Re: {Collins} 651S-1 issue



Bob, Take a look at the optical encoder. I’ve had mechanical issues relating to rotation direction and count. It’s a little mechanical marvel that predates off the shelf encoders and this may be your issue , the rest is up to you.

73, Mike


Sent from Mail for Windows 10

From: Robert Nickels via Collins
Sent: Saturday, October 28, 2017 7:04 PM
To: Collins
Subject: {Collins} 651S-1 issue

My 651S-1 (S/N 2308, red LED display) has an odd tuning problem and I
thought I'd see if this might by chance sound familiar to anyone.    The
10 Mhz, 1Mhz, 100Khz, and 10Khz tuning steps work as expected, but when
you tune in 100Hz steps using the main tuning dial, there is an odd jump
in frequency.   For example:

Display       Actual
8000.0     8000.0
8000.1     8000.1
8000.2     8000.2
8000.3     8000.3
8000.4     8040.0
8000.5     8040.1
8000.6     8040.2
8000.7     8040.3
8000.8     8080.0
8000.9     8080.1

As you continue to tune, the same sequence repeats - I've used 8 Mhz as
an example but the same jumps in frequency occur through the tuning
range.  Sensitivity and everything else seems normal, in fact you can 
tune to any desired frequency if you do the math to correct for these
weird offsets.    There is clearly a pattern here but I haven't yet been
able to correlate what is going on to a particular circuit, other than
it seems that bits are being added.

Since the display shows the correct frequency steps up and down as the
encoder changes, that indicates that the correct BCD data is being
presented to the synthesizer and suggests a problem somewhere in the
A10, A11, A12, or A13 boards.    I've done basic things like re-seating
the boards and checking for damaged components but everything looks
fine.   Since these boards are full of flat-pack ICs made by Motorola,
Raytheon, and Sylvania the chances of doing board-level repair are
somewhat daunting.

So I wonder if there might be any sources for spare boards either to
borrow for substitution or to purchase?   Or, if I'm able to identify a
particular IC, is there any hope of obtaining something like a Sylvania
SM153 frequency divider IC?

Thanks and 73,
Bob W9RAN


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