powkesmore
New member
Can anyone help me get an early Williams Defender working?
Hi, I can't tell you how excited I am to own a genuine Williams Defender. It was always the game I loved to play in the arcade as a youngster (far too many years ago now) and I am pathetically desperate to get the thing working again (my wife currently has that long suffering look she wears when faced by my video game nostalgia).
When I start the machine up there is no video, no startup sound and all four leds stay lit on the ROM board.
I checked the voltages to the boards and various chips and they are all fine, the supply is clean with no voltage 'ripple' showing on the oscilloscope. The board is the old layout. Based on an internet search of repair logs for 4 leds constantly lit, one problem identified was a problem with the initial reset on startup. I checked the reset circuit which seems to be working OK but when I checked the reset pin on the MPU it stayed low even when the reset button was pressed. I followed the track on the circuit board back to a logic gate chip at 5F. The reset goes in but doesn't come out. Looking at the circuit diagrams I deduced that the other two gates on the chip are used by the Video RAM controller which I hoped would account for the lack of anything being displayed on the screen. The chip is a 7411N, I removed it, installed a socket and ordered a new chip, replaced it but still no change (I was gutted). However if I bridge pins 8 and 11 with a resistor (bypassing the gate) I get a start up sound, all of the leds go out and a second later the middle two leds light up. Still nothing on screen. The strange thing is once this is done the reset switch works normally until the machine is turned off then it reverts to 4 leds on constantly with no change when reset is pressed.
I'm afraid it has been many, many years since I've done any electronics but I was a little confused to see that the logic gate at 5F is an AND gate but reading the documentation it says that the inputs to the gate come from the reset circuit and the watchdog circuit but then goes on to say that input on EITHER will trigger a reset but wouldn't that be an OR gate?
I really want to do everything I can to get the original machine working, a friend of mine advised me to pull out the existing electronics and fit a Jamma board but I can't bear to desecrate it that way!
Anyway I would be very grateful indeed for any advice you might have..
Hi, I can't tell you how excited I am to own a genuine Williams Defender. It was always the game I loved to play in the arcade as a youngster (far too many years ago now) and I am pathetically desperate to get the thing working again (my wife currently has that long suffering look she wears when faced by my video game nostalgia).
When I start the machine up there is no video, no startup sound and all four leds stay lit on the ROM board.
I checked the voltages to the boards and various chips and they are all fine, the supply is clean with no voltage 'ripple' showing on the oscilloscope. The board is the old layout. Based on an internet search of repair logs for 4 leds constantly lit, one problem identified was a problem with the initial reset on startup. I checked the reset circuit which seems to be working OK but when I checked the reset pin on the MPU it stayed low even when the reset button was pressed. I followed the track on the circuit board back to a logic gate chip at 5F. The reset goes in but doesn't come out. Looking at the circuit diagrams I deduced that the other two gates on the chip are used by the Video RAM controller which I hoped would account for the lack of anything being displayed on the screen. The chip is a 7411N, I removed it, installed a socket and ordered a new chip, replaced it but still no change (I was gutted). However if I bridge pins 8 and 11 with a resistor (bypassing the gate) I get a start up sound, all of the leds go out and a second later the middle two leds light up. Still nothing on screen. The strange thing is once this is done the reset switch works normally until the machine is turned off then it reverts to 4 leds on constantly with no change when reset is pressed.
I'm afraid it has been many, many years since I've done any electronics but I was a little confused to see that the logic gate at 5F is an AND gate but reading the documentation it says that the inputs to the gate come from the reset circuit and the watchdog circuit but then goes on to say that input on EITHER will trigger a reset but wouldn't that be an OR gate?
I really want to do everything I can to get the original machine working, a friend of mine advised me to pull out the existing electronics and fit a Jamma board but I can't bear to desecrate it that way!
Anyway I would be very grateful indeed for any advice you might have..


