Restoring the Lambda LQ-532V power supply - **end of project** - Page 1
Forum section: electronics / general

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 20, 2011, 09:59:47 am
content: Hello,i bought a few month ago this PS form Ebay in 50$ shipped (REAL BARGIN).to anyone that doesn't know this PS , Lambda PS in the industry standard and it exist many years. this LQ series it there best series yet it's Linear and it's very reliable.the main reason i bought this one because it has the best regualtion that i found - 0.005% and amazing ripple 150uV MAX (yes it's 150 micro volt max ripple at full load). this PS is 40v @ 5A .the first time when i got this PS it seems rusty from the outside so i decided to open it before connecting it to the mains and i saw that the transformer and the transistor have rust on them and some of the resistors has corrosion on them and the electrolytic caps have some white leakage on there leads BUT i desided to connect it anyway and see if it works and surprisely it did. so i decided to restore it form the inside out. replace all the parts that need replacement and paint the chassis.my questions are :1. do i have to replace ALL the capacitors or just the electrolytic one (even that i check the electrolytic with a ESR meter and they all were fine)?2. i know now that rust on the transformer it not damaging it performance (correct me if i'm wrong) . what is the best way to remove the rust and the corrosion form the pcb and components? i was thinking about alcohol (90%) or squeezed lemon juice. what's better?here are some pictures:Uploaded withImageShack.usfront panel:Uploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.us

author: Excavatoree
author_rank: Frequent Contributor
timestamp: April 20, 2011, 11:50:20 am
content: I don't see any need to replace any of them - they look dirty but that doesn't affect their serviceability. You've checked the ESR and found that to be OK, unless someone else knows a good reason to replace them, I'd leave them in there. The non electrolytics are generally non perishable; you would only need to replace them if damaged or non functional.The surface rust on the TO-3 cases isn't a problem, either, in my opinion. The boards look good. Unless I'm missing something, I'd restore the rust as you see fit and leave the electronics alone, unless a repair is needed.

author: saturation
author_rank: Super Contributor
timestamp: April 20, 2011, 01:20:30 pm
content: I concur with Excavatoree, don't change anything that isn't broke. You're lucky!This unit has a very interesting look, it looks like military salvage, but spent a lot of time either in a hot ambient weather, and or humid or it was in a boat.I wouldn't paint the unit either, but you can pretty up the housing with rust remover and sealant [Home Depot stuff] , and just air blow interiors. Although some connectors and joints look awful externally, its very likely the electrical connections are still pristine underneath.To be sure nothing needs to be repaired, you need to performance test it; to run it at 40V at 5A and test its specs. It will run hot, and if something is off, it may blow. If nothing blows, you are good to go.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 20, 2011, 01:35:08 pm
content: i'm a Perfectionist, so i started to clean all the pcb not from all the rust and capacitor acid.will post photos when i'm manage to clean the most of the rust and dirt.Idop.s. i sent the PS to the LAMBDA representive here in Israel (the test was free so...) and there conclusive was:1. the device doesn't manage to work full load.2.rust and acid in the PS and the PCB.3.dry capacitors (but i test them in circuit with ESR meter and they was fine)this device is old and we don't have spare parts to fix it.but i'm almost sure they just open it saw all the rust and corrosion and just look on the acid on the capacitors and just wrote that to cover there as* .because i looked everywhere but couldn't find any mod that they solder anything and even the fuses are the same.about the caps,i don't want change them if they work either but what if they fail in a few years and they take with them a transistor. this transistors are very RARE and hard to find. should i take it under consideration??

author: Excavatoree
author_rank: Frequent Contributor
timestamp: April 20, 2011, 01:50:49 pm
content: Just some additional thoughts:I can't see the unit in person, but if there are leaking capacitors, of course they should be changed. The in-circuit ESR readings may look good because a good capacitor may be in parallel with a bad one.I can't comment about transistor availability, intuition leads me to think that you should be able to at least find a suitable replacement part if the exact part isn't available.

author: scrat
author_rank: Frequent Contributor
timestamp: April 20, 2011, 01:52:21 pm
content: QuoteIn the while you could try finding some of those transistors, maybe you can have them for few bucks, since you're not in a hurry...

author: saturation
author_rank: Super Contributor
timestamp: April 20, 2011, 03:05:12 pm
content: Hi Snakebite,It seems you already know the status of its parts and performance from the best source, the Lamdba rep!Given your location and if you can get a hold of them, replace the electrolytics as they do have a known limited lifespan and in your case case its better to do so, than risk damaging the power transistors.Quote from: SnakeBite on April 20, 2011, 01:35:08 pm

