Wavwsurfer 44Xs it turns off instantly after a few minutes - Page 1
Forum section: electronics / repair

author: Geek459
author_rank: Contributor
timestamp: September 07, 2025, 03:46:52 pm
content: Hello to all members, recently my WaveSurfer 44Xs had some problems with CH1, which I solved by redoing several solderings on the front end.The problem was that at some point the input signal would disappear and the trace would stay in one position, and when moving the vertical position adjustment, the trace would shift and then return to the same point, as if there was a capacitive coupling.Anyway, it was resolved, but after a few months it reappeared, and last day I decided to open it up again to try to fix it ,I wish I had never done it!The channel had started working again except that after a few minutes the oscilloscope suddenly turned off.When I checked the connections, I found that the connector for the right fan had come loose during reassembly.I reconnected it, but shortly after turning it on, it turns off and the power supply goes into protection mode.It should be noted that if it is completely cold, it stays on for a little longer and during this phase the oscilloscope starts and everything works. What I noticed is that the fans spin at minimum speed and do not increase their RPM while the air that comes out is a bit warm. I also thought about the power supply, but it seems too much of a coincidence.During the time it stayed on, I managed to enter the service menu and the internal temperatures were around 50 - 55°c. It's worth noting that I installed two fans on the two ADC heat sinks, and upon refreshing the temperatures, the two internal fans changed speed (increasing it) , so i think the thermal control is ok. And from what I saw, it doesn't show any errors.I've cecked +3,3v I = 13,1A ,-3,3v I = 14,8A ,5v I = 1,5A ,-12v I = 0,7A and +12v I = 0,3A , voltage are ok , current i don't know,but 43W on +3,3 and 48,8W 0n -3,3 may be .Someone know datas of output currents of SP651 power supply?Does anyone have any idea? The other fans have always been running and the enclosure was closed. I've written also on lecroy group.Best regards, Claudio.

author: Geek459
author_rank: Contributor
timestamp: September 07, 2025, 03:48:16 pm
content: I think it's a tough race anyway.

author: Geek459
author_rank: Contributor
timestamp: September 07, 2025, 04:33:21 pm
content: I update some data.+3,3v current is 11,5A-3,3v current is 10,5AThe values from the previous post were without the front end, but without the front end the oscilloscope seems to not turn off, while with the front end it is able to display traces when cold, then it turns off.

author: Geek459
author_rank: Contributor
timestamp: September 07, 2025, 05:15:15 pm
content: I apologize, I made a mistake copying the text.I decided to remove the fan and... surprise! One of the two hooks of the spring pressing the heatsink came off and came out as you can see in the photos, leaving the chip without a heatsink. I fixed it again, reassembled the fan and heatsink and it has been working for 20 minutes. Sometimes coincidences...

author: Geek459
author_rank: Contributor
timestamp: September 07, 2025, 05:17:07 pm
content: Now photos

author: JOSDHO
author_rank: Contributor
timestamp: September 09, 2025, 07:57:16 am
content: It sounds like you’re dealing with a power supply or cooling issue, especially since the oscilloscope stays on when it’s cold, but turns off as it warms up. It’s good that you checked the fans — they should be running at a higher speed when the internal temperatures are around 50-55°C. The fact that the fan RPM doesn’t increase suggests that there might be an issue with the power supply not delivering enough current or the thermal regulation not properly scaling the fan speeds.Since you’ve already checked the voltage outputs (+3.3V, +5V, +12V), I’d focus on the +12V and -12V rails. The power supply could be throttling or going into protection mode if there's an issue with current draw or overheating. You mentioned the SP651 power supply — it might be worth checking its data sheet for current limits on those rails and whether the supply is shutting down due to thermal overload.Also, if the power supply doesn’t stay on even after reconnecting the fan, you might want to check for loose connections on the power supply pins, as intermittent issues can cause the protection mode to kick in.Lastly, since the fans spin slowly at first, the thermal sensor in the PSU might be detecting something abnormal with the heat sinks. Try testing the fan speed manually by using an external power supply or forcing it with a PWM controller to see if the fan operates correctly at higher speeds.

author: Geek459
author_rank: Contributor
timestamp: September 09, 2025, 10:33:09 pm
content: Hi Josdho ,i've tested the dso and now , After fixing the mounting system of the central heatsink, the oscilloscope works perfectly. I also fixed CH1, which was not working. The CH connector from the front end to the acquisition board had some pins that had come unsoldered after 18 years, but it works when held pressed. So, I secured the connector with two M3 screws in the already existing holes, using appropriately shaped nylon washers to avoid pressing on the nearby SMD components. This way, it has returned to functioning at 100% regarding acquisition and functionalities. However, the fans remain at low speed, and the temperatures of the ADCs reach over 85°C. By entering the service menu, I can set the fans to manual and adjust the duty cycle percentage for their operation, yet the temperatures still remain around 80°C after 30 minutes of operation.I've testsed +3,3v,-3,3v,+5v,-12v,-12v, no ripple or fluctuaction,the current on +3,3v rail is 10A and in -3,3v 12A ,i don't know if is ok , in the service manual are not mentioned.The strange is that when i've started the scope once "repaired" the deskew was -41000 in every channel , i've reloaded the firmware but never change , i suspect some problem in the microcode (regarding the fan speed) tomorrow i try to reload the calibration data on D drive , but i do it beacouse i am at the fruit.I've contacted a local lecroy service and i'm waiting for some suggestions.I think that my 44Xs was at the end of his life.

author: Geek459
author_rank: Contributor
timestamp: September 11, 2025, 01:07:46 am
content: Is there anyone who has a wavesurfer 44Xs who can check the indicated temperatures in the service menu and let me know if those of mine are in line, as well as the fan settings? You enter the service menu with 9472. Regards, Claudio.