Very Clear explanation of Linear power supply topography. In fact the best explained i have seen so far. If it was explained with its circuit diagram along with expected voltage analysis at different points in the circuit it would have been absolutely great. Almost most Radio repair videos follow analysis type of explanation which enforces circuit theory normal voltages expected and possible causes leading to faults.
Really nice video tear down i got the same unit, but mine wont go more than 18 v and when you set it to 18 v it's constantly jumping from 17,5 to 18,2 lucky i only need 5v, but it's annoying not been able to set it what it's supposed to be able to set and i don't have a clue what could be wrong i know it's not the potentiometer. Any idea or suggestion where to look would be kindly appreciated
I have one of these but I can’t get the voltage to remain stable ? It’s about 4 years old but only used a few times but trying to set it to say 3.65v is impossible, it just jumps around a lot.
Thanks for sharing this video. I also bought one of these a couple of days ago from a German eBay seller. Since some of the solder joints are really dodgy or at least ugly, and also the case wasn't grounded properly, I ended up taking it apart completely. I also found, that one of the banana plug connectors solder pad has lifted up, which I also want to fix. Here are some pictures: imgur.com/a/t8QIG I also think that the display board seems to be from a different series. There is one thing I can't quite understand, though. There is a connection from the display board to the output plugs - I guess this is where the actual voltage gets measured using the ADC in the display driver IC. But as you can see in this picture imgur.com/L60h5wX the OUT+ is connected to the V- lead on the display PCB, and the OUT- to the V+. The V- on the display board is also directly connected to the "negative" lead coming from the transformer and the GND pin/tab of the 7805 regulator. I'm pretty sure it's supposed to be like that since the unit worked before (did no extensive testing, but it didn't exploded :-)), but it feels wrong to me... Do you have any idea why they have done this like that? I searched the net for pictures and information, but never found anything about this connection, so I'm still not sure if this is completely fine or maybe even a fault. Also there is a small 2-pin plug back from the output board to the main PCB (also visible on the picture above).
Thank you for tearing your power supply down and putting all the great images online. Regarding the possibly switch up wires on the display board, i made a video trying to explain why they did this: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-mWnXjornKW4.html
Just bought one of these (2020) and at first sight it looks as if they have been sightly re-designed. Using TIP3055 rather than 2N3055, and the Bridge rect. is now mounted on the transistor heat sink, not on the bottom of the case. The button on the front is now a cut-out switch, however the fan is still not temperature controlled.
Thanks for watching and commenting, but you're kinda spoiling my next video here ;-). I also like the new version, except for the missing temperature control for the fan. The tear down video coming up soon.
Hi! Very nice product review and functional explanation! I think the best way to "calibrate" the psu display is to have it show for example 12.5v when the dmm is reading between 12.46v and 12.55v like a mathematical rounding. A small tip for you is to mark some points around the coarse current knob for example at 0.5A, 1.0A, 2.0A and so on...
i have this identical power supply, even if marked LongWei "; he had a problem with the diode bridge (bridge really poor and certainly not adequate and not dimensioned); I replaced the bridge with another much more robust, a 20A 400V mounted on of a cooling wing instead of the old diode bridge; I also put 4 10nf ceramic capacitors. The result was really good. Now the power supply is certainly very reliable; it will be cheap, but it does its job really well. Regards from Italy.
nice video... i have Loadstar LP3005D (0-30V 0-5Amps) DC power Supply almost same as shown in video... now the problem with it is, Voltage is increasing only up to 10.5V and not up to 30V.. i have changed Potentios but same issue... Kindly help me to fix it..
I have the same power supply but there has been a problem when I turned it on I got 49.6 volts on the display which is not adjusting. Would you please suggest me what I should check.
You can not adjust the value on the display with the blue potentiometers or by changing the output voltage? If you measure with a multimeter you have the same 49.6v?
I have Lavolta BPS-305 30V 5A. and one of the segments in the display counter is not working. it's never worked from new. Could you please give me any idea what to look for, dry joints? or if I need to replace the 7 segment digit , where could I get one from as the supplier doesn't handle spares. Thanks, John
Dry soldering joints is a good place to start. The way i see it there are only three possibilities: 1. The ICL7107 is defective. Please have a look at the data sheet www.alldatasheet.com/view.jsp?Searchword=ICL%207107 and check if the corresponding pins are activated, so pulled to ground. 2. The signal is there but can't reach the display. Check the soldering joints and the traces. 3. The 7 segment LED display is defective. You can check it like any other LED take a look at the datasheet. If you need to replace a 7 segment display digit, just watch out for the dimensions, color, brightness and the type. For this display it has to be a common anode type. But these are pretty generic and i think they had the part number printed an them.
