It's a bit odd, not consistent.
Sometimes when turning on the ~Reset line out of the TL7705 goes straight to high and stays there and it won't boot
Other times on switch on it will go high then low and the board will reset and boot. the reset switch has no effect pressing it the line does not go high and low again.
And on other times on switch on the line goes high and on press of reset button will go low and back to high. Screen also displays reset flicker.
RESET circuit tweaks
Re: RESET circuit tweaks
Odd... I think the circuit is from the mega st... Might be worth a look?
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
Re: RESET circuit tweaks
Yes - Have been comparing. I noticed the pull up on the reset switch is 1K on MEGA ST and 10K on STF. Have tried both still the same.
Also the caps are different 10uF for the electrolytic where as STF is 47uF.
I will test this circuit out on breadboard for behaviour as I have a spare TL7705. That way I can play around with it easily.
Also the caps are different 10uF for the electrolytic where as STF is 47uF.
I will test this circuit out on breadboard for behaviour as I have a spare TL7705. That way I can play around with it easily.
Re: RESET circuit tweaks
OK - prototype version
This is the exact match of the Mega ST reset circuit from the schematic
Power it up and this is what I am getting on LA. You can see that the inverted reset out is going high and low sporadically.
Second is with selecting reset several times which is the yellow wire to GND.
This is the exact match of the Mega ST reset circuit from the schematic
Power it up and this is what I am getting on LA. You can see that the inverted reset out is going high and low sporadically.
Second is with selecting reset several times which is the yellow wire to GND.
Re: RESET circuit tweaks
Interestingly was also looking at other schematics around the reset circuit and ventured into the MegaSTE as well. It looks like Atari went towards a 556 away from the TL7705 on the Mega.
Re: RESET circuit tweaks
If it helps, here's a photo of my Mega reset circuit, in case something is a different value to the schematic.
If it ain't broke, test it to Destruction.
Re: RESET circuit tweaks
Actually, noticed that a second cap is connected across C3 on my Mega, so maybe this is the problem?
Second cap is a 470uf. The other Mega doesn't have one but is also more unreliable, so might try that on the other one too.
Second cap is a 470uf. The other Mega doesn't have one but is also more unreliable, so might try that on the other one too.
If it ain't broke, test it to Destruction.
Re: RESET circuit tweaks
Thanks Forgottenmyname - I notice your C3 is two caps in parallel. What value are they?Forgottenmyname wrote: ↑Sat Nov 10, 2018 7:51 pm If it helps, here's a photo of my Mega reset circuit, in case something is a different value to the schematic.
20181110_194921.jpg
Re: RESET circuit tweaks
Must of seen the same thing at the same timeIcky wrote: ↑Sat Nov 10, 2018 7:58 pmThanks Forgottenmyname - I notice your C3 is two caps in parallel. What value are they?Forgottenmyname wrote: ↑Sat Nov 10, 2018 7:51 pm If it helps, here's a photo of my Mega reset circuit, in case something is a different value to the schematic.
20181110_194921.jpg