Gaining access to the Acquisition board on a LeCroy WavePro 7200 - Page 1
Forum section: electronics / repair

author: DaJMasta
author_rank: Super Contributor
timestamp: September 18, 2017, 03:55:28 am
content: I stumbled into a pretty good deal on a fancy scope that was in need of repair. I've done some cleaning and diagnostics and I think that the power and sampling system are just fine, but there's some kind of communication error with some of the slower digital devices on the acquisition board (like the pin headers for reading probe data), which prevents it from switching in the BNCs on the front.Anyways, I've checked to a reasonable level of confidence the software and PCI interface card, and I think the issue resides on the acquisition board (or just where the cables are plugging into it, if I'm lucky), but I'm having trouble finding the best way to access the board from the top. Lots of things are removable, but the aluminum cage holding the PC parts and the front panel seems to be mostly riveted, and I'd rather not just strip as many parts off as I can to get at the board (though, it's always an option, I suppose). I removed the bottom panel and got to the bottom of the acquisition board, but since the board is 15"x15" or more and has a bunch of heatsinks strapped to it, it seems like a really bad idea to try and remove it from the bottom and risk it flexing a lot, plus then it would be harder to reattach to the cables on the top side anyways. I've worked in a same form factor older LeCroy scope and the tricks to get that apart doesn't seem to be the same.So has anyone done any work on the acquisition board on the WavePro 7000 series or its derivatives? I'd appreciate any tips on how to get into there short of just removing every screw and cable I can find, and I've been unable to find any service manual (and predictably, it's not in the user manual).I intend to write it up with pics when I'm done, but maybe I can sweeten the deal with a little tease:

author: DaJMasta
author_rank: Super Contributor
timestamp: September 20, 2017, 05:28:12 am
content: Did some investigating.... it's impossible to gain access to the board from the top. But, removing four screws at the top of the BNC connector front piece, the screws in the board, the standoff in the center, and the two main power cables for the acquisition board let you swing the board out to see the top, and oh what a board it is.Reseating the cables in question didn't fix my error, but I managed to put it back together without damaging anything, so I'll call it a success for the night.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 29, 2019, 05:20:36 pm
content: i know this is old thread, but i think its relevant to what follows... i recently acquired a DDA3000 advertised as working. but apart from the hard drive is dead on first run, after replacing and make new installation disk/OS/XStream, CH3 turned out to be broken giving random signal when no probe is connected and gives false trigger. when i switched analog front element between CH3 and CH4, now CH4 is broken. so i think with certain confidence, one of the AFE (was CH3, now CH4) is broken. it happened on all V/div setting. if anyone have some clue on the repair, please advice. how much this module cost? new or used in ebay (i cant find right now on sale). attached show the random signal, acquisition board (CH3 broken, not yet switched), and the internal of the faulty unit itself... nothing looks strange which is more bad on repairing aspect.

author: DaJMasta
author_rank: Super Contributor
timestamp: April 29, 2019, 06:41:29 pm
content: Does your failure respond to chassis vibration, by any chance? Looks a little like momentary interruptions in the signal path with some AC coupling on the transient. Could be an issue with the interface between the frontend module and the signal distribution board or maybe a cap/relay in the signal patch somewhere.May also be worth monitoring the voltages into the amplifier to see if they correlate with the noise (suggesting an intermittent fault of the amp or its power supply) or if they correlate with relay coil voltage (in case it's a contact issue in a relay).

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 30, 2019, 05:25:56 am
content: thanks for suggestion i will try those later. i noticed this when probing aux out signal using AP020. the module can read the signal correctly but there intermittent spikes or jump (and sometime went down to negative momentarily) on the signal, some sort of bias problem i think, maybe a dying transistor?. it seems do not correlate with me knocking or touching the bnc input it just happened intermittently whether with knocking or not. i dont think this has to do with distribution board, since i switched channels, the problem migrate entirely with the AFE module, now CH3 distribution is fine since its now using CH4 AFE module. fyi i cleaned the board top and bottom using soft brush and light blower thinking maybe there dust shorting signal path etc, but it doesnt fix the issue.

author: shakalnokturn
author_rank: Super Contributor
timestamp: March 09, 2020, 08:51:05 am
content: Throw a probe at it, probe the HF path before the front-end ASIC after CR11, I don't expect it would come from there though.Probe LF path after CR1 if nothing shows up there either then the problem is in, or around U1. The usual suspects being the analog MUXes that feed various voltages from the FE control DAC. (I can't read all the IC's on the under-side on your photos, I seem to spot one Siliconix DGxxx?)