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

Discuss technical or other issues relating to programming the Nintendo Entertainment System, Famicom, or compatible systems.

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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 » Wed Mar 03, 2021 3:39 pm

so now I´ve connected my known good bench psu up to the nes´s 5Vin pin and the second I turn the nes on the voltage on the cpu drops to 1.5v. Can anybody explain why that would happen?

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

Post by lidnariq » Wed Mar 03, 2021 3:44 pm

What's the current limit set to?

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

Post by Liengamer » Wed Mar 03, 2021 3:47 pm

400mA slightly higher then what I´ve herad here would be normal

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

Post by lidnariq » Wed Mar 03, 2021 3:54 pm

Are you hitting that current limit?

I mean, something's clearly broken, but it's hard to say what. Thermal debugging (seeing what gets hot when it's given power) is by far the simplest technique, but you'll need to increase the current limit to increase the dissipated power.

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 9:01 am

Ok so now I´ve made a really intresting discovery wich is: Pin 3 on the CPU (reset) is held high for roughly half a second on startup and then returns back to low, also during that time sometimes the power led flashes really fast and sometimes it just stays on but again also for that half a second.
So doesn´t that mean that the CPU is held constantly in a reset state

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 9:14 am

also im geting 5Vpp on the composit output of the signal amplifier

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 9:18 am

also no chips are getting hot or anything wich is really weird even after increasing the current limit by an almost scary amount

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 11:44 am

Liengamer wrote:
Sun Mar 07, 2021 9:01 am
Ok so now I´ve made a really intresting discovery wich is: Pin 3 on the CPU (reset) is held high for roughly half a second on startup and then returns back to low, also during that time sometimes the power led flashes really fast and sometimes it just stays on but again also for that half a second.
So doesn´t that mean that the CPU is held constantly in a reset state
Yes, that's exactly what it means. Your CIC is objecting to something, but it's hard to say what.

You could check the clock frequency of the CIC's 4MHz oscilator, but I think something else is probably wrong first.
Liengamer wrote:
Sun Mar 07, 2021 9:14 am
also im geting 5Vpp on the composit output of the signal amplifier
Yes, that's bad. Check your ground reference. What else is happening on the other pins of Q1?
Liengamer wrote:
Sun Mar 07, 2021 9:18 am
also no chips are getting hot or anything which is really weird even after increasing the current limit by an almost scary amount
How much current? How much resulting voltage? Are you checking things inside the RF modulator too? Where on the PCB are you injecting your +5V?

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 12:43 pm

Firstly the problem with the 5Vpp on the video port was an easy fix caused by a bit of wire shorting it (wich i noticed right after I made this post).
The CIC gets a solid 4mhz square wave from the oscilator. I think its impotant to say that somebody has snipped of pin 4 of the cic in the past.
Now to the 5V problem. I hooked up my bench powersupply directly up to the 5Vin pin on the main pcb ( I´ve removed the power/AV box before) and hooked up the switch to the "enble output" switch on my bench psu and set the current limit at first to 400mA. 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 ( I´ve seen this happen in the past especially with bad ram chips) the only chip that got constantly warmer was the PPU but it didn´t get warmer then 40°C wich I hope is kinda normal.

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 1:06 pm

Ok so now I´ve made a really interesting discovery: pin 5 on the CIC wich is supposed to be NC has the same 4mhz clock signal on it such as pin 6 wich is the clock pin. Is that normal or not?

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 1:09 pm

Also I´ve noticed that the cics restet pins aren´t acturally reseting most of the time only sometimes wich corresponds to the fact that the led is only on sometimes...So my question now is could that mean that the CIC is broken?

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 1:20 pm

Liengamer wrote:
Sun Mar 07, 2021 12:43 pm
The CIC gets a solid 4mhz square wave from the oscilator. I think its impotant to say that somebody has snipped of pin 4 of the cic in the past.
CIC is still responsible for driving the reset signal to the CPU and PPU and the power LED, even if it's disabled. Consider adding two wires to more thoroughly disable it.
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 ( I´ve seen this happen in the past especially with bad ram chips)
You could measure the voltage at various places around the mainboard. Hopefully you might be able to see a lower voltage as you get further away from where you're injecting power and towards where the device consuming the current is.

It's conceivable that the relevant problem is a capacitor instead of an IC...
the only chip that got constantly warmer was the PPU but it didn´t get warmer then 40°C wich I hope is kinda normal.
40C is a fairly typical PPU case temperature. (See thermal pictures here: https://www.game-tech.us/nes2-heat/; forgive the Freedom units)

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 1:27 pm

I will definetly give the "two wire mod" a try . Yes the Voltage indeed gets lower going further away from the source.

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 1:31 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.

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 1:45 pm

connect to "(74HCU04 pin 2/3)" do you mean both pins 2+3 or pin 2 or pin 3

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