Lecroy Waverunner 64Xi-A no power - Page 1
Forum section: electronics / repair

author: analogRF
author_rank: Super Contributor
timestamp: November 27, 2024, 06:16:44 pm
content: My newly arrived 64Xi-A (black case, red acq board, Win7 32bit) does not power on. The power button works (turning on and off) and fans work but that's itBlank screen with no beep or any sign of life other than the fans.I confirmed that the motherboard alone boots normally into windows 7 with external ATX power supply and still with the scope's LCD/front panel (no need for VGA monitor). The CMOS battery is new and no issue there.I want to power up the damn PSU alone with the motherboard and no acq board but I dont know how.The regular PS_ON (green wire) on ATX connector does not power up the PSUDoes anybody know how to power up the PSU and motherboard without the acq board?

author: analogRF
author_rank: Super Contributor
timestamp: November 27, 2024, 07:58:23 pm
content: I have traced back the power on key from acq board to the cpu board power on key. so it's wired like a regular PCbut it seems not to be enough to turn on this thingI think there might be some sense lines that the PSU needs to check and if it doesn't see them it wont power on...who knows where the sense lines are if that's the caseat the moment the only way to power it on is to have all the 3 connectors connected to the acq boardthen it powers on but with blank screen and fans spinning no sign of lifethere is no access to the ATX connector on the cpu board in this state but on the acq board it seems all voltages are ON except the important +3.3V (+/-12,+5,-3.3 are present) so I guess that is the problem although I dont know how this could prevent the motherboard from coming on but I dont have access to the ATX connector so maybe something is also missing thereanybody has any clue?

author: analogRF
author_rank: Super Contributor
timestamp: November 27, 2024, 08:47:08 pm
content: the +3.3v missing on the acq board is indeed the same that also goes to the PC motherboard so that explains why the PC does not bootnow the question is what has happened to the 3.3V.any previous experience?this PSU is mad complex with soldered on daughter boards all over the place for each rail....I asssume the primary side and switching must be ok because all other rails are present except this onewhich measured 0.3V on the acq board. can it be the output caps? physically they look ok.I hope it is not something on the daughter boardthe problem is I cannot power it on to work on it. so I am blind...

author: tooki
author_rank: Super Contributor
timestamp: November 27, 2024, 08:57:53 pm
content: At work, we've seen a lot of WaveRunners fail with power supply failure. Basically, nearly every one we have that's more than about 5 years old has failed. (My colleague has fixed something like 5 or 6 of them by now!!)The problem has been the standby power supply caps failing, and without the standby supply, the rest of the power supply can't start up.I don't know if your model failed the same way (it kinda sounds like a different failure mode), but if the root cause is the same -- cheap electrolytic caps* -- then maybe this gives you a place to start looking.* I told our LeCroy rep that I think it's indefensible that they use cheap caps in instruments of this price class, and that this is something that will play into future scope purchases. At these prices, I expect only top-brand capacitors. It's not as though we are talking about more than a few dollars price difference.

author: analogRF
author_rank: Super Contributor
timestamp: November 27, 2024, 11:44:52 pm
content: standby is not an issue here and all the rails come up except the +3.3Vthe big elec caps are all Nichicon but still I suspect my problem could be a bad cap.i just wish there was a way to power up the PSU alone to do work

author: coromonadalix
author_rank: Super Contributor
timestamp: November 28, 2024, 10:07:07 am
content: can you supply a 3.3 volt to it ? and see the reaction ? do you have some pictures to show us how the psu looks ?they are pc based ?? on such psu, you do have a power good signal ... maybe this one is defective ?Some psu had fan rotation detection too, but it was a supplemental wire(s) ?

author: analogRF
author_rank: Super Contributor
timestamp: November 28, 2024, 11:47:01 am
content: Quote from: coromonadalix on November 28, 2024, 10:07:07 amyou mean apply 3.3V to the output and see the reaction, right?as far as I can tell all voltages are good (+/-12, -3.3, +5, -6) except the +3.3V which goes to botht he PC motherbpard and the acq boardsurely there is a power good signal on the ATX connector but I cannot access itas I said my main problem right now is how to power up this PSU outside the box (with some load connected)the regular PS_ON is not enough and it gets another LOW signal from the acq board to power on but I dont know where that is

author: coromonadalix
author_rank: Super Contributor
timestamp: November 28, 2024, 12:55:16 pm
content: mm maybe some dual verification or powering scheme good luckor someone has some similar scope to do probing ..... does the psu look likePlease can you write the psu markings ??the motherboard is pc104 compatible ?? if it is the same ...

