G5 Mac Power Supply Relay

[torgeson5kqs]

I have a G5 Power Mac power supply model AcBel API2FS34-291 p/n:614-0306 The relay clicks on and off when I push the button to power up the system. Currently the PSU is removed and open. I figured something would cause the protection relay from powering the system. From visual inspection of the power supply there are no burn marks from blown transistors that I can see and no bulging caps. I also did continuity check on the fuse and it's good as well. If anyone has any suggestions or has had a similar issue I'm all ears.

[Toasty]

Re: G5 Mac Power Supply Relay

>>I also did continuity check on the fuse and it's good as well.<<

Only one(1) fuse?

Are the standby 5v (red wire, P1, pin 20) and 25v (white wire, P2, pin 8) voltages present?

You can jumper the On/Off (green wire, P1, pin 14) to any black wire to test. Do any of the voltages 5/12/3.3 -try- to come up? A brief pulse?

[torgeson5kqs]

Re: G5 Mac Power Supply Relay

Sorry this has 2 fuses both are good. I checked voltages on P1 and P2 and nothing for any of the pins. I jumpered P1 with a 56 Ohm 1/4 watt resistor from pin 14 (green) to all the black wires (13 to count) They all had around 3.3 volts some less some more for only about a second. Then they all went to zero when the relay kicked in.

[Toasty]

Re: G5 Mac Power Supply Relay

OK. We need to get the standby voltages up first. That's more than likely why nothing works. Let me get some points for you to check.

When you plug it in with -nothing- connected, does the relay do a double-click or not?

Most of the caps are decent quality Rubycon's on the mains filters and the outputs with a few UCC KY's in there too. All the small caps appear to be LTec's and I see one on the output also. Most likely candidates for the problem.

Toast

[torgeson5kqs]

Re: G5 Mac Power Supply Relay

I have a BLUE ESR meter, can I check the ESR correctly. Or is it like the mid-plane on the iMacs where they are all in series and the reading dosen't come out correctly? Also if I can do that do you have a round about idea of what the ESR is or should be on some of these none standard caps. I'm familiar with the 2200, 1000, 1800, etc. but some of the larger or smaller values I rarely replace and therefore don't have an idea of their GOOD ESR. Let me know if this is what you had in mind or if I should just pull them all out and measure individually?

[Toasty]

Re: G5 Mac Power Supply Relay

I am no where near checking caps yet. Determining the circuit operation is where I start, and answering the question "Why are there no standby voltages?" Figuring out where and how they are created may lead directly to the problem source.

In order for this to work, I need you to answer questions I ask if you are able. If you are not able to answer them, I need to know that also, please.

So, again:
When you plug it in with -nothing- connected, does the relay do a double-click or not?

Toast

[torgeson5kqs]

Re: G5 Mac Power Supply Relay

Sorry, yes is does do a double click.

[torgeson5kqs]

Re: G5 Mac Power Supply Relay

miss-spelling: yes, it does do a double click.

[torgeson5kqs]

Re: G5 Mac Power Supply Relay

I forgot to mention when I was checking the voltages on the pins, I had the fans plugged into the board (having the green wire with a black shorted) the fans actually ran the whole time. Not sure if this helps but appears some power was still going through the board. Let me know what else I should check, I can post pictures as well if you need to see something. Although you mentioned you have the same power supply, either way let me know.

[Toasty]

Re: G5 Mac Power Supply Relay

Orient the board so power input is on the left, fans on the right. This places it so all the markings legible and "right side up".

Place your meter in the 200v DC scale.

* WARNING * SHOCK HAZARD *
You, like many others here, are probably not using an isolation transformer. EVERYTHING to the left and across the top of this supply can be at mains / line voltage or higher. The same that comes from your wall outlet. That includes the top heatsink, the tops of the very large caps and any other exposed connections. Contact with those areas may cause a severe shock, burns, or death. If you are not sure of what you are doing, Don't Do It. ASK FIRST !

> See Pictures attached <

With that out of the way, let's proceed:

Plug in the supply. No jumpers.

Check for voltage across D24. It's the large diode just below T2, the far right transformer between the heat sinks. Negative probe to anode, positive to cathode (banded end). Report.

Leaving the negative probe in place on D24, measure and report the voltages at the cathode end (banded) of the Zener diodes to the right, up by the sealed trimmers, and a few more below them. I'll list them in order coming down the board:

ZD9
ZD8
ZD10 (next to lower heatsink)
ZD7 (left of 3 small caps, cathode is lower connection)
ZD11 (left of 3 small caps, cathode is lower connection)

With the negative probe still on D24's anode, measure and report the voltage on Pin 1 of each of the 5 optoisolators. They are the square little devices with 4 legs above the trimmers. 4 white and 1 black on mine. Pin 1 is the lower left pin. If you look at them closely, the pad they are soldered to on the board is square, and there is a dot on the body of them. Be careful not to short the pins on these.

M5
M2
M12
M7
M8

Remove the negative probe from D24.

