Lecroy MS-250 (MS-500)TEARDOWN+ flying leads wires logic interface repairing. - Page 1
Forum section: electronics / testgear

author: smaultre
author_rank: Regular Contributor
timestamp: December 15, 2020, 01:53:51 pm
content: Today's Lecroy MS-250 was arrived, i test it and found, that one channel have no response on signal.Trying to measuring the resistanse, it shows ~80Ohm instead ~100KOhm on works ones.I try to add test signal directly to the main connector, and this "bad" channel is works fine.I remove the flying leads from main block. But the low resistance on the flying leads still present. I disassemble the main connector side, and see how the microcoaxial cable is set to connectors pads, but there's no any active or passive elements is present here.I disassemble the other side of connector of disfunctional channel, and there i see some passives 1 cap +1 resistor on parallel on the "HOT" pin.And one SMD1206 -like element that "shorts" the HOT wire signal with a GND pad. There no marking on element, but green colored with a green dot on it.Normal channel input range is +\- 10V is it a protection varistor??Who can help with finding the replace??Maybe someone know how to Hack it to the 500th versionOn the 13th picture is interesting "jumper" maybe config?

author: 2N3055
author_rank: Super Contributor
timestamp: December 15, 2020, 08:38:09 pm
content: Quote from: smaultre on December 15, 2020, 01:53:51 pmProbably a TVS of a sort..

author: smaultre
author_rank: Regular Contributor
timestamp: December 16, 2020, 05:33:57 am
content: How can i determinate the voltage?Just burn another one??And, maybe someone have "tear-downed" the MS-500 model?I need some photo about jumpers&installed& maybe flash dump, and what memory it need's 1Gb?, mine have a 256Mb dimm.

author: 2N3055
author_rank: Super Contributor
timestamp: December 16, 2020, 07:51:08 am
content: Quote from: smaultre on December 16, 2020, 05:33:57 amNo need to burn it.. Just test it with limited current. All TVS in datasheet specify voltage when it starts conducting, and full current voltage..Just increase the voltage until it starts conducting... And then search for similar one.. No need to be very accurate...

author: smaultre
author_rank: Regular Contributor
timestamp: December 17, 2020, 02:39:07 pm
content: Thank you!Anybody have the 500 version??? Please disassemble and make some photo!!! It's be super to make a dump of a flash..

author: smaultre
author_rank: Regular Contributor
timestamp: December 17, 2020, 07:31:19 pm
content: https://www.mouser.com/Circuit-Protection/Varistors/_/N-5g3h?P=1yzvlkxZ1z0x4jp&Keyword=littelfuse&FS=True

author: 2N3055
author_rank: Super Contributor
timestamp: December 17, 2020, 07:40:34 pm
content: Those a varistors. TVS has less capacitance..https://hr.mouser.com/Semiconductors/Discrete-Semiconductors/Diodes-Rectifiers/TVS-Diodes-ESD-Suppressors/_/N-azknd?P=1yzvlkxZ1y7tnfb

author: smaultre
author_rank: Regular Contributor
timestamp: December 18, 2020, 01:34:51 pm
content: I test the capacitance with tweezers 20.5pf on working inputs.

author: 2N3055
author_rank: Super Contributor
timestamp: December 18, 2020, 02:39:57 pm
content: When you remove bad part, what is capacitance of broken input?Remove carefully one good protection element from one good channel and measure it: capacitance (with as low test voltage you can so it doesn't conduct), and with limited current try find conduction voltage in both directions.... based on that you will be able to find what it is.. Or at least somebody here will...