34" All-in-One won't power on.

[mrfixitman]

Hi 🙂

I have this HP  Envy 34" All-in-One Desktop, PC 34-c1000 which my son gave to me to repair. It's a little over a year old and it won't power on. I have a been a professional electronic tech for many years and have repaired many computers at the component level.. With the excellent help provided by the HP, "Removing & Replacing Parts" YouTube video, I was able to disassemble the unit.

Here  are the  results of my troubleshooting,

All tests were made with the display panel disconnected. The only cables plugged into the mother board were the three fans, cable from the  power switch board, and the 10-pin power supply output cable as indicated.

• With the  power supply cable connected to the mother board:
  • All pins have 0 volts
  • There are no shorts to ground on any of the power input pins on the motherboard
  • Pressing the power button does not activate any of the voltage outputs from the power supply
• When the power supply is disconnected from the mother board:
• All yellow pins have 20 volts
• Blue pin has 20 volts
• Green pin has 0 volts
• I put an 8 ohm external load on the yellow pins (they are all in common) and though that's only a 50 watt load, it successfully maintained the 20 volt output.

At the minimum, I would expect  the fans to turn on when the power button is depressed but such is not the case. Is it possible you could supply me with the most basic of information, perhaps a schematic, so I can troubleshoot the power supply going into the motherboard? It would be helpful to know if there is a fusible link somewhere along the line or a voltage regulator that's failed. I could just shotgun the power supply module but I don't like buying parts unless I'm sure they are necessary. I would very much like to keep this fine piece of equipment out of the recycle bin.

Thanks very much for your assistance. 👍

[zoey7886]

@mrfixitman, Welcome to the HP Support Community!  

Thanks for reaching out about your query regarding Power Issues with HP Envy 34" All-in-One Desktop! 

We're thrilled to have the opportunity to assist you and provide a solution.  

If you're having trouble powering on your HP Envy 34" All-in-One Desktop, there are several steps you can undertake to diagnose and potentially resolve the issue. Here is a detailed guide to assist you:

Check the Power Source:

• Ensure that the power cable is securely connected both to the wall outlet and to the computer.
• Try a different power outlet or power strip to rule out issues with the current one.

Examine the Power Adapter:

• If your unit uses an external power adapter, check if the LED on the adapter is lit when connected.
• Consider testing with another compatible power adapter if available.

Perform a Power Reset:

• Disconnect the power cable from the computer.
• Press and hold the power button for about 15 seconds to discharge any residual electrical charge.
• Reconnect the power cable and attempt to turn on the computer.

Inspect for Hardware Loose Connections:

• Since you've already disassembled the unit, double-check all internal power connections.
• Ensure that RAM sticks, hard drives, and other components are properly seated.

Check for a Faulty Power Button:

• Occasionally, the power button itself can become faulty.
• Consider testing the functionality of the power button circuit if you have the expertise.

Visual Inspection for Component Damage:

• Look for any visible damage, burnt components, or unusual smells that may indicate a hardware fault.  

Hope this helps! 

Take care, and have an amazing day!  

Did we resolve the issue? If yes, Please consider marking this post as "Accepted Solution" and click "Yes" to give us a helpful vote - your feedback keeps us going!  

Regards, 

[mrfixitman]

Hello Zoey7886 🙂

It' sounds like you didn't really understand what I was asking. Would you please take the time to re-read the explanation of my situation and come up with a thoughtful reply or refer my case to someone that may be more experienced with troubleshooting this type of issue?

Thanks for your help.

Regards,

mrfixitman

[zoey7886]

@mrfixitman, You’re right — if you’re seeing 20V unloaded on yellow and blue with the PSU disconnected, but nothing once it’s tied to the board, the system isn’t sending the “power-on” signal back to the supply. On most HP AIOs, that’s through the green “PS-ON” or control line.

Here are a few things you could try before shotgunning parts:

Check the power button board & ribbon: Sometimes the culprit is as simple as a micro-switch or trace not completing the power-on signal. If you can, short the pins at the motherboard header manually to simulate the button press.

Trace the green control line: With the PSU plugged in, see if the board pulls that line low when you press the button. If not, it points toward the power logic on the motherboard rather than the PSU.

Hope this helps! 

Take care, and have an amazing day!  

Did we resolve the issue? If yes, Please consider marking this post as "Accepted Solution" and click "Yes" to give us a helpful vote - your feedback keeps us going!  

Regards, 

[mrfixitman]

Hi Zoey7886 🙂

Trace the green control line: With the PSU plugged in, see if the board pulls that line low when you press the button. If not, it points toward the power logic on the motherboard rather than the PSU.

If there is already 0 volts on the green wire with the power supply connector inserted into the motherboard, how is the power switch supposed to change the green wire's state to a low condition? Is it normal for the green wire to have 0 volts with the power supply disconnected from the motherboard? That seems to me to be the crux of the problem.

Check the power button board & ribbon

Sometimes the culprit is as simple as a micro-switch or trace not completing the power-on signal. If you can, short the pins at the motherboard header manually to simulate the button press.

I did check the microswitch that powers on the computer. It makes a good connection. As far as shorting the pins at the motherboard, I would need a schematic to know which pins to short. By the way, there are many other components on the switch board so I don't think it's as simple as the microswitch being directly connected to the motherboard.

I believe at some point I'm going to need at least a block diagram to pinpoint this issue.

Thanks very much for your help. 😉

mrfixitman

[zoey7886]

@mrfixitman, Welcome to the HP Support Community! 

We're here to help you tackle that the All-in-One power issue! Don't worry, we've got your back! 

To get you the best assistance, we need to take this conversation to a private chat. We're inviting you to a private message to protect your privacy and ensure that any sensitive information remains confidential. 

To access your private message, just click the little blue envelope icon on the upper right corner of your HP Community profile, next to your profile name.  

We're looking forward to helping you resolve this issue! 

Stay tuned, and thanks for your patience! 

Regards, 

[mrfixitman]

Hello Zoey7886,

I replied to the private conversation which contained no private information. I was told to either contact telephone support or chat support. As far as I can tell, there is neither an option for chat support nor free telephone support. I don't feel like I should have to pay for an answer to a simple question, which is:

•  Before the unit is turned on, what is the standby voltage on the green wire which the PS_ON control line?

Thanks for your assistance.🙂

mrfixitman