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

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Oct 25 20:10:22 EDT 2006


John Miles wrote:
> In the 5370B manual (2940A prefix), it looks like they are running U7 from
> +5 on pin 3 and -5.2 on pin 12.  Probably a drafting error in the -A manual.
>
> -- john, KE5FX
>
>
>   
>> 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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>   
The 5370A A22 circuit diagram appears to be riddled with errors.
U9 is shown as both as an MC10107 (triple exclusive OR/NOR gate) and as 
a Line receiver/comparator.
The signals on A22 J1 coming from A16 are all 5V TTL (74LS175 outputs) 
with 500 ohm pullups to 5V.
On A22 some of these inputs are shown connected in series with 82.5 ohm 
and pulled down to -5.2V with 1000 ohms.
The junction of the 1000 ohm pulldowns and the 82.5 ohm resistors is 
then (in some cases) shown connected to ECL gate inputs or even emitter 
dotted to the output of an ECL gate (U1A). I've successfully used 
resistive divider networks to interface between 5V TTL and ECL, however 
the values shown in the schematic surely cannot be correct and will 
produce incorrect (and possibly damaging) output levels for the ECL gates.

Bruce



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