Lecroy Wavemaster 8300A repair.

[djsb]

Our Lecroy Wavemaster 8300A causes the lights to flicker when we plug the IEC mains lead into the instrument. It also happens when we switch the mains socket on. This is accompanied by a brief spinning up of fans, a flicker of the display backlight and then a constant fizzing sound. I'm guessing that something is amiss with the switch mode power supply filter. When we press the on switch, the instrument turns on. There is a LECROY logo and then a Windows XP boot logo output from the VGA output but nothing but various colours and then a slate colour on the main screen. The rest of the instrument carries on booting up (I.E the LED's on the keypad light up and respond to keypresses).
We have the case lid off, and now I'm wondering how to gain access to the main power supply, which seems to encompass the full width of the instrument. What do I have to remove in order to get to the internals of the power supply for inspection? If you need any photos, please ask and I'll post them during the week. Thanks.


P.S I also posted this on the Groups.io LeCroyOwnersGroup. No replies as I write this

[nctnico]

My Lecroy 7300A also makes a fizzing sound when off, the display turns on and the fans switch on briefly when power is applied so all that seems normal. The fizzing sound is likely the standby power supply which is out of regulation due to a light load.

If the VGA output is normal then you likely have a problem with the AGP (IIRC) video adapter board. In my 7300A this board is of poor quality and fit. What you can try is to take the AGP board out and clean the contacts with alcohol. Give the AGP slot itself a rinse with alcohol as well. TFT panels typically show all kinds of colors and then turn grey when there is no valid video signal coming in. I had a similar issue with my 7300A. Under no circumstance use contact spray!

The flickering of the light could be a power inrush limiter problem but for as long as the fuse/breaker doesn't cut out, I'd leave the power supply where it is. You'll likely make things worse instead of better. If the 8300A is constructed the same way the 7300A is constructed, removing the power supply looks like a hell-ish job to me with lots of chances of breaking things. As usual, Lecroy has not really thought the mechanical design through where it comes to maintainability.

[djsb]

The AGP slot on the Intel mainboard has a Touchstone Technology adaptor card plugged into it. There is a ribbon cable plugged into this adaptor card, which disappears under the mainboard after travelling through a large ferrite bead. I've unplugged the card from the AGP slot and cleaned the contacts with IPA and then plugged it back in (I've also done this to the card that contains lots of XILINX FPGA chips and has multiple cables with a different coloured dot on each cable plugged into it-No change) and the problem persists.
I've got a copy of Clonezilla to boot up so at least I may be able to get the Ultra ATA hard drive backed up to USB. Are there any old video test utilities available that can test the AGP?

[nctnico]

I have made some pictures of the inside of my 7200A in this thread:
https://www.eevblog.com/forum/testgear/upgrading-mainboard-in-lecroy-dda-3000-(aka-wavepro-7300a)/msg2748842/#msg2748842

There are more in this Flickr album:
https://www.flickr.com/photos/133456893@N03/albums/72157711425612368

In the 7200A the ribbon cable from the video adapter board goes to a seperate board where the signal is converted once more and goes to the display through an FPC cable. The problem could be somewhere in there as well.

[djsb]

I've now got the display working (apart from some occasional colour drift). It was a loose ribbon cable on the display board. I now have 3 channels (1,2 and 3) where the waveform trace disappears when the volts per division is set to any value LESS THAN 2 volts and triggering does not work (when the trigger level pointer is next to the waveform the trace does not stabilize). Everything works as expected on channel 4. It appears something has been damaged in the attenuators. As I don't have any systems block diagrams or schematics, it's going to be difficult to know where the problem is.

[hpw]

About the LED. May clean the front panel from any dust (not an easy mechanical task as to remove the fan's).

May exchange the 24 step encoders as time base is the often culprit as jumping steps.

The no dedent models (for fine tuning) no any longer on sky (Bourns without any notch), only detent models order able

[nctnico]

You can try to reseat (disconnect/connect) the attenuators. Unfortunately these are not easy to take out. Reseating  worked for me. If the mechanical part is the same as the 7000 series, make sure the standoff under the attenuator doesn't get undone when trying to undo the screws of the attenuators. Otherwise the whole assembly gets pushed up.

[djsb]

How can I tell if there is damage to the rotary attenuator pots/encoders (they have a distinct step when they are rotated)or if the there is damage to the input stages of the Y amplifiers themselves?
It's strange that on all 3 channels (1,2 and 3) the trace disappears on ALL volts per division settings over 2 volts. I could try to remove reseat any connectors on the assembly that holds the rotary encoders behind the front panel.

[hpw]

How can I tell if there is damage to the rotary attenuator pots/encoders (they have a distinct step when they are rotated)or if the there is damage to the input stages of the Y amplifiers themselves?
It's strange that on all 3 channels (1,2 and 3) the trace disappears on ALL volts per division settings over 2 volts. I could try to remove reseat any connectors on the assembly that holds the rotary encoders behind the front panel.

Rotary Encoders: just smoothly turn any decoder as with 24 steps. If you get a a missing or larger unexpected steps, then it is likely the encoder or the cause of black dust. Even the none detent models, follow a digital step inc/dec.

As LED's completely off, black dust as hell on the mentioned panel.

I simple reduced the fan ALU holder, so remove and mounting gets smoother, but the damping foam have to be replaced. Anyway if you go for any smoother fan's or using 14cm fans with required 12 to 14 cm adapter (3D print)

In addition if you use an XP with a dual CPU (3GHz Models), a special masking driver is required otherwise LED flashing will occur.

I could not go further than XP, otherwise XStream or Touch driver gets any wired.

Also 3V battery to replace as stops the main board on boot.

Happy tuning 



 

[nctnico]

How can I tell if there is damage to the rotary attenuator pots/encoders (they have a distinct step when they are rotated)or if the there is damage to the input stages of the Y amplifiers themselves?
It's strange that on all 3 channels (1,2 and 3) the trace disappears on ALL volts per division settings over 2 volts. I could try to remove reseat any connectors on the assembly that holds the rotary encoders behind the front panel.

You can set the channel parameters like offset, range and so on manually as well IIRC through the user interface. So try this first. Not saying the front panel is without potential issues though but save that for later.