author: FreeThinker
author_rank: Frequent Contributor
timestamp: April 20, 2011, 05:04:21 pm
content: I would remove the transformer and get rid of the rust on the core. These soft iron cores are built up from layers of thinner metal separated by a varnish insulating paint. This gives you the 'laminated iron core' of the transformer and governs lots of things but mainly the eddy currents and associated iron losses. Rust will affect this by shorting out the laminations so a good clean will improve efficiency of the transformer at least and could even make it run cooler. Also check that the rust has not made the laminations separate as this can cause an annoying buzz and again reduce efficiency and create heat. If you find the laminations are loose a coat of varnish on the outside can help.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 20, 2011, 10:21:47 pm
content: thanks guys for all the comments.i manage today to clean all the pcb that sit on the side of the PS (near the big capacitor)also i scrape away almost all the rust from the top and sides of the transformer and i have to tell you it doesn't look that bad . the laminated are brokenonlyat the sides of the transformer. tommorow i will continue cleaning.here are some photos:Uploaded withImageShack.usthe rust you seeing on the transistor is AFTER i cleaned it .Uploaded withImageShack.usUploaded withImageShack.usyou can see on both sides the iron core pops out for the rust and i'm not done cleaning it so i don't think i need to restore the transformer after all...Uploaded withImageShack.usUploaded withImageShack.ussee yaIdo

author: saturation
author_rank: Super Contributor
timestamp: April 21, 2011, 12:24:45 pm
content: After reading all your good work, great cleaning job, and photos it appears like many capacitors are also custom made by Lambda? It would seem not only are the transistors difficult to replace, I'd expect these parts too. Thus, its probably best not to replace anything as I'd surmise these capacitors are far better than commercial grade. I've retracted my previous post.The transformer is also wrapped in an uncommon way, very 'military' look. Again, seems best to just clean it and enjoy what you have, not replacing parts unless it does fail.

author: tekfan
author_rank: Frequent Contributor
timestamp: April 21, 2011, 04:44:03 pm
content: Quote from: saturation on April 21, 2011, 12:24:45 pmI had four Lambda LP-522-FM supplies. The construction is very similar. One of them had a leaky capacitor and wouldn't output the rated current. after changing it everything worked well.The capacitors in this one still look good. Before you change any of them I suggest that you try and tweek the trimmer potentiometers inside and see if it makes a difference.I can see three trimmer pots on the main regulator board. One is probably for the maximum voltage output and the other one for the max current output. The long blue multiturn one may be for the offset correction when the output is set to 0 volts. The red and blue vertically mounted trimmers on the meter board are also for the current and voltage indication.I used a wire brush for cleaning transformers in the past with very good results.The transistors can be easily substituted with new ones (2N3773, 2N3055, etc.)

author: saturation
author_rank: Super Contributor
timestamp: April 21, 2011, 06:27:48 pm
content: This is great to know, tekfan. A few questions:You say you had 4, where are they now? Have they died or have you just moved on and got newer units?How has the transformer faired in its lifetime? Still working?Can you replace the Lamdba labeled capacitors with any Digikey accessible capacitor and still get the legendary ripple performance of these units?Substituting the board transistors, are these very similar electronically or just 'good enough' replacements and did replacing it affect performance?I ask because as I googled these units, a number of old working units appeared for reasonable prices, most are over 20 years old, making the caps and transformers inline to fail 'any day' now.Quote from: tekfan on April 21, 2011, 04:44:03 pm

author: tekfan
author_rank: Frequent Contributor
timestamp: April 21, 2011, 07:39:46 pm
content: I had a rack of 4 supplies that I gave to a friend. They are still working like new. I'm running out of space so they had to go somewere. Besides, I've built enough supplies myself.I once shorted one power supply out and the current limit was set to full. The supply began to heat up without me knowing it. Then I smelled something. It was a capacitor which I put on the supply so I wouldn't loose it. By this time it was melted beyond recognition. I couldn't touch the PS since it was so hot. Inside there is a thermostat that trips at 120°c. I know this is hot enough to boil water but up to this it still seems to be ''normal'' operating temperature. I disconnected the supply and let it cool down for a couple of hours. It worked fine afrerwards. They really don't make'em like they used to.All the capacitors can be replaced with standard ones. The orange ones are mylar and have a tolerance of less than 10% but these almost have unlimited life. Electrolytics are also standard.The TO-3 packaged transistors can be replaced by 2N3773 (it's self a very good transistor). Equal or better substitutes can easily be obtained. All the PS cares is weather it's NPN or PNP and the beta (hfe) of the transistor. No need for HFtransistors since everything is DC. There are some things that are on the main regulator board that are somewhat difficult to replace like the dual transistor pair (small round can with multiple leads on main board). It can be substituted with two small signal transistors that are matched for their beta (of example (2N3904/2N3906). The FM-52x-FM series have the MC1466 / MC1566 (mil spec) regulator IC. This is very hard to obtain but I've built several substitutes for this IC out of discrete transistors.http://i1138.photobucket.com/albums/n537/tekscopes/boardMC1466.jpg?t=1300195211http://i1138.photobucket.com/albums/n537/tekscopes/MC1466replacement.jpg?t=1300195263The PS in this thread seems to have a LM124 (standard quad opamp) for the regulator which is easily obtainable. I wouldn't worry about the transistors because there is quite a bit of protection circuitry around to prevent voltage spikes, reverse voltge, overvoltage, etc.Even the front panel potentiometers can be opened up and easily cleaned if dirty.

