Opinions on a Lecroy 9420 350 mhz dual channel scope? - Page 1
Forum section: electronics / testgear

author: wadmancpu
author_rank: Contributor
timestamp: August 10, 2016, 08:55:16 pm
content: Hello all! I've been looking for a scope for awhile now and I came across a Lecroy 9420 350 mhz dual channel scope. I'm a beginner aside from my experience with scopes in the automotive repair field. I wasn't looking for anything real fancy but as nice as my budget would allow so I pulled the trigger on this Lecroy, should be here in a couple days. I'd like to hear opinions on this model and suggestions on some economical probes. Also, does anyone have an estimated price range for this model? I'm unsure of its value. Thanks!

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: August 11, 2016, 11:45:38 am
content: Quote from: wadmancpu on August 10, 2016, 08:55:16 pmWell, it's roughly 28yrs old, and while back then it was probably one of the most powerful scopes you could buy, these days it's specs aren't great (only 50k sample memory). Also, the low 100MSa/s real-time sample rate means the real-time BW is closer to 35MHz (and that is for a sine wave, for non-sine signals it'll be a lot less). It can capture repetitive signals up to 350MHz in ETS mode but that works only for a limited number of signals under specific conditions.But that isn't a big problem if you only work with low frequency signals. And you'll get some nice measurement and analysis tools with the scope.QuoteIf it's in good and fully working condition (no screen burn-in) I'd say $150 or so.

author: TAMHAN
author_rank: Frequent Contributor
timestamp: August 11, 2016, 03:43:30 pm
content: Hello,if I can remember correctly, there can be a problem in the cooling of the hybrids. Look towards the end of this (German, but no affilation) video to see where a cap is "pushing up" the heatsink on the now irreplaceable HVV200 ISs:

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: August 11, 2016, 04:31:18 pm
content: Quote from: TAMHAN on August 11, 2016, 03:43:30 pmDidn't someone in the Yahoo LeCroy group design a replacement circuit for them?IthinkI've read about it some time ago somewhere (could be wrong, though)

author: Jwalling
author_rank: Unknown
timestamp: August 11, 2016, 06:33:43 pm
content: Quote from: Wuerstchenhund on August 11, 2016, 04:31:18 pmDon't remember that, and I still read the group . You may thinking about the infamous U800 on the Tek 24XX analog scopes. (But I could be wrong as well...)Jay

author: Emo
author_rank: Regular Contributor
timestamp: August 11, 2016, 07:25:12 pm
content: Hi Jay,It was another input chip than mentioned above that Dieter Frieauff rebuilt. It was the HHZ406 replacement.The link to the leroy group;https://groups.io/g/LeCroyOwnersGroup/topic/dieter_frieauff_s_hhz406/989334?p=,,,20,0,0,0::RecentPostDate%2FSticky,,,20,2,500,989334The schematic is in the attached dfEric

author: Martin.M
author_rank: Frequent Contributor
timestamp: August 11, 2016, 07:26:40 pm
content: The replacement instruction is for the input modules what converts 1M :50 Ohm, = HHZ406sometimes - like the scope in this video - this inputs are destroyed, so the 1M is not working and the 50 ohms mode works, but it present you a CAL error about a small dc offset comming from the bad modules.greetingsMartin

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: August 11, 2016, 07:37:23 pm
content: Quote from: Jwalling on August 11, 2016, 06:33:43 pmI guess it was somewhere else then.QuoteIt certainly wasn't the U800 or anything related to analog scopes (for which my interest is pretty low so I wouldn't memorize such stuff).

author: TAMHAN
author_rank: Frequent Contributor
timestamp: August 11, 2016, 08:46:38 pm
content: Could be the one for the power supply, but that one is a hybrid.Either way, my memory also fades. But I havent been following the owners guild for too long, so ...

author: wadmancpu
author_rank: Contributor
timestamp: August 11, 2016, 11:47:37 pm
content: Any thoughts on some decent priced probes?

author: Muxr
author_rank: Super Contributor
timestamp: August 12, 2016, 12:03:01 am
content: Quote from: wadmancpu on August 11, 2016, 11:47:37 pmP6100 are my go to beater probes.

author: GK
author_rank: Super Contributor
timestamp: August 12, 2016, 12:34:25 am
content: I had one of these (though with a ~125MHz analogue bandwidth IIRC). It's POO! Super sensitive vertical offset/position knobs with no accompanying/handy zeroing button. Breath on the front panel controls and the traces instantly disappeared fifty equivalent screen widths either up or down (only a moderate exaggeration). Drove me nucking futs! I had too much crap in my possession at the time; I threw it into the skip from a standing position ~5 meters away! Slam dunk! Hooray!

author: wadmancpu
author_rank: Contributor
timestamp: August 12, 2016, 10:42:56 am
content: So should I plan on trying to sell this when it comes or would it be a good basic unit to learn from? I'm wondering if they all have the issues you experienced with yours or your issues were caused by problems with your unit? Is this machine useless?

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: August 12, 2016, 10:58:23 am
content: I've only been in contact with a 9420 once and that was averylong time ago, but none of the controls were overly sensitive and I doubt that was by default. A jumping control is a sign of a defective pot or encoder, not a design feature. It's a common problem with hardware that is 20+yrs old, and in general easy to fix.I would not sell it if I were you. The 9420 is actually not a bad scope if you are aware of its limitations. If I remember right it has quite sophisticated measurement functions, more than what you'll find on a new beginner DSO.You can still learn a lot from it, including how to handle a digital scope properly.

author: GK
author_rank: Super Contributor
timestamp: August 12, 2016, 01:21:45 pm
content: Quote from: wadmancpu on August 12, 2016, 10:42:56 amMine was a 9400. Not useless but very limited. I obviously wasn't very fond of it. And there wasn't anything electrically wrong with the trace positioning rotary encoders. I suggest that you play with your 9420 and make up your own mind.

author: GK
author_rank: Super Contributor
timestamp: August 12, 2016, 02:16:17 pm
content: BTW, its been a few years now that I turfed my 9400, but IIRC in real time sampling mode it was only really useful up to about 10MHz (on tenth the sampling rate). I don't recall it having anything other than basic straight-line linear interpolation.I've just skimmed/scanned through the 9420 manual and all I can currently see w.r.t. interpolation is this:So it would appear to be the same. If so then that means that you cannot expect it to render a nice sinewave up to the Nyquist limit.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: August 12, 2016, 03:10:55 pm
content: Quote from: GK on August 12, 2016, 02:16:17 pmIn pretty much all older LeCroy scopes interpolation was linear only, and sin(x)/x was actually a maths function. They only moved it to the 'interpolation' settings with their Windows scopes on 2001/2002.So if the 9400 has it (can't remember if it was standard or part of the options) then it will be found under maths, not interpolation.

author: GK
author_rank: Super Contributor
timestamp: August 13, 2016, 03:58:37 am
content: I'm fairly sure my 9400 didn't have sin(x)/x interpolation. Can't find any mention of it in the 9420 manual. In relation to maths functions there was a waveform processing option but that didn't offer sin(x)/x. The digital filters (FIR) are for enhanced resolution with oversampling.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: August 13, 2016, 11:14:21 am
content: Quote from: GK on August 13, 2016, 03:58:37 amAs I said I'm not sure it was even available but if it was it would have been under Maths not Interpolation.But I guess you're right and it didn't have sin(x)/x. It wasn't exactly common back then on DSOs, and even later in the '90s not all scopes had it.