Alan
TV Repair Authority
Feb 3, 2003, 10:14 PM
Post #10 of 13
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Re: [bamajim] RCA snowy picture channels 2-13
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Jim,
Here is what I have come up with from looking at the chips.
I could be more definite if I had the tuner schematic.
All information pertains to the MC44864 chip.
Pins 5, 6, 7, & 8 are the outputs from the D/A cct.
These voltages should changes as the channels are changed.
These will be be very small changes as they are reverse bias voltages for the osc and the tuned ccts.They should go from a low of about 0.2VDC on CH2 to 1.5V max
on the higher channels. I don't think the problem is in here.
Nor do I think that there is problem between the microcontoller and the tuner. The fact that the UHF channels work, pretty well rules the micro out. I think the problem is in the band switching. Pins 14, 15, 16, & 17 do the band switching. I think pin 16 is for VHF and pin 17 is for UHF. The low condition should be about .01V and the high about 1.8V. On CH2, pin 16 should be high and pin 17 should be low. On CH14 and above the reverse should apply. The other pins (14 &15) may also be used. The main thing is that you see a change in the voltage on these four pins in discrete steps when you go from the VHF to the UHF channels. Now the big question that I cannot answer is, how does the cable-ready hook-up affects this?
I have the data sheets for both of these chips if you want them.
Alan
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