Jump to content
potatohead

6 Switcher left player always firing.

Recommended Posts

Well, I spoke too soon. It took me a while to sort out the power supply issues. Put the thing together and ran KABOOM! That worked fine.

 

Turns out the left player fire is always on. Was doing kind of a sanity check with my cart collection. Many of them have not been in a machine for a long time. Discovered that right away.

 

First thought was a stray solder blob. After working on it for a while with a lens, and re-heating the ones there on the DB9 connector, I'm convinced that's NOT it. (I could be wrong on that, but I don't think so) Does it with ANY joystick controller plugged in. Also does it with NO controller plugged in.

 

Probably means static or just age got to one of the chips. :(

 

Can these things be had anywhere still, or do I have to just keep digging and get another VCS to part out?

 

...or is there some other thing that could be the trouble.

 

Almost there! I can play some paddle games. That's sweet. Kind of missed those.

Share this post


Link to post
Share on other sites
Turns out the left player fire is always on. Was doing kind of a sanity check with my cart collection. Many of them have not been in a machine for a long time. Discovered that right away.

 

First thought was a stray solder blob. After working on it for a while with a lens, and re-heating the ones there on the DB9 connector, I'm convinced that's NOT it. (I could be wrong on that, but I don't think so) Does it with ANY joystick controller plugged in. Also does it with NO controller plugged in.

 

Bad RIOT chip. You can get them from Best Electronics, or from a junked 2600. They're socketed, and easy to change. There are only three chips in that console - they're all inside that metal box in the center of the board.

 

-Ian

Share this post


Link to post
Share on other sites
Bad RIOT chip. You can get them from Best Electronics, or from a junked 2600. They're socketed, and easy to change. There are only three chips in that console - they're all inside that metal box in the center of the board.

 

Hehe. I think I spoke too soon. I just pulled up the schematic of the console. It's the TIA. I forgot - the directional control is handled by the RIOT, fire buttons to the TIA. Try this. Pull out the TIA (C010444) and bend pin 36 out just enough so it won't go into the socket, then put the chip back. If it still fires constantly, then you've got a bad TIA. Only other possible cause would be a short, or if that 470pf cap off the pin of the control port shorted (really, really unlikely).

 

-Ian

Share this post


Link to post
Share on other sites

Thanks!

 

Was just reading through the service manual trying to get there! That's exactly the kind of test I need.

 

(well, the thing was only $5 Some assembly required, I guess!)

Share this post


Link to post
Share on other sites

I have the same problem with one of mine,only the right player keeps firing. I changed ALL three chips with ones that are definitely ok, and I still have the problem, so the chip thing is not the cure for my situation.

 

I am going to try that 470pf cap replacement next. Ian, do you know which number cap that would be?

 

Will let everyone know how it works when I do.

Edited by Benzman66

Share this post


Link to post
Share on other sites

OK. The plot thickens. I was looking at the schematic I had close at hand - the schematic for the 4 switch model. The six switch is oh so slightly different. There is an additional chip - a CD4050. This is used to buffer the signals from the joystick buttons (among other things), and was omitted in the four switch model. It's more than likely your culprit here. I even went so far as to unhook the Atari from my TV and take it apart and trace the thing - this chip is definitely present in production six switchers, and is connected between the joystick buttons and the TIA.

 

You can replace the chip, or, simply bypass it. For the left player's fire button, bridge pins 9 and 10 on the 4050, for the right player, bridge pins 6 and 7. Obviously, replacing the chip is the best repair, but it's not really needed - Atari themselves took it right out for the 4 switch models - and briding these pins with a blob of solder would simply change the circuit to be almost identical to the 4 switch. The only other difference is they changed the value of the cap to ground from the fire button inputs - 220pf on the 6 switch, 470pf on the 4 switch. These cap values shouldn't affect anything, I wouldn't bother changing them. They're just there to reduce noise in the circuit.

 

-Ian

Share this post


Link to post
Share on other sites

Benzman66 is yours a sixer too?

 

Mine is heavy, in that it has the shield, but it's a Taiwan.

 

Thanks Ian! Taking your stuff apart is above and beyond the call! Thumbs up man!

 

Will let you know the results soon!

Share this post


Link to post
Share on other sites

Been reading this thread. First of all, thanks guys for taking this up. I have exactly the same problem with my 6-Switch Sears Telegames System. I did all what you guys did before, tracing shorts/gaps in PCB, replacing all chips except the CD4050 since it is not socketed. I actually gave up trying to make my system work until I came across this thread last night. I will try Ian's suggestion.

