A friend of mine asked me to do something about the sluggish RESTORE key in one of his Breadboxes. It turns out that on the old longboards of the Commodore 64, the RESTORE key needs to be hit hard to function due to a misdimensioned capacitor at C38 also known as the ‘NMI Capacitor’. On the new short boards, the problem was fixed. On MJK’s Commodore 64 & LCD Page I found the solution to the problem. If the original capacitor of 51 pF is exchanged by a 4.7 nF one, the RESTORE key functions as well as all the other keys of the keyboard. On all the longboards I’ve seen, the original capacitor has been build into a green resistor case. I ordered 100 new 4.7 nF ceramic capacitors from China for 2-3 $.
In the following images, the ceramic capacitor has already been exchanged. When the component has been swapped, test it by hitting the RUN/STOP + RESTORE key combination. It should now respond with the same amount of pressure as the rest of the keys on the keyboard. The images have been taken from an Assy 250407 Rev. C board. However, on all longboards (from all old Breadbins and some of the early C64C’s with the old boards installed), the location of the capacitor is pretty much the same.
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