author: Richard W.
author_rank: Regular Contributor
timestamp: April 21, 2011, 07:55:08 pm
content: You should replace the thermal grease under the TO-3 transistors and clean the heat sinks to improve the cooling. (The mica-isolators can be replaced with the silicone pendant)I would also replace the mounting-screws, nuts, washers, ... of the TO-3 transistors because they are the transistors collector. The contact resistance should be as low as possible.To clean the boards you can use a mixture of 75% isopropanol and (distilled) water. (Tektronix recommend this for its oscilloscope boards). Please do not use methylated spirits, it leaves a white residue.After all this treatment connect a high power load (car headlight bulb) to the PSU and let it heat up, to get rid of all the moisture.Isolation resistance and protective earth resistance should be measured if possible. Every electrician can do that and check if everything is safe.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 21, 2011, 11:56:08 pm
content: thanks you for you comments tekfan and Richard i will take you comments under consideration.ok guys i finish cleaning half the PS today.tomorrow i will continue .i took apart all the front part of the PS including the transformer and clean it completly (the yellow thing you see on the transformer is soe kind of glue).tommorow i will clean the transistors (i started to disassemble the heatsink that hold them)here are some photos:Uploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usp.s.tekfan, how to do know the part number of the power transistors? i even have the schamatics and don't know them.you can find the schamatics here :http://128.238.9.201/~kurt/manuals/manuals/Other/LAMBDA%20LQ%20530%20Series%20Instruction.pdfthey has all the part number in there BUT lambda part number :-(

author: tekfan
author_rank: Frequent Contributor
timestamp: April 23, 2011, 01:31:45 pm
content: QuoteI don't know the exact part number but I would try and substitute Q2-Q6 (transistors on big heatsinks) with 2N3773, Q1 may be a different one.But i wouldn't go replacing the transistors just yet. They are very rugged and don't fail easily. If you really want to check if any of the transistors is shorted,try to unscrew the blocks that the transistors are screwed on. The small blocks are glued on the main heatsink and don't come off easily. Then unsolder atleast two wires off the transistor and then use your multimeter and check with a multimeter (diode test function).The transistors have a standard TO-3 package pin configuration. Put the red lead of the multimeter on the base and the black to the emitter and then the collector. you should get a voltage drop of about 0,6-0,8 volts. Put the multimeter on the ohms range and then probe the transistor from collector to emitter and then reverse the multimeter leads. You should get a resistance close to infinity in both directions.This method can be used to check any transistor.I wouldn't expect any of the transistors to be bad because you wouldn't be able to adjust the voltage. You wouldn't get any or just full output voltage. Try to adjust the trimmer pots to get full current capacity and output voltage.If I had a curve tracer I would remove the transistors and compare them with different ones, but sadly curve tracers are very expensive.

author: saturation
author_rank: Super Contributor
timestamp: April 23, 2011, 01:47:17 pm
content: A great thread for maintaining this PSU.How about the transformer, tekfan, its been without issue?I think it better to performance test the whole PSU after minor adjustment rather than break any electrical connections unless the unit failed testing.

author: tekfan
author_rank: Frequent Contributor
timestamp: April 23, 2011, 08:09:23 pm
content: Quote from: saturation on April 23, 2011, 01:47:17 pmYes the transformer survived the capacitor melting. The enamel coated wire inside the transformer can take 120°c no problem. You can even have a hard time breaking trough the enamel with a soldering iron if you want to solder the wireI've never had a mains transformer fail in any of my test equipment no matter how rusty or bad it looks.Exceptions are the lowest grade cheap chinese transformers, many of which have failed. Either from internal short (followed by catastrophic meltdown) or internal open winding (followed by garbage bin).I would also check the performance after adjustment. Remember, there's no need to replace components if it matches or exceeds the specs.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 23, 2011, 09:16:40 pm
content: thanks tekfan for you help.i was able to get to the full voltage spec when i tested it before i started to clean it but it tested under NO load so the current was zero so i think the transistors are fine.i have a few questions:1. is it imortent to change the isolation from Mica to silicone or other?2. i can buy mica ,silicone or ceramic isolation ? which one is beter?3. what is the purpose of the isolation ? just to isolate or also to conduct the heat?thanksIdo

