[time-nuts] HP5370A A22 arming assembly circuit diagram error

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Oct 25 23:07:48 UTC 2006


Dr Bruce Griffiths wrote:
> Correction to previous post. (typed U7 instead of U6 VVC connected too 
> ground OK for U7 as inputs are ECL levels. )
>
> The positive supply connection to A22:U7 (LM339 quad comparator) is 
> shown as ground in the circuit diagram.
> This is surely incorrect as the inputs of U6B and U6C are connected to 
> TTL(+5V VCC) signals.
>
> Surely this is not the designers intention
> The positive supply of A22:U6 should be +5V.
>
> Is there a manual change correcting this schematic error that I have 
> missed?
>
> If A22:U6 positive supply is indeed ground, the circuit may still work 
> but its reliability will be compromised by the relatively large currents 
> flowing into A22:U6C&D input substrate diodes.
>
> Bruce
>
>
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>   
Scratch the comment on substrate diode curent.
Although the comparator will not be damaged (max permissable input is 
36V above the negative supply) the inputs will be way outside the input 
common mode range and it will no longer function as a differential 
comparator.

Bruce




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