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Regulated DC Power Supply not working

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AlainB

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Hi,

I bought this power supply in a flea market without checking it first. Now, I can see that it is not working properly.

It is only outputting 22.1 volts on the DC side. Nothing else. The AC side is outputting 17.1 and 5.2 volts. The fuse is good.

After a carefull inspection, I don't see anything that I can suspect to be the problem.

I do not have any schematic for this power supply.

Any help would be appreciated to find the problem.

I have good electronic tools including an oscilloscope if that may help.

Thanks!

Alain

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Most common cause would be the regulator transistor having gone S/C - presumably one, or both, of the TIP3055's.

It could have caused further damage as well.
 
I concur with Nigel.

As he said, one (or maybe both) of the TIP's have gone shorted. You are seeing the unregulated input voltage @ the output of the PSU. Because the series pass transistor"s" are shorted.

Another thing I noted from the pic's....this thing has an output capability of 20Amps.....that transformer is weeeeey to light for that....

Anybody else spot that?

Cheers
 
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Another thing I noted from the pic's....this thing has an output capability of 20Amps.....that transformer is weeeeey to light for that....

On the face plate, lower right hand corner below power switch:

Voltage: 0 ~ 15 V.
Current: 13.8 V @ 10 A
Max Current: 12 A

20 V and 20 A are just the meter face I believe.

Also, if I were to start looking I would be looking at the 3055s first.

Ron
 
I don't know anything about power supplies or diagnosing issues with them, but I'm actually curious about the last two pictures (compared with the second picture) - what is that thing, and why does it appear to be some kind of "homebrew" graft add-on to the power supply (as in, not original to the manufacture of it)? I know cheapo power supplies can have weird component and board layouts, but that part looks odd (traces that go nowhere off the board edge, the edge looks "broken", silkscreen goes off-board, what appears to be a ground wire is red, not black)...
 
I removed the 2 TIP3055 to test them. One is shorted betwen the collector and emitter. The other one seem to behave normally. Using the diodes tester of my multimeter I have a reading when the the red wire of the meter is in contact with the base pin and the black wire is in contact with the collector and/or the emitter.


These TIP3055 are cheap and seem to be easy to find. Tomorrow I will buy 2 of them. But prior to installing them, would there be other thing to look for that may be not working?

Another question: What could be the purpose for the D880 ? ,and what kind of transistor is it? I don't find any datasheet for it. I tested it and it seem to be good anyway.

Many thanks!

Alain
 
Another question: What could be the purpose for the D880 ? ,and what kind of transistor is it? I don't find any datasheet for it. I tested it and it seem to be good anyway.

It's probably a 2SD880 NPN power transistor (3A 60V). It provides the base current for the two TIP3055s. At a 10A load, the TIP3055s may need upwards of 2A base current, which the 324 opamp cannot provide. The 2SD880 provides the extra current gain.
 
After changing the TIP3055's, the power supply is not outputting any voltage any more. But if I put voltage to the base of the D880, using a 50k pot I can get the power supply to output variable voltage from 0 to 22 volts.

What would be next?

I removed and tested the small transistor (C1815) that is going to the base of the D880 and it tested OK. I will replace it anyway.

I have 29 volts at pin 4 and 11 of the opamp (C324C). I removed it from the board. Maybe I was too fast on that one. I should have wait for a reply. If I have to change it would an easy to find LM324 fit instead?

Thanks!

Alain

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Nobody here is concerned that the "extra" board that is being fixed seems like a graft job, and is not likely OEM? I am not saying that such a job must be at fault, but I sincerely wonder what it is for, and why it was put there...?

:)
 
Nobody here is concerned that the "extra" board that is being fixed seems like a graft job, and is not likely OEM? I am not saying that such a job must be at fault, but I sincerely wonder what it is for, and why it was put there...?

:)

hi,
I have the same PSU, its named WATSON W-10AM.
**broken link removed**
**broken link removed**

I opened up my psu and it has exactly the same pcb's as Alains, chop off etc.
Its looks as though its split pcb for a dual psu, chopped.

EDIT:
On checking my psu, I have one Toshiba 2SC3281 in place of the two, 2N3055's [its uses the D880 to drive it]
 
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hi,
I have the same PSU, its named WATSON W-10AM.
**broken link removed**
**broken link removed**

I opened up my psu and it has exactly the same pcb's as Alains, chop off etc.
Its looks as though its split pcb for a dual psu, chopped.

