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SurferJoe46
24-12-2007, 03:34 PM
Got a freebee in the form of a Compaq Presario 5BW Desktop PC, Intel Celeron, WinME, about 384MB RAM, single HDD..etc..etc...

I thought I had a dead PSU...took it out and metered all the outputs...from BLACK to PURPLE..there's a 5.03VDC output.

Any BLACK will do...I think it's pretty much the whole system ground....

Anyway...I DO believe the CMOS is dead-dead-dead...will get one tomorrow....

But in the meantime....here's the question. Can I not get this to boot or even turn on at all unless there is some CMOS charge?

It just sits there and ignores me. Frustrating in that I have had bad and dead CMOS batteries before and I could at least get a black or BSOD screen somehow. Nada! :badpc:

I tested the ON-OFF pushbutton..it has a good contact..but somehow I think that PURPLE 5Volt is just waiting for some sort of signal to turn the whole thing on..Right?

SurferJoe46
24-12-2007, 03:58 PM
......and I forgot to say..."Guess what? I'm gonna try another stab at Linux...again...stand by all!

Speedy Gonzales
24-12-2007, 04:28 PM
I would say if its the CMOS battery, and its flat, it wont turn on, since there's no settings for the BIOS. And, it wouldnt know what its looking at / for.

SurferJoe46
24-12-2007, 04:40 PM
Yeah..but not even a splash or a flicker in the CRT?

Will go out and buy a new CMOS battery tomorrow...it's about 9PM, Sunday 12.23 here now.

Hahahahahahahah...my question is #4 on Google Search already! Wow..them slurp spiders are fast!

SurferJoe46
24-12-2007, 06:01 PM
Well-l-l-l-...just got back from all-night Wal-Mart and got the CMOS battery...but it's still untalkative.

Speedy Gonzales
24-12-2007, 06:04 PM
I would open the case and see if everything is still connected.

Do the cd/dvd's open if its got any??

SurferJoe46
24-12-2007, 06:12 PM
I would open the case and see if everything is still connected.

Do the cd/dvd's open if its got any??

Nothing works..I wonder again about a dead PSU...there's nothing anywhere but that purple-to-black voltage of 5.03 or so....

No nuttin'!

zqwerty
24-12-2007, 06:45 PM
http://www.epanorama.net/documents/pc/pcpsu_connector.html

If this were me the first thing I would do after checking the obvious, wires, plugs, sockets, mains power where it should be, is to change the 1uF 50V electrolytic caps that are part of the switch-on multivibrator circuit in the PSU.

In this part of the circuit they are always 1uF 50V, there are two of them.

They are nearly always positioned near to the heatsink for the Xistor/Fets power switching devices, they should be black in colour which means hi-temp environment capability. If you try this Joe you must discharge the main power capacitors with a 100Kohm resistor each time you power up and then switch off, because the original resistors for this purpose are nearly always open circuit, you should replace them as well, I presume you are familiar with the operation of a multi-meter having read all your postings about repairing motor vehicle electrics etc.

Be careful, those PSU main smoothing capacitors after the mains bridge rectifier can deliver a nasty shock for days after the unit has been powered down if they are not discharged by you if the original resistors are open circuit.

You will need a small soldering iron and reasonable fine motor skills to do this job successfully and it may not be the fault but it has been a lot of the time when a computer does not switch on/only runs sometimes/runs after being switched on/off a few times but there is no obvious damage like blown fuses, burnt circuit boards etc. This is a fairly common recognizable failure mode, I have fixed a number of them.



There is a similar common recognizable failure mode on Monitors as well which is the same fault condition ie no observable damage but does not run.

SurferJoe46
24-12-2007, 07:17 PM
I'm thinking here that I might try to find another PSU...any ideas?

It's a P-III Celeron...and the original PSU is 400Watts according to the sticker.

zqwerty
24-12-2007, 07:35 PM
Read what the model is on the side of the old PSU and google it, must a supplier close to you that has an equiv or recycler that can let you have one for a song, although likely that anything of the age that yours is will have a similar fault to the one I described.

SurferJoe46
25-12-2007, 04:28 AM
Found a new PSU at a dealer in Texas...for $17.00USD. (Comp-Recycle.com)

Ordered it already..but this is Xmas eve morning so they may be a few sheets to the wind right now and for the next few days..we'll see when they e-mail the confirmation.

jinja_thom
25-12-2007, 10:45 AM
If you remove a psu from a pc and apply mains power to it you will get approx 5.?? volts between the purple wire and any black wire and thats all you will get even from a fully functioning psu, this is called 5 volt standby and it provides the power for the switch on circuits on the motherboard to function.
If you want to test the other supplies you have to fool the psu into thinking it is still connected to a pc.
To do this, with the mains power off short the green wire (pin 14) to any black wire on the 20pin mother board plug ( for this I use a bent paperclip) and apply the mains power, the psu will then startup if it is serviceable.
However since these psus are switching psus some of them require an output load to function at all so I always plug at least one device connector into a spare hdd or cd drive before connecting the mains power.
If after all that you cannot get the other supplies to appear then throw it away and replace it.
HTH

SurferJoe46
25-12-2007, 02:37 PM
If you remove a psu from a pc and apply mains power to it you will get approx 5.?? volts between the purple wire and any black wire and thats all you will get even from a fully functioning psu, this is called 5 volt standby and it provides the power for the switch on circuits on the motherboard to function.
If you want to test the other supplies you have to fool the psu into thinking it is still connected to a pc.
To do this, with the mains power off short the green wire (pin 14) to any black wire on the 20pin mother board plug ( for this I use a bent paperclip) and apply the mains power, the psu will then startup if it is serviceable.
However since these psus are switching psus some of them require an output load to function at all so I always plug at least one device connector into a spare hdd or cd drive before connecting the mains power.
If after all that you cannot get the other supplies to appear then throw it away and replace it.
HTH

Ohhhhhhhhhhh...thanks..will do that right now.....(just got back from pulling an engine outta a C30 Chevy dually truck. After a hot hot shower and some seriously good hand scrubbing I will anyway...again, Thanks!

Agent_24
25-12-2007, 10:56 PM
Purple wire is the 5 volt standby line, this measuring 5 volts while everything else is off is normal

also shows that at least half the PSU works