LeCroy LW420 Arbitrary Generator - Page 1
Forum section: electronics / testgear

author: davorin
author_rank: Unknown
timestamp: June 05, 2015, 09:48:59 pm
content: I've never saw this device before.....or being mentioned it here in the forum...Does anyone use this device and is it still of use nowadays?

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 05, 2015, 09:59:51 pm
content: Quote from: davorin on June 05, 2015, 09:48:59 pmI haven't used one but I did consider getting one. It's essentially a PC based AWG running DOS. When it came out (around 1992 if I remember right) it was one of the most advanced AWGs of that time.Even today it's still a very nice AWG, and LW420s in good condition still go for some noticable money on ebay. Some people also replaced the CRT with an LCD.

author: davorin
author_rank: Unknown
timestamp: June 05, 2015, 10:02:10 pm
content: Right...I just lately someone replace the CRT with a LCD or TFT....oddly the display showed suddenly different colors (o;So what would be a reasonable price for it?Just would be a nice fit to my 9354AL (o;And I hope it was also made in Switzerland ;-)

author: nctnico
author_rank: Super Contributor
timestamp: June 05, 2015, 10:53:47 pm
content: Quote from: davorin on June 05, 2015, 09:48:59 pmI used to have one but sold it a long time ago. Unless you have very specific needs for arbitrary waveforms it is just big and noisy. The build quality isn't stellar either. I'm much happier with my Siglent SDG1000 series generator. The pattern generation part of the LW420 is also not very interesting. It doesn't have a digital waveform editor besides just entering 1 and 0. That becomes tedious quickly.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 06, 2015, 06:50:31 am
content: Quote from: davorin on June 05, 2015, 10:02:10 pmDifficult question. For once, The WaveStation LW420 is a really nice (albeit as ntnico says big and noisy) AWG, with decent specs even by today's standard, and comes with GPIB (which none of the entry level AWGs do). On the other side, it's now close to 25yrs old.I'd probably pay somewhere around €200 for it if it's in really great condition and comes with the 1MB memory upgrade. However, most LW420s I saw ended up going for a lot more , which in my opinion no longer made it worthwhile.QuoteCan't remember, but it might very well be, as it's from the same time period where LeCroy made scopes there.

author: dom0
author_rank: Super Contributor
timestamp: June 06, 2015, 09:52:00 am
content: It was made in the US. I think it was discontinued in 1998 or so.

author: nctnico
author_rank: Super Contributor
timestamp: June 06, 2015, 11:03:27 am
content: If you manage to get one put a Intel Pentium overdrive in it to replace the Intel 486. Calculating a frequency sweep using 1Mpts of memory goes from 20 seconds to about 2 seconds. I got a Pentium overdrive new in box from Ebay.

author: nctnico
author_rank: Super Contributor
timestamp: June 06, 2015, 11:49:54 am
content: Quote from: Wuerstchenhund on June 06, 2015, 06:50:31 amThat is because GPIB has been replaced with USB a long time ago. My SDG1010 supports USBTMC for remote control.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 06, 2015, 12:45:11 pm
content: Quote from: nctnico on June 06, 2015, 11:49:54 amNot really, as USB is a point to point connection, not a multipoint bus as GPIB, and once the number of instruments exceeds the amount of USB ports on your PC then it becomes a major pain in the arse (and often long before that).Proper test equipment these days comes with LAN, which is faster, and much more robust than any USB solution.This aside, GPIB is still in wide use, even today.QuoteThe reason the SDG1000 (like all cheap Chinese AWGs) have USB is because it's cheap and simple, and the manufacturer was too cheap to even include a $3 Realtek network chip.The funny thing is that originally promised an USB-to-LAN adapter for the SDG1000, which never materialized (there's no firmware support). They repeated the same with the SDG5000 (which also doesn't have LAN).

