iMac G5 1.8G - Fresh caps, but not quite there...

[mrberad]

Ok I just got my freshly recapped board back and put my imac back together. It boots but the screen very faint and goes totally black. I can tell the desktop is there at times.

I reset the PRAM, SMU and pulled the battery out. Mac's have LED's that let you know if the power is supply is good, the board posts and if the video should work. These are all green. Any thoughts, is a certain amount of burn in required here? I have checked all my connections several times. Any feedback is appreciated.

Wort case scenario is that I get an external video adapter

Thanks

Brad

[370forlife]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

Yes, most computers have a led to tell you if the motherboard is bad, the problem is it only tells you if the +5vsb is there so its not completely accurate.

Is there anything shorting out from the bottom of the motherboard? Try running it on a non-conductive surface and see if it boots.

[Toasty]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

Was it working before the recap? Was the power supply recapped also?

Did you by accident crimp a cable or not fully seat a connector?

[mrberad]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

Thank you both for your feedback. BTW (the power supply is only a year old) I'll take it apart and reassemble to see if there's anything not kosher. I have checked the connections several times with nothing loose or crimped. Its as though the board is working but failing to properly power or video feed the lcd. I get a dimly lit glimpse or two of the os loading and my desktop before it fades to black. It's possible that the LCD is hosed by coincidence or something else on the board is not working correctly. Oh the joy of an all in one. Thanks again.

[mrberad]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

Was it working before the recap? Was the power supply recapped also?

The PS was factory new 1 year ago. The Logic Board (Mac for Motherboard) had 2 visible bad caps which led to video distortion and common among this gen of Macs.

[mrberad]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

I disassembled and reassembled - running rock solid right now. Thanks!

[Toasty]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

Excellent! Good Job!!



Toast

[dbridgma]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

I'm up against the same predicament. I have two iMac G5 17" 1.8Ghz units that I recapped (with new PSUs & inverters).

The logic boards sometimes gets all three diagnostic lights lit...but there's no video. The screen remains black. I disassembled & then reassembled both & was able to get one to boot fully (fans running a normal speed, hard drive spinning up) minus any video. But now neither one will light the third LCD green light or fire the hard drive/fans.

Does anyone know how to determine where the fault is? I think I'm close...but no cigar.

Daniel

[Toasty]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

New PSU's? Where are the old ones?

Since you disassembled and reassembled the unit and "things" changed, perhaps there is a bad connection -or- connector? Perhaps, as I previously suggested, a wire is pinched or crimped somewhere?

Can you shine a light on the "no video" one's screen and see anything? It sounds like a backlight/inverter problem perhaps?

Are there any of the paper thin flat plastic type of cables that slip into a very thin edge connector? Common to find those not reconnected firmly enough or improperly seated.

Toast

[Toasty]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

>>But now neither one will light the third LCD green light or fire the hard drive/fans.<<

Some FYI info about those diagnostic LED's from Apple's site:

• LED 1 indicates that trickle voltage from the power supply has been detected. This LED will be ON when the computer is turned off and your power supply is working correctly.
  
• LED 2 indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.
  
• LED 3 indicates that the computer and the LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated.
  
• LED 4 lights only if the computer detects an over-temperature condition. This LED will be OFF when the computer is turned on and running at the correct temperature.

Toast

[dbridgma]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

Been over these boards about 50 times looking for loose connections/connectors. Can't find anything suspicious. Went back over solder joins because two were not as solid as I'd like. I'm stumped by the failure of the board to activate the 3rd green light (the LCD-related indicator) which signals that the system's likely to boot normally.

The very first time (the 1st) re-capped board was powered, everything went smooth...all 3 lights illuminated & I had video, fans, the whole enchilada. I was ecstatic, however, after powering down and tightening screws & fasteners, only got trickle voltage and PSU lights...no fans or drive initialization. Went over the entire board with a jeweler's loup and reflowed anything that looked dodgy. Turned it back on & it came up for a few moments then the video went south after two minutes. Haven't been able to get back to this state since. I've swapped the boards between the two cases & both recapped boards produce identical results...two greens lights (trickle & PSU power).

Background: ordered a factory-sealed inverter because I had suspicions about the original ones--although these G5's never exhibited video distortion or black screens--just failure under load, spontaneous shutdowns. But the new inverter makes no difference in either unit. Logic board video cable is well seated, and does not have any effect on display output when wiggled.

By the way, to respond to your question above: where are the old PSU's? I contemplated recapping the failed PSU's first, however, given the symptoms, didn't want to start this capping adventure inside those cramped, glue-saturated power supplies. Figured I'd have a better chance if I began on the relatively open real estate of the logic board. So, I now have 3 "bad" surplus supplies, in addition to two working PSUs, but not a single functional system. Bummer.

Daniel

[Toasty]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

>>after powering down and tightening screws & fasteners, only got trickle voltage and PSU lights...<<

Then most assuredly you have a bad connection and/or cold/cracked solder joint(s).

