Dead LeCroy 9414 - Page 1
Forum section: electronics / repair

author: davorin
author_rank: Unknown
timestamp: September 06, 2014, 01:57:47 pm
content: Just wanted to install my 9414 to measure noise from different fans in my 9354AL....worked before like a charm...and now suddenly dead as a mouse...When powering on...no lights on, also fan is not running....when switching off I hear some relay clicking...Don't they have some primary switched power supply to generate all voltages?Running now the service manual through Acrobat pro to make a searchable PDF (o;

author: davorin
author_rank: Unknown
timestamp: September 06, 2014, 02:56:07 pm
content: Got the manual searchable now...Interesting....only thing I can found regarding "removal of power supply" is just this small text:QuoteRemoving the card retianer makes no sense to me....and removing the power supply support makes it somehow loose...but power supply can't be removed....And a very nice design that is so damned close to the CRT neck to kill it by accident...ANyone a suggestion how to safely remove the pwoer supply without killing the CRT neck?

author: grumpydoc
author_rank: Super Contributor
timestamp: September 06, 2014, 03:39:59 pm
content: QuoteRemove the whole front panel including the CRT, then you can put it aside while you get the PSU out - it all pulls off as a single unit and there are just two ribbon cables connecting it to the CPU card - one for video and CRT power and another from the front panel rotary encoders and switches.

author: davorin
author_rank: Unknown
timestamp: September 06, 2014, 04:27:38 pm
content: Ah thanks...will try that tomorrow carefully...My desk is still occupied with my 9354AL and me busy doing different fan testing/measurements (o;Wondering if the power supply is repairable at all...or someone ran into the same problem...but when I look at the schematic and block diagram...all it does is +/-5V and +/-15V....and RefZ..

author: davorin
author_rank: Unknown
timestamp: September 07, 2014, 04:27:30 pm
content: Got the power supply out now....without removing the front panel...besides..the description in the 9410 manual isn't that helpful like in the 935x manual...See nothing suspicious on the power supply module..nor does it smell like burned resistor, capacitor and the like...high voltage transistor is also okay...and from the clicking noise when powering off I suspect some rail DC rail is shortened to ground and protection circuit kicks in...Think I have some 5V 10A switcher supply somewhere on stock..and the +/-15V rails I can feed from my 6632Bs.Okay...got the pin numbers from board 9424_1:Code:1: Line Sync2: GND3: VCC4: GND5: VCC6: GND7: VEE8: VEE9: +15V10: -15V

author: davorin
author_rank: Unknown
timestamp: September 07, 2014, 05:23:10 pm
content: Hmm....doesn't power on when removing the plug with +/-15V going to the deflection board...ANd when switching off the fan turns quickly....assuming the protection circuit looses power more quickly than primary capacitor...causing the switcher to run for a while...What I don't get is the strange circuit around the LM324 controlling the transistor/diode pairs in parallel of the secondary windings of the flyback transformator...

author: davorin
author_rank: Unknown
timestamp: September 08, 2014, 04:35:22 pm
content: Some more findings..though not bringing me to the solution (yet ;o)When powering on, the switcher doesn't kick off at all....and therefore the overvoltage/current protection circuit doesn't get a power supply....so an overload condition can be excluded...Also checked that with either only the CRT deflection unit connected, or only the logic circtuis...Interesting is the fact that as soon I switch the device off...the switcher starts working...as I can see a small 100msec peak on the +/-V rails for the protection circuits....that's also when the fan kicks in shortly...Any idea why the switcher won't start at the beginning?Attached the waveform of the secondary winding feeding the protection circuit...

author: davorin
author_rank: Unknown
timestamp: September 10, 2014, 02:45:14 pm
content: Just replaced some capacitorrs on the power supply board...namely the two big ones (470u) and the two smaller ones around the switching controller hybrid circuit (10uF and 820uF)...Still doesn't kick in when powering on...but oddly...when I shortly power it off and immediately back on again...the DSO runs just fine ;-)Can't seem to find the component which is responsible to start the switcher when power is applied....and wonder why it kicks off when the supply voltage decreases...

author: tautech
author_rank: Super Contributor
timestamp: September 10, 2014, 08:15:14 pm
content: Been watching youwith this scope.Can you solder a lead on the VDD pin of the switcher to check sufficient power is available for startup?If there is, one then might suspect the feedback to the IC?Any datasheet available for that IC?

author: davorin
author_rank: Unknown
timestamp: September 10, 2014, 08:21:31 pm
content: Would be nice to know which one is the Vdd pin on the module...it's just a small PCB molded in some strange resin or the like...I can start the DSO when I power it on/off/on few times...then it works normally...My last resort is to use some AC/DC switching modules from Mean Well, which are low-cost...namely RS-75-15 and RS-50-5 for getting 15V DC and 5V DC.

author: tautech
author_rank: Super Contributor
timestamp: September 10, 2014, 08:47:46 pm
content: You may have to draw out the area around the switcher to gain some understanding.Often in the cheap SMPS's a 10-22 uF E-cap is between the VDD pin and GND and sometimes the supply for it comes from a high value resistor from rectified main for startup, then a "running" supply comes from a feedback winding. Normally a diode in series from the feedback winding.Others rely on the feedback winding and the voltage feedback loop to "kick" off.Grab a few datasheets for switcher IC's and look at various applications for clues to the LeCroy switcher operation.

author: davorin
author_rank: Unknown
timestamp: September 10, 2014, 08:54:51 pm
content: Well my guess was a capacitor with decreased value....reminded me when in good old times I repaired a Panasonic VCR with couldn't be switched on....the owner told me I could keep it if I could repair it...as the TV shop wasn't capable off....turned out to be a bad capacitor lost his value over time...which was responsible to filter peaks of detected load current for the overcurrent protection.Anyway....biggest problem is now to get hands on a transformator to galvanically isolate it from main line to hook up a DSO...Just have a big one here...when powering on the whole basement gets dark (o;Another problem is that the schematic in the service manual is barely readable....