power switch function

[fenix]

Hi, I'm trying to get on an old HP Pavillion 8650C working.
(1999 !) When I had the computer plugged in, depressing the power switch did nothing so I did a continuity check of the switch circuit after removing the plug from the pins on the board. The user said the computer just stopped turning on one day and had no problems prior. When I do a continuity check on the switch, I get a circuit when the switch piece is pushed in, but lose the circuit when I release the switch. There is a click when I push in the switch, and a slightly different sounding click when I release it, indicating that it is possibly closing and reopening the circuit, but I wanted to ask the experts here about this before I go buy a switch. My question is: should the circuit remain closed after I release the button, or is this normal operation whereby it just 'starts' the turn on process by jumping the 2 pins momentarily. Thanks ahead of time for an answer.

 

[wahnula]

Power buttons on ATX PCse momentary-contact, meaning the behavior is exactly as you describe as verified in this link

You can short the power pinouts on the mainboard with a small, flat-bladed screwdriver to have the same effect as a power switch.

Tony

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[wahnula]

Should read: "Power buttons on ATX PCs are momentary-contact"...

Tony

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[fenix]

PS: The reason that I am focusing on the power switch is because the owner of the computer said that the switch starting sounding "scratchy" when it was pressed after the computer started not turning on.

 

[fenix]

thanks Tony, so I guess the next thing to look at is the power supply ? I guess I can't check voltage output since nothing comes on. Any suggestions other than trying a new power supply ?

 

[wahnula]

Try the "screwdriver startup", shorting across the 2 PWR header pins. Might be a bad connection at m/b.

Tony

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[wahnula]

Another note...old HPs are notorious for bad and/or undersized PSUs. I had a 1999 HP Brio (Celeron 900) that had a 90 watt PSU!!!

Be careful when replacing an HP PSU, count the main motherboard connector's pins, should be 20 for that era PC. HP made a proprietary main connector for a few years. I have a link about it somewhere, including pics, post back if you need it.

Tony

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[edfair]

The HPs have a history of having power supplies blow. They are underpowered and use HPs own case design, so you will need to find a source.

From my experience you could have bypassed all the switch testing and gone directly to supply replacement.

If you really want to do the user a favor, you could upgrade the case, power supply, and floppy, although the CD will stick out about an inch and a half. Ugly, but more functional. You might want to check first, however, to make sure the I/O plate can be swapped to a new case.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[fenix]

Jumping the pins did nothing. This computer was on borrowed time anyway (9 year old first gen celeron!)and not worth any more time or money put into it because in my town, good working PIII 833 towers are going for $50-60, and older p4's are about $100, so I'll go with one of them and she'll be better off. I'm surprised the HD lasted this long.Thanks again for both your time.

 

[wahnula]

Here's a replacement, although $45 is a little pricey, and a 200-Watt PSU sounds small, but nine years ago PCs drew way less power than they do today. It clearly states your model number in the compatibility list.

http://www.pcpower.com

probably has a replacement too, but I didn't look around much after I found the first link.

Tony

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[wahnula]

Here's a pic of the two connectors. The one on top is a standard 20-pin ATX, below it is the HP.



Tony

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