Re: HP 9821 - display and tape transport issues #VintageHPComputers

Achim Buerger

The 'die without notice' applies to all TTL chips made by NI in the early 1970s. I had to replace dozens of ICs in my various 98xx calculators and peripherals and in 99% they where made by National Instruments. If I get a defective 98xx board I first check all NI chips by means of a logic comparator. NI seemed to have problems with long term stability of their TTL ICs in the 1970s. The dying already began in the 1990s and still continues. Some times I thought about exchanging all NI chips prophylactic, but that would cause a lot of work in my ~20 devices. Moreover, some chips are hard to find these days.

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