Intermittent power switch HP Compaq 8100 Elite SFF

O

okieman

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We had this PC in the shop to replace a defective NIC card. When I picked it up, the techs said they had problems getting it to turn on, but it only happened twice. So when I set it up at home and connected it, I saw the same thing they described. When I press the normal power switch on the front, a led beside the switch lights up, but the PC never energizes. No sound or activity.

Should I simply replace the switch? Can I test its functionality by closing the connection inside the unit with a jumper? Or is there something more complex with its internal design. It belongs to a senior who would really like to have access to her email etc. (Win 7 64-bit)

I have rebuilt two PCs, but other than that more of a web software guy than a hardware guy. Thx.
 
Should I simply replace the switch?
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You can test by shorting the two pins on the motherboard the wires from the power switch connect to. Use small flat tip screwdriver and a very steady hand.

But if this problem is intermittent, not sure you will learn anything. A power supply that is starting to fail often gives these same symptoms.

If it does turn out to be the switch, I would not bother with replacing it if your case has a front panel reset button. Just move the two wires from the reset button from where they connect to the motherboard to where the two wires from the power switch connect. Then just use the reset button to power on and off from now on.
 
The replacement power supply arrived Monday (three days after the date of the the two-day shipment for which we paid Amazon)
Easy to install, put it all together, and the system will not engage/start when I press the power switch. Shorting out the pins to the switch seems to be all that is left. The senior citizen who owns this device is literally depressed because she can't get online to talk to people. Not always fun to be the household fix-it guy.
 
Shorting out the pins to the switch seems to be all that is left.
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If shorting the two pins works with the new power supply, that suggests the power switch is bad. As suggested above, try moving the two wires from the front panel Reset switch to where the two wires from the power switch connect to the motherboard. Most people rarely, if ever, use the Reset switch so no real loss.

This takes no technical skills - only good lighting. The two wires from the power switch and the two wires from the reset switch connect to the exact same header (set of pins) on the motherboard. Just pull the two wires from the power switch and stuff them out of the way. Then pull the two wires from the reset switch and move them to where the power switch wires were connected. Then you are done. Just make sure you have unplugged the computer from the wall and touch bare metal of the case interior to discharge any static in your body before reaching in near the motherboard.

There will be no residual voltages in the circuits and no voltages inside the computer case are high enough to zap you. The only dangerous voltages are inside the power supply housing which you will not be exposed to.

All those switches do is short the two pins just as you did manually.
 
This MS-7557 mobo does not seem to have a reset button? Just the bundle of wires coming from the front panel that goes to the PB/LED socket on the mobo. Trying to figure out a way to handle this. Long ago I had jumper cables and meters, I moved from electronics into software. Arg. Maybe the other items on PB/LED are non-essential? That way, if I short the pins for the power, no harm done. She will have to power on/off by some method like a switched power strip where plugs into the household supply.
 
his MS-7557 mobo does not seem to have a reset button?
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I didn't say reset button was on the motherboard. The reset button/switch will be on the case front panel - typically near the power button - if the case has a reset switch. The reset switch, if there is one, connects to two pins on the motherboard.

Sadly, to save a few pennies (and its literally pennies) some OEM makers no longer include reset buttons on their entry level cases, but the motherboard usually still has the two pins. If that case does not have a reset switch, or this board does not have the two pins, then you are out of luck.

Often, the only problem with the power button is it just gets full of dust and dirt. A quick blast from a can of compressed air might clear it. A squirt from electrical contact cleaner would be better however as dust often contains oily residues from smoke, pet dander, or kitchen cooking.

I have also seen where the problem with the switch is the metal prongs holding it in place become loose. So the actual switch behind the button slips back just enough so the button, when pressed, cannot press the switch enough to make proper electrical contact. If you can get access to the back side of the case's front panel, you can often just bend those metal prongs back in place to hold the switch in proper alignment again. The problem is, once the metal is bent a couple times, it loses temper and strength, and will likely start to bend out again, eventually snapping a prong off. And a loose, highly conductive metal prong inside a case would not be good.

Sometimes, it is only a plastic, molded holder these switches snap into. If the button was pressed too hard, the switch might pop out just enough to cause problems. You just snap back in and tell the user to be gentle. But the plastic holder typically breaks instead. Then, maybe, some epoxy glue or hot glue might work.

Last resort is a bit Mickey Mouse but you can replace the entire switch with one of these. But odds it will fit the case's front panel are slim to none. So the switch then needs to be run out to the exterior and taped or strapped somewhere where your friend/client can reach it. Just make sure she understands there are no exposed voltages to hurt her. There is only a tiny +5VDC running through it should would not feel even if exposed.
 
Bill, I conflated two sentences. I looked for a reset on the back of the PC and hopefully wires leading to pins on the motherboard. No luck. I took the bezel off the front of the PC to get a better look at the power switch and hopefully color of wires leading back into the unit. Didn't notice another switch nearby. The technical specs for this board say "Pressing and releasing the power button applies a negative (grounding) pulse to the power control logic on the system board. The resultant action of pressing the power button depends on the state and mode of the system at that time ..." Then a table showing outcomes. More complex than I expected. It appears two yellow wires go from the button back to a connector on the board, along with wires for the LED that lets users know about system status. I think at this point I need to acquire a good multi-meter so I can at least test the power button to be sure it is closing the connection. Will try to upload image of the connector pinout.
pb-led.png
 
I looked for a reset on the back of the PC
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No, it would be on the front.

