What kind of IC is this

CRC technobug at comcast.net
Tue Dec 30 21:49:10 CST 2008


On 30 Dec 2008 13:59:20 -0800, Chuck Guzis wrote:

> Do fusible-link PROMs go bad?  At least do they go bad any more often
> than some of the LSI on that board? [...]

Indeed they do. Six months ago I was given a DOA Rockland-Wavetek  
5820B spectrum analyzer that had a disconnected power supply lead.  
Fixing that brought up the unit sans random pixels on the displayed  
alpha-numerics. I finally traced the problem to a 8S115 PROM that was  
feeding a 8X300 (two other CPUs in the beast - Z80s). After decoding  
the ROM I began editing the data to restore the missing 1-bits and  
reprogrammed the very same chip. After the first half of the alphabet,  
the remainder of the letters magically appeared. Once the bit "heals"  
it is possible to reblow it. How long this fix is going to last is  
anyones guess - probably another 20 years...

	CRC



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