Hello,
I got a LeCroy LC684DL which is only showing random signals at all four channels
(see attached images and video at
https://drive.google.com/open?id=0B1j-dj5uKJrYS19VcDBYUGdEbUk ).
Channel 2 and 4 have some "flickering" bits, Channel 1 and 3 remain mostly static. It does not change when the coupling is changed and even showing when "grounded" or fed with the Cal.-signal. The Amplitude does not change when gain is changed, however the pattern can be moved horizontally when the delay time is changed.
The Pattern of the random signals did not change the last two years (got this scope two years ago, but had no ESD protected area to disassemble it).
Do you have any hint what could be wrong or even had a similar behaviour?
The previous owner told me it had gone bad from one day to another. Since it was already old, they just purchased a new one and dumped this one. Inside it was full of dust, which maybe affected cooling or was slightly conductive. I cleaned everything and reseated the RAM modules (in case something corroded) but it did not change anything.
KO4BB has the schematics and service manual, unfortunately this scope seems not to be designed for real repair. Measurements at the main board can not be done in working condition because the cover blocks most access. Anyway, J11 at the controller board has a few supply voltages.
From the manual:
Vcc : + 5.00V ( Min = + 4.9 V, Max = + 5.10 V ) Measured: 4,97 V
Vee : - 5.1 V ( Min = - 5.05 V, Max = - 5.15 V ) Measured: -5,19 V
+15 : +14.95 V ( Min = +14.90 V, Max = +15.05V ) Measured: 15,03 V
- 15 : - 14.95 V ( Min = -14.90 V, Max = -15.05 V ) Measured: -14,97 V
Since only Vee seems slightly out of range and I don't know how accurate my multimeter is, I didn't touch the pots at the power supply. No AC ripple could be measured.
Any advice how to measure the voltages at the main board while it's in the scope?
Since the pattern can be moved I would suspect the error near the DAC or RAM. However it is strange that all four channels failed like this.
What would you say?
My next approach would be cleaning every RAM connector with IPA and also removing and cleaning the DACs.
Regards
Cat