Saturday, 3 December 2016

Atari Breakout PCB repair. W.I.P Part 2

Part 2

Following on from my last session looking at the Breakout PCB, I spent a short while making the wiring connection more complete on the edge connector. I added Coin 1, 1 Player start, Serve and the paddle control. I also added a link to the edge connector for Coin 2; on these early games the coin switches use a common connection along with a normally open and a normally closed contact. If the normally closed contact connection of Coin2 isn't connected to the games common ground connection the game will always think the in Coin2 switch is being activated and stuck on usually stopping you from coining the coining up properly or playing the game correctly.

I decided to begin this session by checking all the the H & V clock signals that are divided down from the master clock circuit on the PCB. They all appear correct and present when using a logic probe to check for signals at the IC's where they are created (K1,L1,N1,N1 9316 IC's).

Next up I look at one of the Rams at L3 just checking for signals, no real idea of thinking about a fix just checking components that could lead to finding a fault; well its missing one of the Chip Enable signals on pin 3, not a high signal, not a low, nothing. Taking a look at the board (even though I already made a quick visual check) it's clear there's a broken trace, most likely from the original multiple wire mod that had been installed at some point.

Image below shows the offending broken trace.  

I checked where this was wired and sure enough one side of the broken trace was connected to pin 3 of the IC that had the missing signal.

I made a repair using an old cut off capacitor leg. shown below.

Powering up the game I'm now presented with some Playfield bricks :)

So in my mind now other than the bad video syncing/tearing issue, the game when in attract mode is missing a bouncing ball along with a paddle 'wall' which should completely cover the bottom part of the screen in attract mode. There is a 74157 IC which controls these component parts of the video graphics, before they are joined to a resistor network to make the final video signal.
The  *Pad signal is missing, again using a bright light to investigate another trace is broken (to the left of the middle IC in the photo below)

Once this is repaired we appear to have a paddle at the bottom of the screen, not completely covering the horizontal plane but good enough for now until I have fixed the bad syncing if the video.

I thought I'd try and find why the ball was not visible, it should be bouncing around the screen in attract mode. There is a signal called 'BALL' this was active, it passed through a circuit linked to the serve button on the control panel and the signal turns into 'BALLL DISPLAY' this signal is stuck low.

Tracing though this part of the circuit I find the 'Serve' signal (derived from the control panel button) is constantly stuck low even when the switch isn't connected, the signal should be 'high' when the serve switch is 'open'.

More signal tracing goes on which leads to a 7432 at location D2 looking at the image below you can see the area around pin 12 look a bit brown and burnt. It turns out pins12 a logic input is directly shorted to pin 11 an input. Also the track in between pins 11 & 12 was shorted to these two pins! That trace is a signal connected to the coin switch circuit. Considering pin 12 is connected to the serve switch I can only guess that at some point someone has put voltage down this connection instead of the serve switch wiring

I decide to chop this pin out to see what's going on with the burnt looks around this IC. After snipping the leg off, I'm greeted with the following mess! This IC has failed big time with parts of it melting to the track below the IC.

This area needs to be cleaned up and checked over before replacing the IC and hopefully seeing the Ball bouncing around the screen.

To Be Continued...