EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: mysticpizza on October 25, 2021, 03:12:19 pm
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Hi,
I picked up a power supply on e-bay. Its a Powerline electronics 30V/10A. It looks ancient.
It appears to work above 4V, but dropping the voltage below this results in zero current.
Is there anything I should be looking at as a quick fix, or is it destined for the bin?
Many thanks
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That can make a great analog power supply for anybody's lab. If you don't want it, don't just bin it, better donate it to somebody who doesn't have one yet. The power transformer alone worth these days a couple hundreds or so.
Shouldn't be too hard to repair, I'll say you should try to fix it.
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I cant imagine its worth much. I think I paid £10 for it.
I don't have the skills to fix it unless its a simple fix like dirty potentiometers etc.
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Yes, definitely repair.
Linear PSUs don't become 'outdated' the way other test gear does. Out of fashion maybe, if you want lots of blaring digits, but definitely don't lose their usefulness, or output quietness!
Edit: The first step is to try and find a manual for it - what's the model number?
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I don't have the skills to fix it unless its a simple fix like dirty potentiometers etc.
And this is where and how you acquire them. If no service manual or schematic can be found (practice Google-fu, an important skill when you repair ancient, arcane electronics), then take the cover off and post some photos. Even with the problem that it has, if it works well otherwise it is worth keeping until you do have the skills to repair it. Your photo obscures the model number, which would be helpful.
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Open it and put some pics with the inside.
Could be because of dried capacitors, or it could be just dirty pots or bad contacts somewhere, or maybe that model doesn't start from zero volts. What range of voltage is printed near the output connector?
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Thanks. I got it for a specific one off job . Charging LifeP04 cells at 3.6 V. It doesn't appear to do that, though it will charge a bank of cells if connected in 12V configuration.
I went and bought a cheap one off Amazon to do the job.
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Ok. I'll have a look tomorrow and post some pics. Thanks
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It's an Powerline electronics Lab 510
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Can you zoom out and provide a single photo that shows the entire interior? There's something missing in your photos--a control board--and I'm wondering where it is hiding.
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There's something missing in your photos--a control board--and I'm wondering where it is hiding.
I think it might be hiding on the underside of the blue tray - i.e. need to take the bottom cover off to find it.
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The first photo, with the rusty transistors, where is that and could there be anything underneath?
I can see generally how this thing works, but finding a schematic would be really helpful. What sort of electronic test equipment do you have available? I'll be honest--if you are starting with 'no skills' then this will be a challenge and a learning experience! But that's what we're here for.... :)
Edit: OK, I see now--the transistors are on the back side of the back panel. There's still a control board somewhere that I don't see.
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Yeah. Im thinking this is going to be beyond me. I have no skills and little equipment.
Oh, well its been interesting looking inside the thing anyway. Its really heavy. No luck finding the 510, but here was another model. I don;t know how to insert PDFS though.
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A bit crusty, but certainly serviceable. It's even modern enough to use fiberglass boards and carbon film resistors.
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Yeah. Im thinking this is going to be beyond me. I have no skills and little equipment.
Oh, well its been interesting looking inside the thing anyway. Its really heavy. No luck finding the 510, but here was another model. I don;t know how to insert PDFS though.
As you and we can see it's in need of TLC here and there. You can do a shotgun approach barring anything else. Unplug it (of course) and re-flow as many solder joints as you want to with a bit of fresh solder to make sure the connection is good. Inspect any other wire connections as you can find that are screwed on and re-tighten them. You might get lucky.
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I have one of much similar build, my first lab supply actually and still one of the most used due to the coarse and fine adjustments. Its most common use is reviving Li-Ion cells from over discharged state.
Mine has poor contacts in the precision wirewound potentiometers so that may be something to check on.
Other than that check the electrolytics starting with the blue Philips one.
If you must bin it out of despair, please consider bining it to France I'm sure I can make some use of it ;D
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I picked up a power supply on e-bay. Its a Powerline electronics 30V/10A. It looks ancient.
