[time-nuts] Re Shera Controller - U7

[EWKehren at aol.com]

I also located a couple of units in my inventory. But U 7 is not critical,  
it was at the time an elegant way to perform two functions. Now that it is 
not  readily available the fix is to use a 6 MHz resonator between pin 9 and 
10 on  the PIC. 6 MHz is not critical for the over all function except it 
sets the  RS232 baud rate. 24 MHz is not critical either except it has to be 
a frequency  the HC4520 can handle. Changing Frequency will change range and 
 resolution. 
Brooks has a later version of the PIC available (V402) but since he has not 
 responded to my emails I do not know how it exactly differs from V133. I 
use 133  and have excellent results tailored to my needs by modifying 
circuits around it  like automatic filter sequencing in case of power failure, 
using 100 MHz counter  and dividing interrupts by 4 to increase sample size.
Since I have extra unmodified A&A boards with the 16C73 for the fun of  it 
we ran a unit tying it directly to a Morion MV89 and got 3 E-12! No 
matching.  Next we will do the same with a FEI 5680 controlling the C field and it  
will require some matching so I expect 2 E-13. Again nothing changed on the  
A&A board.
I have extra populated A&A boards and AD 1861's,  if any one is  interested 
contact me off list
Bert Kehren
 
 
 
In a message dated 5/14/2012 9:57:25 A.M. Eastern Daylight Time,  
vk6bmt at iinet.net.au writes:

Hi Kevin  - I have a spare I can send you.   I responded direct to your 
email  
but no reply.

Merv  VK6BMT  


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