Big, OLD, lambda PS, 60v/15A, LES-F-04-0V

[AllanMN]

Newish here... My quest for cheap test gear has lead straight to an interest in repair skills...to that end:

Here's a Lambda LES-F-04-0V 0-60v, 0-15A PS I got for some motor control experimenting around. Built around 1985, catalog http://us.tdk-lambda.com/ftp/catalog/le_fall85.pdf shows specs of line regulation 0.02%+2mv, load regulation of .02%+4mv from 0 to 15A, (nice...) noise 100mV pp (...not so nice), over voltage protection to crowbar and shut down the output. I assume you have to set this to not be tripped by the normal voltage adjustment. Nice if say, the motor feeds power back during a quick ramp down which might kill the driver I guess.

Initially, I powered it on, started to adjust the voltage and heard a crackling, loud, arcing sound and powered off all within about 1 second. I suspected a capacitor arcing because it didn't have the buzzy quality I have heard transformers make.

I opened it up, starred in wonder at the sturdy/heavy duty quality of it, and considered "what was what" in a block diagram kind of way a while, was able to power on a few minutes with some DMM connected to check values/probing and discovered a shorted big filter cap I'm look for a replace of. It was drawing 10A set to Ov output which increased rapidly going to 1V out (briefly).

A couple questions:

Can anyone improve on my vague block diagram understanding? I find that key to repairing equipment without schematics or documentation. If you know the block diagram level of say, RF transmitters, etc. you can look at scope/DMM values and quickly find roughly where things are awry IF you can power it on and not smoke it.

Also, just studying each of the 2000 components one by one for signs of failure. The bad cap wasn't bulging, leaking nor getting hot (just a barely noticeable amount) dispite the 10A (1000 watts???) draw. (Maybe power factor, clamp on meter funnyness at work...)

I know caps after 30 years are prime suspects. Any other guiding advice for this kind of repair adventure? Tips, tricks, strategies or perils? I'm looking to buy a "blue" ESR meter but this cap appears shorted (under an ohm I think) and I wonder if it would read bad.

[Macbeth]

I've got an ancient LAMBDA LM-B-24. It's 24V DC, 1.4A, 1mv ripple.  All I know is it is designed to be rack mounted or enclosed in some way as all the screw terminals on the back are totally exposed for wiring the different 115/240 VAC mains in and DC out. It is solidly built, heavy, and works fine to this day if I choose to use it. 1985? Back to the future or what? The thing looks like it was made in 1955 complete with it's ancient logo and stuff. I guess it was cold war MIL spec. and Doc Brown brought it forward 30 years. 

[calexanian]

Thats way older than 85! The 3M logo there was last used in the 70's

[AllanMN]

Thats way older than 85! The 3M logo there was last used in the 70's

The new red 3M logo was designed in 1977, true. http://solutions.3m.com/wps/portal/3M/en_WW/Corp/Identity/Identity-Elements/3M-Logo/History/   So idk.... I was going from the Lambda sites 1985 catalog:
http://us.tdk-lambda.com/lp/products/legacy_2.htm

So whatever, it's somewhere in there...

I was looking for comments on my repair-oriented questions, which I hoped would be of some interest to some here. Is there a better electronics forum for this kind of repair project?

Allan

[calexanian]

I have no real experience with the switching lambda supplies, apart from using them.

[AllanMN]

... and discovered a shorted big filter cap I'm look for a replace of. It was drawing 10A set to Ov output which increased rapidly going to 1V out (briefly).

I'm wondering about "reforming" old electrolytic capacitors, this business of slowly putting voltage on them to reform the oxide if they are old and unused and if this works very often.

I replaced the bad cap, slowly turned the voltage up over about 20 minutes and all was well until, pop! the pair to the new cap shorted (0.1 ohms). There are two other filter caps so I'm wondering again if they'll go "sooner, or later".

At a cost of $20-$80 each, it is somewhat costly to just replace them, and the low end of that cost is again, NOS, not fresh from Digikey (more like $50-80).

Allan

[PChi]

From memory I think that the LES series were rather complex. When repairing one I had to redraw the schematic to make sense of it. The front end used a thyristor controlled bridge to vary the voltage on the main reservoir capacitors from about 80 V to 300 + as a first stage regulator. Then it had a full bridge switch mode power supply with a linear post regulator. The drive to the switching transistors isn't too clever so they take a pasting so it's worth checking them.

[AllanMN]

From memory I think that the LES series were rather complex. When repairing one I had to redraw the schematic to make sense of it. The front end used a thyristor controlled bridge to vary the voltage on the main reservoir capacitors from about 80 V to 300 + as a first stage regulator. Then it had a full bridge switch mode power supply with a linear post regulator. The drive to the switching transistors isn't too clever so they take a pasting so it's worth checking them.

I don't have any repair info/schematic but that's what I was thinking I was looking at. Ok, now I see 2 TO-66 (mini TO-3 type) transistors kind of hidden in the corner by the 4 TO-3's which I gather is the linear stage.

