Zaccaria The Invaders Maintenance 2021

Background

Pre-show testing in 2020 found that some of the sounds weren't working properly. The game PCB was removed for bench testing.

27/06/2021 - Sound repair

The game PCB was setup on the bench with the Arduino ICT to trigger the various analogue sounds. Both the invader hit and base fire sounds were not correct. Checking the audio sub PCB found the Voltage Controlled Oscillator wasn't running at CI5 (555) pin 2. There was +7.5V present at pin 3 and I suspected the 555 was bad. Replacing the 555 fixed the oscillator and the two sounds seemed to be working properly.

12/07/2021 - Spare PCB PA20200530 picture quality repair

Whilst the spare game PCB was working, it's picture quality was poor with a lot of bleeding not seen on the 1st PCB even with the video pot adjusted fully. A compare and contrast of the two PCB's video output section yielded the following differences:

PCB No.	Transistor Q4	Pot Value	Center Resistance	Track Resistance
PA20200528	BC548B	22K	4.83K	1.35K
PA20200530	2N2222	10K	0	1.22K

On the 530 PCB I replaced Q4 (a prior repair) with a BC237 and the 10K pot with a 22K pot that I also set with a centre resistance of 4.83K. The theory was that 530 would now match 528 identically for video output.

In the cabinet the picture quality was excellent.