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Processor board fault finding tips


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#1 rich322 OFFLINE  

rich322

    Combat Commando

  • 4 posts

Posted Tue Feb 14, 2017 3:48 PM

I just got hold of a couple of dead Vectrex's, first one had a corroded mains plug of all things! Easy fix.

 

Second one had a duff power switch, which was an easy fix but a bit of a nightmare to re-assemble due to it being spring loaded!

 

Anyway, after getting power on, the unit makes some noises - not quite the right noises and there are some dots and lines on the screen but squashed into a diagonal shape.

 

I popped the processor board output of the good unit onto the screen of the faulty one and the screen is perfect.

 

So the processor board is faulty.

 

It's not dead as it is definately trying to run something.

 

I scoped the X,Y outputs and they are not correct... (as shown by the squashed display).

 

Is it worth going for a cap (tantalum and electrolytic) replacement first, or is there another place I should look at first?

 

What are the typical symptoms of a dodgy DAC or Mux?

 

What does a dodgy 6522 typically do to the display? The 6522 io ports are driving the DAC, mux and are involved in the sound output too so maybe this is iffy?

 

Thanks for any suggestions...



#2 rich322 OFFLINE  

rich322

    Combat Commando

  • Topic Starter
  • 4 posts

Posted Tue Feb 14, 2017 3:57 PM

Ha! I think I just answered my own question, while writing it!

 

Swapped 6522's and the fault moved with it!  I forgot they were socketed.

 

So just need to find a working 6522....






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