EDIT:
On checking my psu, I have one Toshiba 2SC3281 in place of the two, 2N3055's [its uses the D880 to drive it]

As long as fuses are not being blown everytime you turn it on you are more or less OK. No major costs with shorted windings or whatever.....

I would say, replace the LM 324 and switch it on. You have checked the other important parts.... if I remember correctly, the 324 was a quad op amp that was widely used in the eighties. Lot's in PSU's like yours.

That's my take. I am pretty sure if you Google your LM 324 you will find one (or more) somewhere.

That's all I can think of right now.

Cheers

Sorry Eric.....I quoted the wrong post. Ugh!!!
 
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I changed both the small C1815 transistor and the opamp. I used a LM324 and now the power supply is working nicely. I will never know witch one was at fault along with the TIP3055 but I suspect more the opamp.

Eric, if you psu is still open, what is the voltage that you read betwen pin 4 and 11 of the opamp. I read 29 volts on mine and it seem to be very near the absolute maximum rating for this opamp.

Thanks!

Alain
 
hi,
I have the same PSU, its named WATSON W-10AM.
**broken link removed**
**broken link removed**

I opened up my psu and it has exactly the same pcb's as Alains, chop off etc.
Its looks as though its split pcb for a dual psu, chopped.

EDIT:
On checking my psu, I have one Toshiba 2SC3281 in place of the two, 2N3055's [its uses the D880 to drive it]

Weird! I swear, that thing looks like somebody custom grafted a piece of power supply junk PCB and components onto the rest of the circuit; it really looks half-a&&ed, for what is presumed to be test equipment. I don't think I'll be buying one of those power supplies; that just doesn't look right...

:)
 
Weird! I swear, that thing looks like somebody custom grafted a piece of power supply junk PCB and components onto the rest of the circuit; it really looks half-a&&ed, for what is presumed to be test equipment. I don't think I'll be buying one of those power supplies; that just doesn't look right...

:)

hi C,
The label says 'Made in China'..............................

BTW: my psu has worked hard for over 15 years trouble free.;)
 
Eric, if you psu is still open, what is the voltage that you read betwen pin 4 and 11 of the opamp. I read 29 volts on mine and it seem to be very near the absolute maximum rating for this opamp.
Thanks!

Alain

hi,
My PSU on the LM324 pins 4 and 11, reads 28.4V
 
Well then 29 volts should be fine.

Thanks again everybody. This was my first real electronic repair involving more than a broken wire or a bad solder.

I am very happy with the result.

Alain

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hi C,
The label says 'Made in China'..............................

BTW: my psu has worked hard for over 15 years trouble free.;)

My first thought is "that explains it" - but it really doesn't! Lot's of decent and well constructed devices are "made in China"; makes me wonder where it was designed, or manufactured; that board seems like a cut-rate savings method. Obviously, it works - but if I opened up a device and saw that, I would have my doubts about it. Any reputable company would do a re-design and use an actual board there, not something cut-down like that PCB is. Of course, this now makes me wonder if similar methods of production have found their way into a number of products on the market today.

/I also must note that if I paid a lot of money for such a power-supply, and then opened it up to find that kind of workmanship, I wouldn't be very happy...
 
My first thought is "that explains it" - but it really doesn't! Lot's of decent and well constructed devices are "made in China"; makes me wonder where it was designed, or manufactured; that board seems like a cut-rate savings method. Obviously, it works - but if I opened up a device and saw that, I would have my doubts about it. Any reputable company would do a re-design and use an actual board there, not something cut-down like that PCB is. Of course, this now makes me wonder if similar methods of production have found their way into a number of products on the market today.

/I also must note that if I paid a lot of money for such a power-supply, and then opened it up to find that kind of workmanship, I wouldn't be very happy...

And with that said, I would have to agree with you. It really looks like a POS inside.

You just don't expect to pay good money now day's for something so badly constructed internally. And the design is old too....

I remember the old ELEKTOR magazine publishing a very similar design around the early Eighties..also using a LM324....

Sure, this PSU must be a sound and reliable design to still be around after all these years...the construction thereof leaves a lot to be desired though.

Cheers
 
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