Nes not working CPU or PPU maybe?

Nes not working CPU or PPU maybe?
by on (#103817)
Hello everyone,

I have a Nes with the typical grey screen.

New 72pin connector tested all pins they are making contact checked with ohm meter.
Games are working in other units and clean.

Scrubbed the board down and cleaned, both NES and games

Voltage reg is 12v in 5v out.

CPU and PPU both have 5.01v into them.

Lockout chip is disabled both floating and grounded produces same result.

Wondering if there is a way of checking if there is a short in the CPU or PPU i am by no means new to electronics but i am just starting to get into the retro aspects and i am ADDICTED!!!

I understand this is possible a bin or part out job but i am just seeking advice from people that have been doing this for awhile as to whats a common part failure if any?


Thanks all !!
Re: Nes not working CPU or PPU maybe?
by on (#103820)
Do you have a powerpak or some ability to run code on the NES? At this point, my testing pattern would be something like
* Make sure 2A03 M2 and A0 are changing
* Run test rom that plays music without using or relying on PPU
* See if games spin forever waiting for PPU to initialize
* See if 2C03 AD0 is changing
Re: Nes not working CPU or PPU maybe?
by on (#103825)
hey no i dont have a powerpak but i could always program an eprom and put it on a game baord can you point m in the right direction for the code?

thanks :)
Re: Nes not working CPU or PPU maybe?
by on (#103861)
This guy claimed that cutting the 4th pin of CIC doesn't work on some revisions of CIC: viewtopic.php?f=9&t=9279

Just one more thing to check.
Re: Nes not working CPU or PPU maybe?
by on (#103908)
thefox wrote:
This guy claimed that cutting the 4th pin of CIC doesn't work on some revisions of CIC: viewtopic.php?f=9&t=9279

Just one more thing to check.


Ah thanks,

I shall give this a go, and post my findings!
Re: Nes not working CPU or PPU maybe?
by on (#103988)
Okay so i gave it ago it appears to have made no change.

We can rule out the lockout chip now was really hoping for a good result :(
Re: Nes not working CPU or PPU maybe?
by on (#103997)
Lacking any luck figuring out how to make FamiTracker export a ROM that uses the NES's Frame Interrupt instead of vblank NMI, here's something else:

It plays an 11-second loop of audio over and over using the DPCM channel.

Just the same, do make sure M2 and A0 are doing anything before you spend energy on burning a ROM of it.
Re: Nes not working CPU or PPU maybe?
by on (#104001)
lidnariq wrote:
Lacking any luck figuring out how to make FamiTracker export a ROM that uses the NES's Frame Interrupt instead of vblank NMI, here's something else:

It plays an 11-second loop of audio over and over using the DPCM channel.

Just the same, do make sure M2 and A0 are doing anything before you spend energy on burning a ROM of it.


Thanks heaps how do i confirm M2 and A0 are functioning ?
Re: Nes not working CPU or PPU maybe?
by on (#104002)
Do you have any of: a multimeter, logic tester, or a couple of LEDs and a resistor? We just want to make sure that the M2 and A0 pins go to both ground and Vcc at 1-2MHz.

With the multimeter, check for 5Vpp, which depending on the multimeter might appear as as low as 1.8VAC. The logic tester will light up both "logic 0" and "logic 1". The schematic for the LEDs depends on the color (well, forward voltage). For blues and whites:
Code:
Vcc-|>|-+-|>|-Gnd
        |
        +-10k--tester
For reds and yellows, replace each LED with two in series (for a total of 4). Verify that only half of the LEDs light when you touch the tester to Vcc, Ground, and then make sure both appear to light when you touch M2 (and maybe A0)
Re: Nes not working CPU or PPU maybe?
by on (#104168)
Awesome sorry for the late reply.

I will give this a shot tonight or tomorrow.

I have a multimeter so ill just confirm the voltages on those pins.

"We just want to make sure that the M2 and A0 pins go to both ground and Vcc at 1-2MHz."

how am i confirming the 1-2Mhz range?
I am assuming you mean M2 and A0 are connected to ground while powered off?
And while on M2 will = X and A0 will = X

Or is timing play a factor in this?

Forgive me for my ignorance when it comes to CPU's this is a big stretch from TV repair :)
But loving every minute of it :)

Im just going to locate a drawing of the CPU and PPU to confirm address lines
Re: Nes not working CPU or PPU maybe?
by on (#104169)
Some multimeters has frequecy counter. Do you have oscilloscope?
Re: Nes not working CPU or PPU maybe?
by on (#104170)
80sFREAK wrote:
Some multimeters has frequecy counter. Do you have oscilloscope?


Yes i do but its currently dead and have a new one coming but wont be here in time for the weekend.


Well would you look at that i never noticed that, always opver looked the HZ button.

