Author Topic: JP 12V 10A switching PSU only producing about 5 volts  (Read 2290 times)

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Offline netdudeuk

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JP 12V 10A switching PSU only producing about 5 volts
« on: April 17, 2018, 02:02:07 pm »
Hi

The issue is as above.

I don't see anything obviously wrong with the PCB.

I am aware that working with a SMPS is risky but if there is anything that I could quickly check, I'd give it a go.

I cannot find a schematic.

Thanks
« Last Edit: April 17, 2018, 03:11:08 pm by netdudeuk »
 

Offline glarsson

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Re: JP 12 10A switching PSU only producing about 5 volts
« Reply #1 on: April 17, 2018, 02:07:54 pm »
A 10A supply with a 7.5A fuse?
 

Offline bd139

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Re: JP 12 10A switching PSU only producing about 5 volts
« Reply #2 on: April 17, 2018, 02:23:36 pm »
That looks hooky as hell. I'd throw it away.

What was it out of?
 

Offline oldway

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Re: JP 12 10A switching PSU only producing about 5 volts
« Reply #3 on: April 17, 2018, 02:36:47 pm »
Are you a candidate for Darwin awards?  :-DD

Trying to repair a cheap, poor quality, crap power supply without a schematic by making a dangerous repair attempt, you are a good candidate .... :-DD

Do you own at least a good isolation transformer?  |O
« Last Edit: April 17, 2018, 02:38:45 pm by oldway »
 

Offline CJay

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Re: JP 12 10A switching PSU only producing about 5 volts
« Reply #4 on: April 17, 2018, 02:41:39 pm »
Are you a candidate for Darwin awards?  :-DD

Trying to repair a cheap, poor quality, crap power supply without a schematic by making a dangerous repair attempt, you are a good candidate .... :-DD

Do you own at least a good isolation transformer?  |O

Why does not having a schematic make anyone a candidate for the Darwin awards?

I'd suggest that needing one would make it more likely that you can't think for yourself.
 
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Offline netdudeuk

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Re: JP 12 10A switching PSU only producing about 5 volts
« Reply #5 on: April 17, 2018, 02:45:36 pm »
Are you a candidate for Darwin awards?  :-DD

Trying to repair a cheap, poor quality, crap power supply without a schematic by making a dangerous repair attempt, you are a good candidate .... :-DD

Do you own at least a good isolation transformer?  |O

No need for the insult thanks.  I have already acknowledged the risks associated with looking at it.

It wasn't a cheap eBay or the like purchase and the case is labelled with a well known (in the hobby) brand.

The fuse is the one that came with it but I've only typically drawn about 4 amps from it.

I don't particularly need it as I have been using my DP832 instead.

However, as I said, (if someone recognises the board) if there was anything obvious that it could be, I could consider swapping out the part, just for the pleasure of not throwing it in the bin.

 

Offline CJay

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Re: JP 12 10A switching PSU only producing about 5 volts
« Reply #6 on: April 17, 2018, 02:49:39 pm »
Post some pics of the underside of the board.

Make sure the 47uF capacitor is discharged then check underneath it.

Are you measuring the output with load or not?
 
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Offline Nusa

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Re: JP 12 10A switching PSU only producing about 5 volts
« Reply #7 on: April 17, 2018, 03:04:18 pm »
"well known brand" isn't a very useful search term, if you were actually hoping someone would find the schematic for you.
 
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Offline grifftech

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Re: JP 12 10A switching PSU only producing about 5 volts
« Reply #8 on: April 17, 2018, 03:07:05 pm »
What is the voltage supposed to be?
 

Offline netdudeuk

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #9 on: April 17, 2018, 03:10:03 pm »
Post some pics of the underside of the board.

Make sure the 47uF capacitor is discharged then check underneath it.

Are you measuring the output with load or not?

Thanks for the constructive comments  :)

I have been watching out for the 400V cap, and everything else.

There is some browning at the bottom of the PCB but there isn't anything top-side that I can see has over-heated, including under that large cap.

The measurement was with a DMM with no load.

Thanks again.

 

Offline netdudeuk

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #10 on: April 17, 2018, 03:10:54 pm »
What is the voltage supposed to be?