author: tekfan
author_rank: Frequent Contributor
timestamp: April 23, 2011, 10:45:31 pm
content: Quote from: SnakeBite on April 23, 2011, 09:16:40 pm1. No, it isn't.2. Personally I use only mica spacers. I had problems with the silicone ones because if you tighten the transistor down too much it punctures the silicone and touches the heatsink. Ceramic is also good it has slightly better heat conductivity and insulation than mica. On the other hand, mica sheets are thinner and provide a sort of capacitor between the transistor and heatsink (very good in this application since low noise and ripple is wanted). The mica sheets have approximately 750pF capacitance between transistor and heatsink, the ceramic ones only 20pF. I would think the ceramic spacers can come useful in oscillator circuits where low capacitance to ground is needed.Personally I'd use mica sheets because they are more convenient (with thermal grease of course)3. The insulators do just this. They insulate the transistors from each other. Without the sheets all the collectors of the transistors would be tied together and to ground, which would defeat the pourpose of a ''floating'' power supply.And for thermal conductivity aswell. Mica is a very good heat conductor. If you put a mica sheet on your hand and press on it with your finger you will almost instantly feel the heat from the finger. If you take a piece of plastic of similar thickness and try this, it would take several seconds before you would feel anything.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 24, 2011, 01:40:09 pm
content: i started to work on the transistor side of the PS and i taked out one transistor for testing (i wasn't intended to test any transistor but i intended to replace the themal compound so i needed to get it out anyway) .i checked from Base to Emitter on "Diode Test" and i have got a dropout of 0.536v is this OK?from the collector to emitter and reverse in ohms range, i got infinite resistance in the two positions.so i'm guessing it's OK ...on the first image i took apart the three transistor from the heatsink and the black thing that stayed there that the thermostat.and now..the photos:Uploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usmore updates tomorrow.Idop.s. since i am also Computer technician i have this thermal compound (the best on the market , also doesn't conduct electricity)

author: tekfan
author_rank: Frequent Contributor
timestamp: April 24, 2011, 01:53:00 pm
content: Great! Soon you'll have a very nice power supply.The 0.536V drop is within spec. Silicon transistors can have a voltage drop anywhere between 0.4 to 0.8 volts.

author: Cyclenorthman
author_rank: Newbie
timestamp: April 24, 2011, 05:19:37 pm
content: You could also use a conformal coating on circuit boards to seal them after being cleaned.May also help seal other areas.We use it on avionics and other electronics.I have never tried varnish because of FAA regs but see what other members think about that.Just my $0.02 worth.CNM

author: tekfan
author_rank: Frequent Contributor
timestamp: April 24, 2011, 06:11:09 pm
content: I think there was an option with these supplies where the factory could give the insides of it an anti fungus coating. This has to be for some really harsh conditions.

author: Unknown
author_rank: Unknown
timestamp: April 24, 2011, 08:16:54 pm
content: Quote from: Cyclenorthman on April 24, 2011, 05:19:37 pmI would make sure to bake the boards before coating them to get rid of any residual moisture (this is directed at SnakeBite, I'm sure you're much more familiar with conformal coating than I).

author: saturation
author_rank: Super Contributor
timestamp: April 24, 2011, 11:39:17 pm
content: I've had my share of those! But from 1st world countries I've never seen transformers fail, its good to know they can endure when other components fail.Long ago, I'd coat PCBs and repairs with shellac via a paint brush. Its was more widely available than specific conformal coatings.Quote from: tekfan on April 23, 2011, 08:09:23 pmQuote from: Cyclenorthman on April 24, 2011, 05:19:37 pm

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 25, 2011, 10:52:24 pm
content: ok guys here's the update i promissed.tonight i continue cleaning the transistors of the other side (i finished the first side and check all the transistors and they're fine).after i took apart the HUGE heatsink i started to clean all the rust from the transistors.then, i tried to remove the little aluminum squares and they don't want to move!!so i clean the inner "wall" of the PS instead.the resistor(screwed to the wall on the left side) on the wall is a "300 ohm 5% 15w wirewound" resistor but it seems damaged from the moisture should i replace it? (in circuit it shows very close to 300 like 320 ohms) i found this :http://cgi.ebay.com/25W-300-ohm-300R-Aluminium-clad-Resistor-25-W-Watt-x-1-/270703518494?pt=LH_DefaultDomain_0&hash=item3f072fe31e#ht_4056wt_818i also found big broken resistor it's (0.120 ohm 5% 10w wirewound) should i replace it? - it seems that the two pieces still connected with two internal wires. i have one here in Israel and it cost 19 NIS (about 5.5$).i also cleaned the floor on the PS and took pictures of "before" and "after"enjoy...IdoUploaded withImageShack.usafter cleaningUploaded withImageShack.usafter cleaning the "wall"Uploaded withImageShack.usthe back of the PS (the big broken resistor is on the right)Uploaded withImageShack.usUploaded withImageShack.usbefore...Uploaded withImageShack.usafterUploaded withImageShack.us

author: tekfan
author_rank: Frequent Contributor
timestamp: April 25, 2011, 11:45:20 pm
content: As I said in one of the earlier posts the aluminium squares are glued onto the heatsink. You'll need a hammer to get them off (try with a rubber hammer if you have one). Just start by lightly tapping them and if that doesn't work, well I guess you'll have to be a bit more aggresive. You can also use a screwdriver and a hammer to apply a sharp blow to the aluminium square. I had the same problem with my supply.The broken 0.12 ohm resistor should definetly be replaced. This is the current shunt resistor. If it breaks you'll get no output voltage.For the water damaged resistor if it reads OK on your meter I'd leave it. You can always replace it if it fails (I really don't think that's possible). It should cause no damage to the supply if it somehow fails.Very nice job on the power supply so far.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 26, 2011, 08:11:44 am
content: thanks tekfan i manage to remove all of them with a screwdriver and hammer.i will remove and test all the transistors today.i have a question : will it be better to scrape away the heatsink paint that behind the aluminum squares to get better thermal contact with the heatsink ?? (since it's NOT anodised black aluminum i think that the paint acting as a thermal isolator)stay tunned for more updateIdo

author: tekfan
author_rank: Frequent Contributor
timestamp: April 26, 2011, 12:45:50 pm
content: Quote from: SnakeBite on April 26, 2011, 08:11:44 amI don't know if it's worth it. I'd just apply some thermal grease between the heatsink and the squares. You'll probably never run the power supply on full load for a long time while having it set to a low voltage.

