Tektronix TDS420/TDS460 SMPS Green Hybrid - Page 1
Forum section: electronics / repair

author: Smoky
author_rank: Frequent Contributor
timestamp: June 16, 2020, 09:24:48 pm
content: On my last TDS420 oscilloscope repair, I was given a parts scope with a bad power supply.Today I decided to de-solder the green hybrid from it.It had some discoloration on it from a nearby resistor going up in smoke while the rest of the power supply looks like it went through WWIII with wires clipped and obvious signs of a repair attempt.Anyway, since I have it out, is there a sure-fire way to determine if the hybrid is bad as it sits on the bench?I'm expecting a TDS460 parts machine/restoration project on Friday with a good power supply, so it's possible that I can do some comparing while I do some re-capping

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 16, 2020, 10:08:26 pm
content: If it looks good, it can't be badMost of them fail with a burn mark in the middle because the auto-voltage selector got the better of the switching transistor that fused primary current sense resistor that's tied to pin 8 of the green thing.Do you have a scope with a component tester function or a Huntron tracker at hand? I have some reference curves from a working hybrid.Edit: The clipped wires are the auto-voltage selector, hardwiring these PSU's to the correct line voltage is a wise thing to do.

author: Smoky
author_rank: Frequent Contributor
timestamp: June 16, 2020, 10:30:29 pm
content: Yes, I have a Huntron Tracker 2000.Thank you Shakalnokturn!Btw, the part number on the power supply is 119-3939-00.

author: james_s
author_rank: Super Contributor
timestamp: June 16, 2020, 11:35:10 pm
content: Nothing is ever sure fire, but there is a reverse engineered schematic of what is in the green hybrid, it's really nothing exotic. Someone did lay out a replacement PCB for it, I have a board somewhere but never actually needed it because it turned out my hybrids were both good.

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 17, 2020, 11:27:19 am
content: Quote from: james_s on June 16, 2020, 11:35:10 pmIt was team work on the yahoo LecroyOwners group at the time:I put a lot of time into that project although I had no immediate need for it other than curiosity. De-potting those modules is hell!A guy called Martin did the schematic capture I don't know if he's on EEVblog forum.I made a first single-sided layout that Sam ("Scopeman" on EEVblog) reworked into a double sided layout eliminating all the zero ohm resistors.Sam kindly sent me a few milled PCB's and components, one of the assembled boards is in use in one of my LeCroy scopes.For Smoky:http://eninz.free.fr/PSI100004/WORKING_100004_PWM_curves.zip(May not stay online forever, there should be a copy on groups.io anyway...)

author: CaptDon
author_rank: Super Contributor
timestamp: June 17, 2020, 03:03:10 pm
content: The three clipped wires are for the voltage doubler circuit.I hard wired the doubler for operation on 120vac only!!If you apply 120vac you will see the required 300+ voltsacross the pair of capacitors. Be aware the Lecroy schematicis close but not exact and it has several value errors as wellas wrong designators. The switch transistor shorted EBC andtook out the current sense resistor (.15 ohm I think) as wellas all the stuff that normally burns out during this failure.The FR4 material also burned, but I was able to scrape awaythe carbonized areas. The unit never tried to oscillate andproduce drive into the primary, but the upside is it also didn'tblow apart on attempted power up, it simply didn't do anythingand therefore my assumption that the green hybrid was killedduring the original power surge. We took one hell of a hit whenthe utility pole was struck.

author: Smoky
author_rank: Frequent Contributor
timestamp: June 17, 2020, 08:59:41 pm
content: Alright guys, I was able to compare the signatures that Shakalnokturn provided.All of the pins of my hybrid appear to match.One note, I needed to adjust the "range" setting on the Huntron 2000 to make some of the images look identical. There was no mention as to how much voltage/current was injected to create the reference signatures. FYI, the "Med 1" range of the Huntron is 15 VP @ 9.0 mA and the "Med 2" is 20 VP @ 0.6 mA.Here are a few of the results. Pin 7, 8, and 10:So by the end of the week, an additional broken PS with unknown problems will arrive. Hopefully, I can get one power supply working out of the two*Update*The mysterious brown box with a broken 119-3939-00 power supply arrived

