Michael Roma
Active member
I just picked up a non-working MC and am trying to get it back up and running.
I checked voltages on the ARII without the PCB connected first to make sure everything was fine. All voltages were on except the +5V which was high and unadjustable at 5.7V across the positive leg of big capacitors but +4.66V at J17 pin 5 and pin 6 and 2/B on the edge connector.
I figured that the +4.66V was fine and wouldn't hurt the board, plus I wanted to see how far the +5V line dipped under load, so I connected the PCB. I powered it up and of course the game didn't play and +5V LED lit but when I went to test the voltage at the +5V test point I saw smoke coming from the Q2/R5 area of the ARII. I immediately turned the game off and unplugged the game PCB. I powered it back on and test the voltage and they read the same as before.
So I pulled the ARII and replaced Q3 (2N3055) as well as Q2, Q8 and Q9 since I had it out. I put it back in and powered it up again w/o load and was able to dial the +5V down but the -5V is now hovering at -14.9V.
Any ideas what could be causing the -5V to be that high? Will plugging in the game PCB damage it with the -5V that high?
- Mike
I checked voltages on the ARII without the PCB connected first to make sure everything was fine. All voltages were on except the +5V which was high and unadjustable at 5.7V across the positive leg of big capacitors but +4.66V at J17 pin 5 and pin 6 and 2/B on the edge connector.
I figured that the +4.66V was fine and wouldn't hurt the board, plus I wanted to see how far the +5V line dipped under load, so I connected the PCB. I powered it up and of course the game didn't play and +5V LED lit but when I went to test the voltage at the +5V test point I saw smoke coming from the Q2/R5 area of the ARII. I immediately turned the game off and unplugged the game PCB. I powered it back on and test the voltage and they read the same as before.
So I pulled the ARII and replaced Q3 (2N3055) as well as Q2, Q8 and Q9 since I had it out. I put it back in and powered it up again w/o load and was able to dial the +5V down but the -5V is now hovering at -14.9V.
Any ideas what could be causing the -5V to be that high? Will plugging in the game PCB damage it with the -5V that high?
- Mike