author: saturation
author_rank: Super Contributor
timestamp: April 26, 2011, 01:34:26 pm
content: Thanks for sharing the great photos. I'd never guess the current shunt resistor was cracked, but it looks like this unit was serving up some heavy duty amps! Let us know if finding the part is easy. I quickly checked Digikey and they only have up to 3W in stock.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 26, 2011, 02:24:59 pm
content: Quote from: tekfan on April 26, 2011, 12:45:50 pmi know it's Probably overkill to do it but i still done it just in case (it's not hard just wet sandpaper).i also finished cleanning the whole PS (finally..) - i clean the rust and dirt from the resistors that was above the transistors.tomorrow i getting back to uni after the holyday vacation and getting back on friday. what i left to do is a little shopping for a new HUGE 30g thermal compound and the resistor and some new mica isolation sheets for the transistor (because they're extremly delicate and some damage during the removal of the transistors). also i need to buy new screw for the transistors like someone here suggested - even though i don't know if it inportant at all.so see you on sunday (hopefully)IdoUploaded withImageShack.usthis is AFTER cleanningUploaded withImageShack.usUploaded withImageShack.us

author: firewalker
author_rank: Super Contributor
timestamp: April 26, 2011, 03:07:36 pm
content: Very good Job!

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 26, 2011, 05:23:15 pm
content: i have a few more question .i saw in the manaual a paragraph that i don't understand fully. i tooed about two wire and four wire connectionhere's the paragraph :Uploaded withImageShack.usUploaded withImageShack.usis four wire is better then two wires connections? how so ?can someone help me out?Ido

author: scrat
author_rank: Frequent Contributor
timestamp: April 26, 2011, 07:00:40 pm
content: With 2-wire connection, the feedback measurement (to control the output at the desired voltage level) is taken at the output terminals. The resistive drop on the cables causes the real load voltage to be less than the reference (and displayed) value, since the supply control simply doesn't know anything about the drop that gets subtracted.4-wire connection solves this problem by taking the feedback measurement (with relatively high input impedance) closest to the real load, then ensuring the voltage on it to be right even with a sensible drop on the connection cables.So yes, 4-wire is better, but could be overkill if you don't need too much precision or the current is not so high with respect to the cable's resistance.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 27, 2011, 11:50:36 am
content: thanks but do i need to change the load resistor every time i connect different load to the PS?i asked if it's important to replace the transistors screws and bolt?thanksIdo

author: tecman
author_rank: Frequent Contributor
timestamp: April 27, 2011, 01:48:13 pm
content: The load resistor is YOUR load. In other words, you do not need a resistor there, it is just to represent the load applied to the power supply. As stated, the 4 wire is to sense the actual voltage at the load. This eliminates error due to the resistance of the wiring from the PS to the load. If you were pulling i amp and the wires had 1 ohm drop, you would have 1 volt less at the load than at the power supply. This is an exaggeration, but you get the point. Using 4 wire the PS will control the voltage at the load and eliminate this error. For 99% of the applications, 2 wire is fine. Only if you need super accurate regulation at the load would one use 4 wire. As a comment no one should design circuits that are that voltage sensitive on the supply voltage. Also be aware that if a sense wire falls off, when in 4 wire, the output voltage will jump up. Most power supplies put diodes internally to clamp thias condition, so the voltage will only jump up by about 0.7 volts.paul

author: Richard W.
author_rank: Regular Contributor
timestamp: April 27, 2011, 07:42:00 pm
content: QuoteThe contact resistance should be as low as possible to avoid any voltage drop.It's not important to replace them but it is easier as clean themBTW: a fiberglass brush is one of the best tools for cleaning contacts.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 27, 2011, 08:13:59 pm
content: Quote from: Richard W. on April 27, 2011, 07:42:00 pmcontact between what to what ? to3 case to the heatsink ? to3 case to the bolt?when you say "voltage drop" you mean that voltage flow through the screw? the screw is just to hold the transistor in place ! isn't it?

author: Excavatoree
author_rank: Frequent Contributor
timestamp: April 27, 2011, 08:38:41 pm
content: Quote from: SnakeBite on April 27, 2011, 08:13:59 pmRemember, the TO-3 case is one of the three terminals of the transistor (usually, if not always, the collector) Unless there is a insulator between the transistor and the heatsink, the case of the transistor contacst the heatsink, which can be used for the connection. Some transistor sockets use the screw connection, which will work even when the transistor is insulated from the heatsink.Maybe someone else can explain better, but the key point is, yes, sometimes the electrical connection is made using those screws.

