Dumping an NEC D23C4000 Chip

It's possible to remove and refit an unsocketed chip without sacrificing anything....

 

What is on pin 31? GND or VCC? If it's floating (basically not connected to anything that is driving it) then that could explain the randomness. Changing the voltage could just be a fluke (you've changed the reference voltage, so the random floating might just happen to be closer to either 0 / 1 all the time).

 

Thanks Assembler! If you can change the title to "Sega Channel Japan BIOS / Dumping an NEC D23C4000" that would be ace!

Three variants of the US model? I was only aware of two, the Scientific Atlanta and General Instrument and on the Japanese side the NEC NMD-300010.
You're sitting on a gold mine, what I wouldn't give to have a dig though the masses of magic you have over there!
Don't happen to have any of them at arms length and a few moments to pull them apart now do you (Just kidding, I know you're a busy man!)

With a Hakko 808 you can desolder any through hole device! I never knew desoldering could be so easy!

I'll have a check when I get back home, if it is a fluke - it's a damn good one Especially given that I wouldn't have even tried that had I went to work on time... ahhh sleeping in on a Monday morning. Too bad it leads to four days of über-intense work... ahhh distractions

 

I am also interested in that third US model. I have the two common models that you can usually grab on ebay, but I've never seen or even heard of a third.

 

3.6v is incorrect for this chip. It does seem like a fluke that this fixed it, as the issue is likely elsewhere.

But good result is a good result.

 

Reckon it might be because the MaskROMs are dying?
That Guru fellow (from MAME dumping fame) believed that might have been the case.

 

Pin compatible doesn't mean algorithm compatible. I'd imagine its the whole auto ID on A9 that's causing it.

The algorithm a programmer will use to read a chip is slightly different to how a device using the chip would. Which I'd imagine is your issue. Like I said, had all this before.

 

Hahaha, so many variables. Definitely a fluke then?
Either way, we did well everyone!

 

Pin 31 is VCC (5.1V) when connected to a Mega Drive, so there we go! Luck has everything to do with it. I ought to get myself a lottery ticket.

 

x

 

I should be able to dump that.

I assume you only need to read 1, rather than looking to buy a programmer for it?

 

x

 

A lot of programmers do not have maskrom support. Reading them as the equal eprom often doesn't work because of ID on A9, which as the maskrom doesn't support it, you get an error.

Ideally you want to a programmer where you can edit the algorithm for the chip or someone who will add chips you request.

I dont have any cheap suggestions that I know will work for you with maskroms.

 

You know if you were really hardcore about it you could always build your own maskrom read/flasher. I have built my own in the past from a modified EPROM programmer schematic to fit a specific maskrom. Unfortunately it's also possible your chips are dying and that's why it is giving inconsistent dumps.

 

x

 

Glad to hear it! Dumping anything fun over there?

 

x

 

They can be had on ebay for around £30-40 delivered

 

x