 

My only dumb question though, how will I know which is Pin 9 and 10?

Share this post


Link to post
Share on other sites

Look up the specs/datasheet/pinout on a 4050 to see the pin numbering. Should be all over the internet.

Share this post


Link to post
Share on other sites
My only dumb question though, how will I know which is Pin 9 and 10?

 

IC's follow a standard numbering convention for the pins. Looking at the chip with the notch facing up, Pin 1 is on the upper left. Numbering continues down along the left side of the chip, then over to the right when it gets to the bottom, then back up the right side.

 

Like this:

 

   +---+--+---+
 -|1  +--+ 16|-
 -|2	   15|-
 -|3	   14|-
 -|4	   13|-
 -|5	   12|-
 -|6	   11|-
 -|7	   10|-
 -|8		9|-
  +----------+

 

-Ian

Edited by Ian Primus

Share this post


Link to post
Share on other sites

Did tried this last night. I soldered pins 9 and 10 of the 4050 chip. Still won't work. I did replace all the socketed chips (CPU, TIA, RIOT), still won't work. I guess I need to check the capacitors next. Thanks for the input Guys!

Share this post


Link to post
Share on other sites
Did tried this last night. I soldered pins 9 and 10 of the 4050 chip. Still won't work. I did replace all the socketed chips (CPU, TIA, RIOT), still won't work. I guess I need to check the capacitors next. Thanks for the input Guys!

 

Hmm. That's odd. It should have worked. There isn't much else in that circuit. The only other thing I can think of is that the cap is shorted (again, unlikely, there's no voltage on it, and it's a ceramic cap), or possibly that the 4050 has developed some kind of internal resistance to ground - a potential failure mode. The only other part in that circuit is a 10k pullup resistor. It could have opened, but again, it's pretty unlikely, I've never seen one fail on the controller port. Easy enough to check though.

 

Check with a meter between the now-shorted pins 9 and 10 on the 4050 and ground, and see what you get for resistance. Check between pin 6 on the controller port and +5v, and see what the resistance is (should be around 10k).

 

Remove the TIA and slightly bend out pin 36, then reinsert it. It shouldn't fire continuously, but of course the fire button won't work either. At least that would rule out the TIA.

 

Another thing to try, would be to desolder pins 9 and 10 of the 4050, and carefully bend them up and out of the board (this is possible... Just remove the solder from the two pins so they're free, then using a tiny screwdriver or paperclip or something, pull them up and out of the board.). Then connect the pads where pins 9 and 10 used to be. That takes the 4050 out of the equation entirely, in case it has some kind of internal resistance/short to ground.

 

I've not had this particular problem with a six switch before - so I'm going on the schematic, and the knowledge that I did check it against my six-switch Sears Telegames Atari, and it matched.

 

For reference, the Atari joystick is simply five switches - when they're pressed, they connect one pin to ground. Pins 1-4 are up, down, left and right, respectively. Pin 6 is the fire button, pin 8 is ground. Internally, the directional switches go to inputs on the RIOT chip, and the fire buttons go the the TIA. The fire button is wired differently though. The RIOT, an I/O chip, already has the necessary "stuff" inside it to prevent the input lines from "floating" - floating is a condition where you have an input that's not connected to anything. Any stray signal can influence this - such as a long joystick cable getting an induced current. To prevent this from having a weird effect on logic, pullup resistors are used - this ties the line high (off) all the time, through a high value resistor. The line can still be drivin low by proper input, however. So, the RIOT already handles all this by itself, so all the directional switches just go directly to input pins on the RIOT. The TIA does not - so there is an external pullup resistor on the button input, a "deglitching" cap to ground, and in the six switch, a buffer chip (4050).

 

Hopefully some of this makes sense. It's hard to troubleshoot things by "remote control" :)

 

-Ian

Share this post


Link to post
Share on other sites

Appreciate all your inputs Ian. Let me try this tonight. I understand it is difficult figuring this out remotely, but now I do have a better understanding of the circuit and what the pins on each chip does. My console is also a Sears Telegames 6-Switch System.

 

Thanks again!

Share this post


Link to post
Share on other sites

Well Ian, it's closer!!

 

I bridged the pins. (9 & 10) on my unit. What used to happen was the fire input was stuck on. Now, it's off UNTIL the first button press, then it sticks on. It's a new FB2 joystick too.

 

LOL!!

 

Any ideas?

