The AM Forum

my most favorite rig my ic-735 over time has developed a problem with
the dial encoders. when warm, the dial won't tune up freq, but will
tune down freq with either direction i turn it. when really warm, it
takes off by itself running off frequency. there is a lock button which
I hit, then use the up/down buttons on the mike. anyone know
anything bout this?  I hate mechanical problems, never had the rig
open.  ?

Dean,
This is a common problem with opto encoders. You have one output stuck. It can be mechanical or electrical. can you get at the two outputs and can you get inside the encoder. Sometimes it is only a hunk of dust. Encoder wheel could be scratched. or the sensors out of allignment.

Last time I ran into that problem the fix was shimming the shaft. It had a bunch of axial play. Your problem could be something other than mine was however. In your shoes I'd look for a parts encoder on the Evil Eplace. You can get just about anything there.....excepting Alice.

From the IC-735 troubleshooting guide:

"Symptom:   VFO tuning is erratic, sometimes lags or skips when changing frequencies or bands. Sometimes least-significant digit in frequency displays "flutters" back and forth instead of changing incrementally when the VFO knob is turned slowly.

Probable Causes:   Bad rotary encoder.

Cure:   Substitute rotary encoder with a known good one. It is recommended that the rotary encoder be replaced as a complete assembly if it is bad.

Remarks:   If the frequency tunes in only one direction, i.e. either up or down, there may be a problem on the logic unit."

I think they should hire Phil as a consultant.

 ;D ;D ;D

Whoops wrong thread. Phil for Arrl consultant.

Dean you can check the encoder output with a volt meter. Chances are one output is stuck high making logic think that is the leading pulse so it tunes in one direction only.

so others have had this problem, sigh. When I get time, I'll look to see if
there are layout  diagrams on the internet.. getting into these boxes physically is the pain. layout and access is the worst. I tried to fix my TS-50, what a pile
of circuit boards on little cords & jammed layered together. never could
fix it cuz of that.

Dean,
I too have an Icom 735, I use it as my primary receiver.  Sounds gorgeous with an external
speaker and some couplling cap fattening I did bout 10 years ago or so.  Anyway,
I have a complete original service manual, but don't have a scanner.  I gave a professional made
copy of this to Tron 'HLR years ago.  He maybe could part with  it or could walk you through details by fone.   I have not experienced this problem, but I agree with Frank, probably dust in the encoder.
I've seen problem  with similar schemes in shortwave radio's.  Dust.  Cleaning usually fixes it at least temporarily.  I'm good in QRZ.  Let me know bout the manual. 

Jim KF2SY

I had one for years first rig I ever bought new and sold it when I got the 756.
How is the rcvr on AM?
Was not into AM in those days. I may just get another for the nostalgia