author: Richard W.
author_rank: Regular Contributor
timestamp: April 27, 2011, 09:12:36 pm
content: the screws next to the red pointers are the collector connections of the transistor.They are holding the transistor in place and provide the electrical connection.the blue pointers are directed to the interconnection between the transistors.that means: all three collectors are connected in parallel.To split the current (almost) equally to every transistor,the resistance between the red cable (right of the right, blue pointer) must be equal.Because bad contact resistance causes voltage drop and heat, the resistance should be zero.

author: tekfan
author_rank: Frequent Contributor
timestamp: April 28, 2011, 12:20:45 am
content: Quote from: Richard W. on April 27, 2011, 09:12:36 pmThe three resistors on the bottom of the picture are the emitter resistors. These are low value resistors (typically less than 1 ohm). They are to compensate for variables between the three transistors (beta, voltage drop...).For the screws I wouldn't worry too much. Even the most rusty screw has a resistance so low that it won't heat up. Plus the eyelets connecting the wire to the transistor has small teeth that dig trough the oxide on the transistor. The screw isn't actually carrying any current at all because it only holds down the eyelet in direct contact with the transistor. The supply has 6 series pass transistors so 1 amp trough the contact of each transistor is not a lot of current at all.Anyway the power supply is designed to handle margins much worse than this.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 29, 2011, 02:58:08 pm
content: hi guys , i wanted to share you with somethings i thought about.i thought to add two switches on the front panel near the display : one to is two way switch that short the possitive and negative terminal to set the current limiter (i don't put a momentory switch because the manual says that i have to turn off the PS short it out and then turn it on select the current i want and then turn it off and remove the short jumper) and one is three way switch that allows to choose which terminal will be grounded and the third mod is for "floating power" (no grounded terminals).i thought about maybe get another switch to turn off the output (like dave said in the #166 episode he called it a "load switch").also i thought to add a little circuit that tells the user when the PS is on Constant voltage or Constant current modes by turnning on leds on the front panel.my question are do i really need to put a two way switch like i thought or i can just put momentory switch and what lambda saying it just as* covering?i know that i have to put some IC to calc when the PS is it CV or CC the question is which one?it should look like thisUploaded withImageShack.usthanksIdo

author: tekfan
author_rank: Frequent Contributor
timestamp: April 29, 2011, 06:51:38 pm
content: You will need a very big switch to short the power supply if you want to see the current limit setting. 6 amps is a lot of current for any switch.I wouldn't start drilling and cutting holes in the power supply. If you want to have either pole of the power supply floating or grounded you have the front panel banana posts. The ground terminal is in the middle so you can put a shorting bar like this between negative-ground and positive-ground.I have no idea how to do the CV/CC monitoring. Probably the best way is to just get a multimeter and just start probing around to see what voltage changes when the power supply goes into constant current mode.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 30, 2011, 08:07:17 pm
content: it's 5A not 6 .i can find easy switch that can handle 10A @ 125VAC (it can easy handle 40VDC@5A) nad it not very expensive like 3$.i now i can ground using the test leads but i'm too lazyabout the CC/CV it's not very hard because in the manual has very specific description about when the PS is in CC mode and CV mode.basicly :CV is when the load currentnot equalto the I_LIMIT the set by the knob on the front panel ALSO when load voltage equal to the value set by OUTPUT VOLTAGE knob.CC is when the load current isequalto the I_LIMIT ALSO when the load voltage is not equal to the value set by OUTPUT VOLTAGE knob.so i need to build a circuit that make that calculations but i don't have any Experience with IC at all can you help me?Ido

author: Richard W.
author_rank: Regular Contributor
timestamp: April 30, 2011, 10:27:19 pm
content: QuoteThere is a big difference between AC and DC (at least from the point of view of a switch).If you switch any current off, there is a little arc. At AC the arc goes out in the zero crossing, at DC you don't have any zero crossing so the arc burns a little bit longer.

author: SnakeBite
author_rank: Regular Contributor
timestamp: April 30, 2011, 11:17:25 pm
content: anyways it's not a problem at all since i'm using the switch when the PS is off. the Procedure at it writen in the manual is:*switch the PS off*short the terminals*switch the PS on*select current limit*switch the PS off*remove the shortage*switch the PS onso i don't see any problem at all in this case.

author: Richard W.
author_rank: Regular Contributor
timestamp: May 01, 2011, 10:04:55 am
content: OK, then it's not a problem. The only problem would be switching under load.

