Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

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Liengamer
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by Liengamer » Sun Mar 07, 2021 1:47 pm

lidnariq wrote:
Sun Mar 07, 2021 1:31 pm
Liengamer wrote:
Sun Mar 07, 2021 1:27 pm
Yes the Voltage indeed gets lower going further away from the source.
Then try to find where it's lowest.
Its the lowest on the 74LS139 or on the 74HC368

lidnariq
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by lidnariq » Sun Mar 07, 2021 1:54 pm

Liengamer wrote:
Sun Mar 07, 2021 1:45 pm
connect to "(74HCU04 pin 2/3)" do you mean both pins 2+3 or pin 2 or pin 3
They should already be shorted on the mainboard.
Liengamer wrote:
Sun Mar 07, 2021 1:47 pm
Its the lowest on the 74LS139 or on the 74HC368
Which '368? Also, those two ICs aren't near each other. Are you sure that's what you meant? What happens is you provide +5V/ground somewhere else?

Liengamer
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by Liengamer » Sun Mar 07, 2021 1:59 pm

lidnariq wrote:
Sun Mar 07, 2021 1:54 pm
Liengamer wrote:
Sun Mar 07, 2021 1:45 pm
connect to "(74HCU04 pin 2/3)" do you mean both pins 2+3 or pin 2 or pin 3
They should already be shorted on the mainboard.
Liengamer wrote:
Sun Mar 07, 2021 1:47 pm
Its the lowest on the 74LS139 or on the 74HC368
Which '368? Also, those two ICs aren't near each other. Are you sure that's what you meant? What happens is you provide +5V/ground somewhere else?
On my PAL board they are both at the same place.

Liengamer
Posts: 34
Joined: Wed Mar 03, 2021 8:04 am
Location: Germany

Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by Liengamer » Sun Mar 07, 2021 1:59 pm

lidnariq wrote:
Sun Mar 07, 2021 1:54 pm
Liengamer wrote:
Sun Mar 07, 2021 1:45 pm
connect to "(74HCU04 pin 2/3)" do you mean both pins 2+3 or pin 2 or pin 3
They should already be shorted on the mainboard.
Liengamer wrote:
Sun Mar 07, 2021 1:47 pm
Its the lowest on the 74LS139 or on the 74HC368
Which '368? Also, those two ICs aren't near each other. Are you sure that's what you meant? What happens is you provide +5V/ground somewhere else?
On my PAL board they are both at the same place.

Liengamer
Posts: 34
Joined: Wed Mar 03, 2021 8:04 am
Location: Germany

Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by Liengamer » Sun Mar 07, 2021 2:02 pm

Ok so now I´m back a the start again the Power led is now flashing fastly again but I´m still getting 2,5Vavg on the 5V rail so something clearly isn´t right

Liengamer
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by Liengamer » Sun Mar 07, 2021 2:08 pm

But at least now the CPU isnt in a permanent reset loop and now actually gets to execute and "send" some code to the other parts. Now I will do the thermal troubleshooting step agiain.

lidnariq
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by lidnariq » Sun Mar 07, 2021 2:15 pm

Liengamer wrote:
Sun Mar 07, 2021 1:59 pm
On my PAL board they are both at the same place.
??? The '139 is right next to the CPU, near one side of the expansion port.
The two '368s are near the other side of the expansion port and closer to the PPU.
Liengamer wrote:
Sun Mar 07, 2021 2:02 pm
Ok so now I´m back a the start again the Power led is now flashing fastly again but I´m still getting 2,5Vavg on the 5V rail so something clearly isn´t right
Is this with the bench supply still? There's no point in testing with the wall wart until you've got it working with the bench supply.

Also, how are you measuring that voltage? Voltmeter or 'scope?

The power LED is just the 74HCU04 inverting the {/RESET signal to the CPU and PPU} and driving an LED with that. If you're seeing it flashing, you need to check either +5V or the /RESET signal.

Liengamer
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by Liengamer » Sun Mar 07, 2021 2:24 pm

lidnariq wrote:
Sun Mar 07, 2021 2:15 pm
Liengamer wrote:
Sun Mar 07, 2021 1:59 pm
On my PAL board they are both at the same place.
??? The '139 is right next to the CPU, near one side of the expansion port.
The two '368s are near the other side of the expansion port and closer to the PPU.
Liengamer wrote:
Sun Mar 07, 2021 2:02 pm
Ok so now I´m back a the start again the Power led is now flashing fastly again but I´m still getting 2,5Vavg on the 5V rail so something clearly isn´t right
Is this with the bench supply still? There's no point in testing with the wall wart until you've got it working with the bench supply.

