[ICOM] Pro3 Fan Questions

[Matousek Karel]

Hi Bob:

There are two type of Power Amplifier of IC-756PRO3.
Old one has transistor on driver (2SC1972) stage and 2SC5125 on final stage.
In the new one model are FET in use. RD15HVF1 on driver and RD100HHF1 final stage.
The older one seems to be more temperature sensitive then the new one.

Differences are on build temperature sensors. I the old one type of PA is NCTG20 in use directly mounted on final transistor body. In the new one there are ERT-D2FHL503S temperature sensor in use mounted very close the final MOSFET on PCB only. Heat transfer between the temperature sensor and the power output semiconductor are at both types of final stage different.



There are TEMPERATURE PROTECTION CIRCUIT

The cooling fan is activated while transmitting
or when the temperature of the power amplifier
exceeds the preset value. The temperature protection circuit
consists of Q10–Q13 and R50.
While transmitting, Q10 and Q12 are turned ON, and provide
a voltage to the cooling fan to rotate at medium speed.
The thermistor (R50) detects the temperature of the final
amplifier (Q5), and activates Q11 and Q13 to accelerate
the cooling fan when the detected temperature exceeds
70˚C (158˚F). The cooling fan rotates at high speed at 80˚C
(176˚F) or more.
The thermistor keeps the cooling fan rotating even while
receiving until the Q5 temperature drops to 60˚C (140˚F) or
below.


73  Karel OK1CF

>---------------------------------------------------------
>Od: Larry Young
>Přijato: 27.7.2009 6:14:01
>Předmět: Re: [ICOM] Pro3 Fan Questions
>
>Bob: Both conditions of fan operation are likely normal. The fan always is turned on whenever the rig is place in transmir. The fan may come on in receive if the temperature inside the radio rises above a certain degree. This is unlikely to happen if the radio is provided the proper ventilation clearance from surrounding objects and not enclosed etc.
>
>Larry K4LXV
>
>
>
>--- On Sun, 7/26/09, Bob Beatty <rbeatty at mpinet.net> wrote:
>
>
>
>From: Bob Beatty <rbeatty at mpinet.net>
>
>Subject: [ICOM] Pro3 Fan Questions
>
>To: icom at mailman.qth.net
>
>Date: Sunday, July 26, 2009, 10:21 PM
>
>
>
>I have just received a new Pro3 and am having some issues with the fan.
>
>
>
>1.  Without keying the rig, the fan periodically comes on and runs for
>
>about a minute and shuts off.  Is this normal?
>
>
>
>2.  Today (7-26), the fan began to run whenever the rig was keyed and would
>
>stay on from 30 seconds to 1+ minute.  By "keyed", I mean clicking the PTT
>
>and letting up.  This operation seems excessive.  I thought the fan was
>
>thermostatically-controlled and would only run when it got hot enough.
>
>
>
>I do not find the fan action mentioned in the owner's manual and I don't
>
>know if there is a user adjustment for what is happening.
>
>
>
>Any suggestions, opinions, etc. are appreciated.
>
>
>
>73,
>
>Bob W4VQ
>
>w4vq at arrl.net
>
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>
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