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 18, 2020, 09:48:54 am
content: So the green thing should be ok, never 100% sure until it's running the host equipment though.Although I didn't evaluate the current scale I did state in the "Notes.txt" in the .zip file that voltage scale is about 2.5V/div.ISTR that the scope used has a peak test current of approx 10mA which looks consistent with what you get, assuming your pictures were taken on the "Med." Range.

author: CaptDon
author_rank: Super Contributor
timestamp: June 18, 2020, 02:24:21 pm
content: I couldn't get the thing to begin oscillating. It had goodinput voltage with the doubler bypass mod but drew verylittle current from the line input. The SMPS power transistorI put in was basically a H.O.T. used in T.V. sets which reallywas nearly the same as the O.E.M. part which also founduse in T.V. sets. Because the current sense resistor wentopen circuit I just assumed the green weenie was damagedand gave up on it. If the hybrid is actually good you havea real gem on your hands because they have been on theunobtainium list for a least a decade!! I was just happy thatwhen I powered it back up after replacing the flamed outcomponents it didn't try a repeat performance. The replacementcurrent sense resistors were a bit of a kludge, but they were allI had in the drawer that would allow testing. Anyway, glad youare having fun with all the left over odds and ends!!! I checkthe metal scrap dumpster every day for more test gear. Theyhave two bays of gear with black X's on them and slated fordisposal. I have sent several messages asking if I could havesome of the gear (most of it actually works) for our lab (weare in a different building) but no replies. Big industry is sowasteful. The worst waste stream I ever saw was when I workedat Harley Davidson in York!!! Insanity at its finest!!!They would fire you for dumpster diving!!!

author: Smoky
author_rank: Frequent Contributor
timestamp: June 24, 2020, 05:59:53 am
content: OK, I now have two broken power supplies on the bench. One from CaptDon and another off of Ebay. I'm now going to combine the best parts from the two so to have a spare working SMPS on hand.We know that CaptDon's SMPS was struck with a voltage spike, and I know nothing of the other, so I'm going to replace the three IC's that I see. The main PC board has one LM339N and the small board has one LM339N and one LM324N:I'm going to pull the second green hybrid too and do a comparative test using my Huntron to see if they both react the same. I'll take pictures and post the results in small thumbnails using the "med 1" range on the Huntron.CaptDon's SMPS's main PC board has deep burn holes from sizzling resistors yet has a perfect secondary PC board. The Ebay SMPS is missing the large transistor that is bolted to the heat sink near the 680uf bulk capacitors (2SC3688) and its secondary PC board was attacked by leaking electrolyte turning the small pins black.It looks to me like we'll just squeak through this

author: james_s
author_rank: Super Contributor
timestamp: June 24, 2020, 06:44:36 am
content: When you do test it, make sure you put a load on the output you're trying to test. I burned a whole bunch of hours troubleshooting before I realized the reason both of mine were running way high and wouldn't regulate is that I didn't have an adequate load on them. On the bright side, it forced me to understand how the unusual circuit works.

author: Smoky
author_rank: Frequent Contributor
timestamp: June 24, 2020, 06:51:16 am
content: Thank you James!...and as usual, the connector pin's solder joints are cracked at the PC board, and in addition, the pins were bent from bad handling. Here's how I went about fixing it. The cracking of the solder joints is probably partially due to the warping of the PC board over time too.I force on the ribbon cable connector to the SMPS pins. I then flip the SMPS over and re-flow the solder joints. What this does is it takes the stress off of the pins and the pressure of the connector aligns the pins to the socket when the solder is softened no matter how warped the board is.The ribbon cable slips on and off easy now

author: james_s
author_rank: Super Contributor
timestamp: June 24, 2020, 11:53:52 pm
content: Certainly looks like it worked. All I did was straighten out the pins with pliers and then resolder them.

