Re: iMac 24 PSU LITEON PA-3241-02A1 250W



In this iMac a fan blows air across the CPU heatsink, then the GPU heatsink, *then* this PSU. So, uh, yeah, not the best for cooling......

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

The switching transistors are likely working OK -- I am getting the correct voltage at the output. And the new fuse has not blown.

I'd also bet that it's bad caps, even though they all look OK. The audible noise and transient bursts on the output suggest that not enough filtering is going on here.

I'm curious if I can locate which component(s) are making the regular ticking/buzzing sound. I can take the metal end of a stethoscope off and probe around with the end of the rubber tube -- listening for the source...

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

I installed a SATA HDD in the iMac and the PSU is struggling to spin it up. The clicking/buzzing sound has increased to about 3Hz. I'm thinking that this PSU is pretty much toast at this point.

Apparently Apple changed the 661-4995 PSU design sometime in 2009. I have the older unit, like Bosscharles at the beginning of the post. This one is made by Liteon. The replacement PSU, also referenced as part 661-4995 is manufactured by Delta. Looks like a better designed unit. These are still showing up new for about $140....

Re: Newbie - Imac 24 - Liteon PSU - no power at all

sorry for the cross posting...

updates are in this thread:
[url]https://www.badcaps.net/forum/showthread.php?t=38233&page=2[/url]Re: Newbie - Imac 24 - Liteon PSU - ...3&page=2[/url]

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

I soldered in a new 5A slow blow fuse and powered it up on the bench (no load). Fuse held; no magic smoke and the standby 12V pin reads 12.2VDC. OK so far.

Reinstalled the PSU in the iMac. It powers up, I get the Mac "chime" sound indicating it has made it past the POST check. There is no HDD installed so I can't yet test the complete boot process.

The PSU is making a faint buzzing sound which lasts about 500ms and repeats every 2 seconds or so.

The main 12V output reads 12.0V on the...

Re: Newbie - Imac 24 - Liteon PSU - no power at all

Similar situation here -- bought a non-working iMac cheap.

PSU is Liteon PA-3241-02A2 REV. A

Blown 5A input fuse on the PSU. Caps look OK. None of the MOSFET pins are shorted. Diodes and bridge rectifier test OK in circuit.

Any suggestions for other things to check?

Since there are no obvious problem components, I'll try putting in a new 5A slow blow fuse and power it up on the bench. Will check for 12V standby power... and check for magic smoke.

jami...

Re: iMac 24 PSU LITEON PA-3241-02A1 250W

I've got a similar PSU removed from an early 2009 iMac. Liteon PA-3241-02A2. Blown input fuse. No visible damage to any caps, FETs, or diodes. The diodes and bridge rect. seem to test out OK. None of the FETs (or transistors) appear shorted.

Since I don't see any obvious "smoking gun" bad components on this PSU I'm considering installing a new fuse and powering up separately on my bench with 120VAC and checking output voltages.

I'm assuming that if things are working right I should get some 12V standby...