Is it game over for this nice little LeCroy scope? - Page 1
Forum section: electronics / repair

author: hchn999
author_rank: Newbie
timestamp: September 20, 2023, 06:38:26 pm
content: So I've got this "dead" LeCroy WaveJet 334A from work, and very much would like to resurrect it for my home lab - the "service" center was quoting like 3K EUR without even looking at it (saying it's obsolete, they probably want to replace the entire gut of the scope), which is obviously didn't make business sense at work and also way out of budget for my hobby activities.The current symptoms are that the scope won't start at all. "REF" and "STOP/SINGLE" buttons blink continuously plus 3 beeps are heard at regular intervals. According to the documentation (Lecroy Wavejet 300/A Series Service Manual) this is "Error code 9 - REF & SINGLE/STOP lit up - WDP-LSI FPGA configuration error". Not sure if "lit up" is "eqvivalent to "blinking REF & SINGLE/STOP" but this is all I have.Now I was present when the scope went bad, it was in daily use. We simply turned it on (with one probe in CH1 - but nothing connected), it did turn on, buttons lit up, but instead of the logo, the LCD screen went full rainbow(ish). A bit hard to describe, it was as if someone dumped a bucket of different color paint to the screen it was slightly changing with playing colors then if my memory serves, went full white. After a minute or so of marveling about the effect, we turned it off, and any subsequent power in try would result to a symptom above. I want to add that this was used at a pro lab for all of its working life, so no abuse or rough handling is likely, and it was an ESD safe environment.I took the whole scope apart (carefully following the disassembly instructions from the service manual) and there is no sign of physical damage on internal cables or components (burns etc).I have also noted that the WDP-LSI (visual display processor) is likely the big Xillinx chip sitting directly on the main logic (CPU) board. I was hoping that with a bit of luck it's a bad inverter or something relatively simple but this is as far as I got.Are there any LeCroy gurus out there who can at least enlighten me about the likely fault? Is the whole motherboard need to be replaced (game over) or does any further diagnosis makes sense? Any hope for a repair?

author: shakalnokturn
author_rank: Super Contributor
timestamp: September 21, 2023, 01:21:14 am
content: No experience with this model, however the blinking and the way the display initially went dead could point towards a power supply failure.Also because it's the best way to start troubleshooting, check the power supply voltages. If main PS rails appear good thy looking at lower supply voltages (LDO's) around display section and MOSFETs for power switching to LCD.Have you tried VGA output?

author: hchn999
author_rank: Newbie
timestamp: September 24, 2023, 08:35:35 am
content: Thanks for the tip, however I doubt it's the power supply. If I recall correctly I did measure out the 3.3V standby voltage as described in the troubleshooting flowcharts in the service manual (https://www.opweb.de/english/company/LeCroy/downloads/LeCroy--WaveJet-A_Series--service--ID13624.pdf) and also the fan does run (so 12V too must be OK).But I'll try to check all the other supply voltages on the internal headers. This particular model has no VGA output - in fact the only in/out port is an RJ45 for network access in one of the options module slot.

author: Shonky
author_rank: Frequent Contributor
timestamp: September 24, 2023, 09:10:44 am
content: A fan running doesn't mean a voltage rail is good. It means there's "some" voltage. It could be over or under acceptable limits. It could have significant ripple or other noise etc.

author: alm
author_rank: Super Contributor
timestamp: September 24, 2023, 09:18:04 am
content: When people check voltage rails for repair, this usually means checking them with (another) scope for level, ripple and noise. Excess ripple and noise due to problems with for example caps or rectifiers can easily cause the processor to fail to start while more crude devices like fans will continue to run, and a DMM might show a sensible voltage due to its limited bandwidth.

author: tooki
author_rank: Super Contributor
timestamp: September 24, 2023, 09:56:23 am
content: I would certainly look at the power supply first. At work, of the five LeCroy WaveRunner scopes I’m aware of (all models significantly more expensive than your WaveJet), two have suffered power supply failures.

author: p.larner
author_rank: Frequent Contributor
timestamp: September 24, 2023, 03:29:15 pm
content: If it was me i would recap the psu,its not expensive compaired to replacing the main board,good chance it will fix it,also put your dmm into ac volts mode and measure ALL power rails,they need to be as close to zero as possible,anything over a few millivolts means bad caps etc!.

author: dietert1
author_rank: Super Contributor
timestamp: September 24, 2023, 04:06:25 pm
content: I'd guess that scope has a real mains switch and after 10 or 20 years of daily use with strong power-on inrush currents the main power supply buffer cap gets tired. Its an electrolytic capacitor 220 uF/400 V or two 200 V caps.An easy fix. I have done it a dozen times on various scopes and computer power supplies. Modern PFC circuits also require a film cap as local mains voltage buffer. It also gets strong currents and may fail.Regards, Dieter

author: hchn999
author_rank: Newbie
timestamp: September 25, 2023, 02:45:00 pm
content: Quote from: tooki on September 24, 2023, 09:56:23 amYes we have WaveRunners too, but what were the PSU failure symptoms on yours? If in fact it's aging caps wouldn't the failure be gradual and not binary? Say sometimes the scope would start sometimes won't? Caps aging must be a slow process I assume.

author: dietert1
author_rank: Super Contributor
timestamp: September 25, 2023, 04:42:35 pm
content: Hope you will tell us once you fixed it.Another known issue with old Lecroys is the backup battery on the CPU board. It's rechargable but after all those years it may need replacement. The scopes won't boot if the voltage is below a certain limit. One day it happens or when the scope has been on a shelf for some months. We still have some 93xx scopes and they were modded with a trickle charger for that cell, so they will turn when needed - even after years.Regards, Dieter

author: hchn999
author_rank: Newbie
timestamp: September 25, 2023, 10:17:44 pm
content: Quote from: dietert1 on September 25, 2023, 04:42:35 pmSure I'll log all the efforts on this thread (this weekend is the next time I have any time for it). And yes I did measure out the coin battery too - was steady 3V still.

author: cruff
author_rank: Regular Contributor
timestamp: September 26, 2023, 12:12:23 am
content: Quote from: Shonky on September 24, 2023, 09:10:44 amI second this. I run a 12 V fan from a 5 V power supply to circulate air in my office, it spins and quietly at that voltage, not generating much sound.

author: tooki
author_rank: Super Contributor
timestamp: September 27, 2023, 05:56:44 pm
content: Quote from: hchn999 on September 25, 2023, 02:45:00 pmI don’t know what the symptoms were on the one unit, but on the one I know about, that’s exactly what happened. Startup became more and more unreliable until it quit starting up at all.