[ 1. IBM 5150 motherboard of type 16KB-64KB.
  2. IBM 5150 PSU of the type where the fan is DC powered.
  3. The PSU's fan is not turning when the PSU's P8 is connected to the motherboard.
  4. The PSU's fan turns when the PSU's P8 is disconnected from the motherboard. ]




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IBM 5150 (IBM PC) motherboard - type 16KB-64KB

This is the early version of the 5150 motherboard.  It is marked "16KB-64KB CPU".

We will first deal with the -12 volt line, then if unsuccessful, go on to deal with the +12 volt line.  The reason for dealing with the -12 volt line first, is because there is only one component using it, whereas the +12 volt line has lots of components using it.

-12V LINE

On this motherboard, there is only one component on the -12 volt line, a tantalum capacitor.  Click here to see a photo of it.  The subject capacitor is not critical to the operation of this motherboard, and this motherboard can operate without it.  Remove the capacitor either by desoldering, or by using a pair of sidecutters to cut the capacitor off the board.  If possible, use the cutting position shown at here (it will facilitate replacement down the track).  Now plug P8 from the power supply back into the motherboard, then turn on the power supply, and see if the power supply's fan turns.  If the fan turns, you found the faulty capacitor.  If the fan still does not turn, proceed to the following paragraph.

+12V LINE

On this motherboard, there are many components on the +12 volt line.  Those components are five tantalum capacitors, and all of the RAM chips (type 4116).  Click here to see a photo of the five tantalum capacitors.  On this motherboard, if any of the tantalum capacitors on the +12 volt line are faulty, then they will later need to be replaced, otherwise RAM operation is compromised.  Going forward, in turn, remove each of the five capacitors, either by desoldering, or by using a pair of sidecutters to cut the capacitor off the board.  If possible, use the cutting position shown at here (it will facilitate replacement down the track).  After each removal, see if the power supply's fan turns when plug P8 from the power supply is plugged in. ..................


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