IC-251e

[RevGeoff]

I have an Icom IC-245e with a problem which has baffled me.

The frequency at start up for FM is displayed as 45.000, this changes to 45.600 in VFO. In USB this changes to 3kc above nominal frequency, In LSB it goes below by a similar amount. I therefore assume that the PLL is working.
Opening the top cover reveals the tuning machinery,. A slotted disc rotates through an IR LED beam and detects the new frequency. There are no volts on these LEDs, and my cameraphone camera(which can detect infrared) reveals that they do not light up. There appears to be no volts at several of the cmos ICs on this board.

Any ideas, suggestions? I don’t want to scrap it as I like using it, its very effective has a MuTek front end and sounds good on air.

[frsimen]

I’m not sure if your faulty set is the IC251e or the IC245e. The general arrangement of both is similar but the detail isn’t the same between the two models.

From your description you are missing the supply rail for the tuning encoder part of the circuit. In both radios the supply to the tuning encoder is 9V. The first thing to check is for a short circuit, or near short circuit across the 9V supply. If you find one, you will need to track down the cause of that. Suspect tantalum capacitors that may be across the 9V supply, if there are any.

If there is no short circuit, trace the 9V supply back to its source, which is Q30 in the IC245 and Q37 in the IC251. If the 9V is at the emitter of Q30 (245) or Q37 (251), you have a connection problem between there and the tuning encoder circuit. Check the plug and socket which carry the 9V.

If the supply is missing at the emitter of Q30/Q37, there is something wrong in the regulator circuit,

That should give you a starting point. Whatever the problem is, it should be something that you can fix.

Paula

[RevGeoff]

Hi Paula,

thank you. It is an IC-251E, sorry for the typo.
I will check as you suggest.
Geoff