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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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old tv remote control problem
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/s...techassis1.jpg |
#2
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old tv remote control problem
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. |
#3
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old tv remote control problem
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 |
#4
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old tv remote control problem
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?) |
#5
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old tv remote control problem
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. |
#6
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old tv remote control problem
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. |
#7
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old tv remote control problem
frenchy wrote: 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 |
#8
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old tv remote control problem
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 |
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