I have edited the title to include a 'V'.  Twelve volts thanks.
« Last Edit: April 17, 2018, 03:12:36 pm by netdudeuk »
 

Offline netdudeuk

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Re: JP 12 10A switching PSU only producing about 5 volts
« Reply #11 on: April 17, 2018, 03:11:55 pm »
"well known brand" isn't a very useful search term, if you were actually hoping someone would find the schematic for you.

It is a JP Ultrapower 12V 10A Power Supply 240V.
 

Offline bd139

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #12 on: April 17, 2018, 03:16:13 pm »
Looks like the capacitors overheated. Probably dried out, went short or high ESR and then the feedback goes wonky. The crispy goop on top and the burn marks on the board are the indicator.

A big worry is the lack of slots and isolation on that. Not a very pretty design.

Even a 7.5A fuse is pushing it by the looks.
« Last Edit: April 17, 2018, 03:19:22 pm by bd139 »
 
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Offline CJay

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #13 on: April 17, 2018, 03:56:47 pm »
It's been getting hot (that crusty brown glue is a giveaway for that) so, as m'learned friend BD139 suggests, the caps are probably in pretty poor shape but I would also recommend you scrape off that glue as well.

In addition to that I would definitely be checking resistor values.
 
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Offline netdudeuk

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #14 on: April 17, 2018, 04:04:58 pm »
It's been getting hot (that crusty brown glue is a giveaway for that) so, as m'learned friend BD139 suggests, the caps are probably in pretty poor shape but I would also recommend you scrape off that glue as well.

In addition to that I would definitely be checking resistor values.

So really, I may as well dump it then.  It isn't worth the hassle.

Thanks for the input guys  :)

 

Offline CJay

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #15 on: April 17, 2018, 04:14:24 pm »
Up to you, only you can decide how much it's worth, if it's a cheap thing to replace then you're probably right to dump it, if you wanted to learn then it's worth a bit of time and money to repair.

TBH, I manage to lay my hands on a *lot* of 12V 3-5 amp PSUs so I don't bother repairing, nor do I bother collecting them all but the skill and knowledge to do so is always handy if I'm stuck with a faulty supply that's an odd value.

 
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Offline bd139

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #16 on: April 17, 2018, 04:31:30 pm »
Conversely the last one I repaired caught fire instantly so YMMV  :-DD

 
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Online tautech

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #17 on: April 17, 2018, 04:40:13 pm »
The measurement was with a DMM with no load.
Use a scope and a bulb for a load.

Probably output cap stuffed.
The brown gunk is that horrible sealant that hardens and gets brittle but worst of all is hydroscopic. Scrape the muck off and use neutral cure RTV.
Avid Rabid Hobbyist
 
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Offline picburner

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #18 on: April 17, 2018, 05:00:05 pm »
Looking at the second underside pic it would seem that the transistor (TR1?) welds are all cold.
 
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Offline oldway

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Re: JP 12 10A switching PSU only producing about 5 volts
« Reply #19 on: April 17, 2018, 07:07:43 pm »
Are you a candidate for Darwin awards?  :-DD

Trying to repair a cheap, poor quality, crap power supply without a schematic by making a dangerous repair attempt, you are a good candidate .... :-DD

Do you own at least a good isolation transformer?  |O

No need for the insult thanks.  I have already acknowledged the risks associated with looking at it.

It wasn't a cheap eBay or the like purchase and the case is labelled with a well known (in the hobby) brand.

The fuse is the one that came with it but I've only typically drawn about 4 amps from it.

I don't particularly need it as I have been using my DP832 instead.

However, as I said, (if someone recognises the board) if there was anything obvious that it could be, I could consider swapping out the part, just for the pleasure of not throwing it in the bin.
If you consider a simple joke as an insult, it's not my fault ....

But there are truths behind this joke:

1) To troubleshoot a SMPS, it is often necessary to turn it on and make measurements.
The voltage on the primary side is 320 Vdc with an unlimited current far exceeding 30 mA.
This can be lethal.

In the event of an error or wrong operation, you risk not only damaging your oscilloscope, but also electrocuting yourself.

2) It seems that you do not have much experience with SMPS, the proof is that almost all the participants of this topic have noticed that it was a product of low quality and technology and you do not .

As Dave would probably say if he were to review such a power supply: bullshit.

3) to work efficiently and safely, it is better to know exactly where one connects his oscilloscope .... It is, in my opinion, essential to have a diagram.

