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Galaxian PCB repair..
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Question
andykmv
I recently purchased a Galaxian parts pcb from davefjedi as non-working and decided to resurrect it instead of using it for parts.
Symptoms:
No sound, No video.
This log is the challenge of bringing one back from the dead. It might cost me more than buying a working one, but thats challenge of restoration and preservation.
i made a harness adapter using a finger board, card edge connector and a switch mode psu to convert the Galaxian card edge to a pacman wiring compatible card edge so that I could use my Pacman Test Rig for testing on the work bench. (this pcb's power supply section is not populated, hence the sw mode psu)
As i am completely unfamiliar with a galaxians pcb but am now reasonably familiar with spacei invaders architecture and the pacman schematic i figured i would start from the start and work my way through the pcb checking everything. I have got it hooked up now so this job is going to be an inbetweener whilst i am waiting for parts for the pacman #2 pcb.
Step 1 - checking the crystal clock oscillator circuit.
It took me a while to find the crystal oscillator circuit in the schematic as it was on the far rhs of the schematic. Hooked up the DSO for this one. the hex inverter used for this is an odd fish as they used a gated inverter ic 74LS368 - the gates are tied low to enable the inverters to function as a non gated hex inverter. following the hex inverter at pin 7 is a pair of flip flops used to divide the 18.432mhz clock down to 6Mhz. the output of pin 7 is showing an unbalanced clock signal, which the flips flops helped to cleanup into a nice uniform square wave clock signal. both the normal and inverted clocks are being produced, but i have yet to check the frequency - need to find the frequency counter for that or use the dso frequency measurement feature.
Edited by andykmvLink to comment
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