Electronics > Repair

Repairing a LeCroy WaveAce 222 Oscilloscope That Doesn't Power On

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tautech:
Good job but don't you hate it when that happens ?  :rant:

You ask yourself what was learnt......to inspect more carefully or was it a dodgy header connection ?  :-//

Anyways, it's running and that's all that really matters.  :phew:


BTW, who manufactured those Waveaces for LeCroy ?
Are there any clues on the mainboard ?

The_PCB_Guy:

--- Quote from: tautech on April 06, 2019, 07:56:25 pm ---Good job but don't you hate it when that happens ?  :rant:

You ask yourself what was learnt......to inspect more carefully or was it a dodgy header connection ?  :-//

Anyways, it's running and that's all that really matters.  :phew:
--- End quote ---
Yep. You hope it's an interesting problem to fix and that you learn something really neat in the process of troubleshooting/repairing it, but it ends up being something as dumb as a bad solder joint? Oh well, I am glad it's working anyway. Most likely there was a microscopic crack in the solder joint(s) that wasn't visible through a magnifier and reflowing it/them fixed it right up.


--- Quote ---BTW, who manufactured those Waveaces for LeCroy ?
Are there any clues on the mainboard ?

--- End quote ---
I never pulled out the main board and didn't look too closely (other than seeing a vertical double-stacked ceramic cap). I'm afraid I couldn't tell you who actually builds them.

johnny.tifosi:

--- Quote from: The_PCB_Guy on April 06, 2019, 01:21:39 pm ---As promised, here are some initial (general) photos of the layout of the PCB. I would be happy to take more detailed photos upon request.

UPDATE: I desoldered all six of the main capacitors on the secondary side of the transformer and all of them test ok. No issues (as expected, considering their brand). The bad news, of course, is that since the caps appear to be fine, I am not much closer to solving the issue.

UPDATED UPDATE: Well Gents, I take it back. I now have a working scope. Looks like it may have been a cracked joint after all. I resoldered all of the caps back in place with fresh (leaded!) solder, et - voila! The scope works!

Thanks very much for all the help guys!

Matt

--- End quote ---

Hello,

I am trying to repair my WaveAce 112 power supply which happens to be exactly the same and just registered in order to revive this topic (sorry for that). Could you please tell me which are the nominal voltages in the secondary side? Some info I figured out myself is the board has five DC voltage rails. Four are generated by the larger transformer and routed to a ribbon cable, of which one is negative, one is the master positive rail, and two are 3.3V and 15V rails generated by LDOs from the master rail. There is a fifth one generated by the smaller transformer and routed to a pin socket.

Initially, the power supply was not functioning at all and making a periodic chirping sound. Then I replaced a shorted TVS diode in the primary side snubber circuit with a beefier one and I get some voltage readings in the secondary, that is -28V, 3.3V in an LDO regulated rail, 9V to 15V fluctuating in the master rail, 15.4V in another LDO regulated rail and 0V in the pin socket (multimeter measurements). But I still get burned 5ohm resistors (R49) in series to the optocoupler output. I have replaced the TL431 and 4N35 ICs in the feedback circuit to no avail. I attach some schematics I made of the secondary side and feedback circuits by observing the board (still WIP and may have some inaccuracies), I am preparing the primary side schematic too. Any help is much appreciated! Cheers

johnny.tifosi:
Here are the updated schematics, for which I dedicated far too many hours to figure out. Transformer pinout is not certain but you get the gist. Initially the TVS D2 in the primeary snubber was burning, I replaced it with two in parallel and I got two rails to work as described in my previous reply. The master rail is fluctuating a lot though, and the 5 Ohm R49 and Shottky D4 in the feedback circuit are burning after a while. I wonder how the opto output is has only two 5 ohm resistors in series, I haven't figured out the operation of this circuit. It is connected to a pin on the primary side of the transformer, but internally it may be a secondary winding because there is no way it could handle 320V.

johnny.tifosi:
I got access to a differential probe and measured the DC rectified voltage which was perfectly stable at 315V, the V_DS voltage of the MOSFET and the output voltage V_OUT2 (waveforms below). The V_DS was ok-ish with some significant ringing, V_OUT+2 though has some weird voltage drops similar to RC discharges about 0.66s apart. Any clues?

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