LeCroy DDA-125 Stuck in standby (I think)

[TD]

Hello, everone!
This is my first post here. I ran about on hour of searches on the forum looking for answers before post.

 I'm new to all this scope talk, starting classes in 5 weeks and wanted to set myself up with a scope or two.
Anyway, Lecroy DDA-125 was just was dropped off at my door about 8 hours ago. I set it up on the bench for a power up, making sure it was in working condition. It powered it up, booted directly into the main screen. It seemed to be showing a recall screen as I  did not have a probe connected. I power up fast looked great ( screen bright) I adjusted the Position knobs then offset knobs, just a point or two. Checking for activity on the screen. The screen looked great, the unit looks great the Cal sticker are still sealed from two years ago. I walked into the house to print out the user manual. By the time I stepped back into the shop, maybe 5min - 8min at the most.

 The screen was dark (black), The brighter yellow light was now a dimmer green. I select the display button, (nothing), selected Auto setup (nothing), plugged a probe in (nothing). Took a sniffy sniff around for any elect burn smell (nothing). Power off, removed power plug, Power on, the light lit up yellow, snapped into green. Nothing on screen, the power is on. I  don't know much about this unit or scopes, (yet). But it looks to me as if it's stuck in standby mode. I looked at both fans in the rear of the unit only one is spinning. Power off, power on both fans start to spin one stops the second the standby light switches, I hear (faint click) In timing with the light switch, one fan spinning standby light on.

The manual I have said nothing of this situation, Manual does not even really tell you how to pull it out of standby mode. That leads me to believe if you do anything it should pull out of standby. >Any idea's< I will be doing research on this issue. If I find the answer or find out I have to tear her down I will post!  Nice to meet everyone! 

[TD]

If anyone knows where I can find a schematic for this unit or just the PSU of the unit that would be great. I'm used your best buddy (google) so much looking for one. google does not want to cooperate with me any longer. lol! I can't find any schem on any part of this unit. How awesome is that?.

[TD]

Hello, everone!
This is my first post here. I ran about on hour of searches on the forum looking for answers before post.

 I'm new to all this scope talk, starting classes in 5 weeks and wanted to set myself up with a scope or two.
Anyway, Lecroy DDA-125 was just was dropped off at my door about 8 hours ago. I set it up on the bench for a power up, making sure it was in working condition. It powered it up, booted directly into the main screen. It seemed to be showing a recall screen as I  did not have a probe connected. I power up fast looked great ( screen bright) I adjusted the Position knobs then offset knobs, just a point or two. Checking for activity on the screen. The screen looked great, the unit looks great the Cal sticker are still sealed from two years ago. I walked into the house to print out the user manual. By the time I stepped back into the shop, maybe 5min - 8min at the most.

 The screen was dark (black), The brighter yellow light was now a dimmer green. I select the display button, (nothing), selected Auto setup (nothing), plugged a probe in (nothing). Took a sniffy sniff around for any elect burn smell (nothing). Power off, removed power plug, Power on, the light lit up yellow, snapped into green. Nothing on screen, the power is on. I  don't know much about this unit or scopes, (yet). But it looks to me as if it's stuck in standby mode. I looked at both fans in the rear of the unit only one is spinning. Power off, power on both fans start to spin one stops the second the standby light switches, I hear (faint click) In timing with the light switch, one fan spinning standby light on.

The manual I have said nothing of this situation, Manual does not even really tell you how to pull it out of standby mode. That leads me to believe if you do anything it should pull out of standby. >Any idea's< I will be doing research on this issue. If I find the answer or find out I have to tear her down I will post!  Nice to meet everyone!

Ok! so I have stripped it down. I see I have not had any response so I guess I'm posting in the wrong spot or my subject is not interesting enough? Anyway, I have her apart, I have not started to test the power rails yet, that is coming up within the hour. However, I did have some trouble removing the PS for a while there I would have bet that I missed a screw somewhere, but I didn't. The PSU melted the composite material that the plug casing is made out of. It was not a severe meltdown but enough to glue the PSU in place. I"m attaching some pic's of the tear down with some pics of the PSU, mainboard and plug casing. I will keep you post even though no one wants to talk to me. Lmao..lol lol.

[tautech]

I see I have not had any response so I guess I'm posting in the wrong spot or my subject is not interesting enough?

Welcome to the forum.

Fear not, there's a few of us keeping an eye on you....please carry on.
One might expect if this scope hasn't been used for a good while e-caps might have needed reforming but I don't see any, only SMD Tantalums. And while they're much better than dipped bead tants don't discount that one has gone short and shut the PSU down.
Hmmm, that connector....could that be a symptom of failing caps on the mainboard.
Check that PSU first, as it hasn't apparently let any magic smoke out, just check cap values and ESR including the small e-cap for the SMPS IC VCC.
As that connector looks to have supplied current beyond design watch very carefully for any signs of heating anywhere on the mainboard, real careful like. 
Good luck and by all means document this repair step by step.

