Electronics > Repair

Is it game over for this nice little LeCroy scope?

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hchn999:
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?   :-//

shakalnokturn:
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?

hchn999:
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.

Shonky:
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.

alm:
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.

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