Topics

ALC Problem


Pasquale S
 

 

Hi guys

I’m repairing an IC-7000, I put 2 new finals RD70HHF1 and I set bias 100% (1 A for each final)

But I have a strange behaviour ; the power goes up slowly, for example if I set 100 watt , power is 20 watt then goes up until 100 watt; same thing if I set 50 or 70 watt for example.

I change the cable, I use now one without fuses. I have done adjustment 3 times, no effect.  In VHF / UHF my 7000 is perfect, no trouble.

 

Any ideas ?

 

Thanks in advance

 

73s Pasquale IW0HEX

 

Inviato da Posta per Windows 10

 


Pasquale S
 

Hi Paul, thanks for your answer

 

It’s no a problem related to temperature, RF power goes up slowly, very slowly about 5 seconds to arrive 100 watt !!! This is the first time, then it’s faster.

 

In VHF and UHF there is no problem, so I suppose there is no problem with pre-driver and driver, everything runs well.

 

IN HF/50 I changed RD70HHF1 because I had a fault before; in your opionion, can RD70HHF1 be the problem ???? Vth is about 2 volt, it seems too little value.

 

Regards

 

Pasquale IW0HEX

 

 

Inviato da Posta per Windows 10

 

Da: Paul
Inviato: domenica 19 luglio 2020 03:32
A: ic7000@groups.io
Oggetto: Re: [ic7000] ALC Problem

 

Hi Pasquale ,

In what time frame does it go up? , is it slowly or fast , could it be a temperature related thing as something needs to be warmed up .

I think you'd need a oscilloscope to investigate the drama to see where the slow increase is actually happening RF wise like at the pre-driver or driver or even before that as being new finals i doubt if the issue is from there .

Also i'd be checking around the power setting dc rail for any variations but the Cro would be far quicker (if you have one) , 73 Paul .

 


Prabhu
 

Dear Paul,
I also suspect RD70HHF1 ..possibly replace with another one and check with dummy load,


Regards


On Sunday, 19 July 2020, Pasquale S via groups.io <iw0hex=yahoo.it@groups.io> wrote:
> Hi Paul, thanks for your answer
>
>  
>
> It’s no a problem related to temperature, RF power goes up slowly, very slowly about 5 seconds to arrive 100 watt !!! This is the first time, then it’s faster.
>
>  
>
> In VHF and UHF there is no problem, so I suppose there is no problem with pre-driver and driver, everything runs well.
>
>  
>
> IN HF/50 I changed RD70HHF1 because I had a fault before; in your opionion, can RD70HHF1 be the problem ???? Vth is about 2 volt, it seems too little value.
>
>  
>
> Regards
>
>  
>
> Pasquale IW0HEX
>
>  
>
>  
>
> Inviato da Posta per Windows 10
>
>  
>
> Da: Paul
> Inviato: domenica 19 luglio 2020 03:32
> A: ic7000@groups.io
> Oggetto: Re: [ic7000] ALC Problem
>
>  
>
> Hi Pasquale ,
>
> In what time frame does it go up? , is it slowly or fast , could it be a temperature related thing as something needs to be warmed up .
>
> I think you'd need a oscilloscope to investigate the drama to see where the slow increase is actually happening RF wise like at the pre-driver or driver or even before that as being new finals i doubt if the issue is from there .
>
> Also i'd be checking around the power setting dc rail for any variations but the Cro would be far quicker (if you have one) , 73 Paul .
>
>  
>
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The ALC controls the power and this voltage will change due to a number of reasons. 
The set power from the CPU, SWR, temperature, current etc.
Take a look at the ALC line voltage to see what this voltage is doing as the power changes in the time frame you are interested in.
You have POVC, FORL, AMS, ICH, ICL, IDS, RELF, EALC, UNUSB, and ALCL that all affect power by changing the ALC voltage.y
Investigating this area for a voltage that changes with the power output should aim you toward the problem area(s).
If the ALC voltage does not change with the power output then it is likely that the problem could be somewhere else, but I would first rule out this area as it has direct causation on the power output of the radio.