Hi Thanks so much for your reply. I took the cover off for the first time and I was shocked by the very poor botchy soldering. with regards to the 7 segment digit display in question, I noticed that 1 of the contact pins was bent over shorting with the next one. I thought for a second that was the problem but after straightening it the problem of the blank segment still remains. I contacted a few suppliers but they require a part No. the only No on the display is 5101ASR which may be the component type but that doesn't help them to find one. does anybody know how to obtain a parts list for the Lavolta BPS-305-30A 5A, or if they know of an equivalent type. I would be most grateful. Bring back UK manufacturing.
Thanks for sharing this Video. Is the rectifier (which has to disappate almost 8 W alt full load) really only cooled by the chassis of the device? It would be interesting to know how hot it gets under full load. Also the clearance between the pcb on the side and the metal casing looks really low in the video (a small dent and you might have contact there). Same for the spacing between the mains wires and the transformer.
Yes, the bridge rectifier is cooled by the chassis. I didn't look into that because I didn't think an overheating rectifier could become an issue, often times they have no additional cooling and just hang in free air. And 8W of loss seems a bit steep to me, how did you come to this figure?
Due to the fact that 5 A * 1.4 V means that 7 W are disappated at full load (yeah... almost 8). I doubt this can be cooled just by the chassis. I also have a similar model with same specs (but made by a different brand) that has a heat sink mounted between the rectifier and the chassis. The voltage rating of the capacitors in this (50 V) also seems a bit low to me. Mine has around 53V on the capacitors at no load and 63V rated ones.
I'm currently reviewing a switch mode power supply and therefore I got it stuck in my head that the rectifier is on the primary side. But with these linear power supplies the rectifier is on the secondary side and so the maximum current flowing through them is 5A. Although diodes don't just switch on at 0.7V but rather act like a very small resistor, approximately 0.03Ohm. So the forward amperage is dependent on the forward voltage. At 5A the voltage drop is closely to 1V and with two active diodes the power loss should be around 10W. That is a considerable amount of power but the rectifier is mounted to the baseplate and although the heat transfer capability of mild steel isn't as high as lets say aluminium, it is at appr. 80W/mK still quite good and the attached metal casing provides a huge heat sinking area as well as a fan pulling air through the case. That is why I still don't think that an overheating rectifier might become an issue, but as soon as I get my current sink done I will stick a thermo couple to the rectifier and see what it actually does.
Thanks, i got mine from ebay, but the seller i got it from sold off his stock and isn't active anymore. If you want one, just look for deals on ebay and haggle the price as hard as you can, most dealers want to sell them.
@@runthomas You need a line, or a marker on the knob, when the power supply is off and you need to see whereabouts are the positions of the knobs. Are you going to be switching on at maximum voltage? or half or none? Same with amps: full power, half , or none ? Do you not think it might be useful to see the position of the knobs when the machine is off? I do. You should really think before opening your mouth, young Sir. >
@@Bodragon you need to pay more attention when you work...if you cant remember what you are doing or where you are at...i suggest you stick to very basic electronics...maybe an led and a resistor....in time you will progress...but good luck.. you see not all of us work in that way bodragon..some of us know what we are doing.
@@runthomas Well, I actually have three of these power supplies and I'm sorry but because of my age I can't remember the position of every single knob on each individual machine. I say that anything that aids one's memory is far from worthless. But anyway, look! If you don't want a mark on your knob, (and most knobs are actually marked from the factory), good for you. Personally, I think it's just a little thing that adds to the overall usability and workability of the product. If you can do without it, fine. I certainly could get by without it, but do I prefer it? Darn right I do. >
The seller I bought it from no longer sells it, but the cheapest offer i could find is for 30€ including shipment: www.ebay.de/itm/223686920334 But I have no experience with the seller! So this is not an endorsement, by at your own risk.
@@k-tech796 thank you ..looks great ..ill try and investigate shipping to uk...otherwise i can buy one over here for 50 pounds ..which is about 60 euro...nearly twice as much.
