Fixing Atari's QWAK! (1974)

Atari's QWAK! is the third arcade PCB I bought.

I didn't let my current inability to fix the Olympic Tennis boards prevent me from buying more boards.

I bought this board from the guys at QuarterArcade, with the intention of dumping the ROM, to make it publicly available.

I wanted to dump the ROM so badly, because nobody on the Vintage Arcade Preservation Society's website had marked theirs as working.

Here is the circuit board. This picture is from the Ebay listing for the item I bought.

Source: QuarterArcade

Somehow, the pic from the Ebay listing is still on the internet. Do a quick search:Atari QWAK! pcb.

Oh, wait. I put it on the internet. *FACEPALM*

The schematic on the internet is for the Revision - "F".
From looking at my board, I have the earlier Revision - "C".

(I have already done some repairs to the board.)

After I made a test rig, this is what appeared:

It's not impossible to tell, this board has problems.

  1. No score area
  2. No buzzing sound complaining that someone stole the light gun.
  3. No sound
  4. No duck
  5. The screen is not a solid grey

Later, I discovered:

  1. No ROM Output
  2. -12 volts is not present
  3. The duck is there, but something about the enable isn't right...
  4. The game can't be coined up

Since this was before I became proficient at TTL by creating PERISCOPE, I was very clueless but optomistic about fixing this.

So, I just started piggybacking chips. That was literally my method of finding bad chips. Go me.

Later, I was able to realize that I wasn't going to get the game working without the -12 volts being outputted by the negative voltage circuit.

So, I began focusing my efforts there.

After replacing (almost) all the capacitors in the negative voltage circuit, I decided that I needed to replace the zeener diode, and the ua741. It was after that, I realized that a replacement for the ua741 was the NTE941M. I replaced it and the zeener diode.

While replacing the zeener diode, I realized there was some wierd sort of resistor put where the diode was supposed to be.

See? That is clearly a diode symbol.

Boom. Replaced.

After replacing all that, it still didn't work.

By the way, I feel I should mention that this all is happening about half a year after I bought it, and after I replaced about 20 chips... [Insert sheepish grin :)]

Anyway, I'm out of ideas. I replaced the first capacitor in the circuit, but there is no negative voltage present there.

There is a transistor, Q1, at the top right of the board. All of the pins are reading ~1 volt, so maybe I need to replace it?

If that doesn't do it, I don't know what will...

Help me, Obi-Wan-Ken-2N5193/NTE185-Obi. You are my only hope.

I replaced it, and it still doesn't work. Where is a nuke gif when you need one?

I should probably mention that unconnected pads come off easily when desoldering.

(Hey? It's not like I'm trying to damage my board or anything. I'm looking into alternatives for sucking up solder to see If I can prevent that.)

Okay. I have (unintentionally) shotgunned the whole negative voltage circuit. It still doesn't work.

Maybe there is some other reason why it doesn't work?

At this point, it occurred to me that I have never seen a negative voltage circuit with a straight-up DC power supply input. They always have used an AC supply. I am using a DC benchtop power supply. Maybe that's the problem?

I read the section on negative voltage supplies in Practical Electronics for Inventors by Paul Schertz and Simon Monk, and it basically gave me the message that you can never use DC power supplies to power a negative voltage circuit. I plan on buying some center-tapped transformers to see if that solves the problem.

This page was last updated 7/7/2018