author: Smoky
author_rank: Frequent Contributor
timestamp: June 25, 2020, 12:41:51 am
content: I realize now which transistor CaptDon said was taken out by the voltage spike. It's the one bolted to the independent heat sink near the 680uf bulk capacitors. This 2SC3688 transistor is what I found installed:Since the Ebay SMPS transistor was missing in this spot, I needed to open one of the repaired scopes to see what was the original part number used in this location when the 119-3939-00 was assembled at the factory.I turned out to be part number MJF16006A.

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 25, 2020, 12:56:45 am
content: I've run the same PSU's you're working on from both BU508A and 2SD1887 transistors in place of the MJF16006A.The BU508A was slightly better for transition times.

author: Smoky
author_rank: Frequent Contributor
timestamp: June 25, 2020, 01:07:54 am
content: Thank you Shakalnokturn!I'm going to buy the BU508AHere's what else I discovered. No one on the internet sells this Motorola MJF16006AbutI did find the MJH16006A.I did some research and it appears that the only difference is its case size designation.But here's the best part, I decided to open up all three repaired TDS scopes to check the power supplies. I found a MJF16006A used in one power supply and MJH16006A's used in the other two*I ordered a few of the BU508AW's from Digi-Key along with some extra interface pads. I checked the data sheet and the thermal resistance value of the BU508AW is the same as the BU508A:https://www.digikey.com/product-detail/en/BU508AW/497-7196-5-ND/1852124/?itemSeq=330447269The secondary board is now renewed with fresh IC's and a 330uf 6.3V capacitor:In this picture, the wrapping material is brittle and it looks to be fiberglass reinforced, and what appears to be thermal paste is bone-dry, is it best to just add more paste and Super-glue the wrapper back around it? All I have is silver duct-tape laying around as an alternative*Update*I was able to compare both Green Hybrids. I believe CaptDon's Hybrid is indeed faulty. Here are the signatures of the good Hybrid from the Ebay SMPS. Every pin matched the signatures provided by Shakalnokturn without requiring any voltage adjustments to be made to the Huntron Tracker.HuntronHybrid.zip(2152.86 kB - downloaded 160 times.)

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 25, 2020, 10:35:31 am
content: I suppose you're doing a full recap, just in case you aren't don't forget to check the two small electrolytics on the aux. supply near the green module and trimmer. They're usually bad.I'm not sure that is thermal paste, I would have guessed just glue, I doubt there is much thermal consideration on the varistor. Maybe rather blast-proofing.On these designs I've got into the habit of adding a 15V TVS diode between hybrid pin 8 and primary ground because of the chain of destruction previously described.The point (I haven't blown a PSU to check yet) is that the TVS should save the hybrid if the current sense emitter resistor fails.

author: Smoky
author_rank: Frequent Contributor
timestamp: June 25, 2020, 09:09:27 pm
content: Yes, the power supply is going to be fully re-capped.Shakalnokturn, would you mind elaborating how the TVS diode would be installedI'm not very knowledgeable about this stuff yet.Here is a picture of the underside of the SMPS. The Hybrid is removed so the holes are easily visible. I put a red dot next to Pin 8.And would I be using a 15V Bi-directional or Uni-directional type of TVS diode?*Btw, the factory installed TVS diode is installed between the two yellow dots.