The one i have in my hand at home supports
Frequency: 4kHz,40kHz,400kHz,4000kHz,10MHz(±1.5%)

The ones at work are alot better this is just a cheapish one about $40 i use it to get a temp on my keg... lol you gota have ya beer cold!

Would this be suitable or should i go for a drive
Re: Nes not working CPU or PPU maybe?
by on (#104175)
Yeah, that'll work fine.
Re: Nes not working CPU or PPU maybe?
by on (#104181)
Take the 72pin connector off of the NES. Thoroughly cover the pins on the NES motherboard with isopropyl alcohol, and them put the 72pin connector back on it firmly. Now do the same covering with alcohol of an NES cartridge, and insert and remove it a few times from the connector.

If you are getting the grey screen and it's not reset-flashing I am fairly sure the cut lockout pin will not be an issue.
Re: Nes not working CPU or PPU maybe?
by on (#104216)
lidnariq wrote:
Yeah, that'll work fine.

Awesome ill do that tonight and post my findings. just power it up and test the HZ rating on those address lines?



mikejmoffitt wrote:
Take the 72pin connector off of the NES. Thoroughly cover the pins on the NES motherboard with isopropyl alcohol, and them put the 72pin connector back on it firmly. Now do the same covering with alcohol of an NES cartridge, and insert and remove it a few times from the connector.

If you are getting the grey screen and it's not reset-flashing I am fairly sure the cut lockout pin will not be an issue.


Thanks Mike this has already been done i have checked every connection with a Multimeter 100% contact on 72pin connector then tested the board then the game then all 3 linked together appears that the issue is happening before the 72 pin connector
Re: Nes not working CPU or PPU maybe?
by on (#104218)
Just because you got a beep doesn't mean it's not the connector/PCB. If one bit is wrong, you won't get a boot at all. This is such a common problem and is so rarely anything else, I'd bet it's the connector.
Re: Nes not working CPU or PPU maybe?
by on (#104221)
3gengames wrote:
Just because you got a beep doesn't mean it's not the connector/PCB. If one bit is wrong, you won't get a boot at all. This is such a common problem and is so rarely anything else, I'd bet it's the connector.


i have 30 connectors, whats the chances of them all being wrong and working on other Nintendos ?
Re: Nes not working CPU or PPU maybe?
by on (#104225)
Epicfatigue wrote:
Awesome ill do that tonight and post my findings. just power it up and test the HZ rating on those address lines?
Yeah. Measuring VAC might be a good idea too.
Re: Nes not working CPU or PPU maybe?
by on (#104427)
Epicfatigue wrote:
3gengames wrote:
Just because you got a beep doesn't mean it's not the connector/PCB. If one bit is wrong, you won't get a boot at all. This is such a common problem and is so rarely anything else, I'd bet it's the connector.


i have 30 connectors, whats the chances of them all being wrong and working on other Nintendos ?

Have you tried cleaning the edge connector on the mainboard where the ZIF socket plugs in?
Re: Nes not working CPU or PPU maybe?
by on (#104463)
socram8888 wrote:
Epicfatigue wrote:
3gengames wrote:
Just because you got a beep doesn't mean it's not the connector/PCB. If one bit is wrong, you won't get a boot at all. This is such a common problem and is so rarely anything else, I'd bet it's the connector.


i have 30 connectors, whats the chances of them all being wrong and working on other Nintendos ?

Have you tried cleaning the edge connector on the mainboard where the ZIF socket plugs in?


Yeah gave it the clean of its life.

Sorry guys i have not had the time to do these tests i am about to be on holidays so i can actually do some work!!!!
Re: Nes not working CPU or PPU maybe?
by on (#110206)
Alright guys,

So i am finally back and i am ready to get this thing going.

I Now have the following.

Logic Tester
Oscilloscope

After i test the logic where should i go from there?
Re: Nes not working CPU or PPU maybe?
by on (#110207)
How many signals is your logic analyzer? Put a NROM cart in and read M2, PRG /CE, PRG R/W, A14-10, and data lines. You probably won't be able to do them all at the same time. Just take the readings in several chunks, see if you can find a bad/stuck signal.
Re: Nes not working CPU or PPU maybe?
by on (#110209)
I have a Tektronix 466 100mhz dual channel.
My logic Pen is just a cheap one.

http://www.ebay.com/itm/150872984621?ss ... 1497.l2649

What is a nrom?
Re: Nes not working CPU or PPU maybe?
by on (#110210)
Epicfatigue wrote:
What is a nrom?

http://bootgod.dyndns.org:7777/search.p ... kwtype=pcb

No mapper, best chance to work.
Re: Nes not working CPU or PPU maybe?
by on (#110235)
Ah ill hunt down a nomapper and report back when i get one.

All my games are in storage!