Need Defender Guys

[bozo4onion]

Hi everyone, this is my first post here but lurking unregistered I see many here are most helpful. I'm looking for a defender guru. Everyone tells me 99% of defender probs. are PS or voltage but my (original linear) PS checks out great and I have all deadly correct +,-5, 12 power @ the harness connecting to the CPU.

Here's the story: Clean 1981 defender complete and original except a cobbled battery pack which I've removed for now. I bought the game 12 years ago. It broke the first week I had it and I returned it for repair. I got the game back and it broke again. I was too busy to return it right away and now looky....it's 12 years later and I have time.

I really want to fix this game and am having fun so far. Game boots (with sound sometimes) to a crisp rug pattern (refreshes once as usual) then goes to the initial test indicate all OK message. This repeats for hours if you don't switch off. 4 LEDs on rom come on at switch on and go off at switch off no flash. I have absolutely no control other than on/off switch. Of course all LEDs lit on PS.

I removed the cpu for closer inspection and found a transistor with a leg detached. I removed the transistor and resoldered it. This transistor (in the array close to the power connector) on the cpu faced the opposite direction from the others.

    As for me I'm biomed tech. I know how to use my meter. I'm really interested in learning more about how to repair the game. I have little logic circuit experience. I have ordered a logic probe (around here logic probes seem a little outdated, Radio Shack won't carry them anymore) and will be ready to check to see if my watch dog is toggling. I read this is my next step right?

     First, is there anything else to try before the probe gets here? I've heard maybe check DCV @ RAM (how?)

     Second, that backward transistor. I can't find a crisp enough pic. of the board. Is one supposed to face opposite of the others?

Of course I've already plugged and unplugged and jiggled everything. Thanks in advance for help.

[Kevin Mullins]

I've heard maybe check DCV @ RAM (how?)     

Assuming you still have the original 4116 RAM chips.

           ___  ___             
  - 5v -|1   \/ 16|- Gnd   
    Din -|2      15|- /CAS     
  R/W -|3  4  14|- Dout   
 /RAS -|4  1  13|- A6   
    A0 -|5  1  12|- A3     
    A2 -|6  6  11|- A4     
    A1 -|7      10|- A5     
 +12v -|8       9|- +5v   
            --------       

Pin 16 is ground
Pin 1 is -5V
Pin 8 is +12V
Pin 9 is +5V       

Sounds more like a reset/watchdog issue though.
Have you done the usual re-seating of any socketed chip on the CPU board?

[bozo4onion]

Awesome. I'm sure I have 4116.  Just what I was looking for. I really don't know what any of the letters mean (yet) but I can certainly test for +-5 & 12. I'll check these tonight. I guess simple remove and replace to reseat chips? Thanks, I'll post results.

[bozo4onion]

Oooops. Popped 1st chip. Hey, these things will go back either way. Noobed. It is one of the  2 socketed chips on the bottom of the board (close to power)that are labeled 8108,P3 and SN 7474N. The legs are quite corroded and there was a critter web under this one. Should I replace it oriented the same as the other one (and all the others on the board it seems) or opposite?
Learn something new every day.

[SirPeale]

There is a notch in the chip.  Orient it towards the notch in the socket.

[TheShanMan]

Be sure to VERY GENTLY pry the chips out of the sockets too. It's really easy to bend the legs, thus making the legs weak and prone to breaking. Don't try to rush it!

[bozo4onion]

Alrighty then. All chips reseated, some lightly sanded, going now to install board and play my game. Well I'm a glass half full guy, we'll see.

[bozo4onion]

  crap. when installing the cpu, I've done this many times, the ribbon was hard to connect. When I looked closely the pins on the board were bent. Well when I went to straighten them guess what? Yep, 3 broke off. They were barely bent but I guess they don't like to bend back. I guess this is problem #1 now huh. What next? How hosed am I?

[SirPeale]

Are you talking about the pins for the ribbon cable?  Even if it's not that and it's one of the other harnesses, they're pretty easy to replace as long as you can solder.

[bozo4onion]

They are the pins (male) attached through the plastic connector soldered to the board that fit into the female holes of the ribbon connector, to the ROM board I think. If these can be replaced by soldering I will need some technique coaching. They broke off below the plastic on top and I can't see how to get it out from the bottom. Unsoldering the whole connector, all those connections, is a little ambitious for me. I guess I bent these when levering the cmos out of the socket. Thanks for the help, I thought I might be shamed from the board. (Same peale at webmagic?)

[SirPeale]

Same Peale @ Webmagic.

[Level42]

Get a new cable from Bob Roberts and save yourself the hassle.

[Kevin Mullins]

I'm sure it's not the cable he needs ... it's the actual header pins on the pcb that broke.

[bozo4onion]

You are correct Kevin. Does the cable come with the pin connector? Keep in mind this is my first game restoration. Assume I know nothing because well.....I do. I think I will have to explore the art of solder sucking to remove this socket and then find a replacement, right? BTW as previously posted this is not the problem with this board. Should I just save time and money by shipping off for repair? Who's good for board repair?