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Trouble shooting solutions

PostPosted: Oct Mon 17, 2005 4:58 pm
by vbriel
I've decided to start a thred on troubleshooting solutions. This should be a very useful thred for those who get stuck.

Problem: I get cursor in top corner but replica won't reset, no backslash, nothing happens.

Solution: Well, there are several things to check, but since you have a cursor, 5V and GND are probably working correctly. If you can't check frequency on pin 37 of the 6502, check it by voltage. 1mhz will show up like 2.5V instead of 5V (yes, I've used this method in the past).

I recently ran across a bad oscillator and it wasn't putting out a 1mhz signal. This signal is basically the heartbeat for the replica. Without it, the CPU doesn't work. This is always a good place to start when your replica isn't working.


PostPosted: Nov Thu 03, 2005 10:03 pm
by jmcculloch
My newly assembled system is exhibiting the exact problem described above, displaying a square cursor. No keyboard response. Plus, the screen flickers violently. I measured (if I did this correctly) 4.43 volts at pin 37 of the 6502. What's the next step?

PostPosted: Nov Fri 04, 2005 7:33 am
by vbriel
Find a magnifying glass and check each solder point carefully. Concentrate on the IC's (chips) and look for any missed or suspect solder points. So far, most replica's sent back to me had bad solder points. I'd look there before replacing the osc.

Do you have a flatbed scanner? Scanned image of the bottom of the board helps too. I can see what's going on.


PostPosted: Jan Thu 11, 2007 7:36 pm
I have just finished the soldering with my apple I replica and began testing for power to the ICs. I believe everything is in order, but 74HC74 is getting power on both pins 13 and 14. Naturally I figured it was a solder bridge some where, but i have checked the board over several times and could not find one for the life of me. I installed the video related chips to see if i could get a signal with no luck, but this might be because I'm using a very, very old RCA video to co-axial adapter (used to work with my NES). maybe I should mention that I did get a weak signal coming from the video out when i tested it with the multimeter, but I figured that could just be static.

I regret plugging in the video chips (74HC74, 74HC166 and Atmega8 video, just as the guide recommends) as I may have ruined them... but I can always get replacements I suppose... Can you think of anything other than a solder bridge that would be causing 74HC74 to act this way?

I am going to radio shack now to get a real RCA cable to rule out that possibility.

edit: we get signal! (the new cable worked, after hitting the reset button a couple of times i got a cursor going across the screen 8)

PostPosted: Jan Tue 23, 2007 2:28 pm
by vbriel
Any progress with this yet?