6255 5 volt line (pin 8 & 14) will not supply even 5ma although user manual says up to 1 amp is available

[MG]

I am trying to power a CPLD I have mounted on the breadboard area of a SCB-68.

The user manual for my board (6255) says pin 8 and 14 of connector 0 is +5 volts.

It also says "the power rating on most devices is +4.75 to +5.25 VDC at 1 A".

My board drops to 2.6 volts when I connect a 1k ohm resistor from pin 8 to pin 7.

This is not even 5 ma.

Why is the board not able to supply 5 ma?  (I actually would like to get 15 ma).

[HeatherBaker]

Hi MG,

The board will source 5V up to 1A which means that it will always source 5V unless it will take more than 1A to obtain the value. V=IR thus a minimum resistance of 5 Ohms is necessary.  I connected a 1k ohm resistor to pins 8 and 9 and still had 5V and approximately 150 mA of current.  Did you try another line?  

[Seth_B.]

You should also try measuring the resistance of fuse F1 on your board with a handheld DMM.  The fuse protects the +5V line.  If the +5V line has been grounded at some point, this fuse would have blown.  The fuse is located about here:

Regards,

[MG]

Not sure how you got 150mA through a 1k ohm with only 5 volts...but

Yes I tried pin 14 & 9 also.  Same reuslt - the voltage dropped to about 2.6

I found out the 2A fuse on the board is blown. 

Evidently, there is a pull-up resistor in parallel with the fuse.

For now, I'm using an external supply (instead of trying to draw power from the card).

[Seth_B.]

Most likely, at some point the +5V line was shorted to ground while powered on.  This will cause the fuse to blow.  If you want to have this fused replaced, the board will need to be sent in via RMA, so if the board is under warrenty, it may be a good time to do it now.

Regards,