[nctnico]

AFAIK Lecroy used the same basic design for the LC9000 series and LC5xx / LC6xx series. Yours is likely a LC6xx series oscilloscope with a slightly different front. Schematics can be found at http://www.ko4bb.com/getsimple/index.php?id=manuals. Just look in the Lecroy directory and don't forget to donate. Also be creative when the instrument the service manual is for isn't exactly like yours! From what I have seen the models I listed before all share the same basics so any service manual should at least provide a hint on how the circuit works. BTW It seems the overheating of the power plug is a common problem. Forum member Scopeman has listed several common problems: https://www.eevblog.com/forum/testgear/list-your-test-equipment-score-here!/msg1136236/#msg1136236

[azer]

The scope is basically the same as LC684, but with some special disc drive analysis software, so the service manual on ko4bb should be ok.
Other source of information is the lecroy group on yahoo which also has a private file section.
https://groups.yahoo.com/neo/groups/LeCroy_Owners_Group/info

Some more people with similar problems:
https://groups.io/g/LeCroyOwnersGroup/topic/989565#1653
https://www.eevblog.com/forum/repair/lecroy-lc684dl-displays-random-signals/

The connectors seem to corrode easily which probably adds to the overheating problem. Be sure to clean the connector properly after repair, mine was corroded enough so it didn't boot.
Check the resistance from the burnt connector on the main board to ground if there is a short. The PSU boots stand alone so you can check the voltages separately.

[TD]

I caught on to the fact this scope had most of the same hardware as the LC684 about 3 AM so I downloaded the schematics that I could find on the (684). I have all my that I need as that part goes. had to tear it all the way down to get the PSU out, due to the melting of the plug. (glued it) to the acquisition board. anyway, without running any rail test. I decided to fire up the PSU. It powers up, I felt as if would have all night it I let it. Then I plugged the AUX fan, It stayed up without issue.

 At that time cracked the PSU case open, taking a look at the thermal switch, It looked fine. I just did a quick (?) test, it was open as it should be (I think). I did not look up the switch yet, I'm guessing it's open until the temp threshold then closes putting the unit into sleep mode. I had a long night and busy day. Going out now to test (V) on all the rails. I'LL BE BACK! 

[nctnico]

You need to type upper and lower case exactly as it shows in the captcha picture!

[TD]

Ok, this one tripped me up once before just to double check. I look at the thermostat That was reference a few time, Its a TO-220 Package (Bimetal Disc Thermostat), Its part number is (67F085) I have run into this IC once before. If I remember correctly the part number tells all. 1st two digits =( factory spec or not), letter = (type) and last three = (temp/limit).

If I remember right, "Probable not"    This means, the  67 = (factory set, or basic unit).     The (F) = Fan Unit, (F) = Open On Rise<,   If it was (L) it would be (Limit) >(L) = Close On Rise<

Here is where I'm double checking, with you guys.  It's F so (F) = (Open On Rise) So when the unit is at room temp or under the set Rise temp (it is closed) meaning there is a (closed circuit) right. so if it's not closed at room temp its bad right?  I had a big brain fart on this a few years back now I trip myself up every time I run into this little thermostat unit. LMAO RN I know I'm so over thinking this but better safe than sorry.

[nctnico]

When I put the part number in Google I get this datasheet:
airpax.sensata.com/pdfs/6700.pdf
The F models seem to be open at temperatures under the trip point.

[TD]

When I put the part number in Google I get this datasheet:
airpax.sensata.com/pdfs/6700.pdf
The F models seem to be open at temperatures under the trip point.

I had some time on my hand's so I power up the PSU and tested the (67F085 TO-220 package) and it was closed, after looking on the data sheet the (F) is a (Close On Rise) unit, I had the unit removed from the surface that it was mounted on, so I should not have been getting hot enough to set off the rise, It could be getting hot from too much current. So I checked the volts on the lead leg, (8.1v) @ (0.03A). I know the unit is bad due to the fact it is closed when under the trigger temp. I just wanted to make sure it burn up because of too high of current flowing through it.

I'm probably over thinking this and just should through a new one in.  I thought it might be a good Idea just to make sure the proper voltage is at this point. I attached the schematic I'm just not sure of the voltage within it, the schematic only gives so many voltage reference points. I'm not the best at schematics. This time next year I should be a lot better as I'm starting classes in 5 weeks. I attached the Schematic, pic 07 if you look at pic 03 you can see signs of this getting hot at some point. This is why I just want to be same and make sure the current coming to this point is not high. pic 04 reading with it removed, pic 05 with it back in. same reading. not that it would be different but there are a few components attached to this part of the chassis since the back of the 67f will flow current into the chassis ground the white wire goes to a dead pad on the PCB there are no traces running to the pad of the white wire at least not that I can see and its see through if you put it up to the light.