author: SnakeBite
author_rank: Regular Contributor
timestamp: May 01, 2011, 01:29:25 pm
content: Quote from: Richard W. on May 01, 2011, 10:04:55 amanyway i decided to drop the thing of adding any switch because of a lot of reasons...i did a little shopping today and basicly i have all i need now to finish the build.here's is what i bought:*one 0.12ohm 10w 1% resisotor*one foot of 4mm heatshrink*three new binding post terminals*new mica isolation*Arctic MX-2 30g thermal compound*1 meter of banana to alligetor test leadspictures:Uploaded withImageShack.usstay tuned for more updatesIdo

author: SnakeBite
author_rank: Regular Contributor
timestamp: May 01, 2011, 08:52:02 pm
content: ok guys , unfortently i just finished replacing the resistor today because i had a terrible headach and i had to stop working.i hope that on next sunday or on friday i will finish the WHOLE restore including sanding and repainting the chassis and the front panel.basicly what i have left is :*sand the chassis and the front panel.*repaint the chassis and the front panel.*put the next thermal compound on all the transistors (including the two on the PCB).*replace the three broken terminals with new ones.*repairing the power cord (i have to get some new small ring terminals to crimp the new power cord the i've got.--and that it!--here's some photo of the resistor i replaced today.i soldered to the resistor two beefy wires (i think it at least 16AWG) and put some heatshrink on the soldering so it's not short out with anything i also put some mica sheet behind it to help isolate and thermaly conduct the heat away.Uploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.ussee yaIdo

author: tekfan
author_rank: Frequent Contributor
timestamp: May 01, 2011, 09:08:11 pm
content: Great work!I would replace the capacitor near the resistor (the one with one end red). It just goes across the power supply output terminals but it helps a bit to reduce output noise. I'm saying this because several of the same type of cpacitors were bad in my supplies.BTWYou don't need to isolate the resistor with a mica sheet. It's already isolated inside from the case its self.

author: SnakeBite
author_rank: Regular Contributor
timestamp: May 01, 2011, 09:48:41 pm
content: Quote from: tekfan on May 01, 2011, 09:08:11 pmi know it was just as a precaution anyway .i don't think this cap is damaged but maybe i will check it and if it out of spec i will replace it.the problem is in the schemetics this cap is rated as 5.6uf 250v electrolitic capacitor but i don't think it's electrolitic it look like a film cap like that:http://cgi.ebay.com/2pcs-5-6uF-250V-Tubular-Audio-Capacitor-565J-/320674860955?pt=LH_DefaultDomain_0&hash=item4aa9b60f9bdo i replace it with electrolitic or film?another question that i have is about restoring the white captions on the front panel like the lambda logo and other (did i mention i'm Perfectionist) ? i can take a white pencil or something but i don't think it will be that clear on the metal front panel... this captions are like a water tatoo but i don't know where and how i can restore it.can you help me?Ido

author: tekfan
author_rank: Frequent Contributor
timestamp: May 01, 2011, 10:36:09 pm
content: The capacitor is definetly a standard electrolytic. A film capacitor at 5.6uF/250V would be much bigger. If you can't get 5.6 uF you can use the next larger value (eg. 10uF or even bigger).WARNINGWhen using 4 wire modebe very careful to connectthe sensing terminals to the power terminals. If they are not connected the power supply will be putting out more than 40 volts even if the voltage pot is set at 0. That's because the supply senses the voltage at the sensing terminals. In this case it senses nothing and will try to increase the output untill the desired voltage is achieved.If you have some digital circuit connected to the PS but the sense wires disconnected you can kiss your circuit goodbye. Especially if the current limit is set to full.If you want to restore the lettering maybe you could use Chartpak dry transfer lettering. I don't know in what fonts or color you can get it but it seems the most suitable option.It looks like the front panel of this thing (probably one of the most beautiful DIY builds I've ever seen):http://www.timefracture.org/reg.html

author: Richard W.
author_rank: Regular Contributor
timestamp: May 02, 2011, 04:08:13 pm
content: Engraving would be the most beautiful and most expensive way to label your front panel.If the panel is not bigger than a usual sheet of paper you can just scan it and do the "rework" with photoshop or someting like that.At least here in germany you can find a lot of CNC-guys who also can engrave something. Maybe in Israel too?Another idea: Printed adhesive-foil. This kind of mousepad-surface, do you know what i mean?Looks very professional if it is done right.(Just ask your local copyshop)

author: SnakeBite
author_rank: Regular Contributor
timestamp: May 02, 2011, 06:52:50 pm
content: Quote from: Richard W. on May 02, 2011, 04:08:13 pmi don't know what you meanbut i will check it out thanksi thought about something else to take iron paper (the paper that you using to print T-Shirt logo on it and iron it the T-Shirt) , scan and edit the front panel and then print it and iron it on the panel with iron but i don't know if it stick on metal. also i'm not sure the printer prints white color because my friend told me they don't but he not sure too. do you know?Ido

author: Richard W.
author_rank: Regular Contributor
timestamp: May 02, 2011, 07:59:12 pm
content: Here is a link:http://www.macdermidautotype.com/autotype.nsf/webfamilieseurope/AUTOTEXIt is the same kind of foil which is used for membrane keyboards.A printer doesn't print white. You can't mix white from cyan, magenta, yellow or black.

