I recently bought a Lecroy 9424 oscilloscope in an auction: a 4 channel digital (aged) one...
While testing, I found out no valid channel/traces are shown on screen: a weird ugly 8khz repetitive non-sinewave signal is shown on all channels, regardless of any setting chosen...
Started debugging the fault(s)... looking for a service manual...searched the internet, but did not find a manual for free... but found a service doc for the 9450 where the frontend looks very similar... hence started debugging using this one
So far, I found 2 rootcauses for defects:
1. a 74HCT4094 lacking output signals causing some leds not been displaying some settings on the front.
2. the supply of the front-end has a huge 4V ripple on any supply: replacing the 6V supply by a standalone labsupply solves the ripple (6V @ 280mA - no clue if this within spec) --> suspect a LM78GCP regulator being defective.
Right now, there is one problem I could not solve yet: the 1MOhm input (OAC and DC) of channel 1 is failing the built-in calibration. Anythin else seems working...
Does anyone know how this 1MOhm AC&DC input/calibration is working? And/Or a hint to the rootcause to solve this issue? And/or owns the 9424 service manual?
While testing, I found out no valid channel/traces are shown on screen: a weird ugly 8khz repetitive non-sinewave signal is shown on all channels, regardless of any setting chosen...
Started debugging the fault(s)... looking for a service manual...searched the internet, but did not find a manual for free... but found a service doc for the 9450 where the frontend looks very similar... hence started debugging using this one
So far, I found 2 rootcauses for defects:
1. a 74HCT4094 lacking output signals causing some leds not been displaying some settings on the front.
2. the supply of the front-end has a huge 4V ripple on any supply: replacing the 6V supply by a standalone labsupply solves the ripple (6V @ 280mA - no clue if this within spec) --> suspect a LM78GCP regulator being defective.
Right now, there is one problem I could not solve yet: the 1MOhm input (OAC and DC) of channel 1 is failing the built-in calibration. Anythin else seems working...
Does anyone know how this 1MOhm AC&DC input/calibration is working? And/Or a hint to the rootcause to solve this issue? And/or owns the 9424 service manual?