NES PPU problem

Ok guys so in the past i had this post about my NES that has a PPU problem, back then no one was able to help me, but i have faith that someone may know what is the problem and if it is fixable, so im going to do a sorta repost to see if there is anyone that can give me some new info.

Hope anyone can help me

 

I believe I suggested this before but if you're absolutely positive the traces are OK between the PPU and cart, PPU and '373, '373 and cart, then all you can possibly do is replace the '373 and/or PPU because one of them has a defective output buffer.

 

does the '373 are buy-able? or i can only find those on NES's/other electronic devices?

 

It's a standard part, you can replace it with a '373 of any 5V logic family made by any brand. For the best compatibility you should replace it with a 74HCT373 (very common), 74ACT373 or 74AHCT373. Before you desolder it and solder in a new one you can piggyback the new chip on top of the old one then proceed if it's working. If it's not the '373 you'll need a new PPU. You can also verify which signal is damaged with a logic probe, the signal will be stuck in a single state instead of pulsing.

 

i have kind of a new info, is it possible that the problem insted of beeing in 373 beeing on the Hex inverter the 74HCU04N because i was looking at the datasheet and on on the 3rd and 4rd pin (2A-2Y) there was no condutivity and i noticed that because the 4rd pin was kinda deformed so i decided to test out.

 

I'm confused. You're testing conductivity between pins 2A and 2Y? There shouldn't be conductivity, inside a chip isn't a wire, there's a logical inverter made from transistors. The only place where the PPU uses an inverter is on the PPU A13 line for character address decoding. I don't think that's the problem because in that case no graphics would be correct.

 

yeah you are right, taking a year off colage isnt good i barly remember my computer systems introduction class, anyway i will order a few 373's and hopefully that will be the problem.

Damit there isnt a single close hardware store to me, il have to order from ebay,

http://www.ebay.com/itm/NEW-5-X-74H...ltDomain_0&hash=item4aada29390#ht_1884wt_1163

I will post results when i have some.

 

I cant belive what just happened to me, so for some odd reason i went to visit my old msn account, that i havent been there since like 3 or 4 years ago, so when i login who do i see the guy who sold me the NES, so i decided to talk to him, maybe he had some insight on my situation, so i explained him the problem and he never had this problem, in a last change i asked hum about the deformed 2Y pin on the hex inverter, and there i really got pissed, long story short, the guy was trying to disable the lockout chip, and insted of pulling a pin from the lockout chip he puled the pin from the hex inverter, not only that he didnt pull the pin by desoldering the leg, no he actualy riped it from the actual chip, and the seeing how much he fucked up just pressed the leg back inside the chip. I was really sad so i picked up my multimeter and went to test out the voltage so i tested those to pins with positive probe on 2A and negative probe on 2Y and i was getting close to -1.5v that beeing an inverter looks like it working ok but if you could confirm me if everything is ok i would be very thankful.

Sometimes i think the universe is just messing with me DAMMIT.

 

He broke a pin off the wrong chip then stuck it back in? Sounds like you should replace that chip just for good measure.

 

yeah i should but has i said the output voltage is correct but anyway can anyone give me an alternative to the 74HCU04N ?

Also if none of this works i may be getting a new PPU i still dont know for sure, the only way i have to get a ppu is by getting from another NES right?

 

Correct, the PPU is only in NES and Famicom Consoles. Chances are not that likely that a new PPU wasn't previously in a working console already. Though I guess it's possible someone broke the CPU in a console and the PPU is ok.

 

Damm im really Fu**** how am i going to get a PAL ppu its almost impossible to find a PAL NES in the first place (at a decent price i mean) well gess il just wait for the 373 and hope that it is the problem, if not il just sell my NES collection im not paying 60€ for a NES console.

 

You could possibly get one from a PAL Famicom.

 

Just for reference when I said the HCU04 is only used for character tile decoding that was wrong, I forgot that POSITIVE A13 is used for character tiles, NEGATIVE A13 (coming out of the inverter) is used for VRAM decoding.

The problem here is VRAM decoding so the HCU04 can definitely be the problem.
When you measure from 2A to 2Y, that doesn't make any sense since they're non-periodic AC signals that rapidly change over time. There's no way to determine a correct voltage but if the inverter was broken and output couldn't pull low (this wouldn't happen unless the output tried to sink too much current and fried itself), the AC on the input would show as a negative voltage.

Unfortunately it's difficult to find HCU04 chips. While you can drop a normal 74HC04 there instead, the HCU04 might also be used as an audio amplifier (I'm not sure about the NES design, only FC) and the 74HC04 part in most cases will not be suitable. You'll have to track another one down.

 

It still sounds more likely to me that the PPU is fine. This HCU04 that you said the previous owner messed with and broke an IC leg on sounds like it is the problem. I'd think if your PPU was the problem it probably wouldn't function at all.

 

ok so il also order an HCU04 i found this one

http://www.ebay.com/itm/1-PCS-74HCU...ultDomain_0&hash=item4ab1d46154#ht_2472wt_982

is this one ok?

if anyone knows a place that sell these cheap and with decent shipping please tell that link is the only one i could find that had a decent price but 30 days to arrive is a little overkill.

 

It has to be HCU04, because the NES actually use it as a buffer for audio.:thumbsup:

 

ok then il have to make a top up to my paypal account then i will order that HCU04 meanwhile again if anyone know other websites that sell these at a good price please tell me.

 

Don't buy that one, it's surface mount...

 

is there a problem beeing surface mount? il just piggyback it to the original chip, and dissable the original