Re: VAXstation 3100/m76 stray interrupt

[Aaron Jackson <aaron%aaronsplace.co.uk@localhost>]

I am guessing that the 74LS243 is just soldered on the board somewhere?
Perhaps if I replace it my machine will become much more stable?

Aaron


Felix Deichmann writes:

> Am 16.08.2016 um 23:00 schrieb Antonio Carlini:
>> This was when I was in DEC so with a bit of hunting I found the
>> description of the problem. IIRC there was an issue with the 74LS243 bus
>> transceivers.
>
> Interesting. I evaluated parts suitable as Q-Bus drivers/receivers 
> recently and noticed that for example a TI SN74S38 will quickly reach 
> extreme values for high-Z leakage current (I_OH in the datasheet) when 
> warmed with a heat gun (and become out-of-spec for Q-Bus of course)... 
> Values are even quite different for ICs of the same batch.
>
> It could be a similar issue with specific batches of 74LS243, i. e. they 
> will impose an unconsidered load (when the machine was designed) for 
> other participants on the (memory) bus when it gets warm.
> Especially leakage current can be extremely dependent on temperature.
>
> Felix