- Thread starter Chinzilla
- Start date
Just got a delivery with some Texas Instruments LS253s switched out the one I thought looked suspect and.. Success!!! Thank you all for your input. Now onto trying to figure out which chips control the dip switch settings..
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channelmaniac
Professional
Use your multimeter and track continuity backwards from the DIPs. Easy enough.
advans14
Professional
necro bumping this. i have a sys 16b that has almost the same exact - similar issue. dip 1 and dip 2 both switch 1's are stuck on, as well as my jump button appears grounded in some games and not in others. this is for both player one and two, but either the inverse i cannot use it in game. all other buttons work. i can see the inputs pass through the optocouplers and the first two resistor networks.
there is then a LS253 at C16 where the input passes i can see the inputs ground as i press the button, but the output seems a little suspect, which is similar to the Sys 16a board in this thread, but obviously on the sys16b. the ls139 appears ok on my probe, i did try piggybacking the 253, but since its a tri-state i know it can cause issues.
there is then a LS253 at C16 where the input passes i can see the inputs ground as i press the button, but the output seems a little suspect, which is similar to the Sys 16a board in this thread, but obviously on the sys16b. the ls139 appears ok on my probe, i did try piggybacking the 253, but since its a tri-state i know it can cause issues.
channelmaniac
Professional
Is the input on the 253 high until you press the button to make it go low? If it's not, there's a resistor pack with an issue.
advans14
Professional
Yup it is high until pressed. What is weird is on certain games it has different behavior on altered beast it is the jump button and in test it does not activate neither pressed or not. But you can see the input pull low on the 253 when pressed.
In games like bay route in test it is highlighted red in the test which means its consistently held down. And in shinobi as soon as game start happens, the ninja magic activates.
Regardless, i still wonder if the dips have some sort of issue tied with it as well. Either they are frozen on or in other games off in test and its on switch one on both dips. Toggling the dips they meter out ok. So it is a connected ic or some short.
The schematic is rough. Perhaps its one of the 257s or resistor packs on each side of those dips. Something is Happening to that signal.
In games like bay route in test it is highlighted red in the test which means its consistently held down. And in shinobi as soon as game start happens, the ninja magic activates.
Regardless, i still wonder if the dips have some sort of issue tied with it as well. Either they are frozen on or in other games off in test and its on switch one on both dips. Toggling the dips they meter out ok. So it is a connected ic or some short.
The schematic is rough. Perhaps its one of the 257s or resistor packs on each side of those dips. Something is Happening to that signal.
advans14
Professional
Removed both dips to rule out issue. Also to note the stubby cap at c35 is completely gone near the crystal at center of board not sure its purpose but it is rather large to be just gone. Looks like .1uf 5.5v based on my spare.
Person on ebay who sold this “working”. Unfortunately the return window has passed as i was waiting on a jamma adapter.
Besides the 273 and the 139 not seeing what else is around other than some sort of short. Any ideas?
Person on ebay who sold this “working”. Unfortunately the return window has passed as i was waiting on a jamma adapter.
Besides the 273 and the 139 not seeing what else is around other than some sort of short. Any ideas?
advans14
Professional
Anybody? Does anyone know what is upstream beyond the ls139? Seems like sega used this same exact layout in the sys18 games as well.
Feel at this point im stumped. Ive checked the resistor packs, i know im close. Grounding the signal all the way from each spot down to the 253 i still cant get either jump/btn 3 to register (pins 8/J).
Also what would ground out each dip postion 1? Something obvious or not.
Feel at this point im stumped. Ive checked the resistor packs, i know im close. Grounding the signal all the way from each spot down to the 253 i still cant get either jump/btn 3 to register (pins 8/J).
Also what would ground out each dip postion 1? Something obvious or not.
SB_Electronics
Student
Looking at the schematics, there’s an LS244 upstream of the dip switches. Maybe have a look at these (H11?)
SB_Electronics
Student
advans14
Professional
well after replacing a few chips i got it, but unfortunately with the fragile sega traces it aint pretty. the ebay seller is a fucking liar and i left him negative feedback. regardless the missing super cap he ripped out and claimed this game had all three buttons working was a lie. turns out that super cap is close to a trace that goes up to the ls257 pin 4 of c14. which controls the dips and now i can trigger all button 3 inputs. now i have to repair these traces somewhat nicer.
SB_Electronics
Student
Glad you finally found the fault. At least you didn’t go around the board replacing every logic chip. Lucky it’s not too hard to run patch wires. You should see the state of my Sega System 16 
. Though I did purchase it knowing it was for repairs.
. Though I did purchase it knowing it was for repairs.
channelmaniac
Professional
Get a small spool of Kynar wire-wrap wire.
