lecroy lc564

[Daxxin]

All the times powered up for about 5 minutes working fine then when warmed  start to display waveforms with vertical lines glitches on all 4 CH's and display this error 'CL_measure_gain_and_offset cntrl? x '     x is a number not all the time is the same , hlp pls    ,   CL_ stand for clock level?

[Rémi]

Hi Daxxin,

I'm trying to repair an LC334 and it has the same symptoms as yours. Did you find a way to fix the problem?

Rémi

[Armadillo]

Friendly MMI but sound like a helicopter. 

I would say, check the power supply voltages and ripples first.

[shakalnokturn]

Does changing sample rate give different symptoms?

This is probably a known (getting common by now...) problem on the 500MHz sample clock PLL.

Of course checking power supply is always a good starting point.

[Rémi]

Exactly, when I reduce the timebase, the signal looks ok.

Regarding the power supply, this was the first step in the repair process. When I received the oscilloscope it was not turning on. After investigation and the help of the Lecroy Yahoo group I was able to find an open resistor on the primary side of the transformer (R4, 47k). This resistor is known to fail and prevent the power supply from starting.

I also found a message in the yahoo group about the PLL problem. The suspect is a MC12148 VCO chip. I'm waiting for some cold spray to test if the failure disappears when the chip is cold. Attached is a picture of how the problem shows up on the screen.

[Daxxin]

Hi ..even for me with cold spray problem disappear , it was a shortened cap inside the vco metallic enclosure.

[nonlinear]

First of all - do not run lower board w/o cooling if you disassemble the beast!
Overheat is imminent. Use some fan - I use usual big room fan blowing at the
PCB (hate it buzzing in my ear :-) ).

Problem you have looks like some part of the circuit looses the clock or enable signal.
Clock loss is more probable so main PLL is surely under suspect.

1. Voltages of PS.
- clean the blade contacts of PS as they are a common failure point
- check PCB of PS/frontend whether PS contacts have good soldering to the PCB
- check voltages

2. Clock generator.
- try it at different frequencies (horizontal time ranges) - VCO may work at one freq and do not work at the other
- you may try to supply external clock if you have an appropriate rear BNC connector
- VCO control voltage should pulsate if frequency is unstable (if you cannot directly check 500M with oscilloscope or SA)

3. Mechanical sensitivity checks.
- push components (chips, connectors, ...) try to see any changes on the screen

4. SM is available for LC6XX series - try to find where signal is frozen by checking different stages.
- first point are ADCs inputs (checking S/H operation if they loose clock)
- next are ADC outputs
- finally check frontend<>CPU_PCB bus

[Stray Electron]

First of all - do not run lower board w/o cooling if you disassemble the beast!
Overheat is imminent. Use some fan - I use usual big room fan blowing at the
PCB (hate it buzzing in my ear :-) ).

   Take this SERIOUSLY.  There is NO cooling what so ever on the main board in the LC series when the case is open.  The main circuit board is UNDER a large metal plate and blowing air on top of it does NOTHING to cool the main board. One of the LeCroy service manuals mentions using a special duct to insure cooling when troubleshooting them.  Even if you blow big a fan on it, it won't be enough.  Look at Dave's tear down of the LeCroy 9384 and you can see how divided up the main board is with heatsinks and you can see why the air MUST flow along the correct path. (The 9384 is the same basic board as the LC series and, also I THINK, also the LT series).  I've had some luck by using two squirrel cage fans to blow air into the grills on both sides of the main board but the longest I have been able to run my LC without it overheating is 12 minutes.  Without the fans, it overheats in less than a minute. Damage from overheating seems to get progressively worse and so far on mine has been irreversible. 

  YMMV.

[shakalnokturn]

My quick and dirty approach to cooling a 9354 scope, it should be applicable to a LC.
A couple of radial fans would be much more convenient for moving around while probing.

[Rémi]

Thanks for all the recommendations. I will use two fans for cooling the boards while troubleshooting...

[Rémi]

It has been a long time since I started the repair of my LC334AM. Unfortunately I was unable to solve the problem with the PLL. I've changed so far the MC12148 and the 10EL32 chips but it didn't solve the problem. I don't really know how to further progress since the problem appears only when the scope is closed and the metallic enclosure is on the PLL board.

If someone has some idea how to debug...

Thanks

Rémi

[shakalnokturn]

Partly in response to a recent PM from Rémi:

Attached is a service note from Sam Reaves of the LeCroy dedicated groups.
It is for the 9354-4 PLL, I think this should apply to the LC series too.

As for being sure that the SH clock is the cause: You'll need some way of checking that it goes unstable when warm, either a fast scope with persistence, jitter meter, S.A., frequency counter...

[plantex]

Hi Guys

It seems like CL_measure_gain_and_offset failure is a common problem. I have a LC334AM shows the same msg as Remi's.

@Remi
Any luck in servicing your's ossciloscope ?