----- Original Message ----- From: "Mark L. Hammond" [email protected] To: [email protected] 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

Hi Mark, Hi all,

another almost unknown but better and much more accurate combination in order to increase the output of any 78xx regulator is possible by making a divider in the output of 78xx regulator according to the formula:

R1=VR/0.02 ( where VR the nomimal output of 78xx regulator)

R2=VB/0.025 (where VB the difference in Volts between "nomimal" output Voltage of 78xx and "request" output Voltage)

In ----------- ---| 78xx |-----o---OUT ----------- | | R1 o----------| | R2 | -------o-------------- 0V (GND)

Therefore, in case we have a 7805 and we need 6 Volts output:

VR=5 => R1= 5/0.02 = 250 Ohms

VB (Differential Voltage): 6 - 5 = 1

R2 = 1/0.025 = 40 Ohms

You can replace R1, R2 with standard value-resistors: R1=220+27 Ohms R2 = 39 Ohms

The R1 is connected between + OUT and GND-Pin of 78xx. The R2 between GND-Pin of 78xx and GROUND (see my figure above).

*** HOWEVER, in this case the Hotsink (metal plate) of 78xx MUST BE ISOLATED from the 0V !! Just keep in mind that, because the Pin2 is internally connected to metal-plate of 78xx ! So, if the GND(chassis) is equal to 0V and the metal plate of 78xx is directly connected to chassis for better cooling, then the R2 is by-passed through the internal connection of 78xx. (and the R1 is now just a... bleeder !)

Finally, in this combination by using divider (or diodes as mentioned by others) the 78xx regulators lose the "short-circuit" output protection. That is available only in case where the Pin2 of 78xx is directly connected to 0V (normal connection).

Hope this helps.

73, Mak SV1BSX

----- Original Message ----- From: "Mark L. Hammond" [email protected] To: [email protected] Sent: Sunday, August 17, 2008 2:54 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]

---

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