Simtek 25c48

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I have an nvram module in my Defender, and it appears the Simtek 25c48 has gone bad. I haven't been able to find a replacement for it, and in searching I discovered that it seems to be a pretty rare chip. Does anyone know where I can buy one?
 
I have an nvram module in my Defender, and it appears the Simtek 25c48 has gone bad. I haven't been able to find a replacement for it, and in searching I discovered that it seems to be a pretty rare chip. Does anyone know where I can buy one?

Are you sure the chip's gone bad ?

As an alternative you should be able to use a M48Z02 or DS1220 as a replacement. The pinout and and function is basically the same, just they use a battery to keep the SRAM contents instead of flash like the Simtek.

- James
 
Are you sure the chip's gone bad ?

As an alternative you should be able to use a M48Z02 or DS1220 as a replacement. The pinout and and function is basically the same, just they use a battery to keep the SRAM contents instead of flash like the Simtek.

- James

I'm pretty sure the chip went south - the high score table has lots of question marks and some huge numbers not in numerical order, some of the game settings cannot be set, high scores can't be reset, and the cmos test fails. Thanks very much for the cross-reference, I'm glad there's something else out there that'll work. (they're not as hard to find as the Simtek, are they?) The reason I went to the Simtek was because the switching power supply caused occasional corruption in the original 5101 cmos, and the design of the Simtek was supposed to prevent the problem. Any idea how well the other chips would work in a Defender with a switcher?
 
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The reason I went to the Simtek was because the switching power supply caused occasional corruption in the original 5101 cmos, and the design of the Simtek was supposed to prevent the problem. Any idea how well the other chips would work in a Defender with a switcher?

The M48Z02 and DS1220 contain a 'power good' NVRAM controller in the package. So it won't enable the ability to write to the chip until the 5v is powered and stable.

I've used them on Defender, Joust and Robotron without issue and only have switching supplies.

- James
 
Thinking about it if you just want to test if the simtek is bad, just put in a 6116 or 2016 SRAM in place of the simtek, power the machine up reset the factory settings and then run the CMOS test in the self test.

If the CMOS self test passes then it looks like the Simtek. If it fails then it could be a couple of other things.

The 2016/6116 SRAM won't save scores after the poweroff but will allow you to test.

- James
 
Great idea. I'm impressed by how much you know about the interchangeability of all these chips - is there anywhere (other than in your head) that lists cross references for common arcade chips?


Thinking about it if you just want to test if the simtek is bad, just put in a 6116 or 2016 SRAM in place of the simtek, power the machine up reset the factory settings and then run the CMOS test in the self test.
- James
 
With any luck, I should have a new chip in a couple of days. Thanks for the help, this board is a great place. :)
 
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