old tv remote control problem

[frenchy]

This is an ultrasonic remote control chassis inside a 1961 RCA ctc-10
tv I'm restoring. This thing is working, sort of, seems weak, have to
put remote real close to the microphone on front of set for it to work
most of the functions. Hand unit has been recapped (a paper cap and
electrolytic) which made it work a lot better, as well as the 40mf and
5mf caps in the chassis. Moving the keyer tubes around can make one
function work better, another worse, or work, or not work, like the
functions are all borderline besides the tubes. Tubes test good. 1st
12ax7 is shielded.
Having trouble figuring out the voltages I'm measuring, mainly on left
of this diagram, 130 instead of 100, 61 instead of 165. I can't even
figure out why it SHOULD have 165 volts there, shouldn't the 2 megs of
resistance after the 175v shunt it down to about 60v I'm getting? I
changed c1001 with no effect. I am testing it on a bench with no mike
plugged in as per the schems, and just 120v going into the power
connector. Can anybody interpret these voltages and see anything that
sticks out like a sore thumb as to possible culprit? I just do not get
how that SHOULD be 165v at the mike plug, having trouble understanding
that, on top of the fact that I'm measuring only 61v.
thanks!


http://mysite.verizon.net/resoctff/sitebuildercontent/sitebuilderpictures/remotechassis1.jpg

 

[[email protected]]

Hi,
Greetings from Brazil!

I think there is a leakage somewhere. You have 2Megs but no connection
to a ground, so you should have the same 180Volts on J1001. You are
missing 120V!! I don't think C1002 is the problem since you have -1.2V
on pin2 of 12AX7. J1001 is a suspect, the TV is very old. Either the
connector may be conducting or the wires that go to the mic.

 

[frenchy]

So you are saying that I must have voltage shorting out to ground
somewhere between the 2 1-meg resistors and the mike socket? I am not
an electronics whiz, just a 'cap changer', so want to make sure I
understand what you are talking about. I measured voltage off the 180
with my own separate 1-meg resistor and got 88 volts so I figured oh
well that's normal, you're saying it isn't normal and I should still
have 165 volts after the 180v goes thru 2 megs? Thanks!
Frenchy

 

[frenchy]

Ok I measured resistance between the 175v point and the socket +. I
got about 2 megohms. So I don't see how that can be leaking?
I then snipped the wire that goes from R1002 to R1001, so then I just
had the 175v, the 1 meg soldered right onto the cap c1029 so no leakage
point there, and other end of R1002 on a bare lug. I still measure 88
volts coming off that, and 60v if I add another 1 meg to it. I still
don't understand how I'm supposed to be ending up with only 10 volts
less than 175 (165), when I am measuring 88 with purely the 175v and 1
meg resistor on it? Could I have leakage of the 180 itself somewhere
else? (but in that case why would I still have 180 to begin with?)

 

[Marcos_Ce]

What kind of multimeter are you using? Maybe it's internal resistance
is not high enough. Also try checking resistance between J1001 and
ground.

Let me know.

 

[frenchy]

I get infinite resistance from the J1001 (mike + terminal) to ground.
I've got two different multimeters and they read about 10 volts
different, one is a Tripplet 9020. The schems say " * voltages
measured with 1 meg in series with meter" but it's got the asterisk on
that note, and none of the voltages have an asterick so figured it
didn't apply. But if it does apply, when I put a 1 meg in series with
the meter, I just get the same old reduction in the meter readings,
i.e. 175 reads as 88 etc. I've checked all the resistors in the bottom
portion of the 175 volts and they check out ok.

 

[Ken Weitzel]

I get infinite resistance from the J1001 (mike + terminal) to ground.
I've got two different multimeters and they read about 10 volts
different, one is a Tripplet 9020. The schems say " * voltages
measured with 1 meg in series with meter" but it's got the asterisk on
that note, and none of the voltages have an asterick so figured it
didn't apply. But if it does apply, when I put a 1 meg in series with
the meter, I just get the same old reduction in the meter readings,
i.e. 175 reads as 88 etc. I've checked all the resistors in the bottom
portion of the 175 volts and they check out ok.

Hi Frenchy...

Are you sure you're using 1 meg?

Ken

 

[frenchy]

From another source, I think my problem may be that I am just not
taking into account the internal resistance of the meter which is
making it read low over that 2 meg of resistance that's already there,
and that I have to do a voltage divider calculation to convert what I'm
reading into the 'real' voltage. I need to find out what the internal
resistance of my meters is but I am starting to believe this may be my
problem (not the TVs problem!)
thanks...Frenchy