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1 astrocade powers to black screen..one powwr switch does zip.


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#1 Glen's Retro Show OFFLINE  

Glen's Retro Show

    Chopper Commander

  • 162 posts

Posted Wed Aug 24, 2016 5:02 AM

Hi. Well i have 4 astrocades.. 2 work..
3rd powers onto a black screen.. (this is an early unit cpu in this one is socketed! Has plastic rf shield. And gray reset button and red cart holder.Swapped all custom chips..still black screen. I hear this can be a ram iissue....and been suggested to cut the power leg on each one,by one until it boots..but hate to cut them..i am,good with soldering...but i have also
Swapped power brick..still black screen
..and yes chips and brick was swapped from a working unit. Also swappwd rf.
4th, used to power up and play..then power switch does nothing..screen stays static.. No power at all..also swapped power brick with a goodone and chips with a good one ans rf.....nothing..any idea's? A bad cap? Places to,check??
Thanks,my,friends
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#2 kenzre OFFLINE  

kenzre

    Space Invader

  • 22 posts

Posted Wed Aug 2, 2017 11:08 PM

Have you had any luck finding the solutions to your problems? I don't get up here much, so that is why I haven't responded prior to this.

If you have a volt-ohm meter, the 1st thing you want to check is the voltages. There are 4 different values to look for:

 

10V ( this is power to all custom chips, the last stage of the Oscillator and the RF modulator.)  Ground to pin 40 of the custom address chip. (the middle one.)

5V any small chip, usually the highest number pin (I.E. pin 16 of a 16 pin chip.) to ground. 4.5 to 5.5V. Iv lower than 5V, you probably have a shorted part somewhere on the board

-5V This goes to the modulator and to pin #1 of the RAM chips, located under the keypad.

the last supply can be either 15V or 12 V. It goes to pin 8 of the RAM chips...only. To know which one you have, look in front of the silver colored, finned heat sink. If there is a jumper there, you have a 15V unit. If it is a 1/2W 47ohm (Violet, Yellow, Black, Gold) resister it is a 12V unit.

 

If any of these are more that 15% off, that is the area to check. You'll find the schematic on ballyalley.com in the service manual last 3 pages.

Ken Lill



#3 Glen's Retro Show OFFLINE  

Glen's Retro Show

    Chopper Commander

  • Topic Starter
  • 162 posts

Posted Thu Aug 3, 2017 5:44 PM

It's always great to hear from the master Ken Lill.

I will check this out i hope this weekend. But no this is the first answer to my two astrocades dilemma.

And thanks to Adam for telling me to check the post :)




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