The older it is the better it is, because it will be easier to fix.
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That looks like a real nice beefy power supply, if you don't want it then sell or give it to someone who does. In working condition that's worth a couple hundred bucks or so. As-is it's worth whatever someone will pay for it.
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That looks like a real nice beefy power supply, if you don't want it then sell or give it to someone who does. In working condition that's worth a couple hundred bucks or so. As-is it's worth whatever someone will pay for it.
+1 for getting it working again.
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These linear power supplies are usually easy to fix. One of the most common problem is dried electrolytic capacitor. But do not rush to change them all. Some may still be in good shape, especially the large ones.
You should be able to find a schematics for a similar one. Is there any opamp ?
I suppose yes, at least IC102 and the one above. Please make a detailed picture of this part to see the markings of the opamps (or supposed).
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A simple google search gives this thread with schematics and parts of LAB 521 which should be quite close.
https://www.vintage-radio.net/forum/showthread.php?p=827131 (https://www.vintage-radio.net/forum/showthread.php?p=827131)
Opamps are probably also 741.
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is there a 731 lurking in there or just opamps?
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It appears to work above 4V, but dropping the voltage below this results in zero current.
Is there anything I should be looking at as a quick fix, or is it destined for the bin?
1. the four power transistors bolted to the large heatsink at the back: carefully remove the nuts and bolts (two per transistor) and clean the rust off all nuts, bolts, AND the transistor casings where the bolts make contact. the transistor cases are generally the collector, and any bad connection here will cause mis-behaviour. you should be able to do this without any need for desoldering. make sure not to leave out any insulators (on the bolts) you remove in the process.
2. test. if still faulty, replace the two large electrolytic capacitors. as a temporary test, you can just solder (smaller) replacements across them.
3. if still faulty, replace other electrolytic capacitors.
the unit is well worth repairing. even if the electronics was fried beyond repair, it would still be worthwhile rebuilding the power supply.
cheers,
rob :-)
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throw away? Don't do it, but if you decide to do it leave the gps coordinates of where you will leave it :)
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If it works and delivers a current to a load over 4 volts (meaning you can power something with it), it basically works, meaning the big caps, transformer and rectifier diodes work.
Since it does not work under 4 volts, the control components are in question. The big potentiometers could just be dirty or otherwise wonky, as previously suggested, or maybe one of the big control transistors (even just rusty screws as mentioned), or some other little cheap component.
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I agree with Wallace.
If its working over 4V, the power transistors are OK. You can clean them, but it will only be cosmetic.
I have fixed dozens of such linear PSU. Most often, the power transistor are OK. When they are fried, there is no output.
Most often also, the big capacitors that filter the input line are OK, or do not affect the functioning of the unit.
The problems comes with the small electrolytics capacitors associated to the opamps that cannot then regulate properly the output. In some cases the opamp could be damaged. But
first verify the capacitors.
For units that stayed for a long time on the shelf the potentiometers can pose problem. In some cases ,just turning them a few time fully CW, CCW will fix the problem.
There may also be a pot on the board that can be adjusted to change the minimal voltage of the unit. There seems to be at least one in your pictures.
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If those are 4-40 or 6-32 nuts / bolts, those should be cheap enough to pick up a couple dozen or so at the hardware store.
If you know how to run an ohmmeter, I'd also start by checking the continuity of every bolted connection and correct everything that has a high-resistance connection.
That may go a long way to restoring full functionality.
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It looks a bit crusty on the pwr transistors but easy enough cct to fix. Please fix it! It will serve you well and the next person for life easily. Good linear PSUs.....are an absolute must for any good bench repairer.
Looks to be some commonality between their PSUs
https://www.vintage-radio.net/forum/showthread.php?p=827131 (https://www.vintage-radio.net/forum/showthread.php?p=827131)
edit: beaten in link
2N3055 pwr transistors, LM723 op amps basic diodes.......easy enough and cheap enough to repair by replace.