slodload iMac 400 GLOD == PAV?

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Jon
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slodload iMac 400 GLOD == PAV?

I picked up a dead iMac 400 in Berry (red) for $25. I thought it might be an easy firmware update fix, like my 350. Nope, it was a bit more in depth to even check the bare mobo. To start, someone had partially disassembled it to get the RAM and HDD outm and prbably investigate the problems. Turns out they had also physically broken the inside of the USB ports. So, an order from Mouser by my father-in-law and several days later I replace the port. The mobo runs fine in my 350 chassis, and now I can plug the iPod into something other than the iBook. The current problem is that the 400 chassis seems to have the GLOD. My problem is finding the fix for it. Google doesn't seem to have much for slot-loader fixes.

With either mobo in the 400 chassis I get:
- Green power LED
- No HDD power, just a slight sound at first power up as if it got a slight amount of power
- 3.3v indicator LED on mobos flickers rapidly occassionally
- When I hold the power button for a few secs to get it to shut off it does, then there is a "hiss" from the speakers, as if a cap or something was discharging in the audio circuit. Certainly not from anywhere but the speakers.
- No CRT twang, no video from the 400 mobo on external VGA port.

I'm guessing it's either the flyback that causes the CRT to not come on, and then the PAV cuts power? Maybe it's not getting enough 5/12v power? Anyone got a diagnosis? Basically it gets power to light the LED, and not much else goes on.

Each mobo works fine in the 350, and I stuck a brand new PRAM batt in the 350 mobo and put in in the 400 chassis, nothing changed.

Thanks.

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Hey, Try the voltage tests

Hey,
Try the voltage tests for the iMac. I have taken the relevant material from a PDF and put it on my website. Let me know what you find: http://mrmacintosh00.spymac.com/imac/volttest.html

Kyle-
(edited for spelling, and again because im a noob)

Jon
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Thanks for the link! That's

Thanks for the link! That's the kind of info I've been wanting, but I didn't think to check for service manual stuff, as I was just looking for GLOD info... Anyway, I put the 350 mobo and it's orig and known working DCB in the 400 chassis. The first couple tests check out for trickle power. Then, the power-on voltage tests give me readings of about 10.5V on pin 2 of J7, 4.5v on pin 4 and about 2v or less on pin 14. I might have to dig up a digital meter in my pile to get better numbers. The analog I've got steps from DC3v to DC15v, and reading the sweep for 12v and 5v isn't great, but it is certainly less than 11v.

So, it seems that 3.3v and 12v power is shot. Does 3.3v get stepped down from 12v in the DCB? This DCB worked(or works) fine in the 350 chassis. Since I do get some power, it's probably not the fuse on the PAV, right? I'll have a look a the .pdf you link on your site and see if I get anywhere else.

Again, thanks for the info!

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Hey Jon, Glad I could help.

Hey Jon,
Glad I could help. Page 214 in the PDF is the "No Power" troubleshooting chart. You did get +5v at J9 right? If so, that means the PAV board is good, according to the PDF. Yes, you are getting something, so the fuse is good.

Try taking the DCB that is in the 350 right now and putting it in the 400 chassis, and switching the DCB thats in the 400 chassis and putting it in the 350 chassis with 400 board. Now, measure again, particularly the DCB voltages.

>"Does 3.3v get stepped down from 12v in the DCB?"
I have no idea.

Let me know.

Kyle-

Jon
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Re: Hey Jon, Glad I could help.

Hey Jon,
Glad I could help. Page 214 in the PDF is the "No Power" troubleshooting chart. You did get +5v at J9 right? If so, that means the PAV board is good, according to the PDF. Yes, you are getting something, so the fuse is good.

Ok, thanks for the page number. That'll help save me from digging through thte whole thing.

Try taking the DCB that is in the 350 right now and putting it in the 400 chassis, and switching the DCB thats in the 400 chassis and putting it in the 350 chassis with 400 board. Now, measure again, particularly the DCB voltages.

350 chassis, 350 DCB, 400 mobo: trickle 5v, C10 ~-1.2v (21v P/ON), J7 pin 2 ~11v, pin 4 4.5-5v, pin 14 3.3v. On power on the CRT crackles and twangs, systme starts fine, tries to boot.

400 chassis, 400 DCB, 350 mobo: trickle 5v, C10 ~-1.2v (21v P/ON), J7 pin 2 ~11v, pin 4 4.5-5v, pin 14 ~2v. On power on, no CRT activity, no mobo activity. Mobo 3.3v LED shines bright for half a second then goes dim and flickering.

Thanks for the help and tips.

Jon
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Also, in your take-apart guid

Also, in your take-apart guide, you don't show removing/installing the screw in the middle of the DCB, inbetween all the tall caps, close to the bottom of J7.

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From the service manual, "est

From the service manual, "esting J7 for Voltage on the Logic Board: The following voltages measure if the down converter is providing the required voltages and are only present if the system is powered on." So, I would interpret that to mean the 400's DCB is bad. But, you said you have tried the known-working boards in the 400 chassis, so I'm not too sure. The next option in the service manual is "Bad LED-Power Switch board," but no diagnostics are listed. If you really have some time on your hands, you could try to dig out the power/led board and swap them around or something. Otherwise, I'd lean toward a bad PAV or CRT.

Thanks for the tip regarding the DCB - I'll try to edit that page again sometime.

Kyle-

Jon
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Re: slodload iMac 400 GLOD == PAV?

With either mobo in the 400 chassis I get:
- Green power LED
- No HDD power, just a slight sound at first power up as if it got a slight amount of power
- 3.3v indicator LED on mobos flickers rapidly occassionally
- When I hold the power button for a few secs to get it to shut off it does, then there is a "hiss" from the speakers, as if a cap or something was discharging in the audio circuit. Certainly not from anywhere but the speakers.
- No CRT twang, no video from the 400 mobo on external VGA port.

New staus update:
I've stripped the casing from the iMac to get a look at various parts such as the PAV for signs of scorching, etc. It's been sitting for weeks without power, so I plug it in and turn it on and it does a CRT "twang" like normal, then a click, and then it's back to the same-ole-same-ole. Subsequent power-ups have no twang, as earlier. I know the hiss/popping/whatever sound that it makes whensoftpowered off (power button held for a few secs) comes from the speaker, a I put a finger on the cone and felt the movement. THere may be some noise from the DBC, but most is surely from the speaker itself. I'd like to get it going so I can sell one of my 3 iMacs, but I'd rather do a component level repair than a board swap, for the experience as much as anything else. Would a flyback be what I should try? $30 and some involved desoldering doesn't sound fun but if somebody can fully recommend it, that's about my next step.

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