author: SnakeBite
author_rank: Regular Contributor
timestamp: May 08, 2011, 06:30:14 pm
content: ok guys i'm finish to put all the transistors on the heatsink and i tried to remove the two transistors on the PCB(voltage regualtors) but whoever solder this board solder the screw so i didn't manage to remove them to replace the thermal compound.don't think it was easy i started yesterday and finish just now worked on it all day.what i have left if to paint the front panel and the chassis and replace the binding post which i will do tomorrow.pictures:Uploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usMore updates tomorrowenjoyIdo

author: firewalker
author_rank: Super Contributor
timestamp: May 08, 2011, 10:45:26 pm
content: Nice!Enjoy your new psu!

author: SnakeBite
author_rank: Regular Contributor
timestamp: May 09, 2011, 08:09:35 pm
content: ok guys it my last post i finished everything.today i repainted the front panel and the chassis. also i solder the new binding post terminals .when i got the PS i made a little transparent plexiglass that i had and cut a square to protect the back terminals from shorting out.i also scrap away some of the paint for the ground cable.photos(sorry about the focus)sanding:Uploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usUploaded withImageShack.usthanks for your supportIdo

author: vk6zgo
author_rank: Super Contributor
timestamp: May 10, 2011, 03:44:52 am
content: An excellent job! Congratulations.I think you may find this website of interest:-http://jvgavila.com/This guy restores test equipment,Ham radio,etc,& has lots of little tricks & techniques which come in handy.I lack the patience these days to undertake the painstaking work that you have done,& that Jose' does,but Idefinitely admire it.VK6ZGO

author: deephaven
author_rank: Frequent Contributor
timestamp: May 10, 2011, 08:01:47 am
content: Congratulations on completing a fine job. I followed with interest you painstaking progress through the restoration process. It's great to see a nice piece of equipment being lovingly brought back to a decent condition.

author: david77
author_rank: Frequent Contributor
timestamp: May 10, 2011, 08:09:06 am
content: Great job! I'm sure this PSU still has a lot of life in it and will serve you well for years.Just one thing: That mains cable on the back made me shudder, you know that mess with insulation tapewrapped all around it. Also what's missing there is a proper strain relief, that's an accident waiting to happen!Personally I'd rewire that terminal board at the back so that it not carries mains voltage and add a proper strain relief and mains cable at the back.

author: saturation
author_rank: Super Contributor
timestamp: May 10, 2011, 11:23:41 am
content: Amen! and Snake's taking the time to document it in photos for us.Quote from: deephaven on May 10, 2011, 08:01:47 am

author: tekfan
author_rank: Frequent Contributor
timestamp: May 10, 2011, 12:44:12 pm
content: Wow! That supply looks even better than whenit was new. I really like the dark color. Yes, this one will serve you for many years to come.

author: SnakeBite
author_rank: Regular Contributor
timestamp: May 10, 2011, 03:35:25 pm
content: Quote from: david77 on May 10, 2011, 08:09:06 ami planed to do it but i could find #6 ring terminals i did only superficial search but i will get some don't worry...i also thought about coating the transformer with varnish but i didn't want to delay the project ending just for this two things.i tidy down my bench after the last photos and here is it now:Uploaded withImageShack.usthanks for all your supportIdo

author: Balaur
author_rank: Unknown
timestamp: June 04, 2013, 03:25:02 pm
content: Hello to all,I found all this very fascinating as I've just acquired a LQ-521-W that work very nicely and it's also in good shape. Cheers and thanks to SnakeBite and all the contributors.I'm sorry for reviving this thread, but I wonder if anybody has any of the manuals that were originally found athttp://128.238.9.201/~kurt/manuals/manuals. The site is no longer available and I haven't managed to find other copies.Best regards,Dan

author: robrenz
author_rank: Super Contributor
timestamp: June 04, 2013, 03:43:44 pm
content: Wow, Most excellent work SnakeBiteSomehow I missed this thread until now.You might consider one of the rust neutralizing paints likeExtendfor the transformer, It does a great job of stoping rust and sealing the surface.Again, great job.

author: AllanMN
author_rank: Contributor
timestamp: February 13, 2014, 04:02:04 am
content: Quote from: Balaur on June 04, 2013, 03:25:02 pmSame question. I just opened up a lambda LES-F-04-0V supply that looks similar and looking for repair info.

author: edavid
author_rank: Super Contributor
timestamp: February 13, 2014, 05:36:53 am
content: Kurt's manuals have moved tohttp://exodus.poly.edu/~kurt/manuals/manualsHowever, Lambda is very good about emailing manual PDFs if you ask them.

author: AllanMN
author_rank: Contributor
timestamp: February 13, 2014, 06:20:32 pm
content: Quote from: edavid on February 13, 2014, 05:36:53 amThanks!

author: ItSmokes
author_rank: Newbie
timestamp: February 16, 2019, 06:13:17 pm
content: I know these comments are old, but I find the discussion very interesting. I recently found an LP-532 power supply for cheap in an antique store and would like to restore it. It would be very helpful if anyone can tell me where I can find a schematic for it.

author: apis
author_rank: Super Contributor
timestamp: February 16, 2019, 07:09:46 pm
content: This thread is a good illustration why you should upload images to the forum instead of using external "services" like imageshack, this thread is still comprehensible but in many cases the pictures are necessary to understand the conversation so when the images disappear threads become useless.