[R-390] More C709 info

[Jim M.]

I dont recall if you said or not - did you try replacing the PTO tube?  The 
tube in my SW PTO went bad a few months ago, sensitivity dropped but it 
would still tune.  Checked fine in the tube tester.  Decided to replace it 
anyway, and that fixed it!  So even if the tube tester says its "OK" try a 
new one anyway.
Jim


----- Original Message ----- 
From: <n4buq at knology.net>
To: <R-390 at mailman.qth.net>
Sent: Thursday, May 04, 2006 9:36 AM
Subject: Re: [R-390] More C709 info


> Well, sadly, replacing C709 didn't help one bit.  I'm about to give it up.
>
> I checked R704 (lifted one side of the coil) and it's about 160 ohms.  I'm
> not sure what else could be wrong.  Someone suggested the coil might have 
> a
> shorted turn.  Possible.  It shows no sign of physical damage, though.
>
> The only thing I haven't been able to check are the bypass capacitors.  I
> suppose one (or more) of them could be leaking.  I'm dreading replacing 
> any
> of those, though.  Not sure how many "brands" of PTOs did this, but this
> PTO has a "bank" of about six 0.005 caps encased in a waxy substance that
> holds them together into a single "block" of individual capacitors.
> Replacing one would be nearly impossible unless one leaves the old
> capacitor in place and runs the new one in a different position.
>
> I'm either going to leave it alone (the radio DOES work), or completely
> strip it and replace everything I can still get parts for.  I did this to
> the second crystal oscillator in my other R390A.  It helped just a bit, 
> but
> not all that much so I'm hesitant.
>
> I'm still curious what other folks are seeing at the "raw" output of the
> PTO.  I dragged down the ME-26D/U and I'm seeing about one volt at the
> output connector.  I'm getting about 2.8V ptp on the 'scope, but since
> neither one is calibrated (and the 'scope is acting up anyway), it's 
> pretty
> much anyone's guess as to the actual value, but suffice it to say, they
> both are both showing a pretty low voltage so neither one may be that far
> off.
>
> Sorry for the long post, but it really bugs me not to be able to isolate a
> problem and fix it (provided there really IS a problem and this voltage
> output isn't all that abnormal).
>
> Thanks,
>
> Barry - N4BUQ
>
> On Wed, 3 May 2006 20:56:43 -0500, "Barry" <n4buq at knology.net> wrote :
>
>> I'm not trying to peak it for a certain frequency.  I realize it needs to
> be
>> as flat as is possible; however, I want the PTO's output to be of
> sufficient
>> level so as not to have to compensate for that somewhere else in the
>> receiver.
>>
>> As Tim said, my general voltage level is quite a bit lower than it
> probably
>> should be anywhere in the tuning range.  Lifting the capacitor and seeing
>> the voltage level rise like that is, to me, an indication of significant
>> leakage.  I'll know when I try the good capacitor.  If I'm correct, I
> should
>> see a slight rise in voltage level due to resonance.
>>
>> Thanks for the comments!
>>
>> Barry - N4BUQ
>>
>> ----- Original Message -----
>> From: <Flowertime01 at wmconnect.com>
>> To: <R-390 at mailman.qth.net>
>> Sent: Wednesday, May 03, 2006 6:54 PM
>> Subject: Re: [R-390] More C709 info
>>
>>
>> > Barry,
>> >
>> > Why are you still trying to peak a VFO in the middle of its frequency
>> range,
>> > when you know you want a flat output across the range?
>> >
>> > Why do you want more mixer noise at 500KC in every band than you want 
>> > at
>> say
>> > 100KC and 900KC?
>> >
>> > What part of flat like a pancake are you missing?
>> >
>> > Roger.
>> >
>> >
>> > _____________________________________________________________
>> > R-390 mailing list
>> > Home: http://mailman.qth.net/mailman/listinfo/r-390
>> > Help: http://mailman.qth.net/faq.htm
>> > Post: mailto:R-390 at mailman.qth.net
>> > Unsubscribe: http://mailman.qth.net/mailman/options/r-390
>> >
>>
>> _____________________________________________________________
>> R-390 mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/r-390
>> Help: http://mailman.qth.net/faq.htm
>> Post: mailto:R-390 at mailman.qth.net
>> Unsubscribe: http://mailman.qth.net/mailman/options/r-390
>>
>>
>>
> _____________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/faq.htm
> Post: mailto:R-390 at mailman.qth.net
> Unsubscribe: http://mailman.qth.net/mailman/options/r-390