A friend of mine has an old 8088 computer that he wants to get running again, the computer turns on like it should but it gives keyboard and hard drive errors and there it sits, what I ended up finding out is that the +5 volt output of the power supply is fine but the +12 volt output is only putting out +9.6 volts.
Normally I would just replace the power supply but this thing is OLD very proprietary and only one came up on eBay and they wanted $50 for it, so I am trying to fix it.
The +12 volt output has a 1000uF 16v capacitor on it which I pulled out of the circuit which then caused the voltage to fall to +7.xx volts, the capacitor looked fine (no brown goo coming out of the top of it) but I replaced it anyway.
The output is still at +9.6 volts though, and what is odd is that the input voltage to the output diodes is reading as 20 volts AC which then goes through two PR3002 3 amp diodes that have their outputs soldered together, with a standard 0.7 volt loss per diode it should only be loosing 1.4 volts on the DC side.
But... I pulled them out of the circuit they each test infinity in one direction but they are both testing at about 0.478 on the "Diode Tester" function of my DMM instead of 0.7xx like silicon diodes should be reading as.
So...
My question is should these two PR3002 diodes be reading as 0.478 or should they be up higher in the 0.7xx range? Or am I barking up the wrong tree?
And before you refer me to the data sheet I already looked in several different places they all list of lots of useful info just not what a "Diode Test" on a DMM should read.
Data sheet: http://www.datasheets360.com/pdf/-6167918509033483484?comp=3559
Also, the circuit board in this is listed as a: "Leadman PC-130A".
Normally I would just replace the power supply but this thing is OLD very proprietary and only one came up on eBay and they wanted $50 for it, so I am trying to fix it.
The +12 volt output has a 1000uF 16v capacitor on it which I pulled out of the circuit which then caused the voltage to fall to +7.xx volts, the capacitor looked fine (no brown goo coming out of the top of it) but I replaced it anyway.
The output is still at +9.6 volts though, and what is odd is that the input voltage to the output diodes is reading as 20 volts AC which then goes through two PR3002 3 amp diodes that have their outputs soldered together, with a standard 0.7 volt loss per diode it should only be loosing 1.4 volts on the DC side.
But... I pulled them out of the circuit they each test infinity in one direction but they are both testing at about 0.478 on the "Diode Tester" function of my DMM instead of 0.7xx like silicon diodes should be reading as.
So...
My question is should these two PR3002 diodes be reading as 0.478 or should they be up higher in the 0.7xx range? Or am I barking up the wrong tree?
And before you refer me to the data sheet I already looked in several different places they all list of lots of useful info just not what a "Diode Test" on a DMM should read.
Data sheet: http://www.datasheets360.com/pdf/-6167918509033483484?comp=3559
Also, the circuit board in this is listed as a: "Leadman PC-130A".