Thanks, I did run the P# in google,  I have not cleared my history in a long time, I just found a bunch of units for sale, all the way through the 2nd search page. I just cleared my history and BAM! there it was third down from the top. Thank You! funny how google works. I can google something at work, come home run the same search and get completely diff results. It's all in your history, Cookies, search habits. So as a reminder to all, keep your history clear!  or else you look like a moron (like me)

[TD]

Wife & I just got back from a short trip. The part was here, (67F085) TO-220) Thermal sensor, I replaced it, she fired up, the screen came on.  It looked great for about 5-10 sec then, BAMM, POOW FOLLOWED A UPERCUTT.    Same thing happened again!  I did watch a video with same scope model with the same problem. The guy just left it out. I don't feel too comfortable with that unless it's common. Looking for a little help with the Volt / Amp values at this thermal switch. One thing I'm pretty sure of, it's not burning up due to heat from overwork or heat from the mounting plate its mounted to.

 The only thing that comes to mind is, another issue drawing more current that spec, on the same run as the thermal switch. Then the switch is doing its job and popping first.  I have looked over the schematics with a fine tooth magnifying glass     I'm just not sure of the volt amp that should be here. I'm not the best at reading schematics yet, with that said I gave a copy to a friend to look over have not heard anything back in few day's so I guess it did not stick out like a phat thumb. If anyone knows the current values at this switch could you pass it on to me?  Or take a look at the schematic that I posted and let me know. Thanks!  Schematics are attached to my last reply! Thanks Again!

[TD]

Well, I found out the first time I check the Volts there I was getting an incorrect measurement, due to such a tight area and making contact with the wrong post. I did, however, pull the PSU board completely out of the PSU(CASE, then grounded it. Powered it back up, I'm at 6.6V pulling 9.20mA. I'm still not sure on specified voltage and current at this point in the circuit, though?  I can track >J7(the switch) to >J1(Line Input) Does anyone know if my test measurements are within spec or not?   

[TD]

Feeling a little a lost ATM, Really wanted this scope up and running before my (electrical class). Class starts in 4 weeks now.  What I have found out or identified today! If I pull the PSU put it back in it will work for 30 to 60 sec then fall back in the same routine. Once it goes into standby mode (SB) it doesn't matter If I  power off/on, it will do nothing, just boots straight into SB mode. If I Pull PSU put it back in, It will boot just fine for short time.(30-60 sec). I have monitored the temp of the (67F085) along with volts during the boot up until it sinks back into SB mode, Temp 18-19c no higher. This if far from the 85c needed to activate the switch. 

There has got to be another reason for this unit going into (standby) other than the (67F085 thermal switch). I did eventually get the sideboard out of the PSU case and found the numbers to the (resistors) and the (PMOS Transistor) within the same circuit trace as the (67F085). They tested fine as well. I believe the pMOS-transistor is an N type. lack of ex I still get that backward sometimes.  I have to do one more test because I believe the (67F085) is closing but not do to temp. Otherwise the (67F085) just fine out of circuit there is not continuity a crossed it, telling me it's (open) as it should be.

 I'm go start all over starting to get lost. will have to keep better notes. I'm guessing this is a lesson that comes with experience in this field. We know I don't have much of that yet, that's why I'm going to school for the knowledge to gain the EX. Anyway, if anyone has any idea's and/or recommendation on the issue, the problem or test I can run to track this problem down, I'm all ears or eyes in this case but same diff! it would be nice to have my own scope in class then I won't have to wait for others. Thanks again.

[tautech]

PM member Scopeman mentioned in reply #4 and link him to this thread.

[TD]

even though none of the PSU caps show any sign of leaking, bulging, or any other signs of failure.  do you still recommend the desoldering and ESR reading all of them? Also to check the SMD Tantalums on the main board will I have to desolder them as well to check their values?  Also since the power supply output voltages all read as they should, except for the -2 is -2.5 but I don't think that is a sign of short. since the output is good would you disregard the issue being in the power supply and concentrate on the main board? or could the PSU still be outputting proper volt and still have a bad cap or other problems?

[nctnico]

I'd start by going through the schematics of the power supply and see how the thermal switch is connected to the rest of the circuit. What kind of voltages is it connected to and what is the load. I find it odd it is completely fried like that. Just leaving it out is not a good plan.

