Blank Screen

Get help here getting your replica 1 going

Postby vbriel » Oct Mon 17, 2005 4:52 pm

I ran into that today while working on a kit for a customer. I haven't found the source yet but it could be a couple of things. The 74HCT166 is critical to the operation of the video circuit. I have found dim displays, bad sync problems when this chip isn't soldered good. The video circuit is only 3 chips and a handfull of components so checking over everything shouldn't be too hard.
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Postby mrbill » Oct Tue 18, 2005 12:58 am

I occasionally get this as well. I usually just clear/reset a couple of times and everything is fine.
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Postby vbriel » Jan Wed 18, 2006 7:53 pm

I've been working on this issue today since I really prefer your replica 1 to work perfect. I know this is a minor bug that goes away pressing clear screen a few times but I still am trying to get to the core issue. I took my replica back to rev A video firmware and found the problem to still be there. Doing some fuse changes to the way the ATMEGA8 fires up in the fuses helped but didn't cure it all the way. Then I realized that I switched over to 74HCT166's a while ago when the HC series became harder to find. I didn't notice any problems but now I'm seeing them.

Question is, does anybody with a 74HC166 on their replica run into a blank screen on powerup? I'm going to locate some 74HC166's and see if this really is the source of the problem.

Vince
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Postby vbriel » Jan Sun 22, 2006 11:39 am

I believe I have found the answer to the problem. A while back I switched from the 74HC166 to the 74HCT166 on the shift register. While the specs of the IC's don't show any difference in timing, voltage or anything else that I can find there must be a difference. I found a supplier of 74HC166's again and tried one out and found this resolved the powerup issue. Mouser electronics carries them or contact me if you need one.

Vince
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Postby daustin777 » Dec Sat 23, 2006 2:44 pm

I've just built my kit and I am experiencing the same issue- no cursor on power-on, or after 'clear' button. Pressing 'clear' seems to solve the problem. FYI- My kit came with the 74HC166N.

-David
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Postby vbriel » Dec Sat 23, 2006 3:27 pm

What power supply are you useing? ATX or DC wall wart style? If you are using dc can you try an ATX?

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Postby cclaunch » Jan Thu 04, 2007 7:13 pm

My machine exhibits similar behavior. About once every third time power is applied or once every third time that the clear button is pushed, my monitors show vertical white bars across the screen and some distortion that suggests that the sync is not locking correctly. A clear works fine to show me the correct prompt.

I have a 74HC166N made by Phillips, which was a replacement for the one whose pins I bent irreparably when assembling the kit.

ATX power, PS2 keyboard, using two entirely different monitor systems. The first is an outboard composite to VGA converter into an LCD monitor. The second is passing the composite through a VCR front jack through my video switching system, upconverted to S-Video, and sent to my ceiling mount NEC projector. Both behave identically with about the same chance of the display problem.

Otherwise it appears that all is well with the kit.
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Postby daustin777 » Jan Thu 04, 2007 9:41 pm

vbriel wrote:What power supply are you useing? ATX or DC wall wart style? If you are using dc can you try an ATX?



I was using ATX. I've tried using 6v via wall wart and it powers on with:
Code: Select all
F
@


On subsequent powers via 6 vdc it is blank. "Clear" button gives the cursor.

-Dave
--David Austin-- replica 1 se, CFFA1, MicroKIM, [kits]
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Postby vbriel » Jan Tue 09, 2007 2:48 pm

The F is the keyboard encoder reading keystrokes on power up. I've just modified the code so that there is a small delay on power up.

Also, I think I know how to fix this issue if you want to use the wall wart power supplies. I've found some brand 74HC74's cause this problem and some don't. It is hard to get the exact brand you want from Jameco but I tried 74LS74 flip flops and they appear to work great! More tests need to be done to be certain but I think this is going to really help with this problem.

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Postby AutoMusic » Mar Wed 14, 2007 2:43 pm

I have a Replica-1 rev C board that has this problem. I have just replace the 74HC74 with a TI 74LS74 as Vince suggested and can report this seems to have solved the problem. I have been using it for the last several days and have not had a blank screen yet. Works great! I am using an AT power supply not a wall wart so this could be a fix for anyone with this problem. Works for me. Thanks Vince.
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Postby Jeroen » Oct Tue 09, 2007 12:52 pm

Sorry for bumping this. (but I just recently joined) But is it possible that one chip doesn't work cause the power regulator circuit on the replica-1 is too "noisy" for it? Maybe some filtering caps would work......

Not sure if this was solved already.
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