[ICOM] re: IC-275H scan problem

[Gary Fiber]

Icom uses a 145.000 MHz for the adjustment. I don't remember if you would 
use another frequency that voltage would be different. Point is using a 
frequency like the National Weather Service or some other frequency that is 
strong and constantly on the air may work.

The generator provides the center frequency and you adjust the voltage to 
the 3 volt level so it sees 145.00 as center at that time. You are 
adjusting the Quad Coil attached to Pin 8 of the MC-3357P chip so you want 
to be fairly accurate with your signal source. The good news is most 
synthesized transceivers are very accurate these days so far as the signal 
transmitter. You will have to be careful not to modulate the transceiver.
You could possibly use a nearby transmitter as others here have suggested. 
Many times you could end up with a receiver overload issue doing it that 
way.  Maybe having a friend drop by and run the transmitter from another 
room into a dummy load and low power may just work.  Even the old Heathkit 
dummy load works at VHF and should radiate enough to perform this adjustment.

Since its not working now you could tinker and see how close it is to 3 
volts without a frequency being input. In any event I would take a 
measurement before doing an adjustment to see where the voltage is 
currently. Looking at the service manual there are two other adjustments 
for the Center meter. I don't think those need be touched unless you do get 
access to a signal generator.

The Digital VOM will do the job fine so far as measurement goes. We 
generally used Fluke 77 DVM's at Icom when I worked there. for other 
alignment we used scopes and spectrum analyzers.

Gary K8IZ


>Hi Gary:
>           You have been very helpful in figuring out what to adjust, my 
> problem now is that I don't have a signal generator to tackle the 
> adjustment.  I do have a low priced digital vom, can the adjustment be 
> made using that by measuring the voltage at W64? I am looking at minimum 
> $125 and a few weeks downtime to send the radio away and have it 
> serviced, what are the odds of successfully tweaking L23 without having 
> the signal generator?
>73
>Warren n0wf

Gary Fiber K8IZ
GROL PG-19-6691
Washington State Resident