"Pressing and releasing the power button applies a negative (grounding) pulse to the power control logic on the system board. The resultant action of pressing the power button depends on the state and mode of the system at that time ..." Then a table showing outcomes. More complex than I expected.
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And a million times more complex than it needs to be.

All pressing the button does is short the two pins, (# 7 and 5 in your image). This shorts the +5Vsb (standby) voltage to ground which in turn, signals the computer to turn on. Pressing the button again shorts that same +5Vsb voltage to ground again. But the system, knowing it is already running, signals the computer to shut down (go into standby mode) this time.

Note whenever the power supply is plugged into the wall (and the master power switch on the back of the power supply - IF there is one - is set to on), the computer is really in standby mode.

Again, the fact you can signal the computer to power on and off by shorting pins 5 and 7 is pretty conclusive the front panel power switch is some how broken, or one of the two wires came off. All the switch does is short the two wires on pins 5 and 7 together.


Edit comment: Corrected autocorrect: changed complete to complex.
 
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No response to the pin shorting. I know there is juice to the mobo, because ea time I plug in the power cord to the back of the PC, a small green LED on the board lights up. Running out of ideas.
 
Did a CMOS reset and attempted to boot. No luck but at least it is beeping: four beeps, two seconds, four beeps, etc. Tested the CMOS battery - was down from 3V to 0.23V so replaced it with new. Also re-seated the RAM. Beeping but no boot.
 
I guess I misunderstood you earlier. I got the impression you had shorted the two pins and it started normally.

Anyway, 4 beeps is not good. You typically want 1 short beep at boot which indicates a successful POST (power on self test).

Depending on the BIOS used for that system, the beep codes mean different things. 4 beeps could mean bad RAM, bad Flash/checksum, failing motherboard or more.

Note a primary characteristic of CMOS memory devices is they almost instantly (within a couple clock cycles) dump any data they are storing whenever the "holding voltage" is removed from the device. When you pull the battery, the holding voltage is removed, and all the user changes to the BIOS are instantly lost - the BIOS was "reset".

Always, after replacing a CMOS battery (or any time you reset the BIOS), you MUST boot directly into the BIOS Setup Menu, then set the date and time, and ensure the drive "boot order" points the correct boot drive first, then "Save and Exit" (this is critical) out of the BIOS Setup Menu to boot normally.

If you don't set the date and time and "Save and Exit", you often get a checksum error which, by the way, is indicated by 4 beeps with some BIOS systems.
 
The last time I successfully booted this device was the morning before delivering it to the repair shop. Dead in the water since I brought it home. One of my hardware friends suggested I may be looking at getting a replacement mobo. I'd like to test the two RAM sticks before going that far, but such testing requires having a functioning PC with appropriate slots.
 
I'd like to test the two RAM sticks before going that far, but such testing requires having a functioning PC with appropriate slots.
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Not just a functioning PC, but one with a motherboard compatible with that specific RAM.

Since there are two sticks, pull one and test with one at a time. Swap and test again. It could be one stick is bad. Just make you unplug power from the wall to remove all the +5Vsb voltages present across many points on the motherboard, and make sure you touch bare metal of the case interior BEFORE reaching in or picking up the RAM. And never touch the electrical contacts of the RAM. Handle only by the edges.

If it is the motherboard, sadly, it could be more than the motherboard - like the CPU too. Do you even have the Windows installation disks? Re-installing the OS is often needed even if you can find an exact replacement board. It might be best to look at a new computer. Walmart has several refurbished computers for under $300. They are nothing special, but most come with Windows 10 preloaded. That's good because of better security. But realizing learning a new OS is not something senior citizens want to do, I recommend getting Start10 which brings back the familiar W7 Start menu and desktop and for just $5 (after a decent 30 day trial period) is well worth it. Or there is Classic Shell which many like too, and it is totally free. StartIsBack is a third alternative that many like and it is just $3.

These refurbished computers come with a 1 year warranty too. But if the budget allows, I would definitely go for a new computer instead.
 
Her previous PC was even more ancient, so a cousin in another state gave her this refurbished HP. No disks. After I experiment with the sticks, I may indeed be looking at another computer. I'm really glad you posted those three options for making Windows 10 more familiar. I had not heard of them at all!
 
I'm really glad you posted those three options for making Windows 10 more familiar. I had not heard of them at all!
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I started with Start8 on Windows 8 because the Luddite in me could not get used to the W8 desktop/UI at all. It did not help I, like many, just did not appreciate that "Metro" style desktop being shoved down our throats. While the W10 desktop/UI is much more intuitive than W8's and I've learned to live with it on my secondary computers, I use Start10 on this my primary computer, and my notebook. The best $5 for programs I've ever spent. And as I noted above, you have 30 days to try before you buy, so to me, you can't go wrong.

I have tried Classic Shell and it is nice too, and totally free. But Start10 just "feels" more polished to me - as I might expect from a paid vs free program. I have no experience with StartIsBack but people I trust have said they like it. It too has a 30 day trial period and for $3, no big loss either way.
 

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