iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

[torgeson5kqs]

I have a few of the above mentioned power supplies with Pin 8 showing no voltage when jumpered. The correct voltage should be 5v and comes from the WT7515 chip. I've replaced that chip along with the 3845B and W1P (Q1) chip and still can not get voltage to show up. I know that Q1 is typically a culprit, and this supplies power to the 3845B chip, is it possible that the other surrounding 1P or W1P chips or it's counter parts the 2F are bad as well? I'm not sure how to test if these are bad or where to go from here. By the way all other voltages on all other pins are correct on my unit according to the voltages listed below except for pin 8.



Voltages measured from ground are as follows:

3, 5, 7, 11, 14, 16, 17, 18 - Ground (-)

1, 2, 12 - 3.3v

4, 6, 20, 21 - 5.1v

8 - (Power Good) - 5v

9* - (Standby) - 5v

10, 13, 19 - 12v

15 - On/Off - jumper to ground (14 or 16) to run supply

22* - 24v (may read about 21v until switched on)

* Always present when unit is plugged in but not switched on.

[Toasty]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

Voltages with respect to Common negative output ? :

Pin 1 - WT7515

Cathode - D1

[torgeson5kqs]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

unjumpered the voltage on pin of wt7515 is .8v and cathode of D1 is 9.6v

jumpered the voltage on pin of wt7515 is .8v and cathode of D1 is 10.3v

both from common ground.

[Toasty]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

Re-Do post - site was down and it didn't get in...

Only time that should show voltage is when its turned (jumpered) on.

Check D1, R6, R13, R14

[torgeson5kqs]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

voltages listed below while unit was jumpered
D1 - 10.2
R6 - 0
R13 - 9.3
R14 - .8

voltages listed below while unit was unjumpered (same)
D1 - 10.2
R6 - 0
R13 - 9.3
R14 - .8

[Toasty]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

No. Check the 4 components for -values-. Dig up your SMD resistor code book.

Voltages should -not- be present on PGI/PGO when not on(in standby).
Voltage comes from the outputs to the WT7515 chip. So, there is another problem if you have readings when in standby.

In standby, you should only have:
FPOB = ~4.5v
PSONB = ~5.2v
VCC = ~5.2v

...and those all come from the 5vsb

Toast

[torgeson5kqs]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

Ok the resistor values are below but I don't know about the diode.

D1 - ? shows black cathode band and then just a red strip looks l D14, D17, D13 ( I think they are all the same)
R6 - 51 ohms code is 510
R13 - 94 Mohms (seems rather high) code is 946
R14 - 845 ohms +/- 1% code is 90A

R13 - I looked up another power supply and it appears to be 9.31 kΩ (≤1%) code shows 94b

[Toasty]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage



I know what they are, are they good?

[torgeson5kqs]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

Uhhh very sorry. All of these were measured in circuit with Extech RC200 tweezer multimeter.

D1 - 1.88 volts (not sure how to measure this) or reads 772 ohms on diode setting

R6 - 50.4
R13 - 9.23 Kohms
R14 - 840 ohms

I checked a couple of bad supplies and they all read about the same values for these. So they appear to be good, yes?

[Toasty]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

D1 should conduct one way and be infinite the other on diode test.

Others match their markings so no problems.

Something is wrong in that you are getting voltage on PGI/PGO in standby mode.

[torgeson5kqs]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

The D1 does show infinate one way and conducts the other, I have a total of 4 of these power supplies and they all show voltages on standby very close to the values I mentioned in post #5. The reistors and diodes also show values within spec with regard to ohms. Again these were all tested in circuit, should I pull a couple out and test?

[Toasty]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

No need to pull out and test values.



There is another problem if you have voltages here in standby.

No. Wait. I have a better one...

[torgeson5kqs]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

Ok point taken...So have we reached a dead end here then?

[Toasty]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

Nope.

Find out why.

See post 6, again.

[torgeson5kqs]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

here is what I have on the WT7515 in standby

1 - .8
2 - 0
3 - 4.6
4 - 5.2
5 - 5.8
6 - 1.1
7 - 2.9
8 - 3.3
9 - 5.8
10 - 5.8
11 - 3.3
12 - 3.0
13 - 5.1
14 - 0

In standby, you should only have:
FPOB = ~4.5v PIN 3
PSONB = ~5.2v PIN 4
VCC = ~5.2v PIN 13

When jumpered I have
1 - .8
2 - 0
3 - 0
4 - .4
5 - 12
6 - 0
7 - 5.1
8 - 3.3
9 - 12.1
10 - 12.1
11 - 3.3
12 - 5.2
13 - 5.1
14 - 0

All I can think of is that there is a short or their is an overage of voltage that is spilling over from a component for lack of a better phrase. I've checked for shorts on many of the SMD's with no luck.

[Toasty]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

Looks like a leaky opto in some way. Like the supply is getting bits of a signal to run, when it shouldn't.

In standby, what voltage do you have across the main caps?

[torgeson5kqs]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

I get anywhere from 167 to 170 volts on the main caps depending on which power supply I check.

[Toasty]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

That's correct. So this means the main side is not being turned on. PFC is not on.

On you should get ~384 volts.

[torgeson5kqs]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage

whats the correct voltage accross the caps supposed to be when the unit is on?

[Toasty]

Re: iMAC G5 Power Supply API4PC46-290 REV.A pin 8 no voltage



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