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My calibration adjustment is maxed out but the display is 2.5 khz off . what should I look for to repair this.

Is there a adjustment inside other than the small knob on the outside? Would the 5 volt supply to the display cause this?

Is there a way to compensate for the error?

Thanks, Robert KH2BR

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On the front of the radio there is an adjustment pot and it is maxed out all the way to the left. That pot works.

I don't know of any adjustment for that inside of the radio.

schematic shows calibration pot as 5 k. It measures 4.88k. ..? resistor R14 to ground? schematic shows 1k, I see? marked 820 ohms and measure 798 ohms ..
resistor on top side of pot? R15 schematic shows 33k I see and measure 2.7k
there is 5 volts at the top of resistor R15. calibration pot center tap needs a little more voltage to move counter 2.5khz.

Any suggestions ???? I could replace R15 with 2k ohms .. ???? the 33k could be a mistake in the schematic..? can others verify ??

Robert

You are correct !!? 40 meter crystal is 4 khz off and cant get it any closer to 21.5 mhz

Well, I have all the crystals on frequency and still have a counter calibration error. It is less, like 1.7 khz with the pot turned all the way to the left.
the marker frequency is spot on. that leaves the counter mixer and there is a crystal frequency adjustment inside. There are no instructions on how to make the adjustment. the crystal frequency is 18.5 mhz. I can change that frequency by -3khz on one side of the pot adjustment to +1.7 khz on the high side.

So, how would we do this adjustment ? 1- turn marker on.? 2- dial in 7.2 mhz, lower side band .? 3- set cal pot to mid range.? 4- zero beat marker signal.
at this point the display should be off frequency.? ?5- with a insulated hard plastic tool, adjust tc2201 in counter mixer display to 7.2 mhz.

It worked so far, I need to check the other bands !!

I’ve had the same issues with the USB and LSB xtals had to change caps to get them back inline.
Any one know of a xtal manufacturer that can makes these HC49U. Back in the day I used Jan crystal. I’ve looked around and found Transko down in Anaheim CA but they don’t have any 9 mhz blanks.

you might want to sweep your crystal filters also. I have read on the internet somewhere that they also age and change frequency.

I have to many projects going on and cant give you any other information.