[REPAIRED] In-stock factory new RAM replacement option

[rogerimp]

[UPDATE!] Finally successful repair, scroll down for the conclusion, and I changed the title to reflect a perhaps useful finding from my journey.

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Hey all! Long story short I brought a $30 junk naomi back from the dead, had a bunch of fun for a bit, but sadly it's a bit dead again now. I'll outline what I did:

• It needed a BIOS eprom and a new backup battery, got a multibios.
• Booted up to a bad IC18
  • A clue for later: some games ran okay but when a game was problematic, NAOMI would run at ~2fps with a visible flicker between frames
• Replaced IC18
• Things working great for a while! Used with a NetDIMM and wipi netbooter, a computer PSU with molex adapter, and an IONA jvs board.

Unfortunately, went back to bad, very similar to before, during the boot & chime and in test mode the screen refreshes about ~2fps with some graphical glitches. RAM self test goes extremely slow and hangs eventually.

So I tried:

• Measured voltages on the test points on the top of the board, all voltages are +0.1-0.2 above rated so looks good
• Replaced all SMD aluminum caps today... was really hoping that would do it
• Re-thermal pasted the CPU
• Tightened down big regulator heatsinks

So interestingly, the graphical glitches are gone but I'm still getting the flickering thing, and the RAM self test halts after IC29 good and IC35 good, before getting to IC09.

ONCE, the RAM self test did finish and reported good on all ICs, but I'm not sure I can fully believe that. It's quite possible that one of them is failing and that time caught it when it was intermittently working.

I have one more UPD4516161AG5 on hand. Though at this point replacing one of the RAM modules would be a guess.

One theory would be that IC09 is failing if that's where the self test always halts. I don't have a replacement for that one but I'm going to have a look for one, for lack of a better idea.

I'd love to hear any ideas, *especially* if anyone has seen and diagnosed this kind of a fail state with really slow refresh rate and flickering. Thanks!

 

[rogerimp]

I recently learned that these ram modules are in pairs, so I replaced IC16 as well (I had previously replaced IC18 .) Still flickering at ~2fps.

I reflowed the solder on all the RAM ICs on the top and bottom sides of the board, no change there either.

 

[rogerimp]

Finally a conclusion. After no luck going piecemeal (and passing RAM tests though it was definitely bad RAM!) I did a clean sweep of all the RAM modules. I replaced all 8 with factory sealed new modules. And, glory behold, it works again!

I have a pretty cool takeaway from this that is maybe worth sharing: I looked around for some currently-available RAM modules and found that Digikey stocks the IS42S16100H (Datasheet, Product page). From everything I read on the datasheet this seemed like it might be compatible so I took a chance on it and, so far, for me, it works flawlessly.

Benefits:

• No hunting around for old PC RAM
• No desoldering old PC RAM modules
• Plentiful stock (6000+ at time of writing)
• Cheap ($1.50) and ships fast

So if you are repairing a NAOMI 1 and are feeling lucky, maybe give these a go! (Would these work on NAOMI 2? I don't know anything about the hardware differences but please comment if you do)

 

[Ace`]

IS42S16100H is a nice option for the graphics ram but has anyone come across a modern replacement for the 64M PC100 ram used by the cpu?