author: analogRF
author_rank: Super Contributor
timestamp: November 28, 2024, 02:22:32 pm
content: Quote from: coromonadalix on November 28, 2024, 12:55:16 pmhis is an older model. My acq board/FE board/motherboard are all different than his but the PSU is exactly the same.my acq board is the red one and the FE board only has spring loaded board to board slots (no screws like you see in the video)on the motherboard there is no PCI104 slot. just the regular PCIE slot and the interface board that only has one tiny eeprom on it (plus 2 ethernet connectors and one sata connector that all go to the acq board - no other component) is a small narrow board unlike the big PCI104 board you see in the videobut the PSU is the same also the front panel board is identicalEDIT: probing it is not a problem. the problem is how to run the PSU out of the box and not connected to the acq board.I know the issue here is (at least) the missing +3.3V rail. I was hoping to probe it when it is live to see where the problem is.Now I have to just blindly use multimeter to probe around randomly and see if I can find out what is wrong.I think the main rail which is used for feedback and regulation is the +3.3. also it seems to be the highest current capable rail

author: analogRF
author_rank: Super Contributor
timestamp: November 28, 2024, 02:44:41 pm
content: some pictures

author: analogRF
author_rank: Super Contributor
timestamp: November 28, 2024, 02:45:17 pm
content: the orange wires are the +3.3V in question

author: analogRF
author_rank: Super Contributor
timestamp: November 28, 2024, 02:58:05 pm
content: I believe to some extent (maybe to a large extent) this PSU could be similar to Cherokee SP551 for which the schematics are available.specially the output circuits looks similar to me. that PSU doesnt have the daughter boards and I think everything was laid out on two boardsso the big difference could be that they just redesigned it with daughter boards...at least the output circuits looks similar at first glance to what I haveEDIT: by the way this SP551 PSU is used in the old Lecroy Waverunner 6000A series

author: coromonadalix
author_rank: Super Contributor
timestamp: November 28, 2024, 03:15:35 pm
content: there was a threadhttps://www.eevblog.com/forum/repair/lecroy-power-supply-(cherokee-lineage-power-sp651)/and check the attached pdf pinout draft from another placehttps://groups.io/g/LeCroyOwnersGroup/topic/wavesurfer_44mxs_b/7707066warning PLS DO CHECK if it somewhat fits ?

author: analogRF
author_rank: Super Contributor
timestamp: November 28, 2024, 03:37:40 pm
content: Quote from: coromonadalix on November 28, 2024, 03:15:35 pmthanksI have seen that thread and the document.right now one of the two double diodes on the 3.3V rectifier read odd in circuit so I have to desolder it and see how it isyes there is a green wire on teh 22 pin J3 and also the usual green wire on ATX connector (that goes to the PC motherboard and is directly traced back to the power on switch) they are not connected. So the person who did that pinout thought that the green wire must also be another power on signal coming from acq board and I suspect that too and I am inclined to ground it (as well as grounding the usual PS_ON on the ATX) so maybe that will start the supply. Someone on groups.io had aleady said that two power on signals are diode OR'ed on the PSU and both need to be grounded to turn it on....I'll trace the circuit before just blindly grounding any green wire that I see!

author: analogRF
author_rank: Super Contributor
timestamp: November 28, 2024, 04:57:15 pm
content: you see this!this is insane. those diodes and mosfets are not "screwed" to the heatsink. they are "punched" onto the damn thing.no way to take them out unless I take the whole thing out and the board takes in so much heat...even then it is hard to replace any of them. I dont have the tool to punch them back in I have to screw it but with just the right size...then dont have a tap...whoever designed this thing was insanefirst the disassembly is so complicated and you have to disassmble the whole scope to the last wire and screw to get here...then this

author: coromonadalix
author_rank: Super Contributor
timestamp: November 28, 2024, 05:12:12 pm
content: i would have said they are allen based ?? i dont see the usual rivet stuff, i could be wrong, i saw once allen key center hole ??but stupid design indeedoh member joeqsmith had some fun in a similar scopehttps://www.eevblog.com/forum/testgear/teledyne-lecroy-waverunner-64xi/is it possible to ask him if he still as this puppy and maybe just maybe probe the green wires ?

author: analogRF
author_rank: Super Contributor
timestamp: November 28, 2024, 05:15:33 pm
content: since someone had asked ,when I apply 3.3V to the output of that rail it takes in 74mA.there is a 51 ohm resistor across the output of that rail. Multimeter also measures around 44 ohm thoughi think I will remove the caps first but i highly doubt them to be bad. they look ok and they are nichiconoutput msfet switches (paralleled) are not short or anything.my guess is that they dont have their gate voltage and that comes from the daughter board

author: coromonadalix
author_rank: Super Contributor
timestamp: November 28, 2024, 05:17:38 pm
content: caps seems fine on the photos, i would not touch them at 1stcheck the previous answer while i was writing, you posted ...cracked solders, daughter cards pins ?? ...

author: analogRF
author_rank: Super Contributor
timestamp: November 28, 2024, 06:36:56 pm
content: Quote from: coromonadalix on November 28, 2024, 05:12:12 pmYes they are some sort of rivets but with no end cap on the other side because the heatsink surface has to be flat. No allen key screw.yes I have seen his thread. it's ironic that when he was posting those messages my scope was being manufactured at factory!so I think our scopes are at least 7-8 years apart if not moreI have traced the green wires and they are indeed OR'ed together with diodes and 1k pull-ups to the 5V standby.So definitely both need to be grounded to turn this thing on. One on the acq board and one is the usual ATX PS_ON on the CPU board

author: analogRF
author_rank: Super Contributor
timestamp: November 28, 2024, 06:42:27 pm
content: I have seen two people who had failed output diodes in their power supply but on the -3.3V which is fine in my caseit could be the diode in my case but the thing is it is parallel with a 51 ohm resistor and thus not possible to test in circuit.all i can say is that it is not shorted.the other one which is not parallel to the resistor checks fine in circuit