modessitt
Volunteer: Encyclopedia Submission Moderator
Here's the schematic:
http://www.pinrepair.com/gp/manuals/gp-sch-vcu.pdf
I have diagnosed my failure to boot to be a lack of -5vdc at connector J8. Found a burnt .68-ohm diode on the VCU board which I have replaced. However, I still have no -5vdc.
Traced voltage through and have voltage on one side of the capacitor leading to the -5 output, but nothing coming out. As the cap is in series, I should be reading something coming out, right? All the diodes read as good, but I have no voltage at either side of that first 1N4004.
I pulled the cap and there is some very small crud around one axial leg that leads me to believe it may have blown. However, the schematic calls for a 22uF 16v cap, and the part in the board is a 150uF 25v cap (just like the other two electrolytic caps on the board. Should I put a 22uF in? I don't have a 150uF handy.
Another thing that might be causing the problem is that I am reading voltage into pin 10 of the TL497 chip, but nothing on pin 8. Now, it might not have anything there, but the documentation for these games isn't the greatest (as noticed by no parts designations).
What do y'all think? Should I throw a 22uF 25v cap on there and see what happens?
http://www.pinrepair.com/gp/manuals/gp-sch-vcu.pdf
I have diagnosed my failure to boot to be a lack of -5vdc at connector J8. Found a burnt .68-ohm diode on the VCU board which I have replaced. However, I still have no -5vdc.
Traced voltage through and have voltage on one side of the capacitor leading to the -5 output, but nothing coming out. As the cap is in series, I should be reading something coming out, right? All the diodes read as good, but I have no voltage at either side of that first 1N4004.
I pulled the cap and there is some very small crud around one axial leg that leads me to believe it may have blown. However, the schematic calls for a 22uF 16v cap, and the part in the board is a 150uF 25v cap (just like the other two electrolytic caps on the board. Should I put a 22uF in? I don't have a 150uF handy.
Another thing that might be causing the problem is that I am reading voltage into pin 10 of the TL497 chip, but nothing on pin 8. Now, it might not have anything there, but the documentation for these games isn't the greatest (as noticed by no parts designations).
What do y'all think? Should I throw a 22uF 25v cap on there and see what happens?