# [amsat-bb] Re: G-5500 7806 regulator question

i8cvs domenico.i8cvs at tin.it
Sat Aug 16 18:56:50 PDT 2008

```----- Original Message -----
From: "Mark L. Hammond" <n8mh at embarqmail.com>
To: <amsat-bb at amsat.org>
Sent: Sunday, August 17, 2008 1:54 AM
Subject: [amsat-bb] G-5500 7806 regulator question

> Hello All,
>
> It appears that the 7806 voltage regulator in my Yaesu G-5500 control box
has gone bad; the output is measuring more like 10.8 Volts (!).   This
explains why both position indicators were off by a factor of 2 (e.g.,
elevation meter showing 90 deg, array pointing 45; azimuth meter showing 180
deg, but array pointing 90 deg., and so on).
>
> Question---has anybody used a 7805 to replace the 7806 regulator in this
control box?
>
> I don't have a 7806....so this brings the next question--anybody have a
7806 (or 2) that they want to sell?)
>
> Thanks,
>
> Mark L. Hammond  [N8MH]
>
Hello, Mark N8MH

Each load across the 7806 regulator is represented by a 500 ohm
potentiometer with in series a 15 ohm resistor.

The load across the wiper of the 500 ohm potentiometer is 10 K
and so it is not considered in the following calculation.

If you replace the 7806 with a 7805 regulator the current flowing through a
resistor R= 15+500 = 515 ohm will be I= 5 / 515 = 0.009708 A and the drop
of voltage across the 15 ohm resistor will be only
V= 15 x 0.009708 = 0.145 volt

Since the voltages for the AZ and EL instruments are supplied by the
operational amplifiers Q3 and Q4 respectively you can adjust VR1 and VR2
to get again a full scale indication.

The 5 volt voltages for computer control are supplied by the operational
amplifiers respectively Q3 for the AZ and Q4 for the EL so that when the
AZ is rotated fully clockwise the potentiometer VR3 must be adjusted to get
exactly 5 volt DC on pin 6 of the external control 8 pin DIN connector and
VR4 to get 5 volt DC on pin 1 when the EL is fully rotated by 180 degrees
(flipping)

Looking the 8 pin DIN connector from the back of control box (external view)
pin 6 is the first hole clockwise and pin 1 is the second hole clockwise

Conclusion:

It seems that a 7805 will work

73" de

i8CVS Domenico

```