[TD]

So I dug deeper into the PSU, removed the 120v rail. Once I removed that I could see the big 35x40mm CAP under there. I found a small ceramic cap that was bad, burned right there the board. Now the pads are gone. I removed the resistor that was connected to the same pad as well. I will give a detailed report with pics tomorrow. Have a good night!

[TD]

I Thing I found the problem or at least a good start hiding under the 120V rail, 
 I have found a bad small ceramic CAP and 1 metal film Resistor tied together & one large cap, uF test good but high ESR on the large cap.  I'm having some trouble finding the Exact replacements. especially on the R and small cap.  you can see in the attachments the burnt the board. As I desoldered they just fell apart, even with good heat and fast DE-solder time.  The pressure from my nail start to crumble it with out heat. small CAP will show nothing for capacitance or Ohm on DMM.  So I have posted pic's of the issue and parts. could use some help locating the replacements. I have put a few hours into it with low results.

Large CAP: 450V-330uF-M105C, On Body ( iC LMUM)  35x40MM W-H, I have find close on this one same volt, uF & temp. but size is a little off.

Small CAP:    390pF-  +/- 20%   On Body (391K-1KV-Y5F) Small ceramic cap. green color. having hard time finding this one.

Resistor:   Yellow-White-Black-Gold,  49Ohm I belive metal film resistor. I have find some close but not Exact.

If anyone has good conection of parts & can hook me up with a place to find and or purchase these that would be great. Like I said I can find close. but do to lack of exp with these parts I don't know the trick to the trade yet in finding parts.

[tautech]

Digikey or other big suppliers should have this stuff but another that I've got stuff from Tedss.
www.tedss.com/Capacitors

For the 390pF the value won't be of as much concern as the voltage rating and quite likely 220-680pF will do the job.
It's part of a snubber that may have put under stress as the other components associated with it have drifted over the years and then had to operate outside design spec.

Large cap, physical dimensions can be taller from the pics, the voltage must not be less and the value need be close to the same or a little higher. Too high will increase inrush current and possibly hurt the diode bridge that supplies it.

Link us in to anything you find for confirmation that it will be OK.

[casinada]

Correct me if I'm wrong but that resistor colors look like orange white black gold, that should be 39 ohms 5% resistor. It should be very easy to find almost anywhere. That looks like a 2 Watt resistor. The capacitor is very standard too.
Good luck with your repair. 

[TD]

Correct me if I'm wrong but that resistor colors look like orange white black gold, that should be 39 ohms 5% resistor. It should be very easy to find almost anywhere. That looks like a 2 Watt resistor. The capacitor is very standard too.
Good luck with your repair. 

That would be nice. they are old the white has already come off just from me touching it. 49 Ohm @ 5% is not normal and hard to find.  I was originally looking at it under my florescent light but now that you say something I looked again I believe your right   Thank You (Good looking out!)
I think it measures out to 15mm Long  4mm Thick with calipers. The schematic says's 2. all capacitors are minimum 50 volts.   1. All Resistor values are in Ohms, 5% 1/8W  Unless otherwise specified.  This resistor seems too large for a 1/8W resistor usually a 1/8w resistor is about 4mm long. not all the time but in most cases.

[TD]

Damm:-// I went back out and found some more of the same size and manufacture some gray body. found abut 8 of them all different color codes, most had at least 2 of the same code on the board, but now after finding an orange and more yellow.
Its yellow lucky me. looked at it under the glass and its yellow. at least you got me excited for a few min. I ran the 39 Ohm and found it right away.
I still have no idea of the volt current in this section of the board the schematic is not that informative at least not to me. I'm looking at the LC684DXL schematic as the unit looks to me the same.
The are no volt or amp references on the J1 Rail not that I can find. If someone could take a look I have attached it in the thread. Just to let me know if I'm a moron or not.
 I'm sure someone with more experience then I could look at the board and schematics and figure it right out. but I'm not there

[TD]

thanks found everything @ tedss.com

[tautech]

Correct me if I'm wrong but that resistor colors look like orange white black gold, that should be 39 ohms 5% resistor. It should be very easy to find almost anywhere. That looks like a 2 Watt resistor. The capacitor is very standard too.
Good luck with your repair. 

That would be nice. they are old the white has already come off just from me touching it. 49 Ohm @ 5% is not normal and hard to find.  I was originally looking at it under my florescent light but now that you say something I looked again I believe your right   Thank You (Good looking out!)
I think it measures out to 15mm Long  4mm Thick with calipers. The schematic says's 2. all capacitors are minimum 50 volts.   1. All Resistor values are in Ohms, 5% 1/8W  Unless otherwise specified.  This resistor seems too large for a 1/8W resistor usually a 1/8w resistor is about 4mm long. not all the time but in most cases.

Go with 1 W. (12 x 4mm)