LeCroy LC534AL / LC574A power supply repair attempt - Page 1
Forum section: electronics / repair

author: FireFlower
author_rank: Regular Contributor
timestamp: November 27, 2015, 01:23:58 am
content: Hello,I have one LeCroy LC534AL 1GHz oscilloscopes at university's club that needs a bit servicing. Problem is AT power supply but cannot find LC534AL service manual but I found its big brother LC574 service manual and seems like it uses same power supply.How big level of reverse engineering you guys are normally doing here? I see somebody tried to reverse engineer this thing back in 2014 but seems to have given up because schematics seems half way there or his problem was A1 hybrid module 100004 because it seems to be complete.What is wrong this PSU? I have no idea, blown fuse at least but doesn't seem magic smoke has escaped anywhere so have to do some measuring to find out what is broken.

author: FireFlower
author_rank: Regular Contributor
timestamp: November 27, 2015, 01:31:47 am
content: PSU seems to be identical on both models, so editing topic a little bit and linking hereService manual for LC574A model and page for psu schematichttp://www.schematicsunlimited.com/l/lecroy/lecroy-lc574a-service-manualPages 475 (riser board) and 476 (main psu board)Possible hybrid module reverse engineering:https://xa.yimg.com/kq/groups/10892261/995199750/name/LeCroy_PS1724_Hybrid_PSU_COMBINED_V4.pdf

author: tautech
author_rank: Super Contributor
timestamp: November 27, 2015, 01:43:39 am
content: SMPS PSU?If so identify the controller IC and check datasheet/s for the manufacturers "typical application".You'd be surprised how often it is followed exactly, then it can be real easy.

author: FireFlower
author_rank: Regular Contributor
timestamp: November 27, 2015, 02:01:28 am
content: I see only Power Supply Inc to be manufacturer,only IC's on board are three LM339N which are quad comparatorsbut board seems simple enough and with schematics I should find out where short is much easier than tracing back where lines are and what connects to them.

author: FireFlower
author_rank: Regular Contributor
timestamp: November 27, 2015, 02:52:30 am
content: Seems like Dave has looked at almost same supply unit with other LeCroy product but I have older AT single lane power line, lets see what I find when I get back from work and have time to measure things.

author: Pat Pending
author_rank: Regular Contributor
timestamp: November 27, 2015, 06:34:39 am
content: I was faced with one of these failed PSUs from another mfg's piece of test kit with no schematic.That sat for a long time until one day, quite by chance, I spied the same PSU in Dave's LeCroy teardown video.Luckily LeCroy had used the same brand of SMPSs and had revealed parts of the PSU cct.That helped but wasn't essential until I built an ESR meter and found the culprit.

author: FireFlower
author_rank: Regular Contributor
timestamp: November 27, 2015, 02:11:35 pm
content: Well has to wait a bit, a problem occured at work so I came just to have a few hours sleep and back to work. Just 1000 boards to be fixed asap

author: FireFlower
author_rank: Regular Contributor
timestamp: November 28, 2015, 11:17:23 pm
content: Started to measure things today, as said earlier board has no any indications except blown fuse that something ain't working.I measured today secondary side voltage lines and didn't indicate short that could cause primary side fuse to blow. Also tested connecting the main board power connector to unit and see did values change but no problems with that either, so it definitely is PSU which is broken.So the fault has to be transformer or primary side components. I measured all power resistors, they seem to be fine, measured C1 and C2 1200µF caps with LCR meter and got 1080µF with 120Hz test frequency, so they seem to be fine also. Then I noticed T2 transformer which seemed to be covered in red goo and took it off to measure it also. Used 1kHz to measure pins 3-4: 120.2mH, pins 2-5: 4.220mH, pins 8-9: 1.2µH, pins 9-10 111.1µHPrimary side of T2 is pins 3-4, secondary sides: 2-5 and 8-9-10 where 9 is common for pins 8 and 10. T2 seems to be driving two transistors which seemed to be fine when I measured them. So does T2 values seem odd to you or are those typical?Well anyway I am done for today.

author: chinapp
author_rank: Contributor
timestamp: January 10, 2016, 02:13:42 am
content: what's the power in your area ? 220V or 110V ?if it is not 110V,then the 100004 hybird maybe down, it's a autorange block in my opiniongood luck to you