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 25, 2020, 10:28:11 pm
content: I shove them as on picture. (Unidirectional)The idea is that if the fuse is too slow (anyway it's before the bulk capacitors so there can still be plenty of energy left once it has blown) and the current sense resistor R7 fuses that can leave over 300V on hybrid's pin 8 through R10 - 470 ohm resistor.Internally pin 8 is a 1k ohm resistor (the available schematic that states 10k needs correcting, you can confirm 1k ohm value with your Huntron between pins 1-8) then a NPN base. Emitter is to ground. Total resistance is low enough to wreck the crap out of the hybrid in this scenario.Adding the TVS should limit the voltage on pin 8 to something safe allowing for R10 to fuse while leaving the green hybridgreen.The TVS you marked with yellow dots is part of the active clamp.Consider the one I add a unproven improvement

author: Smoky
author_rank: Frequent Contributor
timestamp: June 26, 2020, 06:12:04 am
content: Here is a picture from above where R10 is located. The white cement current sense resistor R7 is just to the left:To confirm Shakalnokturn's statement regarding Pin 8 as being a 1K Ohm resistor, here is Pin 8 on the Huntron set to the "Med 1" range:In the Huntron handbook, when the range setting is on "Med 1", a 1K resistor would appear as a 45 degree angle:*Some of the parts to complete the SMPS arrived todayI took a gamble with the 680uf bulk capacitors. My last batch of Nichicon LGX 680uf capacitors came in low when measured (~580uf). So this time around, I bought six of the LGX 820uf caps. They measure around 725uf! I'd rather have the caps be 50uf higher than specified than 100uf low:The usual 2200uf Nichicon capacitors that I use were out of stock too. I went through the Digi-Key catalog and sprung for these Panasonic FR caps. They had the second highest capacity for ripple current, ~3820mA. You're also limited to what size of capacitor can squeeze in between the secondary PC board, which goes back in next:Saturday delivery

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 26, 2020, 06:37:55 am
content: For the sake of covering the Power Systems Inc. PSU's subject: One of the more common failures after bad electrolytics is the opto going leaky and causing intermittent failures to start or shutdowns.(Opto isn't used in the regulation loop.)

author: CaptDon
author_rank: Super Contributor
timestamp: June 26, 2020, 01:36:50 pm
content: That advice on the opto seems wise. When plugged in and powered onfor the first time the scope would run for 10 minutes and then shutitself down. Simply pressing the soft touch power button would turnthe scope back on and it would run the rest of the day without failure.

author: Smoky
author_rank: Frequent Contributor
timestamp: June 28, 2020, 06:03:57 am
content: Chalk-up another win for the EEVBlog CommunityAfter an hour of idling, the power supply remains stable as can be. The DMM is clipped to Pin 1, the -15V rail:I installed the 15V TVS diode where Shakalnokturn suggested. I also checked the clearance between the SMPS and its tray and there is plenty of area and height for the diode. No interference whatsoever:I also replaced the original white Motorola CNY17-2 Optocoupler with a new one made by Vishay:In the upcoming weeks, I plan on building a variable resistive load to test the outputs for stability and ripple.If anyone has tips on how to tweak the SMPS's DC voltage rails, please chime-in. I see four variable resistors mounted on the secondary board but I'm not sure if it's just as easy as turning them. If so, we're done!

author: shakalnokturn
author_rank: Super Contributor
timestamp: June 28, 2020, 08:50:35 am
content: Congratulations on the resurrection.I have a personal note on the setting of the trimmer near the hybrid, measurements taken from a working PSU as a reference for readjustment after replacing the hybrid.As for the mag-amp regulation trimmers, yes it is as easy as turning them, preferably warm and definitely loaded.I doubt it has much importance but I'd start with the highest powered output and work down.

author: james_s
author_rank: Super Contributor
timestamp: June 28, 2020, 06:41:35 pm
content: All four voltages are independently adjustable, it's pretty cool. It was a pain to figure out how it worked but with some help from other members here I finally wrapped my head around it. I used a 12V automotive brake light bulb as a test load for all four outputs and tweaked them one at a time, the order makes no difference. Once you put it back in the scope it's probably worth re-checking the voltages and tweaking as needed but in my case it was not necessary to mess with it further.

