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BeaglzNZ

Member Since 10 Jun 2017
OFFLINE Last Active May 10 2019 8:33 PM

Posts I've Made

In Topic: 130 XE - No Video Output / Boot Up

Sat Apr 27, 2019 8:56 PM

That would concern me. Before you do much else, at least verify continuity for every pin on your newly-socketed machine to the next component in line. You may well have damaged a pad or trace during your removal-and-socket procedure on that box. If youve damaged a FREDDIE connection, that will affect the validity of the test results.

 

Yep - double checked the continuity of the 40 pin socket and everything is good. No shorts either between pads. 

Will have another closer look at it next weekend.


In Topic: 130 XE - No Video Output / Boot Up

Sat Apr 27, 2019 8:32 PM

OK - so the progress today:

 

  • Removed CPU, Antic, GTIA, PIA & Pokey and tested in my 800XL (equivalent ICs were already socketed) - They all appear to be working as in the computer booted up.
  • De-soldered my Freddie IC from working 130 XE and installed a 40 pin socket - now that computer is reporting 8 bad memory chips - great!
  • Put the Freddie from the 'dodgy' computer into working computer and no life.
  • Put known working Freddie into 'dodgy' computer and now get a black screen - secondary problem somewhere. Interestingly the Sys-Check isn't initialising with the this configuration.

 

Progress of sorts today although now have a lot of memory chips to de-solder from the PCB - got a load of 41645 arriving Tuesday all going well, hope I ordered enough for 2 computers! Off to order a couple of Freddie chips and keyboard membrane as well. 


In Topic: 130 XE - No Video Output / Boot Up

Sat Apr 27, 2019 5:03 PM

 

Do  you have an oscilloscope? If so, check pin 28 of the GTIA first. That's the system clock (NTSC or PAL) input into the computer and sets the overall timing for everything. If you're getting the right signal there, next check the clock input (Phi0) into SALLY at pin 37, and the two clock outputs (Phi1 and Phi2) from SALLY at pins (3 and 39 respectively). Phi2, in particular, sets the basic pulse of almost everything else in the Atari. 

 

If you get a Phi2 signal at pin 39 of SALLY, next check the same signal at pin 7 of POKEY, pin 29 of ANTIC, and pin 25 of the 6520 PIA. The signals at POKEY, ANTIC and PIA should appear sharper and somewhat better defined than the raw signals off SALLY because they go through some buffering circuitry to try to create a sharper square-wave pulse. 

 

If you don't have an oscilloscope, you can still check for clock pulses (though not measure them) with a <$20 logic probe. You should get fast pulses at all the pins I mention above.

 

Thanks for the above - I don't have an oscilloscope but do have a logic probe. Have set it on TTL and connected to 5v and ground. Not getting Pulse signals - only high or low. Getting nothing on Pin 29 apart from a brief single pulse on ANTIC. Looking at the main ICs looks like the previous owner has done some work and damaged some pins. Will go back to the start and swap the ICs into my known working computer and see what happens.

Just about getting to the stage of selling as a 'repair project'!


In Topic: 130 XE - No Video Output / Boot Up

Sat Apr 27, 2019 4:03 PM

 

So check the Freddie chip in another motherboard, probably it is dead Freddie which is common damage.
By the way I told you past before, there is a clock problem if you have no reaction on video output at all.

 

 

Thanks for that - my working 130XE doesn't have the Freddie chip socketed so a bit of surgery required if I am to attempt to swap them.

Still learning about checking for the Clock signals - a lot of the suggestions have been around 'check for clock signal' but no real tips on how to actually do this and what readings to expect - all part of the fun of 'learning on the fly'.

Cheers.


In Topic: 130 XE - No Video Output / Boot Up

Fri Apr 26, 2019 3:57 PM

Programmed a GAL16V8 this morning and as far as I know it has programmed fine but no difference to video output. Dug for some more info on the Freddie chip and CLK seems ok on input but not pulsing on output.

If it was a memory problem I thought the Sys-Check would bypass this and operate - DIP switches are set to do this.