Mega Force PCB?
- Thread starter big10p
- Start date
I haven't heard of this. How does it work?
Can't find a link at the moment.
It's a simple probe (I just use an old multi meter lead) that connected to the green input of my test monitor with a switch.
If the switch is one way the green video signal comes from the PCB under test but if the switch is the other way the green signal comes from the probe.
Touching data or address lines with the probe will show on the monitor as green if they are timed with the video signal thus possibly showing which parts of the circuit are related to video.
It's a simple probe (I just use an old multi meter lead) that connected to the green input of my test monitor with a switch.
If the switch is one way the green video signal comes from the PCB under test but if the switch is the other way the green signal comes from the probe.
Touching data or address lines with the probe will show on the monitor as green if they are timed with the video signal thus possibly showing which parts of the circuit are related to video.
I learn something new every day. 👍
Last edited:
I've managed to get spites displaying properly. Issue was basically a bad connection on the sprite RAM.
This board has water damage and corrosion all over the place, so this is a general problem. Pretty sure this is going to be the main issue with the background tiles, as pressing down on the board in the right place improves things.
Text layer looks good.
Fixing the earlier via continuity issue also brought sound back to life. Almost jumped out of my skin! Lol. Has issues like tunes are a bit off, and a couple of missing sound effects, but as stated earlier, sound is being left until last.
This board has water damage and corrosion all over the place, so this is a general problem. Pretty sure this is going to be the main issue with the background tiles, as pressing down on the board in the right place improves things.
Text layer looks good.
Fixing the earlier via continuity issue also brought sound back to life. Almost jumped out of my skin! Lol. Has issues like tunes are a bit off, and a couple of missing sound effects, but as stated earlier, sound is being left until last.
It's a nightmare as trying to reflow joints, the solder just doesn't want to flow and stick. Fibreglass pen helps, but I don't really want to desolder, clean and reflow every joint on the board. Lol
Right, I think I've managed to fix all grahpics issues, but further play testing is needed. The tile issue was indeed just down to bad contacts. I had already replaced a few of the tile ROM sockets due to corrosion, but decided to replace all the remaining ones too, as they looked OK-ish, but not great. I managed to locate the main issue was with 3 particular ROMs, by proding around while the game was running. Turns out a previous trace repair I'd done when fitting a new socket had come adrift. I prefer to try and fix traces if possible, instead of simply fitting a trace wire. Another issue was with a particular ROM. I'd cleaned them all up as best I could, but a leg on one ROM was pitted, and on closer inspection, had a hairline crack right across it. I ended up pulling off the leg and soldering on a new one, as solder didn't want to stick to the old, pitted leg.
Next up is sound. I'm guessing the missing sounds will be down to a fault in one of the channels, but the Bomb Jack schems aren't going to be much use to me, as that game uses three 8910 sound generators, whereas Star Force just has Z80 based sound.
Next up is sound. I'm guessing the missing sounds will be down to a fault in one of the channels, but the Bomb Jack schems aren't going to be much use to me, as that game uses three 8910 sound generators, whereas Star Force just has Z80 based sound.
Thanks. I have spent a lot more time on this than experienced fixers like yourself would need. Trying to get my head around how everything works etc. Still plenty still left to learn. Almost gave up a couple of times, but it feels great to have got this far with it. 🙂
No way I'd have got this far without SLICE, btw. Being able to watch the functioning of ICs and working out if something looks off has been extremely useful.
Last edited:
I'm still learning. Most fixes teach me something new.
Keep at it and the experience you gain will be invaluable for other fixes.
The slice is a great tool. Big shoutout to @GadgetFreak for making it.
Keep at it and the experience you gain will be invaluable for other fixes.
The slice is a great tool. Big shoutout to @GadgetFreak for making it.
Sound fixed. 🙂 With no schem to give me any clues about the sound circuit, I used my audio probe to find the sounds, starting at the opamps. Tricky, as the missing sounds (explosions, one of the tune channels etc) aren't always playing, so trying to probe and play the game at the same time. 🫠
Anyway, I discovered that this board uses three SN76489 sound generators, and one was outputting the missing sounds just fine. So, the signal must be going AWOL before reaching the amp. Turns out sounds are piped through three 4066 analogue switch ICs, and the one handling the missing sounds was ropey when probed. Replaced it and now all good.
I'm happily calling this board fixed and am very pleased. Thanks for all the help. 👍
Anyway, I discovered that this board uses three SN76489 sound generators, and one was outputting the missing sounds just fine. So, the signal must be going AWOL before reaching the amp. Turns out sounds are piped through three 4066 analogue switch ICs, and the one handling the missing sounds was ropey when probed. Replaced it and now all good.
I'm happily calling this board fixed and am very pleased. Thanks for all the help. 👍
Del Griffith
Active member
Great job mate, Perseverance won that battle. Brilliant game to rescue as well
What a mega repair 😁,well done,great fix.
favouredson
Super Star
- Credits
- 1,253CR
Nice work.
Now for the conversion...
Now for the conversion...
I'll definitely be giving that a go. 👍
I'm a bit confused about the Baluba ROMs. They're numbered 0 to 17 in MAME, not 1 to 18 like Star Force, and look like they're ordered differently?
Here's my top board (pre-fix photo):
And, this is a photo of Baluba from the net:
Where does ROM 0 even go?
