Online Score and Review---Leader LPS-152 & LFG-1300S (work in progress) - Page 1
Forum section: electronics / testgear

author: JS
author_rank: Frequent Contributor
timestamp: September 06, 2018, 07:34:24 pm
content: Hi, I score a Leader LPS-152 (power supply, ±25V@1A plus 6V@5A) and a LFG-1300S (function gen, 2MHz, 6 WFMs, sweep gen, ext AM and FM, bunch of aux outputs in the back)So, when I was trying to get them I couldn't find any full reviews, anything more than some comments on them being really nice. Seeing there are a ton of them on fleabay I think it might be useful for some people some better info I could give to the community I think it could be a good time to make one. The seller was really nice, I went to his house and test it with all his gear as I wished, so I came home with a pretty good idea of what I was bringing with me. He didn't want me to take them right away, as he was missing a calibration and a mains voltage conversion for the generator but I have all it takes to make those so I told him it was fine. One thing he mention he did was bring the power up slowly with a variac, as should be done with old gear to reform the filter caps, so they should hold some time, I could get some nice ones in a few month, getting good caps locally is close to impossible.One thing to notice on this instruments is the really nice feel of the controls, LPS pots are very stiff and smooth, even being single turn pots you can get very nice control while turning them at any point of the range, as good as you can see the needle for sure. The Function generator has much lighter feel on the pots but also very smooth, in all but the push pull one, for the DC offset, bummer they didn't used an extra switch there.LPS-152 power supplyA quick check on the PS showed it was bang on, calibration for it it's just front panel meters so pretty straight forward, mechanical zero, electrical zero, connect a DMM to it and check readings at full scale readings in voltage and current meters for all three outputs. A bunch of trimpots on the side, I didn't have to touch either, just mechanical zero.The function generator is a different story, I still need to make the voltage conversion but for now it will be fine with the 110V transformer I have. It did required some calibration, user manual and service manuals are available online. You shall check voltages first, PASS. Sweep gen needed a few tweaks, check the generator signals, adjust freq, etc... all in both manuals if you want to check. One thing I did check on the guy's 34401 was the output attenuator, 70dB attenuator on 10dB steps, all bang on to 0.01dB!Let's discuss the power supply. It has a 6V 5A output, a 25V 1A and a tracking -25V 1A supply, currents are independent, voltage of the negative supply can be anything between the positive and 0V, and will keep tracking the ratio of the prior in case this gets tweaked or current limited. Checking for ripple, in voltage regulation, with a 9.1Ω resistor getting warm, it showed ripple between 100µVpp to 250µVpp in either of the outputs, couldn't see any significant HF noise, checking with the 34401 showed µVs RMS for its full BW. For current limiting mode the things change a bit, 5mVpp for the +25V output, 40mVpp for the -25V output and 120mVpp for the 6V output. Checking the manual to see why ±25V are so different, the compensation cap on the feedback network for the current limiting mode is different, so making it slower for the -25V output and this could cause lower rejection of ripple. The ripple looks related to mains voltage, as triggering the oscilloscope from the network shows a steady waveform, low BW ripple, more on this later, a picture maybe, I forgot to capture.One thing I was interested is the dynamic response of the supply, so I connected the resistor in series with a switch and made a few captures till the bouncing was decently low. Getting from CV to CC operation has quite a bit of overshoot in all ranges, as much as you would expect with the big output cap it has. For the ±25V outputs, the time constant of 2ms for the current transient is just the time constant of the 220µF output cap and the 9.1Ω load resistor, so nothing strange there, seems to work fine. For the 6V output is a bit harder to see, I used the same 9Ω resistor and the time constant looks about right for the 1000µF output cap, so I didn't check it further.Going from CC to CV +25V output shows a time constant of ~40ms, no overshoot, just a exponential rise, while the -25V source follows it in 250ms, so there it's coming, you just need to wait for it. Same thing going down as you'd expect. Individually testing the -25V looks pretty similar to the +25V output, not like the slow tracking, but 40ms to rise and the 2mS to go down.Captures from the scope are attached to look at the transients for the ±25V supplies, to get good captures for the 6V output I should get a powerful (25W) 1Ω resistor or something in that range.LFG-1300S function generatorWith the function generator I should expend a bit more time, but for now looks really nice, frequency in the dial is spot on after some calibration but stability isn't great, as you would expect from an RC oscillator, but not as bad as a crappy ceramic for the ranges, in the teardown I will show the quality of the components. Functionality wise looks promising, rise times are pretty fine, for it's 2MHz max output, square wave has some rounding on the leading edge but you can still tell it's a square wave. The discrete output amplifier wants to have a compensation pole at about 9MHz but with 1pF cap good luck dealing with PCB hook, so plenty to play around with. I wander if the maximum frequency could be changed, as the 1M range selects a 1nF cap for the oscilator, what would happen with an even smaller cap. It wouldn't be able to reproduce squarewaves of 20MHz or be flat to that high but even a few dB lower signal could come handy as I don't have other means to generate that at home right now.The control pots feel really nice as I already mentioned, symmetry of the pulse can be controlled in the whole range from fully 0% to 100%, no problems there. The sweep generator works as expected, to have a good range of sweep the start frequency should be on the low side of the range, as maximum frequency is limited by the range and the minimum frequency is selected in the dial. The rate goes down to a bit under 20ms and up much longer than the 5s specified, this makes possible to work with low frequency sweeps, as a 5s sweep wouldn't allow a very low frequencies to be used. Fast rates allow to use as internal FM of a sawtooth which could come handy to check some things. AM and FM are external inputs but work as expected, AM has it's own calibration to set the front panel controls to work as expected, making the maximum amplitudes 50% of the range makes possible to set modulation and carrier to max without clipping the signal. I will come back with some numbers at some point, I'd like to be able to trim the offset a bit better, and the cal procedure doesn't specify how to deal with that, and I can't see a trimmer for that in the schematic but I did found some parts in the PCB that were not present in the schematic.For a teardown of the power supply you can find a nice one from arantius, here is the post,https://www.eevblog.com/forum/testgear/leader-lps-152-power-supply-teardown/msg1786799/#msg1786799For the function generator I need to get something better than my phone to get the pictures but they will come. It looks really nice inside, single sided PCB with top quality components. Trim pots for calibration properly labeled, placement could be better as for some you need to put the screw driver from the side as a front panel PCB gets in the way.For what I've seen so far they seems pretty good gear. Prices varies widely, I got them for about $100 each, here is a great deal, no questions asked, I've seen better deals on the usual sites but shipping and fees would make it way worse for me. I've also seen much more expensive ones, remanufactured, blah blah. The power supply doesn't have much inside, check the caps and change them if you can and for calibration you just need a DMM and some loads to measure current without shorting the inputs. Manual suggests a chunky rheostat but didn't seem necessary for me. The calibration of the LFG is a bit more involved but nothing crazy you can't get around in a few hours with a DMM, a scope, a variable DC source and an audio generator (which could be your phone I guess). I got the whole package with two sets of wires for each device, some brand new Siglent accessories from some of his newest acquisitions.I hope you enjoyed it and find it useful if you are after one of this puppies!JS