The first thing someone who would have experience would have done is to do some reverse engineering and draw a "DaveCad" schematic at the very least of the primary circuit.
You did not do it, which shows no professionalism on your part.

So, yes, if you happen to have a serious accident repairing a dangerous smps, poorly made while it is not worth it, you deserve a Darwin Award .... maybe not in the top 15,  :-DD
 

Offline netdudeuk

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #20 on: April 17, 2018, 07:25:59 pm »
Looking at the second underside pic it would seem that the transistor (TR1?) welds are all cold.

You have good eyes.  Yes, it is TR1 and a slight push on it showed all three pins moving freely backwards and forwards.

A quick reflow and here is what I see without a load.

 

Offline netdudeuk

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Re: JP 12 10A switching PSU only producing about 5 volts
« Reply #21 on: April 17, 2018, 07:32:29 pm »
Are you a candidate for Darwin awards?  :-DD

Trying to repair a cheap, poor quality, crap power supply without a schematic by making a dangerous repair attempt, you are a good candidate .... :-DD

Do you own at least a good isolation transformer?  |O

No need for the insult thanks.  I have already acknowledged the risks associated with looking at it.

It wasn't a cheap eBay or the like purchase and the case is labelled with a well known (in the hobby) brand.

The fuse is the one that came with it but I've only typically drawn about 4 amps from it.

I don't particularly need it as I have been using my DP832 instead.

However, as I said, (if someone recognises the board) if there was anything obvious that it could be, I could consider swapping out the part, just for the pleasure of not throwing it in the bin.
If you consider a simple joke as an insult, it's not my fault ....

But there are truths behind this joke:

1) To troubleshoot a SMPS, it is often necessary to turn it on and make measurements.
The voltage on the primary side is 320 Vdc with an unlimited current far exceeding 30 mA.
This can be lethal.

In the event of an error or wrong operation, you risk not only damaging your oscilloscope, but also electrocuting yourself.

2) It seems that you do not have much experience with SMPS, the proof is that almost all the participants of this topic have noticed that it was a product of low quality and technology and you do not .

As Dave would probably say if he were to review such a power supply: bullshit.

3) to work efficiently and safely, it is better to know exactly where one connects his oscilloscope .... It is, in my opinion, essential to have a diagram.

The first thing someone who would have experience would have done is to do some reverse engineering and draw a "DaveCad" schematic at the very least of the primary circuit.
You did not do it, which shows no professionalism on your part.

So, yes, if you happen to have a serious accident repairing a dangerous smps, poorly made while it is not worth it, you deserve a Darwin Award .... maybe not in the top 15,  :-DD

Well, I know that there are no modern SMPS ICs on there and I can see that it is a SRBP board, not FR4.  I can see that there are no slots between the high and low voltages.  I've seen Big Clive, etc, go over this time and time again.

I had no intention of connecting a scope to it.  I have seen Dave's how not to blow up your scope video more than once.

The reflow process seems to have fixed the issue.  So, apparently, no schematic or a single measurement required.

As far as professionalism is concerned, this is a hobby, not a job.
« Last Edit: April 17, 2018, 07:39:21 pm by netdudeuk »
 

Online tautech

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #22 on: April 17, 2018, 07:54:54 pm »
Looking at the second underside pic it would seem that the transistor (TR1?) welds are all cold.

You have good eyes.  Yes, it is TR1 and a slight push on it showed all three pins moving freely backwards and forwards.

A quick reflow and here is what I see without a load.
:-+
It's surprising now many PCB faults you can find with just careful inspection.
Even more when using a jewelers magnifying headset.  ;)
Avid Rabid Hobbyist
 
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Offline picburner

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #23 on: April 17, 2018, 08:17:18 pm »
Fortunately you did that pic with a particular inclination, impossible to see the defect from the other pics.
The instructions in fact say that the no-load voltage is 15V while with the full load it falls to 14V.
 
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Offline coromonadalix

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Re: JP 12V 10A switching PSU only producing about 5 volts
« Reply #24 on: April 17, 2018, 08:36:40 pm »
as noted   you have cold joint solder on the two to220 transistors / rectifiers  and som in the middle of the board, you see small rounds in the solders .... redo the board at first before anything else ...  and im sure it is not an 10 amps psu   or its the wrong fuse at 7.5 amps on the pcb ??
« Last Edit: April 17, 2018, 08:38:54 pm by coromonadalix »
 
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