author: dzalf
author_rank: Newbie
timestamp: August 16, 2020, 01:21:28 pm
content: Dear Smoky and guysI am currently working on exactly the same Power Supply for a TDS420 that I am trying to resurrect.Please excuse me for posting here but you already have fresh experience with this PSU. Regardless, I will create a new post on my repair procedure but I wanted to ask you if you could help me out on something in particular regarding the LF1 module from this power supply (it's the potted black Line Filter).Here's the main problem I am facing (in short): I received this power supply with an exploded varistor (the taped one) while the diode was in good condition. I replaced them with a P130L10 varistor and a 1N5406T-G diode. Then, I fully recapped the supply, fixed some traces and replaced all the ICs.Once ready, I plugged the supply to a fused 240 VAC line (UK mains) and the varistor went kaboom! Big big explosion!. (see attached images)Based on my measurements around the primary side from the PS I suspect that the problem might be an internal short in LF1. It has 3 leads that go to the points marked as E12 (orange cable) E4 (yellow cable) and E3 (blue cable).I measured a dead short between E12 and E4. E12 goes to the negative pin from C1 and E4 goes to pin 2 from the bridge rectifier.I wanted to kindly ask you if you could please measure the resistance between these two points to confirm that this short is my main issue (which I believe it is).Once again, my apologies to all for flooding the thread with a new issue. I just want to confirm my suspicion based on someone who has a working supply.Best wishes to you allCheersdzalf

author: Smoky
author_rank: Frequent Contributor
timestamp: August 17, 2020, 02:46:23 am
content: Dzalf,I have two PS boards in front of me. One is a populated/restored/working SMPS and the other is stripped of its components. I see clearly the locations of E12 and E4.On the working SMPS, and when I set my DMM to 2K Ohms (diode test), I get a quick beep as I alternate the probes between E12 and E4. Similar to what you'd get crossing a capacitor.

author: dzalf
author_rank: Newbie
timestamp: August 18, 2020, 01:21:54 am
content: Dear SmokyI want to thank you for your help on this. I appreciate your time for measuring the resistanceBased on your measurement I can confirm that the potted component marked as LF1 is definitely shorted. I measured a dead short (0.35 Ohms) between the E4 and E12. This means that one of the AC nodes from the rectifier is directly connected via the short to the positive node from C2, which to my understanding is not right at all.After some research, I found that this power supply is well known for being also used on some Lecroy Oscilloscopes. According to the diagram (attached) LF1 is only a line filter and removing it should allow me to further test the power supply (granted that nothing else shorted after the big kaboom).This is where it gets interesting:Based on the schematic, LF1 only bypasses the AC line. I removed the glue from the black potted part marked as LF1 for inspecting the area and I noticed that underneath there are two jumpers for the L and N from the AC line meaning that this component atop "LF1" is NOT a line filter rather a bank of capacitors (maybe?) which makes me wonder: what is the real purpose of this component then? Additionally, I still do not understand why that part has 3 wires coming out of the potted body, this would prove my theory that it is a group of caps instead.Thank you once again for your timeEDIT: While browsing the forum I found this post:https://www.eevblog.com/forum/repair/tds-460-power-supply-problems/and it turns out that the potted block is a custom rectifier! Chances are that I might have a hard time trying to find a replacement, so I am thinking of looking around eBay for a second hand PSUStay safedzalf

author: Smoky
author_rank: Frequent Contributor
timestamp: August 18, 2020, 02:11:40 am
content: I pulled the Tektronix part number sticker off of LF1 and found another Power Systems Inc. part number under it.I think bypassing it is a common practice from what I've read.If you need any more measurements, just let me know but I think components would need to be lifted to get accurate results.All of the help I received from Jame_S, Shakalnokturn, CaptDon, and the rest has been spot-on

author: james_s
author_rank: Super Contributor
timestamp: August 18, 2020, 04:30:14 am
content: Isn't that potted block a circuit for automatically selecting a voltage doubler or a full wave rectifier configuration for 120/240V auto switching? Mine didn't have any issues in that part of the circuit so I didn't look too closely at it.