author: nctnico
author_rank: Super Contributor
timestamp: June 06, 2015, 01:05:46 pm
content: Quote from: Wuerstchenhund on June 06, 2015, 12:45:11 pmGPIB allows 15 devices on one bus (and one master) with a maximum length of 20 meters. USB is 'limited' to 127 devices on one port (using hubs) and can be extended to around 50 meters with simple range extenders. I agree LAN is better but it brings along a lot of overhead (IP stack) for the test equipment to handle and all kinds of security issues especially when equipment is running Windows.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: June 06, 2015, 05:59:59 pm
content: Quote from: nctnico on June 06, 2015, 01:05:46 pmRight, but the difference is that with GPIB that works in reality, while for USB that is more or less a theoretical limit only as often even 15 USB devices won't work flawlessly together.QuoteWhich increase latency, which again can screw up your devicesQuoteThat's not really an issue these days when almost any chipset and FPGA contains at least one network interface already. IThis aside, USB isn't the most ressource-saving protocol either (esp. USB 1.x and 2.0).QuoteThere are even more security issues with USB, who has been the target for many attacks in the past.LAN also isn't necessarily more insecure than GPIB, especially if the T&M network is kept separate from other networks and not connected to the open internet. This aside, Windows devices are not a higher security risk than non-Windows devices, but actually more easy to secure as it's widely known how to tighten it up, and new flaws issues get made public and (in the case of Windows versions that are still supported) also get fixed regularly. With non-Windows devices, it's pure guesswork what holes exist in a device simply because there are no regular security audits and intrusion tests, and even if a problem is found then it's pure luck if the device manufacturer can be bothered to actually fix it and provide an update for its customers. You wouldn't believe how many devices are out there that are still vulnerable to Heartbleed, and which will never get fixed (and worse, who's users will often never know that there is an issue).

author: Kryten 2X4B
author_rank: Contributor
timestamp: June 07, 2015, 04:39:23 am
content: A few ago years I bought an LW420 at a local auction for AU$140. When I first powered it up there was nothing on the screen but HD access could heard while the system was booting. Before doing any trouble shooting I connected a VGA screen directly to the video card and got a colour display. LeCroy used two switchmode supplies in the LW420 one for positive rails and the other for negative. The rectifier diode for the -12V rail shorted and took out many of the components on the input side of the transformer in the neg supply without blowing either of the input fuses. Mr Murphy said "A $300 CRT protects a $0.30 fuse!! Anyway after tracking down two faulty ICs and a shorted cap on the main AWG board the LW420 was fully operational. I don't know if the AWG board components caused the supply to fail or failed because of the lack of neg supply. I must say the LeCory did a really good job with self-test as it made it easy to locate the sections of circuit that were faulty.

author: davorin
author_rank: Unknown
timestamp: June 07, 2015, 02:27:36 pm
content: Wasn't aware this device contains an Intel processor...Hmm...the seller lowered the price from Euro 699 to 649......what a bargain (o;

author: davorin
author_rank: Unknown
timestamp: June 08, 2015, 10:08:46 pm
content: And now it is at Euro 645 :-)So if I wait another 200 days I'll buy it (o;

author: analogRF
author_rank: Super Contributor
timestamp: July 23, 2018, 02:35:57 pm
content: Quote from: nctnico on June 06, 2015, 11:49:54 amwould you mind explaining how you replaced the display with LCD?thanks

author: wishboneash
author_rank: Contributor
timestamp: December 15, 2021, 10:06:51 pm
content: I have a LW420 that has a dead display too. The -12V supply is shorted out. I see 0.5 ohm to ground. I can hear the HDD doing something and the two signal outputs are red. Hoping that the main part of the AWG is OK. I measured over 3Mohm on the -12V supply on the board after disconnecting the power supply connector from the PS unit. The +12V, +5V and +15V supplies look good. Will have to get into the power supply unit and do some investigation. Thanks.

author: wishboneash
author_rank: Contributor
timestamp: December 17, 2021, 11:33:53 pm
content: I found out that the second switched mode power supply has failed completely so all the negative voltage power supplies are dead (-5V, -12 and I believe a -2V supply). I externally provided the -5V and -12V supplies and I got the unit to power on but I got a message on the screen saying it needs the firmware installed (from floppy). Is there anyone in internet land who has such a floppy? Thanks.

author: shakalnokturn
author_rank: Super Contributor
timestamp: December 19, 2021, 12:16:39 am
content: You'll have to subscribe to the group to download.The file there that seems small enough to fit a floppy is one I uploaded at the time I had a LW420, can't remember where I got the file from then... I never got the LW420 working anyway.There are also HDD images available which may turn out simpler than getting a working FDD and floppy combo.https://groups.io/g/LeCroyOwnersGroup/files/Old%20firmwares%20archive/LW420/Lecroylw420-311.IMAhttps://groups.io/g/LeCroyOwnersGroup/files/LW420%28A%29

author: Kryten 2X4B
author_rank: Contributor
timestamp: January 16, 2022, 02:16:25 pm
content: In my post from 2015 I mentioned that the rectifier diode for the -12V supply was shorted, that caused all the negative rails to fail. Apart from the diode, I had to change the controller chip, the reference, the primary side MOSFETS, and some resistors including the one for current sensing. Without the negative supplies running you will hear the HDD trying to boot but there will be nothing on the display as the video is disabled prior to the LeCroy logo being displayed and the video passes through some MAX442s which run on +/-5V rails so without -5V the display will remain blank.The HDD in mine failed before I had imaged the HDD, the plan was to use a CF card. Since then I got a disk image and the LW420 is running with a CF card and passes the self-test.

