LeCroy Wavejet 332 DSO Repair

[Jay The Engineer]

G'day Forum Goers,

I recently acquired two LeCroy wavejet digital scopes. One is the 332 model (350Mhz, 2GS/s) and the other being the 322 (which is 200Mhz from memory). They both boot up and run but the 332 has had CH1 blown to buggery,  it has actually blown a hole half way through the board where a surface mount cap and resistor use to be on the input. It looks like from there it lead off to the relays. It has done a fair bit of damage in that area but I think its fixable with a bit of care. I will pull the scope apart and get some pictures over the next few days Otherwise the 2nd channel works fine so I have been using it for basic stuff but being able to use math and cursor functions on both waves would be handy.

The other scope also has a blown channel but no where near as bad, (I do have a picture) its only the first capacitor that's is visibly blown and it looks like you could just solder one strait back in with some care. Im assuming some massive voltage has been fed up them to do this but my question is it likely to have damaged the actual signal processors or do these input resistors / capacitors that are blown act as a sort of protection circuit for the rest of the front end meaning that it should still function ok. I realise that it probably wont be good for 200 /350Mhz again. Also if I do attempt to reconstruct it do I need to use special components. Im thinking standard resistors would be easier to work with but will they stand up to the high frequencies, likewise will run of the mill caps do the job or do I need to source specialised stuff.

The 2nd 200Mhz scope has a display issue where the top half of the screen is jumbled up, I took the lcd apart and reseated the ribbon cables on everything and nothing changed, is this likely to be repairable? 

I will insert pics of the display, the 200mhz (less damaged then the 350) front end and the 350MHz in action with a sound wave from some inxs vinyl. I would appreciate any input, especially weather these are good scopes or not. From my limited use of tek and agilent  digital scopes these seem as good, probably simpler / nicer to use as a novice but dont have the complex math functions of the late model agilent but these are from 2007 and owe me nicks so it can be forgiven (ill have to revert to pen and paper for phase angle ect).

I am half way through an electrical engineering course and have function generators, crt scopes and all the other bits and bobs I need to experiment with my labs at home but if I can get at least one digital scope going properly it would be a great addition to the arsenal.

Thanks allot,
Jay

[tautech]

Welcome to the forum Jay.
These should be a good punt I would think, even if you make only one goody from the 2.
The concern for me on the blown PCB, are internal layers if any damaged?
At least you have a hopefully good channel to compare measurement to.

In the meantime, you should swap parts around to get the 200 MHz model display working correctly.
OR
Careful inspection of both units HW may indicate they are identical except for firmware.
Depending on the modular construction, you might be able to swap the input PCB's to fix the 350 MHz model.

[Jay The Engineer]

Sorry about the heading, it was a typo.

Both scopes have blown channels, I should have been clearer but even I get confused at what im writing. The only difference I can see between the two is a resistor on one of the front end boards. There seems to be 4 different resistor positions depending on the model.

I think the board is 4 layer (2 each side) but there doesnt appear to be much under the damaged areas (would the layers underneath be ground planes?). There is a fair bit of through hole stuff as you would imagine and on the 350Mhz model the board has blown components on both sides around the relays whereas the  200MHz one only has the one cap that i can see.  you can trace the blown components from the bnc across and through the board into a relay.

Is it likely the damage has gone any further then the obviously blown components? I have a bad feeling that it wouldnt have done the rest of the front end any good. Maybe blown relay contacts ?

What is the issue likely to be with the screen? damaged edge ribbon? display processor? etc etc ?

Thanks,

Jay

[tautech]

Both scopes have blown channels, I should have been clearer but even I get confused at what im writing. The only difference I can see between the two is a resistor on one of the front end boards. There seems to be 4 different resistor positions depending on the model.

Take your time to become very familiar with these scopes, as it may be to your benefit to the tune of 2 x 350 MHz scopes. 

There seems to be 4 different resistor positions depending on the model.

Are all of these populated?
They may set the bandwidth.

I think the board is 4 layer (2 each side) but there doesnt appear to be much under the damaged areas (would the layers underneath be ground planes?).

You will need to check for continuity/shorts.
You may need to clean these areas up.....carefully to prevent any future tracking on the carbonized areas.

Is it likely the damage has gone any further then the obviously blown components?

Possibly, but proceed with the repair and take it as it comes.

Screen, sorry could not offer advice other than to use your scopes to compare signals to isolate where the problem might be.

[abel_li]

Hello there.
I got a faulty 312 model and the power supply was fixed very badly. Now I need some HD photos on the back of the power supply. Thank you very much. My email address is: abelee@foxmail.com