Also, how are you measuring that voltage? Voltmeter or 'scope?

The power LED is just the 74HCU04 inverting the {/RESET signal to the CPU and PPU} and driving an LED with that. If you're seeing it flashing, you need to check either +5V or the /RESET signal.
I´m measuring the same amount of voltage on either one of them. And yes I am measuring with my scope but my voltmeter showes the same voltage. I will now go back to using my bench supply.

Liengamer
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by Liengamer » Sun Mar 07, 2021 2:36 pm

So now I´ve testest it with my bench psu and it behaves exactly the same...

lidnariq
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by lidnariq » Sun Mar 07, 2021 2:41 pm

At this point, I don't really have anything more to say. You need to figure out what's dragging the voltage down, and you need /RESET to go high (and the LED to stay lit). If you're seeing flickering on the LED, you need to figure out whether that's because of the +5V supply or the /RESET line and then figure out how to fix that part.

Also, the '139 and '368 aren't next to each other and you didn't address that.

Liengamer
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by Liengamer » Sun Mar 07, 2021 2:46 pm

lidnariq wrote:
Sun Mar 07, 2021 2:41 pm
At this point, I don't really have anything more to say. You need to figure out what's dragging the voltage down, and you need /RESET to go high (and the LED to stay lit). If you're seeing flickering on the LED, you need to figure out whether that's because of the +5V supply or the /RESET line and then figure out how to fix that part.

Also, the '139 and '368 aren't next to each other and you didn't address that.
Yeah thats probably a good plan.

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Ben Boldt
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by Ben Boldt » Sun Mar 07, 2021 6:28 pm

Liengamer wrote:
Sun Mar 07, 2021 12:43 pm
Then I cranked up the current up to 750mA wich it immediately drew, but the strange thing is none of the chips are getting noticably hot or anything like this
If it takes 750mA to get to the voltage up to 5V, and normally an NES takes 200mA, (.750-.200)*5 = 2.75W extra somewhere. That is a lot -- something must be getting hot and you haven't found it. It could be a capacitor, a circuit board trace, 7805 regulator, something inside the RF box. Leave it run like that for a minute or two and feel around everywhere, you should be able to find it. Touch everything with it running (there is no danger or high voltage). If you turn it off it might cool down fast and not find it.

Liengamer
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by Liengamer » Fri Mar 19, 2021 7:34 am

I´ve finally found one of the problems wich was a broken psu. Currently im just using my new bench psu ( the old one I originally tested it with was faulty and reported wrong values) but now I´ve stumbled onto another problem wich is I´m getting garbled video and sometimes the power led doesn´t even light up but all of the chips are now getting perfect 5 Volts and the whole system isnt drawing more then 410mA

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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by lidnariq » Fri Mar 19, 2021 10:42 am

Power LED is driven by 74HCU04 inverter U9.

Inverter converts /RESET signal into +RESET which drives the low side of the LED.

Since you've added the "two wire" CIC disable, that means that another inverter is now converting +RESETBUTTON into /RESET. It's relying on the CIC's built-in pull-downs on +RESETBUTTON, and the button on the front of the machine pulls that signal high. If you have an oscilloscope, measure what's happening on all the relevant pins (74HCU04 pins 1,2,8,9)

Liengamer
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Re: Nes Power Led flashes realy fast+getting only 2,3Vavg on 5V rail

Post by Liengamer » Fri Mar 19, 2021 2:02 pm

lidnariq wrote:
Fri Mar 19, 2021 10:42 am
Power LED is driven by 74HCU04 inverter U9.

Inverter converts /RESET signal into +RESET which drives the low side of the LED.

Since you've added the "two wire" CIC disable, that means that another inverter is now converting +RESETBUTTON into /RESET. It's relying on the CIC's built-in pull-downs on +RESETBUTTON, and the button on the front of the machine pulls that signal high. If you have an oscilloscope, measure what's happening on all the relevant pins (74HCU04 pins 1,2,8,9)
Ok so I´ve measure them all with my scope. First thing that is kinda suspect to me is the fact that on all of the from low to high "inverted" pins I´m only getting 3.9V and not 5V like on Vcc on the inverter. The second weird thing is the fact that im getting no voltage what so ever on inverter 5 (pins 10/11) is that normal or is something broken there?

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