Overclocking the 8-Bit Menace

[Joes2Silly]

I was able to wire up the NES and the new clock. I then wired up a switch to the NES and clock so I can switch from 1.79 Mhz to 2.0 Mhz without any modification or other crud. So I plug up my NES and the overclock was a success! Well sort of. I got it to run at 2.0 Mhz but I can't get it to run at stock speed! The weird thing is that when I have the switch on stock speed and I power it up, I get a blue screen. I designed the switch with a plug and play style system, and the weirder thing is that when nothing is plugged and I power it up, I get another blue screen! What should I do to fix this problem? Worse case scenario, I will just keep it overclocked and not worry about the stock speed

[Rekarp]

blue screen means a dirty connection between the cart and slot. Clean them and you should be ok. Try disabling the lock out chip as well

[Joes2Silly]

I already have disabled the lockout chip

[CronoTriggerfan]

Just try basic troubleshooting first. Check cold solder joints, jumps, an error in switching, a screwed up ground line, etc. If all else fails, compare your wiring to this guide, it's the one I used on an NES a while back and it worked like a charm.

CTFan

[Joes2Silly]

I'm going to check the cold solder joints this afternoon, I don't think it is the ground wire because the NES is working while overclocked, and what do you mean by 'check jumps'? I think if I re-solder the wire on the original clock I may get it to work

[Epicenter]

The most probable issue is the original clock signal is being damaged, attenuated or destroyed before it can reach the CPU. Your entire clock signal run, from either source (clock oscillator/crystal, switch, and lead to the CPU's clock input pin) should not be over 12 inches if you can possibly help it. The wire should be thin, like that of a shredded PC IDE ribbon cable. It's best if it's shielded, though this is not particularly necessary, and if you do shield it, that shielding should be grounded properly to cut back on EMI interfering with the coherency of the signal. Try moving the leads as well, as proximity to ICs and other components may introduce harmful high frequency noise and reduce stability/make the clock signal useless. Since only one of your selectable clock settings is exhibiting objectionable behavior the issue is most likely in that section of the circuit alone, or partains to the length of that portion of the cable run.

To ensure proper connectivity of all the points in your clock selection circuit redo all your solder joints and use separate flux when you make them, if possible (rather than flux-bearing solder.) They should appear bright and shiny. If they are dull gray, they are cold solder joints and will inhibit good electrical conductivity.