltage inputs along with MOVs and PTCs.The internal transformer for generating the high voltage output looks to be good quality and securely mounted. Good quality Omron relays are utilised for selecting the various functions.Main chipsets seem to be a C8051F340, 8 bit 50Mhz device from Silicon Labs, and a PCF85176H display driver from NXP.

author: threephase
author_rank: Regular Contributor
timestamp: September 15, 2019, 08:48:05 pm
content: Few more pictures from the teardownBoard is reasonably easy to remove from the case. It was found to be clean with no evidence of solder / flux residue around PCB. Solder connections all looked to be good.The moving contact assembly for the rotary switch is clipped into the PCB, but can be removed to reveal the contact arrangement inside. PCB tracks for the rotary switch and push-buttons are typical for this style of meter.A number of multiplexer ICs were found around the input jacks which I could not find in depth details of, but appeared to be Chinese clones.Inside of front case was all clean, typical plastic spring clip providing the detent for the rotary switch, and the push button contact pads held in place within their own plastic moulding screwed into the front case.

author: threephase
author_rank: Regular Contributor
timestamp: September 15, 2019, 08:56:36 pm
content: I found the unit to have some quirks in the way it operated, mostly around the insulation resistance tests.For a timed test, the insulation resistance is displayed, but there is no countdown timer available. For a DAR or PI test, the display is swapped and a countdown timer is seen, but there is no display of the insulation value. At the end of the test you can page through the PI / DAR ratio and the relevant insulation resistance values to calculate the ratio.What did surprise me is that the meter did not switch off the test voltage output at the end of a DAR or PI test. I would really appreciate it, if there is anyone else on here that has a UT505A or UT505B, could verify if their unit operates the same, as I am wondering if mine has developed a fault.What did amuse me is that, the remote probe from a Fluke 1587FC insulation multimeter, does fit into the remote probe socket on the UT505A and operates it perfectly well. Their remote probe is sold by Uni-T as a separate item, and does not come with the meter and I could not find it available in the UK.I have a blog on element14, that displays all the test results and shows the meter in operation, if anyone want to know some more information about it.https://www.element14.com/community/groups/test-and-measurement/blog/2019/09/11/uni-t-ut505a-insulation-tester-reviewThanks for reading!