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Old 04-04-2020, 12:34 PM   #1
falcontech
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Default Power Mac G4 Mdd Acbel power supply (not Samsung)

Hello
I have a problem with an acbel, I can't start it, I have changed almost all the capacitors including the 100uf 400v, but it doesn't want to start, the LED on the front turns on for a moment and then fades away, there were two burnt capacitors on the secondary but they did not solve the problem I hope someone can help me now it has become a challenge (on the other hand I managed to repair two samsung) if someone needed the photos I can attach them thank you very much
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Old 04-04-2020, 07:38 PM   #2
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

How about you post some straight shot, high resolution picture of the PSU front and back. Also tell us which capacitors you have replaced.
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Old 04-05-2020, 04:04 AM   #3
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

ok
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Old 04-05-2020, 04:55 AM   #4
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

Quote:
Originally Posted by CapLeaker View Post
How about you post some straight shot, high resolution picture of the PSU front and back. Also tell us which capacitors you have replaced.
Meanwhile, I have attached the map with the components, the replaced capacitors are highlighted in yellow, later I will let you have the photos, unfortunately the capacitors in the photos will not look good because of the tangle of wires, so from the map you will understand better
Attached Images
File Type: jpg Map Caps.jpg (511.6 KB, 20 views)
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Old 04-05-2020, 09:43 AM   #5
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

Quote:
Originally Posted by CapLeaker View Post
How about you post some straight shot, high resolution picture of the PSU front and back. Also tell us which capacitors you have replaced.
here you are served
Attached Images
File Type: jpg IMG-20200405-WA0015.jpg (189.8 KB, 8 views)
File Type: jpg IMG-20200405-WA0016.jpg (205.8 KB, 17 views)
File Type: jpg IMG-20200405-WA0020.jpg (200.6 KB, 15 views)
File Type: jpg IMG-20200405-WA0021.jpg (185.8 KB, 13 views)
File Type: jpg IMG-20200405-WA0022.jpg (152.3 KB, 13 views)
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Old 04-05-2020, 10:40 AM   #6
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

when you tested this power supply, did you force it on or did or did you just put it back into the G4? Did you check if any secondary output rails are shorted on the PSU? How much DCV are you getting on the 450V caps?
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Old 04-05-2020, 10:48 AM   #7
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

I just tried to connect it on the g4 to check if it works but I have not done any test with the tester, please tell me what test I have to do so the headlight
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Old 04-05-2020, 12:23 PM   #8
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

first i would force it on without being hooked up to the computer.
if you plug it in, you should only have STBY voltage (always on).
if you force the PSU on, well everything should be on. if not, look what DCV you have on the 450V capacitors. Look if any of them voltage rails on the secondary is shorted.
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Old 04-05-2020, 12:35 PM   #9
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

the standby voltage where should I measure it? and which tracks do you mean on the secondary? if you can send me a photo to make me understand where I have to measure, the measurement of 450 volts I understood it thanks for your patience
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Old 04-05-2020, 01:04 PM   #10
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

if it can be useful I have another working acbel
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Old 04-05-2020, 01:41 PM   #11
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

A switching power supply has a primary (high voltage, remember the 450V cap) side and you have to be careful, as you are connected to power mains. Your GND reference point for the multi meter is the negative post on the 450V main filter capacitor. The same PSU has also a secondary (low voltage) side. Your GND reference point for it is on the GND point on the PSU or chassis GND. If you look on the back side of the PSU you can clearly see where the primary / secondary line is. Hope this helps for a quick start.

If you plug in the PSU, you should see roughly 320V or so on the 450V capacitor, since it isn't turned on (yet). Once the PSU is turned on, the power factor correction circuit will boost that 320VDC to like 400VDC. That is how you know if the PFC is working or not. After all, if the PFC isn't working, there wont be any 25vsb.

