I think I have bad CHR RAM.

[bozo55]

I got a decent condition loose Famicom off ebay, and it cleaned up really nicely.  The only problem is I get weird sprite flashing glitchyness...

In Akoumajo Densetsu (legit cart, working in other systems)  the character sprites flicker every couple seconds in a rather constant fashion.  The hearts leave a funny artifact as they fall down the screen and the weapon icon seems to glitch out too.  The background graphics seem fine. 

I was led to believe the cause would be the CHR RAM.  If so, can anyone guide me as to which one to buy and who sells some?

Thanks so much to anyone who can lend me some advice.  I paid a fair bit for the Fami and would hate to see it sit there like a fancy paperweight.

[HVC-Man]

First let's clarify some terminology. The 2KB / 16Kbit SRAM dedicated to the PPU inside the Famicom is the PPU RAM. CHR RAM always refers to cartridges, not the console.

Second, make sure your cartridges and console are very clean before moving on to PPU RAM replacement.

Before you buy SRAM, you need to open your Famicom and determine the package type of the PPU RAM. I've seen two styles, SDIP24 and SOP24 (or through-hole and surface mount 24 pin).

Buyicnow.com sells compatible SRAM here.

http://www.buyicnow.com/it.php?i=636
http://www.buyicnow.com/it.php?i=640

[bozo55]

First let's clarify some terminology. The 2KB / 16Kbit SRAM dedicated to the PPU inside the Famicom is the PPU RAM. CHR RAM always refers to cartridges, not the console.

Second, make sure your cartridges and console are very clean before moving on to PPU RAM replacement.

Before you buy SRAM, you need to open your Famicom and determine the package type of the PPU RAM. I've seen two styles, SDIP24 and SOP24 (or through-hole and surface mount 24 pin).

Buyicnow.com sells compatible SRAM here.

http://www.buyicnow.com/it.php?i=636
http://www.buyicnow.com/it.php?i=640

Thanks so much man, you're a lifesaver!

The only cart I tested with was Akoumajo Densetsu, but it works fine in my AV Fami.  I thoroughly cleaned the cart slot... I sprayed it with MG Electronics "Electrosolve" contact cleaner and used a thin white T-shirt wrapped around a credit card to scrub the pins.  The connector pins are shiny and clean, and make a firm connection.  The cart itself was very thoroughly cleaned as well, the pins have no dirt/oxidization and boots every time on the Fami and AV Fami.

I will reopen the system and examine the soldering on the board to make sure nothing looks in need of reflow.   The board is an HVC-CPU-07 and I believe the PPU RAM was through hole. 

Once again, thanks for taking the time to help me out

[HokusaiXL]

I have that same board, and it's all through hole.  Though that's odd that you're having issues.  Sure it's not just the pins flattened out?

[bozo55]

I have that same board, and it's all through hole.  Though that's odd that you're having issues.  Sure it's not just the pins flattened out?

The pins seem perfect.  At least from the outside.  I'm going to open it up and look for bad solder joints.

I noticed the glitches are worse playing the game on an Everdrive vs. the real cart.  On the real cart the worst problem is a screen tear that runs the whole way down... happens every 10 or so seconds.  Sprite glitching is harder to reproduce on the real cart. 

I tried running a test service cart rom with the everdrive and it passed the tests but the screen tearing was still there. 

P.S. It's not the TV.  My NES does not tear on this T
The pins seem perfect.  At least from the outside.  I'm going to open it up and look for bad solder joints.

I noticed the glitches are worse playing the game on an Everdrive vs. the real cart.  On the real cart the worst problem is a screen tear that runs the whole way down... happens every 10 or so seconds.  Sprite glitching is harder to reproduce on the real cart. 

I tried running a test service cart rom with the everdrive and it passed the tests but the screen tearing was still there. 

P.S. It's not the TV.  My NES does not tear on this TV with the same RF adapter.

My NES and Famicom both screen tear over RF on 2 different CRTs with different carts, power supplies, RF adapters... The NES does not tear with composite.  Looks like A/V modding the Fami will be a necessity.

The sprite flickering seems to happen only with certain games, and the sprite flickering seems to get worse once the system has been running for a while.  Once the system warms up, it flickers the same on CVIII/Akumajo Densetsu on real carts and Everdrives.
Post Merge: September 17, 2015, 06:26:39 pm
After more testing I discovered that disconnecting the P2 controller seems to eliminate the problem.  Disconnecting it will not fix it until I reboot though.  Is that really possible or was all that completely coincidental?

Update:  The flickering happens without any controllers connected, but not all the time. I'm going to try to re-tension the cartridge port.  If that doesn't work I'll try the Ram chips.  If that doesn't work I will give up and find a donor board as the case on this Famicom is excellent.

Update 2:  Retensioned and reflowed cart slot.  Reflowed another couple spots on the board that lacked solder or looked cold.  Didn't solve the problem entirely.  Cleaned the cart slot and my carts one more time with isopropyl alcohol.  Things seem to be working fine, for now...  Glad it seems to be an easy fix.  I doubt it's the RAM since the problem was intermittent.