LeCroy 9384

[jens399]

Hello, i have a problem with the power supply. I found out that one loading capacitors was shorted. There are two in series connection behind the rectifier. Sorry i have only a very bad schematic, so i can't tell you the devices name, but you see them in Dave's video here on 19:25. My one is very clean, the scope was not much used. I chanced them two times, the second time the rectifier too. I also checked the Caps for leak current before, because i don't know how old they are. It was ok. Both times the scope worked for 15 minutes, than the fuse blows. And the Caps become very hot. Thats what i don't understand. Why does this happen? The primary current was about 1,5A what ist normal i think.

Does anyone have any idea? It would help me much, because it's a very good scope and i would be very sad if i had to scrap it.

Thank you very much in advance

[mij59]

Hi,

Could be a case of bad cap's.

Did you check the power supply rail voltage ?
Got a capacitance / esr meter?

[swingbyte1]

hi, Capacitors should not get hot.  This means they are using real power and as we all no an ideal cap is purely reactive.  In the real world, real capacitors exhibit series resistance and with age some capacitors series resistance increases and this is what disipates power as heat.  Replace the capacitors that get hot with new ones.
When things stop working after warming up you usually have a mechanical issue.  It could be that the heat from the hot components is tripping a thermal sensor or opening/closing a gap in the circuit thats causing the trip.

Good luck

Tim

[jens399]

hi, Capacitors should not get hot.  This means they are using real power and as we all no an ideal cap is purely reactive.  In the real world, real capacitors exhibit series resistance and with age some capacitors series resistance increases and this is what disipates power as heat.  Replace the capacitors that get hot with new ones.

The first capacitors were produced in 2007. After that i ordered other them form another supplier. They could not tell me how old they are. But i checked them for leak current. I will try to form them again. Maybe that will help. There are not so many supplier that can deliver such caps.

When things stop working after warming up you usually have a mechanical issue.  It could be that the heat from the hot components is tripping a thermal sensor or opening/closing a gap in the circuit thats causing the trip.

No it's not a mechanical issue. There ist a Fuse at the PCB 5A that burns.

Good luck

Tim

Thanks 

[jens399]

Hi i found out that the internal switching for 110/230 Volt ist out of order. I need a readable schematic to repair this. i could find only this http://www.opweb.de/en/model.php?id=7987 but here i can't read anything. Does anyone have a schematic. i need only the page with the power supply. Thanks

[AlfBaz]

The schematics in the service manual here no good?
http://www.ko4bb.com/manuals/index.php?dir=LeCroy

[jens399]

Thanks thats the scan i already have. I need Page 7-203 oder 415. It's not possible to read any devices designation. I can't identify how they switch the input voltage.  What's in these little box?

[PA0PBZ]

Are you sure it has to switch between a low and high AC input? In the manual they say: Power: 90–250 V AC, 45–66 Hz, 350 W, which looks like it is continuous.
And there is something looking like a NTC on the top side of the switching device (RV1?)
But yes, the quality is so bad that it leaves a lot of guessing.

[jens399]

yes i think so, it's a 9384c maybe it's a little bit different?

[Wuerstchenhund]

There is a Service Note from LeCroy which recommends to disable the auto-range circuitry in the PSU of LC Series scopes. As the 9384 (which is a bit different than other 93xx scopes) is very similar to the LC Series (which just has a color screen and faster processing over the 9384) it should apply to the 9384 as well:

https://xa.yimg.com/df/LeCroy_Owners_Group/LC5xx_17+-+Removing+Autorange.pdf?token=Vnc-19ohshZAcdrCQ6T4pAE8pc9Pylz2JnZderIIxjyF9Ai4gXZuWOTAox4H7jgzDIR4-cSBU6IXAJorCMrJOICIdaDMTylVVJVQO3-64XllzmYeBZWvJEEMnyr4rKk9C6pi-7qovwa6s8xf-iwyChVY-LqCflSwhoVY_FFEWxlrlywZXl0JY33Tf6v8NLMU9WWhIkdLUi-qHOnJhIWz1hsZgGzoZvzh_U0CncBnSQ&type=download

Apparently the auto-range circuitry was pretty prone to failure, so LeCroy recommended to remove it from all LC Series scopes.

[swingbyte1]

Hi,
1. join the Yahoo Lecroy group
2. the main board of the 9384 is the same as the lc574 so download the manual for that as the schematics are better and main help with other parts as well.  CPU board is not the same.
good luck