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[TenTec] T-Kit Model 1220 2M XCVR PLL fix

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Subject: [TenTec] T-Kit Model 1220 2M XCVR PLL fix
From: jfarr@hal-pc.org (John Farrington)
Date: Sat, 13 Sep 1997 13:03:46
Some kit builders may have intermittent problems with the VCO and
phase-locked loop not locking when the power is turned on: the
indications will be either (1) the displayed frequency at power-on
will have 1 or 2 digits that do not correspond to the last frequency
used before power-off; (2) at power-on the frequency display will
remain totally dark for a period of time ranging from a few seconds
to indefinite, during which the rcvr audio will generate white noise.
In the second case, usually the frequency display will come alive
and the PLL will lock if the power switch is flipped off and on a
few times.

It was first thought the PLL crystal Y1 (4.000 mHz) was faulty
because the PLL would immediately lock and the frequency display
would come on if it was physically tapped, but the intermittent
problem continued after the crystal was replaced.

The problem was traced to the PLL frequency synthesizer IC at U5
(a MC145170P):
a search of Motorola's Web pages and a phone call to their
Semiconductor Division revealed that the original MC145170P had a
tendency to lock up after power interruptions, so it had been
replaced by the MC145170P1.
After replacing U5 with the new version, the PLL functioned correctly.
This problem may not occur with all 1220 T-Kits because of component

  John Farrington, KE5ZB    <  jfarr@hal-pc.org  >
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Here are brief extracts from Motorola's Web pages:
       * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

(1) http://www.mot.com/SPS/MCTG/MDAD/pll_overview.html#mc145170


The new MC145170-1 is pin-for-pin compatible with the MC145170.
The MC145170-1 is recommended for new designs.

 (Note: production number is MC145170P1, not ...70-1)
                 (remainder deleted)

(2) http://www.mot.com/SPS/MCTG/MDAD/pll_bulletin.html

                             PLL Overview

                   MC145170-1 Engineering Bulletin
The MC145170-1 PLL frequency synthesizer has an on-chip POR (power-on 
reset) circuit. This POR circuit performs two functions: 
(a) initialization of the device to divide the OSCin frequency by 
    eight with this divided signal appearing at the REFout pin and 
(b) resetting an imbedded test register to user mode. Whenever the 
    device is not in user mode, it appears to the user to "lock up".
The POR circuit has been found to malfunction during power cycling 
when power is interrupted for short intervals. The intolerance to the 
duration of the power interruption is dependent on supply ramp-up and 
ambient temperature.

         (tabular data deleted for brevity)

If power cycling for short intervals is a requirement in an application,
the immediate corrective action for the above limitation is to use the
reset sequence shown in Figure 13 of the data sheet.
The MC145170-1 is undergoing a design enhancement to the POR circuit. 
This enhancement will greatly improve (reduce) the power interrupt 
time even with long supply ramp up times at cold temperatures. 

           (remainder deleted)

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last update: 07Apr1997

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