author: Smoky
author_rank: Frequent Contributor
timestamp: August 18, 2020, 06:27:55 am
content: Reading the service manual, there should be between 90-250 VAC between pins 1 and 3 on connector J1. That's the 3-pin plug that brings power to the SMPS from the Auxiliary Power Board A07. So something has to bring all of those voltages into line. I can see where I can be asking a ton of questions.The potted block (LF1) appears to be just glued to the top of the PC board. It has no pins that go through to the foil side. I can tell because having two boards to compare, one of the LF1's is glued down crooked and angled. So it has just the three wires (yellow, orange, and blue).I have repaired six of these now but they are from the U.S. market running at the lower region of the voltage scale (~120 VAC). No problems.Maybe in the European market, where the 200+ VAC inputs are more common, the SMPS's were more prone to failureMy guess is too that the eventual capacitor failures on the Acquisition board, the Attenuator board, etc combined with rotted traces and shorts, caused currents to rise across all LV outputs on the SMPS making it run hotter and working its little self to death

author: shakalnokturn
author_rank: Super Contributor
timestamp: August 18, 2020, 08:15:49 am
content: The 3 wired potted black box is the automatic line voltage selector.It works like the voltage selector switch on ATX PSU's, allowing or disabling the voltage doubling during rectification only the switch here is a triac.It's a good idea to remove it and hardwire to the correct line voltage anyway.If you want to know what's in there out of curiosity or to rebuild one, there's a hand drawn schematic around internet. You can also download one of the low end LeCroy DSO service manual (9304 or 9314) where the voltage selector is not potted and appears on the PSU schematic.

author: dzalf
author_rank: Newbie
timestamp: August 18, 2020, 10:29:33 am
content: Quote from: james_s on August 18, 2020, 04:30:14 amDear JamesYou are right. Apparently it is the autovoltage selection circuit. Apparently, I could give it a try without it and it should work just fine on the fixed 240 VAC from the UK.I will keep trying until I get happy resultsCheersdzalf

author: dzalf
author_rank: Newbie
timestamp: August 18, 2020, 10:40:38 am
content: Quote from: Smoky on August 18, 2020, 06:27:55 amDear Smoky,Thanks for the info. You are right, the potted block is only glued to the board and the three wires go to the points we've discussed before. I agree that perhaps these power supplies were more prone to failure under the higher voltages here in the UK.In my case, the varistor has exploded immediately after plugging the power supply to mains voltage and therefore I cannot consider over-heating as the main issue.I am seriously thinking of removing the potted auto-voltage selector and give it a try. This test will have to wait until I get new fuses because I've blown all my stock alreadyI will get back to you after running more tests before feeding electrons to the little beast. Meanwhile I will run more tests on the components from the primary side since I am a bit worries that something may have got damaged after the last explosion (hoping that the varistor gave its life for the sake of them)Cheersdzalf

author: dzalf
author_rank: Newbie
timestamp: August 18, 2020, 10:52:16 am
content: Quote from: shakalnokturn on August 18, 2020, 08:15:49 amDear shakalnokturn,You just confirmed what I read in other forums regarding these power supplies: the potted block is an autovoltage selector or what they refer to as "custom rectifier".In my opinion, manufacturers should NOT be allowed to use potted and/or proprietary components or subsystems which could make devices irreparable. Same case for the main transistor driver block (green thingy).I actually found the reversed-engineered diagram from the auto-voltage selector however, to my knowledge, no one has built their own or at least they have not made it available to the market (and by now, it might be too late as these PSUs are more than "obsolete" in a way).Finally, thanks for the info, I will check out that service manual right away.As I told the other guys, I will try to get back to you all (hopefully) with better results. I will definitely try just removing it and testing again. I desperately want to make it work because I've spent many hours (and ££££) recapping, cleaning and re-soldering a bunch of stuff on it.Stay safe y'all!Cheersdzalf

