Monstermug
Active member
So I bought a space duel fairly cheap. Was untested which usually means faulty but for the price it was probably worth it in parts.
Received it and it looks to be in very good condition.
Plugged it in and got nothing. Tested voltages and all voltages was good.
Usually I work simple repair work with the PCB attached to the harness and cramped behind the cab but I had enough of this. It was time to make a vector repair bench.
Space duel requires +5v, 10.3vdc, to run the logic side and +22v and -22v to run the analogue vector side.
So I hacked up a quick and dirty jamma adapter for +5v. For 10.3v I had to use the +12v rail on the Jamma adapter. This 10.3vdc is usually unregulated and when measured in a cab can usually go as high as 14vdc. Added some test points to make it easier to attached probes etc. Also added two wires, 1 for +22v and 1 for -22v for later on when I want to enable the Vectors. With no other input except from a simple test button attached I ended up with this contraption!
This will get me by on the logic side at least. For +22v and -22v I plan to use my triple output bench supply with -22v just reversing the polarity of the leads.
Plugging it in, I can see the CPU pin 40 pulsing like crazy. Pulsing reset lines usually means there is a problem with the following:
Open or shorted address lines, bad CPU, bad buffers or bad rom or ram.
Before I did all that I decided to do simple checks on AVG chip, CPU and verified Roms. They all checked out fine.
As the CPU was pulsing like mad the nex thing I opted to check was the address decoder circuit. Started off with R2 and noticed pin 12 was floating. Piggy banked a 74LS42 on and still the same problem. Checked pin 25 of 6502A chip and that was pulsing. This meant there must be a break in the trace somewhere down the line.
Followed the trace back and sure enough, found a scratch on the circuit board.
Checked continuity and sure enough it was a break. Patched it up with some wire:
Plugged it in with the +22v and -22v and got a bucket load of success!
Love easy fixes!
Received it and it looks to be in very good condition.
Plugged it in and got nothing. Tested voltages and all voltages was good.
Usually I work simple repair work with the PCB attached to the harness and cramped behind the cab but I had enough of this. It was time to make a vector repair bench.
Space duel requires +5v, 10.3vdc, to run the logic side and +22v and -22v to run the analogue vector side.
So I hacked up a quick and dirty jamma adapter for +5v. For 10.3v I had to use the +12v rail on the Jamma adapter. This 10.3vdc is usually unregulated and when measured in a cab can usually go as high as 14vdc. Added some test points to make it easier to attached probes etc. Also added two wires, 1 for +22v and 1 for -22v for later on when I want to enable the Vectors. With no other input except from a simple test button attached I ended up with this contraption!
This will get me by on the logic side at least. For +22v and -22v I plan to use my triple output bench supply with -22v just reversing the polarity of the leads.
Plugging it in, I can see the CPU pin 40 pulsing like crazy. Pulsing reset lines usually means there is a problem with the following:
Open or shorted address lines, bad CPU, bad buffers or bad rom or ram.
Before I did all that I decided to do simple checks on AVG chip, CPU and verified Roms. They all checked out fine.
As the CPU was pulsing like mad the nex thing I opted to check was the address decoder circuit. Started off with R2 and noticed pin 12 was floating. Piggy banked a 74LS42 on and still the same problem. Checked pin 25 of 6502A chip and that was pulsing. This meant there must be a break in the trace somewhere down the line.
Followed the trace back and sure enough, found a scratch on the circuit board.
Checked continuity and sure enough it was a break. Patched it up with some wire:
Plugged it in with the +22v and -22v and got a bucket load of success!
Love easy fixes!
