Sorry, no information in that area. Maybe someone else that reads the comments knows the pinout voltages for the inverter or can point us in the right direction.

Regards,

Jim

Would you happen to know the pinout voltage for the backlight inverter? For a imac G5, 1.6ghz. (6 pinout)

That is what someone supplied to me for labeling. It may be where the wires go on the circuit board as a reference point. However, don’t worry about those specific references, just the wire numbers when measuring the voltages.

Jim

It could be that when the PSU is placed under load, that is when the problem shows itself. It could be that something else is bad on the PSU.

Thanks for the input about the Dell motherboards. Dell was not the only one to have problems. I just heard a report that Samsung TVs had a similar issue with bad capacitors too.

Regards,

Jim

I can’t figure it out but all of the voltages are like you said above. Could one of these things start working again after being discharged all the way? I am going to put it in the computer and see what happens. I have one of these and my parents also have one. Theirs stopped working so I took mine out and traded with them. Weird that it seems to be working.

Also on your pinouts #8 PG-Blue is 5 Volts. Another thing to note is that you can’t use the case for the ground on your meter. I used a paper clip to jumper 15 & 16 so I used an alligator clip to clip on to the paper clip for ground.

I was also told by a Dell tech to look for the X pattern on top of the capacitors, these were the bad ones. We had hundreds of GX270 motherboards go bad because of these bad capacitors. The replacement motherboards had capacitors with a K stamped into the top of the capacitors. This might help folks to figure out which ones an likely to be bad.

Thanks
Guy

I would say that you probably need to check those voltages first. Also, if the first LED does not light on the logic card with the PSU plugged in to the AC, but not turned on, then that is showing that something else is probably wrong with the PSU other than the capacitors.

Regards,

Jim

Thanks for the fast response and help:-)

Regards,

Kim

The powering down and powering up problem is typical of the the bad capacitor problem. I always say, you’ve got to fix what you find bad. In this case, having bulging caps on the MOB can in fact cause the problem you describe. I would definitely fix the MOB with new caps to begin with. Then, if you still have a problem, the original bad capacitors on the MOB could have caused something to go out in the PSU other than the PSU caps themselves.

Refer to my other Apple articles for more information.

Regards,

Jim

Excellent information!

All electrolytic capacitors have a finite life:

The voltage across the plates of the capacitor, in normal use, causes electrolysis in the electrolyte solution. i.e. breaking down the solution into its constituent atoms/molecules. This process ‘consumes’ the solution because the solution is converted into various gases. The rate of consumption is highly dependent on the voltage applied (higher voltage=more electrolysis!).

As the capacitor ages, this process begins to accelerate and eventually sufficient gas is produced to cause a pressure build-up within the capacitor, eventually causing the capacitor to ‘vent’ (pop or explode!). The score-markings on the top of the capacitor are there to ensure the capacitor ‘vents’ in a controlled manner.

A partial venting will also cause electrolyte solution to leak out, which further accelerates the capacitor’s demise.

Testing capacitors:

While measuring the capacitance of a capacitor seems like the right thing to measure, actual measurements on bad capacitors will either show a good reading, matching the value stated on the side, or, most likely a higher reading. Strangely the capacitance actually INCREASES as the capacitor is dying!

In DC filter applications higher capacitance is normally a good thing because it provides more filtering of the high-frequency ripple from the SMPSU. However in the case of comparing an electrolytic capacitor’s stated value to the measured value, this indicates a dying capacitor – This provides a poor-man’s capacitor test: Look for higher than normal readings (in addition to basic visual tests)!

The real parameter to check is the Equivalent Series Resistance (ESR). This resistance is in series with the capacitor and so cannot be measured with an ohm-meter – A special ESR meter is required (I use a Peak ESR60 £90).

The ESR of a capacitor is important because it IS the parameter that increases as the electrolyte is consumed. The ESR is also represents the power loss in the capacitor (Ploss = Resr x I^2), this power loss causes heating of the capacitor, which further accelerates the electrolyte consumption.

It is very normal to see capacitors in a SMPSU that look normal (no signs of bulging, etc) but actually have a high ESR reading and are in fact faulty – Always test the ESR of all capacitors (individually out-of-circuit).

Again a poor-man’s test for ESR is to simply feel the temperature of the capacitor. If it is hot, then there are significant losses caused by the ESR.

Finally, increasing the capacitance values of replacement parts may seem like a like a good idea to reduce ripple currents, but be warned that going too high may mess-up the dynamics of the SMPSU causing it to become unstable!

Hope that helps, sorry if it’s already been said (haven’t waded through the comments!!!)

Si

I have a question for you, I can see on the underside a small SMD diode has blown. Is there anything that can be done about this or is it time for a new PSU?

Thanks very much in advance for your response

Nj

It is always a good idea to replace all the caps that are included in the PSU capacitor kits. Just because you do not see any others bulging, does not mean the other caps are good.

It is possible you have something more than blown caps as being the problem on the PSU. The fact the voltages are bad is a sign of a faulty PSU. If you are not careful when soldering on the bottom of the PSU circuit board, it is possible that now, one of the other components is damaged. I would inspect your soldering work carefully to make sure there are no solder bridges or cold solder joints.