[ICOM] IC-751A errata in Service manual & more

[Jim W7RY]

Yes.
The service manual is wrong when it comes to the VCO alignments.  Turn the 
dial until you hear the filter relays switch. then stop.  When the relays 
do switch, that is where you measure the VCO voltage. I believe the 
resistor is the correct place.

There are four VCO ranges. Tune the VFO dial with the TS switch engaged (or 
in the AM mode) to speed up the dial. You can watch the VCO voltage change 
as you turn the dial. When the voltage jumps up (also where the filter 
relays switch) you will be in the next VCO range. As I remember, the 
voltage is highest at the highest frequency of the VCO range. Adjust to the 
specified voltage when the VCO is on the highest (shown on the VFO) frequency.

For the RTTY shift, there is a procedure for adjusting the RTTY shifts. The 
procedure is in the service manual.  I simply use the monitor function and 
an external audio generator and adjust for zero beat. I just went  through 
the alignment on my 751A and the service manual was accurate for the RTTY 
alignment.

I hope this helps.

73
Jim W7RY


At 07:55 PM 4/24/2005, you wrote:
>Hi Everyone,
>I'm looking for the correct PLL adjustments procedure as I suspect
>the service manual has some errors in this section.
>Specifically - what adjusts the 3 volts at R46 on 8,15, & 22 Mhz? It sure 
>isn't
>L201 as one might think from the manual I believe.
>Also - has anyone dealt with FSK being too narrow shifted? (100 Hz in 
>place of 170).
>Tks in advance, Isaac, 4Z4TL
>4z4tl at iarc.org
>http://www.iarc.org/~4z4tl
>
>
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