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Just bought a 5200. Questions about screws, power, and unknown mods

vcs mod pokey pcb power

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#1 ruthsarian OFFLINE  

ruthsarian

    Space Invader

  • 18 posts

Posted Mon Aug 8, 2016 8:17 PM

I recently picked up a 5200 4-port. It's missing several case screws. Can anyone confirm the correct screws used for the case? I think the screws that came with this 5200 are type b #6-20 3/4 sheet metal screws. Is that what it should be or perhaps these were used to replace the original screws that were of a different type? Here's what was in my 5200:

case_screw.jpg

 

It didn't have a power supply, but I found one elsewhere. It's an 11.5v version. I tested it with a multimeter and it's outputting 14.5 volts. From what I've found the voltage regulators in both the case and the switchbox should be capable of handling over 30 volts. Do I have any reason to worry about using the power supply? 3 volts over seems like a big difference, is that typical or should I start looking for another power supply?

 

The traces (or is it the soldermask) on the back side of the board on is wrinkly (see the POKEY to C104 wire image below). Is that normal or is it a sign of something I need to be worried about?

 

It looks like the VCS adapter compatibility mod was applied to this board, but I also see a capacitor between pins 1 and 17 on the POKEY and a wire on the underside between pin 1 of the POKEY and C104. Is this a known mod? Any idea what it's for? Trying to smooth out power to the POKEY perhaps?

pokey_cap.jpg

POKEY1_C104.jpg

 

In the middle of the rat's nest that is the VCS mod, I see a resistor and a capacitor (?) wired in parallel from between the two resistors connecting R11 and C10 as part of the VCS mod. There's also a diode wired to either side of R10. Any idea what they're for?

c18_mod_splice.jpg

 

The parts side of the pcb, marked CA018087, has no revision. The solder side, marked C018085 is rev 7.

 

I will probably apply the mod to separate the power from the RF. I was also thinking about doing the mod for composite and/or s-video, but doing that would make the VCS mod pointless, right? If I did the composite/s-video mod I could pull the VCS mod out. If I did that would I need to reconnect pin 24 on the cartridge slot to ground?

 

Thanks for any help/information you can provide. I hope to get this 5200 up and running soon.



#2 CZroe OFFLINE  

CZroe

    Chopper Commander

  • 233 posts
  • Location:Newnan, GA, USA

Posted Tue Aug 9, 2016 5:25 AM

Old non-switching power supplies using transformers always output a couple extra volts when they aren't under load. If it's not a switching PSU then it's probably even closer to spec when you power up the system with it.

#3 ruthsarian OFFLINE  

ruthsarian

    Space Invader

  • Topic Starter
  • 18 posts

Posted Wed Aug 10, 2016 8:23 AM

Old non-switching power supplies using transformers always output a couple extra volts when they aren't under load. If it's not a switching PSU then it's probably even closer to spec when you power up the system with it.

 

You're right, it's 12 volts coming into the voltage regulators on the pcb when it's powered up. it powered up fine and works with the switchbox. Now trying to figure out whether or not I want to remove the VCS mod before I add composite video.



#4 CZroe OFFLINE  

CZroe

    Chopper Commander

  • 233 posts
  • Location:Newnan, GA, USA

Posted Wed Aug 10, 2016 9:05 AM

 
You're right, it's 12 volts coming into the voltage regulators on the pcb when it's powered up. it powered up fine and works with the switchbox. Now trying to figure out whether or not I want to remove the VCS mod before I add composite video.

Good luck!

My 4-port didn't get the VCS mod but it did have all the other rework changes yours has. It also has the bottom shell from a 2-port.

Edited by CZroe, Wed Aug 10, 2016 9:05 AM.


#5 ruthsarian OFFLINE  

ruthsarian

    Space Invader

  • Topic Starter
  • 18 posts

Posted Sun Aug 21, 2016 2:39 PM

I picked up a second 5200. This one had all the screws in it and signs that it was never opened before. The two screws beneath the joystick holder area are 1/2 inch #6 sheet metal screws. The others are 3/4 inch. I picked up replacement screws at Home Depot and they work great.

 

The second 5200's motherboard has no work on it at all. The cap between pins 1 and 17 on the POKEY is not there, nor the extra wire between pin 1 on POKEY and ground on C104. nor any of the other, non-VCS mod things over on the right side. I'm still curious what they do.

 

The second 5200 was displaying a garbled screen almost as if it had bad/no sync. I plugged in several carts and nothing happened. However when I plugged in Q-bert, I could start a game and the Q-bert and monster sprites appeared on screen, clean, over the garbled background. So it wasn't a sync issue nor a CPU issue. I swapped out the GTIA and ANTIC chips from my good 5200 into the new 5200 and found it was the ANTIC that was bad. I'll order a replacement from best electronics.

 

One thing I did notice is the sound was a little blown-out on the new 5200. I'm wondering if that POKEY mod might have anything to do with fixing that. But before I risk a $20 POKEY, I was curious if anyone might have any insight into the non-VCS mods I mentioned in the first post. I'd like to think they're documented somewhere if they're (as I suspect) factory mods.



#6 zylon OFFLINE  

zylon

    Quadrunner

  • 6,155 posts
  • 5200 HSC Mod
  • Location:Kennesaw, GA

Posted Wed Aug 24, 2016 7:14 PM

Not sure about that, but I know the polystyrene caps near the RF box are responsible for most sound issues. If you press on them with your finger and the sound improves, replace them.

 

From what I've seen, these final systems were sold with the 2-port power supply. It is a little different in output and I've been wondering if the factory mods were not related to the difference.

Attached Thumbnails

  • game repairs 109.jpg

Edited by zylon, Wed Aug 24, 2016 7:15 PM.


#7 onemoretime OFFLINE  

onemoretime

    Chopper Commander

  • 152 posts
  • Location:dayton, texas

Posted Thu Sep 15, 2016 6:45 PM

Regarding the wrinkling...... if it makes any difference, I have a nos board from Best that came out of the bag with wrinkling.



#8 ApolloBoy OFFLINE  

ApolloBoy

    Quadrunner

  • 5,698 posts
  • Location:San Jose, CA

Posted Mon Oct 31, 2016 9:49 PM

It looks like the VCS adapter compatibility mod was applied to this board, but I also see a capacitor between pins 1 and 17 on the POKEY and a wire on the underside between pin 1 of the POKEY and C104. Is this a known mod? Any idea what it's for? Trying to smooth out power to the POKEY perhaps?
attachicon.gifpokey_cap.jpg
attachicon.gifPOKEY1_C104.jpg

I actually just recently read the 5200 service manual, and that particular mod is supposed to help prevent joystick jitter by (you guessed it!) smoothing out the voltage that goes into the POKEY.





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