[G4] Power supply woes

[Harry Freeman]

Greetings ( + )!( + )

On Oct 11, 2005, at 9:35 AM, jim carbone wrote:

> Hi Doug,
>
> Thanks for the quick response.
>
> My only concern with just buying a new PS is that it might just blow 
> that fuse and I'll be high and dry again. Do you think this is likely, 
> or is it worth the gamble to start here?
>
> Again, I truly appreciate your help on this!
>
> Thank you,
> --jim
>
>
> On Oct 11, 2005, at 12:27 PM, Doug McNutt wrote:
>
>> At 10:24 -0400 10/11/05, jim carbone wrote:
>>> Here's what is says on the fuse, "250V 8A 51S" I don't know what the 
>>> "51S" stands for.
>>
>> It is an 8 ampere fuse which will safely switch a 250 volt AC power 
>> source. The S probably stands for 'slow blow" which is the opposite 
>> of the fast fuses typically used on electronic equipment. It may have 
>> been chosen to support the harmless inrush current which charges the 
>> filter capacitors as power is applied.
>>
>>> Anyone with similar troubles in the past that can help me get up and 
>>> running fast? Time is so important to me right now that I'd even 
>>> just overnight a new PS here if that meant I could save a few days 
>>> of hunting down and blowing out more fuses.
>>
>> It is unlikely that the fuse or a power surge is at fault. Either 1) 
>> something is drawing too much current at the output side  or 2) the 
>> power supply has a failed capacitor, diode, or switching transistor. 
>> (1) is unlikely because the power supply is probably current-limited 
>> by design.
>>
>> The fastest way up to speed is a replacement supply. It would be 
>> smart to start up first with unnecessary equipment - a second disk  - 
>> disconnected.
>>
>> Finding internal maintenance information of the power supply is next 
>> to impossible. You may find a part number on the controller chip. If 
>> so it can be Googled and you might find suggested circuitry from its 
>> manufacturer. An isolation transformer on the workbench is a 
>> requirement for working with the cover off. The first parts of the 
>> power converter are directly connected to the power line and it is 
>> unsafe to measure with any grounded equipment like an oscilloscope.
>>
>> -- 
>> -->  The best programming tool is a soldering iron <--
>> _______________________________________________

Jim, if you have an OHM meter one thing that you might want to try is:

***** Caution *****
You will need a low voltage battery operated OHM meter because an AC 
powered meter might cause you more trouble than you already have.
*******************

1. First unplug your platform from the AC source and obtain a grounding 
strap that you will connect to the platforms chassis ground.

2. Second unplug the PS and measure between each of the PS connector 
wires, and chassis ground. The reason being that a component may have 
shorted out, or a wire that was being pinched has finally had the 
insulation separated and a chassis short has developed. The problem 
here is that once you have opened the chassis the pinch point may have 
been eliminated. Therefore you should do a through visual inspection, 
looking for wires that look like they may have been pinched or the 
possibility of some small piece of wire that may have found it's way 
onto the Mobo.

2. Second is to measure between each of the PS connector wires (i.e. 
between the 1st wire, then between the 1st and the 3rd, then between 
the 1st and the 4th etc. Then repeat starting between the 2nd and the 
3rd, then the 2nd and the 4th etc., until you have checked for a short 
between all of the leads. You can do this towards the PS and towards 
the Mobo.

Once you have assured yourself that there isn't a dead short between 
any of the PS leads you can proceed with replacing the fuse, if the is 
to be your first choice or with the replacement of the PS.

As for the fuse "250V 8A 51S" I think that the 51S stands for the time 
delay before failure. However remember that fuses are not a precise 
device. I have seen fuse failure just because it was time to fail. Is 
the fuse just separated or does it look like it had a catastrophic 
failure, i.e. is there a burned or exploded look to the fuse?

My choice would be to measure the PS wires and then replace the fuse. 
If the fuse blows again, then replace the PS.


Best Regards, /\*_*/\

Harry (*^_^*)
* We are all visitors to this time, this place. We are just passing 
through. Our purpose here is to observe, to learn, to grow, to love... 
and then we return home.
Australian Aboriginal proverb