Feb 202016
 

Sometimes lightning does strike twice.

I was recently sent an Asteroids Deluxe PCB which was exhibiting corrupted vectors.

When I got the PCB, I put it on my test rig and was presented with the following in TEST mode;

IMG_20160215_160220667

GAME mode;

IMG_20160215_160158687

The symptoms were pretty much identical to the last Asteroids repair log I posted.  Note however this is an Asteroids Deluxe, however it is pretty much identical hardware to Asteroids except that Asteroids Deluxe has a pure digital sound circuit via a Pokey chip (Asteroids is analogue and no Pokey).

I immediately probed the 74LS42 decoder at E6, which had two outputs stuck HI.

IMG_20160215_160124793

So I desoldered it;

IMG_20160215_161027015

Tested it in my IC tester;

IMG_20160215_181037047

Socketed and replaced it with a fresh decoder;

IMG_20160215_161344449

Fire her up again;

IMG_20160215_160348150

Now working, except that the PCB would sometimes crash or refuse to boot.  I was able to determine that three of the six ROM sockets were worn.  So I replaced all of them for reliability;

IMG_20160215_162641553

IMG_20160215_165025775

IMG_20160215_162807350

Now working 100%.