Loosen the mounting screws so they're just seated and with the unit off alternately push and pull on components across the board while watching the LED's. You want to be able to flex the board just a bit while doing this.

If you are contemplating disposing of the PSU's, please let me know. These are untouched, correct?

Toast

[dbridgma]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

I'll go over the boards again according to your instructions. I suspect that you're correct...there's a bad connection lurking somewhere. But finding it is the challenge.

By the way, I did the 20 1800uF & 5 1000uF caps. But notice that there are two Nichicons in the (lower right) corner of the board that I didn't replace--for some reason Warholic's kit did not include those two. Not sure why he calls these 25 a "full set" for the first generation iMacs.

I have 3 unmodified PSU's pulls (for 17" iMacs), although I opened the cases to examine the condition of the caps, never attempted any desoldering. If you're interested I'd part with them.

Daniel

[Toasty]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

Any cap with the score marks (vents) should be replaced on that board.

Toast

[Toasty]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

>>If you're interested I'd part with them.<<

Absolutely. Virgin territory.

I'll PM you.

Toast

[mrberad]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

Ahh the video culprit.
"The logic boards sometimes gets all three diagnostic lights lit...but there's no video. The screen remains black. I disassembled & then reassembled both & was able to get one to boot fully (fans running a normal speed, hard drive spinning up) minus any video. But now neither one will light the third LCD green light or fire the hard drive/fans."

I am the original poster and this is what I found when I rewired the board a second time and got video. I experience the same as above.

First the area to focus on is on the left side of the board. Their is a gray piece of plastic that rises just left of the external ports (USB, fire wire, ect.). This piece of plastic has a torx screw and a metal tube holding it up. This plastic piece also must seat perfectly into a small black slot (presumably the Video Card). At the same time you have a gray wire connector that must connect underneath the logic board on the left fairly close to the slot for the gray plastic piece (you may have it on the pins down by the left speaker /PSU). The other wire connector runs to the top left of the board and connects underneath the super drive. Double check this area and your video should pop up.

All the stuff is easy to screw up because its so subtle and Steve jobs is the only guys who knows what to call these parts (My guess that this is that this is the Video Power bridge). I may have to crack my iMac again and i will post pics.

I hope this helps.

[Toasty]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

@dbridgma

PSU's received today. Thanks!

Absolutely amazing! All 3 are completely different in layout. No wonder this is such a great boggle to figure out. What applies to one, does not apply to the other in terms of position, value, test points. Jeeze!!

Another bad week to give up drinkin'

Toast

[dbridgma]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

Yes, many interesting differences among the various early iMac PSUs. I looked, but didn't dismantle that odd menagerie of caps incrusted in glue.

So, to recount, I discovered that I'd mis-soldered extra 1800uF 6.3v caps onto the midplane in the group near the heat sink. There's supposed to be a cluster of 14 (with a unused row of 2), and I stuck 2 extras in there. From left to righ It goes: row 1: 4 1800uF 6.3v row 2: blank (row of 2) row 3: 4 1800uF 6.3v row 4: 6 1800uF 6.3v

Well, I initially booted the mis-configured logic board and ran it for a period. But since that maiden voyage I continue to get only tricke & power supply light illumination. Correcting the cap number & postition did not fix the pro blem.

Over the weekend I realized my error while reviewing Jim Warholic's diagrams, & so today I corrected it (with caps Toasty kindly supplied) but no joy: the system will not boot...only two lights. So I'm casting about trying to find what to do next. I've put a lot of time and effort into these two G5s...with no encouraging results thus far.

Guess I'm wondering if there's a way, besides hitting the mini-switch buttons on the board, to clear errors from previous boot attempts while the board was misconfigured?

Daniel

[Toasty]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

Yes, do the system reset bit with the switches. Again, carefully checking to be sure nothing is pinched. Keep the mobo screws just slightly tightened and push/pull where you can to see if anything changes. Double check any edge connectors & cables for tightness and correct fit.

mrberad had been through this disassemble and reassemble process and after doing it again, the unit came up for him.

Toast

[dbridgma]

Re: iMac G5 1.8G - Fresh caps, but not quite there...

So, as a last resort tested all capacitors I replaced with an Anatek ESR unit that I got recently...and all replacement capacitors check out. They all come up with a .8 or .9 ESR reading on my Blue ESR meter. All solder-joins seem sound...or at least they check out when probed. So the good news is: I didn't destroy any caps when soldering them.

But I've still got no (3rd) LED diagnostic light, & cannot boot either G5. The single successful boot is looking like it was a fluke.

I suppose I probably mangled something during one of the multiple assemblies/dissassemblies of the iMacs. Annoying but, probably indicating that these Macs are done. Maybe the board-mounted gpu just finally went south.

Guess I'll have to junk them, cuz I've run out of stuff to try. Chock it up to the learning curve, I suppose.

Daniel