author: Smoky
author_rank: Frequent Contributor
timestamp: August 19, 2020, 04:58:15 am
content: I thought it would be interesting to measure the current that is drawn while the PS-1690 SMPS is running inside of the oscilloscope.I have a Tektronix A622 current probe and it easily clamps around the group of wires from each of the four voltage rails.Let's see how each rail compares to the max current ratings of the SMPS.The TDS400 series scopes I own are totally re-capped, including the backplane boards. They also pass their self-tests and SPC routines. I have one opened-up on the bench

author: Smoky
author_rank: Frequent Contributor
timestamp: August 19, 2020, 05:07:47 am
content: Here is the -15 Volt rail, pins 1 and 2. The circuit is rated for .75 Amps.I set the current probe for 10mV/A.It appears it draws just under 100mA.

author: Smoky
author_rank: Frequent Contributor
timestamp: August 19, 2020, 05:13:40 am
content: Here is the -6.4 Volt rail, pins 6 and 7. The circuit is rated for 5.5 Amps.I switched the current probe to 100mV/A.This appears to translate to ~3.9 Amps.

author: Smoky
author_rank: Frequent Contributor
timestamp: August 19, 2020, 05:25:35 am
content: Here's the +15 Volt rail, pins 8 and 9. The circuit is rated for 3.5 Amps.The current probe is set for 100mV/A.I see around 2 Amps being devoured.

author: Smoky
author_rank: Frequent Contributor
timestamp: August 19, 2020, 05:36:53 am
content: And the last one, the +5.1 Volt rail, pins 16-20. The circuit is rated for 15 Amps.The current probe is set to 100mV/A.Looks to me to be a little over 10 Amps being drawn.Hopefully, I figured these right. The current probe was a gift from a retired professor from NC State along with his broken TDS420

author: Smoky
author_rank: Frequent Contributor
timestamp: August 19, 2020, 05:56:58 am
content: When doing the current measurements, I made sure that the "Current" arrow (I) on the probe pointed away from the SMPS.Looking back at the +15 Volt rail, it appears to have a bit of noise riding on it. I'll compare it to another scope later onAboutthe Varistor, I read that it is a Littlefuse part:https://www.digikey.com/product-detail/en/littelfuse-inc/V150LA20BP/F3033-ND/1009262

author: shakalnokturn
author_rank: Super Contributor
timestamp: August 19, 2020, 12:43:27 pm
content: Thanks.Real consumptions are always good to have for those who need a replacement PSU solution.What state was the TDS in during current measurements?I'd expect some variation mainly on the -6.4V rail between stopped and sampling at the highest single shot speed.

author: Smoky
author_rank: Frequent Contributor
timestamp: August 19, 2020, 05:41:53 pm
content: Hi ShaK,The scope was sitting idle with Channel 1 displayed for all of the measurements.Since you mentioned it, I went back to the -6.4v rail and re-started the scope.During the time of the power-on self-tests, the -6.4v rail drew ~4.4 Amps, once completed, the current dropped back to ~3.9 Amps:I then activated all four channels and tried both HiRes and Sample at its highest setting. The current draw was the same for both, ~4 Amps even:On a side note, if anyone happens to have the Field Adjustment Software for calibrating these scopes, please let me know. I was curious so I contacted Tektronix to see how much it would cost to calibrate a TDS420 or 460. They quoted me $650 per unit plus shipping.

author: supramike
author_rank: Newbie
timestamp: March 25, 2025, 04:34:24 am
content: This is the mod. Part number is hidden under Power Systems Inc sticker. I got it fromhttps://groups.io/g/LeCroyOwnersGroupI wouldn't have minded if they just used a 110/220 physical switch like most PSUs for the voltage doublingGood vid on PSU voltage doubler circuit for those wanting to get another perspective of its operation.