[Kenwood] TS-820S and ALC - more-2

[Clif Holland]

An understanding of how ALC works and close study of the map is in order.

ALC is a method of reducing gain in the IF strip to keep from overdriving 
the finals. The meter just indicates how much the gain is reduced, the 
higher the reading the more reduction in gain and the lower the ALC voltage.

The normal ALC voltage is 2.8VDC. As this goes down toward zero the ALC 
meter goes up so a pegged ALC meter indicates a lack of ALC voltage IE: 0V. 
As the voltage builds up the meter goes down. There can be several causes 
for this.

1. The static ALC voltage is not correct. Step 1-2 in the service manual 
sets the RF1/ALC voltage. Is it correct. Must be or the S-meter would be 
pegged in RX.
2. The ALC voltage is controlled by Q5 on the RF unit, are those voltages 
correct?
3. The ALC is applied to Q18 in the IF unit. If it's leaky the voltage can 
take time to build up.

First step Check the RF1 voltage
Next remove the ALC line from the IF unit and see if the meter behaves 
correctly, IE: In tx mode the ALC is at zero when in SSB and no mic gain. If 
so Q18 is bad/leaky.
If the ALC line is still held low (full scale meter) after removing Q18(ALC 
line) from the circuit that goes back to Q5 on the RF unit or the time 
constant circuit, R44 2.2M resistor, C39, or R43.

My money's on the FET Q18. Have fun.


Clif Holland KA5IPF
www.avvid.com




----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "Kenwood" <kenwood at mailman.qth.net>; "Clif Holland" <clif at avvid.com>
Sent: Sunday, March 11, 2012 5:35 PM
Subject: Re: [Kenwood] TS-820S and ALC - more-2


> On 11 Mar 2012 at 13:32, Kenneth G. Gordon wrote:
>
>> > Don't adjust anything. Clean the relay in the middle of the bottom.
>> > Business card and contact cleaner ONLY. Nothing abrasive.
>> >
>> > Clif Holland KA5IPF
>>
>> Thanks, Clif. That was going to be my first step, since that is about all 
>> I can
>> do at this point...
>
> OK. I removed and carefully cleaned the relay with a folded piece of 
> typewriter paper.
> Removed some black ick between some of the contacts. Then I used a SMALL 
> amount of
> DeOxit, and then a SMALL amount of ProGold afterwards by wetting another 
> piece of folded
> paper and working it between the contacts.
>
> Replaced the relay, and the cover.
>
> When first turning on the rig and keying the mic with no audio, ALC still 
> pegs over against the
> right stop. Waiting a few minutes, then keying the mic, the ALC has slowly 
> dropped back until
> it is just at the top edge of the "safe" zone.
>
> Another set of clues:
>
> With mic gain set at 2, rig loaded up to 225 mA input on 20 meters into a 
> dummy load, 14260
> KHz. USB , when first keying the mic with no audio input, ALC pegs to the 
> right. Continuously
> keying the mic on and off with no audio input, the ALC drops back in steps 
> after each
> "keying" until it reads near the bottom (left) end of the scale.
>
> Keying the mic, then speaking into it, instantly pegs the ALC reading even 
> if I have the mic
> gain raised only just enough to give me an indication on the plate meter 
> when speaking..
>
> If I then hold the mic keyed, the ALC reading VERY VERY slowly drops back 
> steadily.
> Although the meter switch is still set to ALC, using the mA scale to get a 
> better idea of how
> slowly, it drops back 10 mA (on division) in 45 seconds. After 15 minutes, 
> it rests at the
> bottom of the scale.
>
> It seems to me that I have an open resistor, cold-solder joint, bad 
> capacitor, or bad diode
> somewhere in the ALC circuit or related.
>
> Now what? Any suggestions?
>
> Ken W7EKB