Now put your negative probe on one of the black wires on the secondary low voltage side of the power supply and probe with your positive probe all the other color wires. Note what these wires do (like 25vsb, 5V, sense etc.) and the corresponding voltage you had measured. Post it here and then go further.
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Old 04-05-2020, 01:59 PM   #12
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

Ok
all clear, but if the power supply does not turn on, theoretically on the output I shouldn't have any value I suppose, (maybe I'm wrong) that's what I couldn't understand when you told me to measure the low voltage
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Old 04-05-2020, 02:10 PM   #13
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

Well, we don't know why it doesn't turn on. Question is: Is a problem with the PFC? Is it a problem with a shorted voltage rail on the secondary (3.3,5,12,25V and -12V). Is it a bad -12V regulator... we don't know. I'd check the PFC first.

ATX power supplies have always ONE stby voltage rail that is always on. Then there is an soft on / off pin has either stby voltage on it and it needs to be pulled to GND or it has no voltage on it and needs to be pulled high to STBY. STBY is something like 3.3 or 5V and is always on.
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Old 04-05-2020, 02:17 PM   #14
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

very well you have been very clear, tomorrow I will give you news because it is already night thank you very much and see you tomorrow
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Old 04-06-2020, 07:31 AM   #15
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

Hello
Then on the 450v capacitor I have 390v, on the low voltage outputs I only have 25.4v of the white wire, on the others (5v yellow, 3.3v orange, 12v red) nothing comes out
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Old 04-06-2020, 08:08 AM   #16
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

Quote:
Originally Posted by CapLeaker View Post
Well, we don't know why it doesn't turn on. Question is: Is a problem with the PFC? Is it a problem with a shorted voltage rail on the secondary (3.3,5,12,25V and -12V). Is it a bad -12V regulator... we don't know. I'd check the PFC first.

ATX power supplies have always ONE stby voltage rail that is always on. Then there is an soft on / off pin has either stby voltage on it and it needs to be pulled to GND or it has no voltage on it and needs to be pulled high to STBY. STBY is something like 3.3 or 5V and is always on.
I wait for your instructions
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Old 04-06-2020, 08:19 AM   #17
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

O.k. That means the PFC on the Primary boosting the voltage is working. Is the blue wire -12V there? Basically you have it narrowed down that one of these 3 voltage rails is bad. Check the diodes for 5v, 3.3v and 12v, maybe one is shorted?
You can check the transformers input and output winding's. If they measure an open (OL) than it is bad.
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Old 04-06-2020, 08:26 AM   #18
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

Quote:
Originally Posted by CapLeaker View Post
O.k. That means the PFC on the Primary boosting the voltage is working. Is the blue wire -12V there? Basically you have it narrowed down that one of these 3 voltage rails is bad. Check the diodes for 5v, 3.3v and 12v, maybe one is shorted?
You can check the transformers input and output winding's. If they measure an open (OL) than it is bad.
Ok
have patience, these are tests that I have never done on the power supplies, what are the diodes? those on the heathsink? and if you can also tell me how I have to try the transformers, I have no idea there are so many feet and I don't know how to do it and how to set up the multimeter ... sorry and thanks for your patience, maybe after this I will be able to repair all the power supply

Last edited by falcontech; 04-06-2020 at 08:57 AM..
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Old 04-06-2020, 08:28 AM   #19
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

Quote:
Originally Posted by CapLeaker View Post
O.k. That means the PFC on the Primary boosting the voltage is working. Is the blue wire -12V there? Basically you have it narrowed down that one of these 3 voltage rails is bad. Check the diodes for 5v, 3.3v and 12v, maybe one is shorted?
You can check the transformers input and output winding's. If they measure an open (OL) than it is bad.
Yes, there is a blue wire and -12v is written on the printed circuit board
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Old 04-06-2020, 08:38 AM   #20
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Default Re: Power Mac G4 Mdd Acbel power supply (not Samsung)

I have a short on the red wire, the yellow one and the orange one mark me a value but the multimeter does not sound
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