VBB and standard 8375 Agnus, will having a 100nf Cap harm the chip ?

[Mr.Bits45]

Hello,

I hear its important to NOT use a 100nf capacitor on pin 40 of a standard 8375 agnus or it will damage the chip.
I can't see how putting the 14mhz signal through a 100nf cap to ground would harm it.
The cap has a very, very high resistance and pin 40 is only a clock out, it would almost be the same as having it connected to nothing.
Has anyone lost an agnus this way ?
I have been running my Raemixx500 with a standard agnus with the cap on pin 40 for about 3 years now, does get hot, crash or play up at all.
I look forward to reading some comments.

Thanks

 

[levo-ace]

The clock is an AC signal and the cap would shunt some of that to ground and reduce the amplitude of the signal going to the processor to the point that it would not be enough to run the chip .

 

[Mr.Bits45]

On the 390544-01, pin 40 is a 14MHz clock and typically connected to nothing.
It does not go to the CPU.

 

[Mr.Bits45]

Can we please talk about pin 40 - 14mhz, not used and if it goes through a 100nf capacitor to ground.
How can this damage the Agnus ?
I am not talking about the clock that goes to the CPU, that's 7.14Mhz.
With all the people out there I thought there wound be more discussion.

 

[Benutzer]

At 14mHz, a 100nF capacitor depending on type might present as a significant load to ground at these high frequencies.
The job of a capacitor is to smooth out or let AC pass through (in your case to ground).
I am not sure what the output of the Agnus can handle long term.

Olli.

 

[levo-ace]

Using an on-line calculator , 14Mhz on a 100nf capacitor gives a resistance value of 0.11R . Almost a DEAD SHORT and definitely not good for whatever is driving it !

While not necessarily a 'bad' thing in itself ( there could be a built-in current limitation on the circuit or other failsafe ) , the extra heat generated in driving a short to ground could be .

https://www.allaboutcircuits.com/tools/capacitor-impedance-calculator/

Try it yourself , 14Mhz and 100nf .