*HOT SIDE MEASUREMENT*
Place the negative probe on the negative lead of C11 which is the small cap at the upper right of T2, between T2 and the upper heatsink. Place the positive probe on the cathode of D35 which just to the left and down from C11. Report voltage.

Toast

[torgeson5kqs]

Re: G5 Mac Power Supply Relay

I've doubled checked all these and below are the readings from my DVM at the 200 VDC setting. My optoisolators are all black (NEC) seems odd that you would have just one black and the rest white. M2 was the only one that didn't have a voltage (bad possibly). I must say very thorough on your explanation and the picture diagram, your effort did not go unoticed. Cheers.


D24: 5.1 Volts

ZD9: 11.9
ZD8: 11.9
ZD10: 4.9
ZD7: 12.5
ZD11: 24.3

M5: 22.6
M2: 0
M12: 12.7
M7: 12.7
M8: 5.1

Place the negative probe on the negative lead of C11 which is the small cap at the upper right of T2, between T2 and the upper heatsink. Place the positive probe on the cathode of D35 which just to the left and down from C11. Report voltage.

14.8 Volts

[Toasty]

Re: G5 Mac Power Supply Relay

Excellent. Voltages match mine ±0.1v

Measure from the negative of the output side connections, where all the black wires join on the board, to the -tab- (not the screw) of D8. D8 is mounted on the upper side of the lower heatsink, adjacent to T2 and just to the left of the D24 diode from earlier. Both pictures show it clearly, and it's right above the "D24" text on the 2nd picture. The designation is probably hidden by the goop on the board.

Report voltage.

>>My optoisolators are all black (NEC) seems odd that you would have just one black and the rest white.<<
Depends on which ones were cheaper that day and if the factory ran out of that color plastic or not. I would note that the M5 is probably a different number than the other 4.

>>M2 was the only one that didn't have a voltage (bad possibly).<<
No. It just wasn't turned on yet.

Toast

[torgeson5kqs]

Re: G5 Mac Power Supply Relay

Reads right at 25v

[Toasty]

Re: G5 Mac Power Supply Relay

Well, then something is wrong with the first readings I asked for....

Ahhh! I see why. The connection in Post 2 should have been to the purple wire, not red.

"Are the standby 5v (red wire, P1, pin 1) and 25v (white wire, P2, pin 8) voltages present?"
Should have been (purple wire, P1, pin 1)

You've just shown the 25v standby is working and that feeds the 5v standby regulator too.

Negative lead to the same ground connection as before and then go directly to the purple wire connection on the board at the output section. That is the 5v standby. To the right and up a bit is the 25v standby. Measure both please.

Toast

[torgeson5kqs]

Re: G5 Mac Power Supply Relay

The purple is 5.1v and the white is 25v. Before I used the chasis as the common ground not the black negative wires, my bad.

[Toasty]

Re: G5 Mac Power Supply Relay

Good. That means the startup section is active and we can concentrate on what's wrong with the main section.

[torgeson5kqs]

Re: G5 Mac Power Supply Relay

Ok, great what do you need me to check next?

[Toasty]

Re: G5 Mac Power Supply Relay

I want to check the output MOSFETs for shorts.

Unit unplugged from mains.
Black probe to the common output ground, black wire bunch as before.
Check each of the 3 output lines (3.3v orange, 5v red, 12v yellow) for any voltage. I don't want you to damage your meter with the next step.

If not zero, wait until they drop to zero before proceeding.

If zero, change the meter to the Diode Check setting.

Check the 3 outputs with the red probe and report the readings.
You can probe them on P2 if it's easier. Expecting readings of 0.030Ω to 0.300Ω

Then reverse the probes with the red on ground and probe them with the black and report.

Toast

[torgeson5kqs]

Re: G5 Mac Power Supply Relay

All these readings are from the P2 as you suggested. These are with the black probe to common ground, with my meter set to diode (2000 ohms in my case)

yellow=216
red=23
orange=128

These are the readings with the red probe to common

yellow=168
red=23
orange=142

I also checked the readings on P1 as well for both and they were either slightly higher or equal readings.

[Toasty]

Re: G5 Mac Power Supply Relay

The readings all look fine.

*HOT SIDE MEASUREMENT*
Meter set to 500v DC or better.
Carefully wedge the negative meter probe into the fins of the upper heatsink so it is not going to move and will allow you to do 2 things at once.

Plug the unit in.

1) Without using the resistor, jumper the unit on (green to black on P1)
---> and at the same time or very quickly afterward <---
2) with the red meter probe, measure the voltage at the cathode end of D2

D2 sits right in front of the bank of the 3 large capacitors.
Expect nearly 400v here which will slowly decrease down to 170v or so.

Let me know if that is the case. Or, does it remain high?
You may need to repeat 1 & 2 a few times if you don't get near 400v. (380v is close enough )

The relay kicking in and out when you jumper it only allows a brief pulse to this circuit. That is why you have to get the reading quickly.

Toast