My dead Quadra 840AV

yeyo2128

New Tinkerer
Dec 27, 2022
5
1
3
Hello fellow Vintage Apple Enthusiasts

I come with a query related to my Quadra 840AV.

I've been trying for a few months to get it going but have been unsuccessful. In summary, the problem is that the computer acts as if it is dead, the fan does not spin, the LED does not turn on, the hard drive does not spin, nothing, literally nothing. Not a single sound or sign of life. There is no difference between having the computer connected or disconnected from the electric power because there is no reaction, either turning it on from the button or from the keyboard.

Given the symptoms, my obvious assumption was power supply issues.

First of all, I have to clarify that although I am a big fan of vintage Apple products, my knowledge of electronics is completely non-existent. I have read a lot on these forums, reddit, etc, to learn about the main issues and understand some concepts. That is how I understood about the already known problem of capacitors and how it is necessary to change them. The recap has been already performed on the logic board.

Continuing on the subject, since I totally don't know what can fail in a PSU, I decided to buy another one, which took a lot of effort to find. Yesterday, after a month of traveling from the UK, the aforementioned PSU arrived. To my surprise, the result was the same: The computer continues to act dead.

Yes, I bought it as untested, but what are the chances of having two totally dead power supplies? :(

Given the above, I come to you to request in the kindest way possible that you could guide me and help me understand where the problem could be in my Quadra. I live in Mexico, and it is quite rare to find, compared to other countries, specialized places that could carry out repairs of this type. For the recap, it took me months to find someone who could do it.

Assuming it is the power source, what can go wrong with it? How can it be repaired? I have read articles about replacing them and using a modern ATX, but the instructions, given my zero knowledge, are as if they were in Chinese and I do not understand anything. I don't know if that would be a good option.

It should be noted that I have a Power Mac 7300/200 that when I turn it on, the fan and HDD start spinning, but the motherboard is dead as there is no chime and no signs of life. That makes me think and confirm that the problem with my Quadra is with the power supply, I suppose that if it worked, there would be signs of life and I could start to see if there are other problems such as with the logic board or the HDD. Just like what happens with my 7300/200

I'm so sorry to write so much text and sound abusive asking for help, but this computer that has great sentimental value to us is driving me crazy. Any comments or advice will be greatly appreciated.

Thank you very much in advance for reading my story, have a great day
 

wottle

Active Tinkerer
Oct 30, 2021
526
274
63
47
Fort Mill, SC
Did it ever work after the recapping? Was it working before you replaced the capacitor?

I'm not sure if the problem can happen on the 840, but I have a Mac Color Classic (all in one) that would refuse to boot with the keyboard (there was no soft power button on the Color Classic), but I read a recommendation to leave it plugged in over night with the physical power switch set to ON. When I hit the keyboard power button in the morning, it chimed and booted up. Been starting reliably ever since.
 

yeyo2128

New Tinkerer
Dec 27, 2022
5
1
3
Did it ever work after the recapping? Was it working before you replaced the capacitor?

I'm not sure if the problem can happen on the 840, but I have a Mac Color Classic (all in one) that would refuse to boot with the keyboard (there was no soft power button on the Color Classic), but I read a recommendation to leave it plugged in over night with the physical power switch set to ON. When I hit the keyboard power button in the morning, it chimed and booted up. Been starting reliably ever since.

Yes, it indeed worked perfectly. It was owned and purchased by my mom 30 years ago. The issue is that the last time it was powered on should have been 7 years aog, at least. Then in sat in storage.

I think your recommendation wont work in the Quadra since it doesnt have the power switch on/off. It is just a button than turns on, not like the switch in compact macs.

Thanks for your answer!
 

wottle

Active Tinkerer
Oct 30, 2021
526
274
63
47
Fort Mill, SC
So it was unable to power up before the recapping.

Then you sent the logic board for recapping, and it still refused to start up.

Then you replaced the power supply, and it still refused to power up from either the power switch or the keyboard?
 

yeyo2128

New Tinkerer
Dec 27, 2022
5
1
3
So it was unable to power up before the recapping.

Then you sent the logic board for recapping, and it still refused to start up.

Then you replaced the power supply, and it still refused to power up from either the power switch or the keyboard?
Yup, indeed. It is just how you described it.
 
  • Like
Reactions: wottle

wottle

Active Tinkerer
Oct 30, 2021
526
274
63
47
Fort Mill, SC
The possiblilities I can think of are:

1. You got extremely unlucky and both power supplies are non-working.
2. There is a problem with the logic board that is preventing it from sending the power on signal to the power supply. There's probably a way to short out some pins on the power supply connector to trigger the power supply to start pumping the correct 12v/5v to the logic board. Maybe that is not working, so the power button on the logic board and the keyboard are both affected.

Maybe someone one here has one they can share feedback on how to test the power supply outside the case. That would allow you to verify if it's #1 or #2. If you can confirm your power supplies are functional, then it's a matter of tracking down why the logic board isn't triggering the power up.
 

yeyo2128

New Tinkerer
Dec 27, 2022
5
1
3
The possiblilities I can think of are:

1. You got extremely unlucky and both power supplies are non-working.
2. There is a problem with the logic board that is preventing it from sending the power on signal to the power supply. There's probably a way to short out some pins on the power supply connector to trigger the power supply to start pumping the correct 12v/5v to the logic board. Maybe that is not working, so the power button on the logic board and the keyboard are both affected.

Maybe someone one here has one they can share feedback on how to test the power supply outside the case. That would allow you to verify if it's #1 or #2. If you can confirm your power supplies are functional, then it's a matter of tracking down why the logic board isn't triggering the power up.
Thank you very much for your answer. I totally agree in both of your assumptions. Sadly, I lack the knowledge to test both options in order to realize where the failure is. I dont know how to test the PSU

Hope anyone can help me

Thanks a lot, have a nice day