[amsat-bb] Re: Yaesu 5500 Rotor Problem

John Kopala jkopala at gmail.com
Wed Jul 20 20:56:02 PDT 2011

Jeff, KB2M,

I am sending the schematic for the G-5500 separately.

Disconnect Azimuth and Elevation wires 1, 2, and 3 from the Control box.
Check the resistance across the 1 and 3 leads.  It should be 500 ohms.
Check the resistance across the 1 and 2 leads.
It should be between 0 and 500 ohms and should change as the rotors are turned.
If these tests pass, the problem is in the control box.  If not, the problem is the pots in the rotors.

If the pots are OK, the problem is somewhat more complicated.
Looking at the schematic, there are separate circuits for the meters and for the feedback level
to your automatic control.  If the IC's failed, the ones involved are Q3 and Q4 which are 4558s.
Since these are dual circuit ICs, that would mean 4 failures at the same time.  Not likely, but possible.

More likely the problem is either in the Q1 power supply circuit which provides the power for Q3 and Q4
or the Q2 regulator, a 7806, which provides the voltage to the pots.  A failure in these circuits would
kill the meter readouts and the voltage feedback to the automatic control.

John Kopala
> Date: Tue, 19 Jul 2011 16:54:10 -0400
> From: "Jeff KB2M"<kb2m at comcast.net>
> Subject: [amsat-bb]  Yaesu 5500 rotor problem
> To:<amsat-bb at amsat.org>
> Message-ID:<003b01cc4656$05d2e1e0$1178a5a0$@net>
> Content-Type: text/plain;	charset="us-ascii"
>   I'm having a problem with my 5500 after a thunderstorm. What is happening
> is that the rotor works manually, but doesn't display az and el information
> on the control box. Also when I try to use computer control it goes all the
> way to stop in both azimuth and elevation. I'm thinking this might be in the
> control box, as both az and el are doing the same thing, the control box
> being the single point of failure. Did anyone ever have this problem? How
> can I diagnosis what chip might be at fault without a schematic. I vaguely
> remember having this same problem after a close  lightning strike with my
> prior az el Yaesu box about 14 years ago but don't remember what chip I
> swapped out, or how I determined which one was at fault. This getting old
> thing really sucks. Any help would be appreciated.
> 73 Jeff kb2m

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