Author Topic: Repair of Lecroy AP020 Active Probe (TearDown Photos Included)  (Read 417 times)

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Offline riyadh144

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Hi,
A couple of weeks ago I came across a good deal on a Lecroy LC584AM, and I couldn't miss out on a 1Ghz Scope for $400, so I picked it up, of course it came with no probes, what is the use of a 1Ghz scope with 200MHz probe that I already had, I started looking for probes to get, I bought sever HP 10441A 500Mhz mini probes from an ebay seller 30 something $ each and man they are wonderful  (Check them out), and I bought a 1Ghz probe claimed to be new.

Enough Waffling, I get the probe and for some reason I have a 38V dc offset on the screen, I thought maybe I didn't know how to operate an active probe, but yeah that probe was bad, anyway the seller agreed to get me another one. But for now I decided to fix the probe. I believe it is on the input side on one of the FETs.

I came to that conclusion by tracing the 3.8 volts (10:1 probe)  to its source, I started from the output of the scope tracing the input all the way back, and I figured it is coming from the probe input, at first it was the caps but I removed and checked them for ESR and they are fine and spot on then I figured that the first time that 3.8V occurs on the signal path was the V2 labeled FET on pin 1. I tried measuring the internal diodes, I only found one and it was behaving weirdly, so I figured this must be the culprit.

Even if I cannot repair it I thought I would post the teardown photos maybe someone can benefit from them

Some Photos are repeated just in case one of them doesn't show a component value.

https://imgur.com/a/T1y4d8X

Regards
 
« Last Edit: May 23, 2018, 08:48:43 am by riyadh144 »
 
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