Yes, that's what I see: plus/minus 40 to 150v in the first stage. I suppose that was needed to provide full amperage over the full 0 to 60V with convection cooling.

Thanks for the reply.

[jgore]

I also just got a non-working lambda LES, 36v and 14.5A. TDK-Lambda was helpful - I called and within a couple of hours they emailed me a scanned manual which has a schematic and a few diagnostic tests as well and calibration steps.

In my case, I think one of the tests has a misprint: it says to check a diode that I cannot find one the board or on the schematic (CR 172) despite a lot of searching. I ended up not needing this test, but would be interested if you end up finding it.

[AllanMN]

I emailed them. A schematic would be helpful. Actually, much bigger new caps are now available in the same physical size but without a schematic I'm hesitant to make changes like that. My second stage output caps are 6700uF/75v and a same size 24000uf/100v is only $26:
http://www.digikey.com/product-detail/en/E36D101LPC243UDA5M/565-3679-ND/2096028

or 50000uf, same size $55:
http://www.ebay.com/itm/New-GE-50000uF-75V-Large-Can-Capacitor-Screw-Terminals-50000mfd-75-V-/140630611664?pt=LH_DefaultDomain_0&hash=item20be3cd6d0

What is going on with yours?

I need to adjust the voltage reading--it's low a few 1/10ths.

Allan

[nctnico]

I wouldn't replace capacitors in these kinds of PSUs with much larger (or smaller values). Some have a shunt regulator to discharge output caps. A much bigger capacitor may cause it to overheat.

[PChi]

If I remember correctly the LED voltmeters use the classic 7106 or similar DVM IC but the designers loomed various wires together so the meter is plagued by noise from the switch mode stage. The meter specifications have a wide tolerance, one customer complained, so just adjustment may not be enough to correct the reading.

[AmericanLocomotive]

Just shoot Lambda an e-mail with the full model number. They sent me the full schematic and manual for my '64 vintage rackmount PSU.

[AllanMN]

Just shoot Lambda an e-mail with the full model number. They sent me the full schematic and manual for my '64 vintage rackmount PSU.

Yes, I did, and got it. Very helpful. I do wish the many inductors on it had values on them. Nice adjustment ("calibration") procedures.

Allan

[Macbeth]

Just shoot Lambda an e-mail with the full model number. They sent me the full schematic and manual for my '64 vintage rackmount PSU.

That's the kind of service that makes you stick to a brand. I find the Japanese the worst at giving away schematics and service manuals - and insisting on sending everything to an authorised service centre that is not allowed on pain of death to give away secret service information. I just refuse to buy anything from companies like that.

Of course I am now finding a similar lack of concern with the Chinese, but it seems more due to laziness than a corporate ban on giving information out.

However, I have the likes of EEVBlog and it's members who "tear it apaart" and the amazing Tinhead who has reverse engineered these instruments and provide much better info than the Chinglish versions. That made my mind up on my Hantek MSO.

I would love to do JTAG boundary scans and stuff too. But what does a DIY'er use - software/hardware wise? I can't afford the pro stuff at all which is geared up for factory testing rather than simple fault finding / reverse engineering.

[AllanMN]

I agree, it adds a lot of value. And in this case, 30 years old, it has it's costs to keep available, and somehow I think they would be correct in part, that not providing it that long after sale, would not likely impact current sales. But it does create "good will" (the accounting term for brands/companies of high quality and reputation).

[megajocke]

Just shoot Lambda an e-mail with the full model number. They sent me the full schematic and manual for my '64 vintage rackmount PSU.

Yes, I did, and got it. Very helpful. I do wish the many inductors on it had values on them. Nice adjustment ("calibration") procedures.

Allan

Did you get it working in good order?

I'd be very interested in the schematic.

[AllanMN]

Not yet. Waiting this week for a mail order replacement cap.

[jgore]

Mine ended up working well - I found one shorted resistor lead and also someone had tried to replace one of the caps in the 300v divider and installed it backwards. Now, it seems to work and the meter is accurate where I have used it; though many of the internal test points are somewhat off of what the troubleshooting guide says. I need to build a load to really test it with, but so far, so good.

It seems more like it is meant to be installed permanently, than used as a bench supply. I added some banana jacks and a switch on top of the front panel. I could add a few more features like a switch and jacks for the remote sensing and a switch for grounding to + or -. These additions have to go on top or on the side since the display circuitry sits behind the entire front panel.

Overall, I really like it - high current, solid build, does constant current, and is air cooled.

[AllanMN]

... someone had tried to replace one of the caps in the 300v divider and installed it backwards. Now, it seems to work...

Those are what failed here. How many of the original 4 sky blue Sprague caps are there? I'd like to keep the 2 output caps and $50.

[jgore]

Mine has 2 1500u 200v on the input stage, one of which I replaced. The output has a single 34500u, which is specific to that model.

[AllanMN]

You must have a different model in the LES series than this.

I was curious if the originals had been replace or not.

[jgore]

Sorry, I forgot. I have the EE version, which is the one on top in catalog you posted.