Electrical – Crystal oscillator replaced with exact frequency for clock

crystaloscillator

I'm repairing my Nintendo Donkey Kong arcade PCB and I have no pulse when tested with my logic probe. I found out that the crystal oscillator (2 pin HC-18U) was not connected to the board, since the legs have rusted completely and broken. The 2 pin crystal is a 61.44 MHz HC-18U model. It generates the clock for the Z80 processor.

Can I use a crystal with a different frequency, without damaging the components or affecting the game?

I can't find any two legged crystals, only 6 legs flat VCXO type… could that work?

Thanks

Best Answer

This crystal (61.44 MHz) is used in video board generator. It has no relationship to Z80, which uses a different 6 MHz crystal, so your reference to CPU confuses readers.

As shown in the schematics,

enter image description here

the crystal is a part of a sophisticated HF-oscillator, so a VCXO-type programmable crystals/oscillators will unlikely serve as direct replacement.

You have two basic options, either to find this vintage crystal (or similar one) and hope that its ESR will match the original, and the circuit will start oscillating. Or replace the entire generator with a modern programmable oscillator, program it to 61.44 MHz, and drive the isolating transformer T1 directly with modern electronics. You might need to keep the Q2 as power amplifier.