Share this post


Link to post
Share on other sites

I'm reading through the thread again.

 

Don't have a meter handy, and I'm just gonna go with the resistor being good. Very doubtful it's open, besides that doesn't seem to go along with the latch behavior.

Share this post


Link to post
Share on other sites
I bridged the pins. (9 & 10) on my unit. What used to happen was the fire input was stuck on. Now, it's off UNTIL the first button press, then it sticks on. It's a new FB2 joystick too.

 

Hmm. This is weird. It's so hard to do this remotely! Check the pullup resistor for pin 6 of the controller port. Try swapping the TIA from another Atari - that's the quick and easy way to rule that out. If it still won't work, desolder pins 9 and 10 of the 4050 and pull them out of the board - then connect the pads where they used to be. That rules out any kind of internal resistance short that could have been created. Check carefully for bad connections all the way from pin 6 of the controller port back to the 4050 and then back to the TIA.

 

-Ian

Share this post


Link to post
Share on other sites

Thanks a bunch.

 

I'll work through those. I don't have another TIA at the moment. I can deal with the 4050 too.

 

On the upside, I just got my first attempt at composite video working! Thought this one was a good practice one.

 

(gonna have to get a meter...)

 

Anyway, it sure looks nicer.

 

Thanks for the tips. I'll let you know what happens!

 

I did the quickie Ben Heck resistor only mod. In my case, it appears almost no resistance is required. Gonna have to find a cart that has grey scales to be sure though.

post-4836-1235360308_thumb.jpg

Edited by potatohead

Share this post


Link to post
Share on other sites

First of all, I noticed in the forum that the problem I have with my 6-Switcher is almost prevalent to the problem being experienced by other 6-Switchers in this board, so I decided to post this, hoping it would help.

 

Ian, thanks for the advice. I pulled out the terminals of Pins 9 and 10 (Left Player) from the board. Then I soldered their traces on the PCB. IT WORKED !!!

 

The last solution I tried for this issue was just to solder pins 9 and 10 on the PCB but still, the terminals of the chip for 9 and 10 is still connected to the board. There might still be some internal resistance in this case (according to Ian), which could be the reason it didn't work.

 

Finally, my Sears 6-Switcher is working the way it should. Thanks guys for the inputs, hope this thread helps.

 

 

erick

Share this post


Link to post
Share on other sites

Hey all!

 

Success here too!

 

Clearly that chip does exhibit an internal failure. My solution ended up being the same thing. Pull up, or cut (which is what I ended up doing) the two pins, then solder the pads together to get the chip out of the fire button circuit.

 

Popped in a few carts and all is going well.

 

I'm twiddling with the video mod now, hoping to solder up a board and mount it. Then it will be done!

 

Nicely done Ian! I sure appreciate it. Not sure I would have arrived at that solution.

 

Just a quick log:

 

1. Check for bridged solder joints.

 

2. Bridge pins 9 & 10 for left player stuck firing

 

[constant firing went to a latched sort of mode where it wouldn't fire until I pressed the button, then wouldn't stop!]

 

3. Remove pin 9

 

[back to constant firing]

 

4. Remove pin 10 from board.

 

That worked!

Edited by potatohead

Share this post


Link to post
Share on other sites

Glad you guys them working! It's odd that the 4050 developed that internal short/resistance/whatever. Especially weird that potatohead's started latching. That's not supposed to happen...

 

Ideally, you could replace the chip. But, again, Atari omitted it in later models completely, so it's not really necessary to have it buffering the line.

 

-Ian

Share this post


Link to post
Share on other sites

I think I'm gonna leave it as is and just be careful about connecting to that port. Those boards are OLD. I worry about tearing traces and such.

 

If the other port acts up, then I'll bite the bullet and throw a socket in there.

 

Yeah, the latch was wierd.

Share this post


Link to post
Share on other sites

YUMPIN` YIMMINY!

 

Just a few days ago, I dug up my old 2600 and tried it after I-don't-know-how-many years- I have the same problem (all of my tests indicated the same problem: a bad 7749 chip).

 

Isn't it nice, a plug-in IC?

Edited by CV Gus

Share this post


Link to post
Share on other sites
Being mine is the right player firing, does anyone know which pins correspond? Thanks

 

 

This website has schematics that can help- just follow the lines.

 

You might have to look up the controller PIN layouts to see what does what.

 

For example, PINs 5, 7, and 9 pertain to the paddle controllers.

 

For your right fire, I think it's PINs 6 and 8.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...