Troubleshoot Buss Resistor packs

[danny davis]

When you have circuits that use those resistor packs that are bussed not isolated resistors

The Resistors inside are bussed, how does a tech troubleshoot them?

If one or two resistors inside the resistor pack are shorted or open , how does a tech know that since the resistors are bussed together? How can i use my DVM to tell which resistor in the resistor pack is shorted or open?

I have seen these resistors packs that are bussed in logic circuits, they have diodes in parallel with each resistor in the resistor pack, what are these diodes used for with a bussed resistor pack?

I have seen them used for logic gates that have multiple inputs

 

[godfreyl]

They have one pin that is common to all the resistors so you can test each one separately.

 

[danny davis]

Yes but what would your DVM meter read if one is open? or shorted?

 

[godfreyl]

The same as it would read with any other resistor that is open or shorted. I don't understand your problem with this. :-?

 

[danny davis]

If one of the resistor is open or short, doesn't it change the values for all of the other resistors since the are bussed?
in circuit testing or out of circuit testing?

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yes the company i work for uses them like that

They use SIL resistor packs with logic gates that have multiple inputs

example: a 8 input NOR gate

They will have an 8 SIL resistor pack with diodes in parallel one for each input of the NOR gate

So each input of the NOR gate has a Diode and Resistor but they are bussed

1.) First question is why they used a bussed SIL resistor pack and Not an Isolated ISL resistor pack

2.) What does the Diode do that is bussed just like the SIL resistor pack in parallel with it?

I don't get why they use Bussed SIL resistor packs VS isolated SIL resistor packs , isolated resistor packs are not bussed together

So have the resistors bussed together does what ? for logic gates, LED's, pull up and pull down?

Why not use isolated resistor packs for pull up and pull down , LED's current resistors, logic gates?

 

[godfreyl]

If one of the resistor is open or short, doesn't it change the values for all of the other resistors since the are bussed?

No

in circuit testing or out of circuit testing?

Out of circuit testing is always better. It doesn't matter what sort of component you are testing.

1.) First question is why they used a bussed SIL resistor pack and Not an Isolated ISL resistor pack

Less solder joints and smaller space.

2.) What does the Diode do that is bussed just like the SIL resistor pack in parallel with it?

Presumably it's to protect the gate.

 

[danny davis]

They Are switching Silicon Diodes placed in parallel with the SIL resistor pack

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They Are switching Silicon Diodes placed in parallel with the SIL resistor pack

 

[danny davis]

The Resistors are pull down or pull up resistors using the SIL pack for pull up and down down resistors, but they place diodes in parallel for each pull up and down down resistor

What does the diode do in parallel with a pull down or pull up resistor? the diode is not zener its silicon switching diode