author: wishboneash
author_rank: Contributor
timestamp: June 04, 2022, 04:22:29 pm
content: I got mine to work after working on the power -ve SMPS. Turned out to be a failed rectifier on the -12V supply along with a blown MOSFET on the output side. I added some protection for the rectifier by adding a bypass capacitor for switching transients. Perhaps the diode was not rated correctly for reverse breakdown when the inductor switched off. With some help on the LeCroy IO group, I got an HDD image which I put onto a SD card and now it boots up perfectly. It's a nice AWG and there seem to be many around with the failed HDD which can be easily converted to a CF or SD card drive.

author: wishboneash
author_rank: Contributor
timestamp: September 06, 2022, 06:21:34 pm
content: I have a question for anyone who is familiar with the LW420 regarding the marker generators. I am trying to generate two frequencies at 50.000MHz and 49.995MHz. I am able to generate a proper 50.000MHz marker on one of the channels, but for the 2nd channel, I can't get it to generate the 49.995MHz marker (it allows some totally different frequencies like 66.xxx MHz and some other multiples unrelated to 49.995MHz). Is this is a limitation of the AWG in how it generates fractional frequencies using a common clock, or does mine have a problem? Unit passes all self-tests so that is not the issue. Perhaps a newer (than mine) firmware addresses this issue? Thanks for any insights.

author: MaxFrister
author_rank: Regular Contributor
timestamp: September 10, 2022, 10:41:40 pm
content: I have a working LW420 but I haven't used the marker generators. Tell me exactly what you are doing and I'll try it and let you know

author: wishboneash
author_rank: Contributor
timestamp: October 15, 2022, 06:26:47 pm
content: Excuse my late reply, just came across yours.I am trying to generate markers for both Ch1 and Ch2 outputs.Ch1 is outputting 50.000MHz and Ch2 is outputting 49.995MHz. I can't seem to get independent markers which are the exact right frequencies for both channels. Externally, I am mixing both these marker signals to get a 5kHz signal which is then filtered, amplified and used for driving some other circuitry. I can't use the Ch1 and Ch2 signals because their amplitudes are quite small (10s to 100s of mV) so the mixer doesn't work too well, hence the markers.Thanks.

author: nctnico
author_rank: Super Contributor
timestamp: October 15, 2022, 07:36:35 pm
content: The markers are generated digitally and AFAIK both channels share the same clock generator. I strongly doubt you can have output frequencies on the markers that have your required precission. Likely you'll see them jitter when measured with an oscilloscope. An alternative is to use comparators on the output signals. Still I don't understand why you get small output amplitudes. You should be able to crank these up. Did you configure the anti-aliasing filter properly? IIRC you can set these manually on the LW420 to trade smoothness of the signal versus bandwidth.

author: wishboneash
author_rank: Contributor
timestamp: October 16, 2022, 02:21:51 pm
content: Quote from: nctnico on October 15, 2022, 07:36:35 pmYes, that's what I thought - it was using the same 400MHz clock for the markers. I can't use the Ch1 and Ch2 outputs for the frequency mixing is because I need the low amplitude signals from CH1 and CH2 for other circuits. It's a bit of a complicated set up unfortunately. I ended up using an external amplifier off one of the Ch1/Ch2 signals to generate the larger signal needed for the mixer (I need to adjust phase on one of the RF channel outputs only). Hope this clarifies. In any case, it's clear that this AWG can't generate arbitrary markers especially if the frequencies are fractionally related.

author: nctnico
author_rank: Super Contributor
timestamp: October 16, 2022, 05:06:01 pm
content: An external splitter and attenuator are not an option?

author: MaxFrister
author_rank: Regular Contributor
timestamp: October 17, 2022, 12:37:36 am
content: From page 13-5 of the manual:QuoteFrom page 14-4 of the manual:Quote

author: wishboneash
author_rank: Contributor
timestamp: October 17, 2022, 02:26:28 am
content: Quote from: MaxFrister on October 17, 2022, 12:37:36 amGreat. I should have RTFM!

author: iosifM
author_rank: Newbie
timestamp: March 02, 2025, 09:02:56 pm
content: I have one and it worked well until this morning when it failed the self test. I get 330 DEVICE ERROR. I'm looking for the service manual or any idea where to start looking. Thanks.