So remove the orange cap and then bridge the JP1 and JP4? Yeah not sure what happened to the exploded cap at all, could that be whats causing the problems, any idea what type of cap that is and are they easy to get hold of?
JP1-4? If that is what it originally was then yes. Not sure if that is a cap or simply a link to go OVER the trace (ie Sega didn't want to make a multi-layer board). All that will do is introduce the clock signal back to the encoder. Also restore pin 7 to what it was as well, this is the NTSC/PAL selection pin, ground for PAL ,+5v for NTSC. You essentially want to get the console back to original condition to try and locate a fault. PIN number corrected. I am really going to have to stop replying from work and relying on my memory for this stuff.
If a SMD cap looking thing has no markings on it, then it's most likely just a jumper bridge piece. I had to remove 2 of these doing my region/ language mod to my model 3. They had a ohm resistance of 0.00 when I checked them. Safe to say you should be able to just bridge the gap and go from there. To be 100% sure, check the rest of those bridge caps next to the trace in the picture. You should get an ohm reading of 0.00 or something really close to it.
On closer inspection i think that orange cap was once actually soldered to where that dxploded cap is on the board!!?
You are confusing capacitors and resistors. 0 ohm resistors are just jumpers, not caps. You shouldnt be removing caps
Right ok i have removed the orange cap and it looks like the exploded pcb mounted cap has taken the right solder pad with it aswell! Now can i bypass this cap by soldering a wire from point 1 or 2 to point 3 in the the picture below, also the orange cap was solder across the 2 solder pads at point 4 do i want to leave these pads divided or join them together??......
point 4 looks directly connected. Anything connected to those 2 pads is doing nothing. I wouldnt bypass the cap that was at poin 2 - find out its value, solder a wire to its legs and connect to pin 2 and 3 - fixing the circuit
^ Soldering a wire from point 1 or 2 to point 3 will most likely be fine. That's assuming the "resistor" was just a bridge jumper. It looks like the pads on point 4 both go to the same circuit. I'd leave it alone. Look closer and you'll see the PCB has a different color there from the rest of the blank areas. That's because there is a copper trace underneath that seems to connect the 2 solder pads. The bottom one at point 4 was most likely added by someone for the extra cap or resistor or whatever it was you removed. I meant resistors not caps. Derp. Derp! DERP! DERP!!!
I havent a clue where that cap has gone so i am unable re-use it. Arent the caps with no value marked on them just blanker caps??
What revision is the board? I might be able to find some large pictures to figure out how to fix the wiring or else I may have the NTSC equivalent model to make comparisons.
I found only 1 picture of a VA4 but it was a PAL model and only showed the top side. If anyone here has a model 1 VA4 JAP Sega Megadrive please see about getting us some high res images of the board top and bottom to identify the circuit traces and such.
The capacitor lost is 100nf (nanofarad). It's transporting the chroma carrier to the CXA1145 chip. Without it you will have B&W image at the composite out (or very faint colors if there is still enough signal irradiated from the trace to the CXA chip)... You may also want to follow the trace that goes to the CXA pin 7 (the capacitor goes to pin 6) as that pin has the PAL/NTSC mode selection in it.
"I recognise my failing and will be sure to correct it" (wh40k fans should know that). Sorry for the wrong info, to me, the amount of solder on the leg of that cap doesn't look factory (looks like it was drowned in it). Also corrected the pin placing, serves me right for replying from work.
Once you get that megadrive working,why not try out one of those switchless mods. I can confirm that they work very well and look much better than those manual switches. Also that megadrive board looks like a early version that probably uses 5v signal for reset. I would recommend using the switchless mod code from d4s. I could never get sebs hex code to work with mmmonkey hex invertor mod.Yes it worked but once in ntsc mode noisy picture/sound. The d4s hex is clean and does not require a hex invertor and for this reason is much simpler. mmmonkey as the link on his old website at the top for the d4s hex code. megadrive 1 switchless mod continued second page ""The more difficult one"
Just done this mod and it works 100%. I have noticed that the switch selection is JPN50hz/JPN60hz/PAL50hz/NTSC60hz i would have preferred PAL50hz/NTSC60hz/JPN50hz/JPN60hz. Is there any easy way to achieve this?
I'm too hungover to draw order ATM so I'll explain it. JPN language is ground and PAL video is GND. NTSC and ENG are open connections. AH screw it, here's a picture of needed order... That should be the needed order. I wired mine up the way I did because of switch placement on my model 3. Set it so that forward is my default NTSC/ ENG then PAL/ ENG followed by JPN/ NTSC lastly JPN/ PAL.
Cheers for the diagram!! I have noticed a few very small gfx glitches on some games (not sure if this is because im using a Mega Everdrive) but not sure if there in the normal games or not!?
