Monstermug
Active member
Always wanted an original teckhan bombjack but didn't want to pay the high price associated with it. Remembered playing it on the Amstrad at a social club when I was a kid and absolutely loved it. Been looking out for one for last five years. Saw a faulty bombjack advertised on UKVAC a few weeks ago. Issue described was that it was dead and non booting.
Sure enough, when I plugged it in all I got was a black screen and a terrible Humming sound.
Decided to check the main Z80 cpu and it was watchdogging. Tested the Z80 Sound cpu on the 2nd layer and reset was going crazy. No reset at startup and pulsing like crazy.
Quickly turned it off as signals was out of whack everywhere I poked. Decided to attack this one systematically. There was a decent clock signal so that wasn't the problem. Logically I decided to examine the main cpu board first. Tested the roms and found rom location 12 was bad. The chip was faulty as my eprom programmer couldn't even read it. All the other roms verified with mame. Burnt a new Eprom in the hope that it would now boot.
Sadly I still had a blank screen and a humming sound. At least one step closer!
At this point, I walked away scratching my head. Signals were still over the place. Not sure of what to do next, I decided to give the board a clean. It was very dusty with numerous dead spider coffins under the socketed chips. I always get a little fright when I pull out a chip only to find a miniature facehugger ready to pounce at me.
Whist dissembling the top board from the bottom board I noticed that the ribbon cable was plugged in the wrong way! I felt it was a bit strange that the stack had both parts facing upwards rather than them being connected with the solder side facing each other like on most dual stack pcbs. It also makes it easier to work on being stacked with components facing up.
So I plugged the ribbon cables in the right way and orientated the pcbs back to what I think was it's original position.
For those that don't know, the red line on a ribbon cable donates pin 1 which should correspond to the pin 1 on the circuit its being attached too.
As I set out to wash the pcb, I did so and carefully dried it and put it back together.
I get great satisfaction from a clean and shiny pcb
Confident that the ribbon cable was now connected the right way around, I plugged it in and was greeted by this!
Yay! Would have got up and danced around but there was no sound. And still a terrible humming.
Broke out Philmurs audio probe the amps and op amps and got no sound anywhere. I knew there wasn't any signals going in for them to amplify.
The Sound Z80 cpu now was now correctly initiating on power up and not watchdogging as before but had no signals coming from most of the address lines. Took it out and tested it.
It failed miserably.
Found a correct Z80 CPU for it and plugged it in.
A thing to note is that this board requires a 780C processor as I initially tried a 8400 and that didn't work. So now with the correct processor in, I tried it again.
Now the game had sound! Played a few games and got my bombjack fix for the day.
Yay
Sure enough, when I plugged it in all I got was a black screen and a terrible Humming sound.
Decided to check the main Z80 cpu and it was watchdogging. Tested the Z80 Sound cpu on the 2nd layer and reset was going crazy. No reset at startup and pulsing like crazy.
Quickly turned it off as signals was out of whack everywhere I poked. Decided to attack this one systematically. There was a decent clock signal so that wasn't the problem. Logically I decided to examine the main cpu board first. Tested the roms and found rom location 12 was bad. The chip was faulty as my eprom programmer couldn't even read it. All the other roms verified with mame. Burnt a new Eprom in the hope that it would now boot.
Sadly I still had a blank screen and a humming sound. At least one step closer!
At this point, I walked away scratching my head. Signals were still over the place. Not sure of what to do next, I decided to give the board a clean. It was very dusty with numerous dead spider coffins under the socketed chips. I always get a little fright when I pull out a chip only to find a miniature facehugger ready to pounce at me.
Whist dissembling the top board from the bottom board I noticed that the ribbon cable was plugged in the wrong way! I felt it was a bit strange that the stack had both parts facing upwards rather than them being connected with the solder side facing each other like on most dual stack pcbs. It also makes it easier to work on being stacked with components facing up.
So I plugged the ribbon cables in the right way and orientated the pcbs back to what I think was it's original position.
For those that don't know, the red line on a ribbon cable donates pin 1 which should correspond to the pin 1 on the circuit its being attached too.
As I set out to wash the pcb, I did so and carefully dried it and put it back together.
I get great satisfaction from a clean and shiny pcb
Confident that the ribbon cable was now connected the right way around, I plugged it in and was greeted by this!
Yay! Would have got up and danced around but there was no sound. And still a terrible humming.
Broke out Philmurs audio probe the amps and op amps and got no sound anywhere. I knew there wasn't any signals going in for them to amplify.
The Sound Z80 cpu now was now correctly initiating on power up and not watchdogging as before but had no signals coming from most of the address lines. Took it out and tested it.
It failed miserably.
Found a correct Z80 CPU for it and plugged it in.
A thing to note is that this board requires a 780C processor as I initially tried a 8400 and that didn't work. So now with the correct processor in, I tried it again.
Now the game had sound! Played a few games and got my bombjack fix for the day.
Yay
