50 Hz to 60 Hz - investigating the motherboard

[Tom M.]

I am trying to understand what exactly is behind the 50 Hz and 60 Hz modes that the Mega Drive or Genesis models operate at.

So far I have found out, that on model ONE there are 4 jumpers labeled JP1 JP2 JP3 JP4, and if JP3 is ON the system is 50 Hz, if JP4 is ON the system is 60 Hz. Correct me if I am wrong.

On model 2, I have come across several tutorials on modifying Mega Drive II that more or less copy one source and they tell me to disable a line as pictured here:

http://farm4.static.flickr.com/3088/2792789405_7b9c880fd5_o.jpg

I have no clue WHY because people who wrote the tutorials do not explain their steps...


On another site I have found this picture:

http://wolfsoft.de/wordpress/wp-content/uploads/2010/02/smd2_switchless_cut_5060hz.png

...which actually explains to me what is going on, at least partly...



To sum um I have following questions?

1. On model 1 - the only thing to turn Mega Drive 50 Hz into 60 Hz is to disable JP3 and enable JP4? Or do I have to do anything else on the motherboard?

2. On model 2 - pin 46 + ground = 50 Hz, pin 46 + 5V = 60 Hz - if this is true, should I cut that trace as pictured on the first photo and connect the line from pin 46 into that 5V area instead? Will this turn model 2 into 60 Hz machine? Or what exactly has to be done to get a 60 Hz machine? Or should I just look for those JP3 JP4 and do the same thing as on model 1?

[TmEE]

The JP spots are connected to an IC pin... when that pin is GND you get 50Hz, when VCC then 60Hz. On most MD2s, the pin is 46, some with different ASIC have a different pin.
That is all there is to it, when you mod you just got to make sure the pin is not tied GND/VCC before installing your switch, otherwise you get no operation (short between GND and VCC) or stuck region (aka ineffective switch).
The signal is internally pulled high, so your switch only needs 2 wires : the signal wire and the GND wire, that way you also minimize the chance of causing a short circuit between GND and VCC.

[Tom M.]

when you mod you just got to make sure the pin is not tied GND/VCC before installing your switch

so having a look at this picture:
http://wolfsoft.de/wordpress/wp-content/uploads/2010/02/smd2_switchless_cut_5060hz.png

if I cut the line from pin 46 to GND and connect it to 5V (as labeled) - I will get 60 Hz....?

[TmEE]

You can leave it disconnected too, it will stay in 60Hz.

[Tom M.]

OK. Another question. You say I can leave it disconnected - GND vs PIN 46 to be at 60 Hz.

But on the mother board, there is JP3 that is connected by short piece of wire which would be easier and less damaging to cut off. What if I disconnect JP3 and nothign else? Will the console by 60 Hz with PIN 46 still being connected to GND?

[TmEE]

you have to make sure the pin floats, and if there is something on JP3 or JP4 you got to remove those.

If you want permanent 60Hz just cut the trace going to pin 64 near the ASIC and you don't have to worry about anything anoymore

[Tom M.]

you have to make sure the pin floats, and if there is something on JP3 or JP4 you got to remove those. If you want permanent 60Hz just cut the trace going to pin 64 near the ASIC and you don't have to worry about anything anoymore

JP3 is connected, JP4 is not - this is easy since it's a wire

pin 64? I thought it's 46... confusion...

[TmEE]

sorry, pin 46

[Tom M.]

and you said to cut the whole trace to the pin 46

what if I cut only the GND - still the same? I'm asking because I don't get where the 5V would flow when the whole trace would be cut....

so is this enough to get a 60 Hz english MD2?
http://farm4.static.flickr.com/3088/2792789405_7b9c880fd5_o.jpg

[TmEE]

The pin is internally pulled up by a resistor inside the 315-xxxx chip. If you disconnect it completely, it will act like its connected to 5V.