CPD1604S Vertical Collapse

[vol.2]

Originally Posted by Alex KL-1

The IC 604, it follow the truth table in the datasheet? Too busy at moment to analyze it but, a question: perhaps 0V in the pin 1 causes 0V in the outputs?

Yes, IC304 definitely follows the truth table of its datasheet. The incorrect voltage on Pin 1 causes 0V on Pin 5 output.



Pin 1 should be HIGH, and the 4 outputs it controls should all be HIGH, instead it becomes HLHH

So the 2.7V on base of Q613 maybe is the problem. Or possibly the lack of 6.5V on the collector of Q613 causes the 2.7V to appear on the base.

I don't know the chicken or the egg unfortunately


Edit: I'd like to add that I isolated IC250, Pin 10 to try and see where the 23V is coming from that shouldn't be there, and without Pin 10 connected to the rest of the circuit, it no longer has the 23V on it, but I still see 23V all over Q254 and the Vertical Position potentiometer. Not sure why it's wrong, but I also can't see how it's connected to the issue with IC604.

[Alex KL-1]

Also makes wonder if D608 are not resistive or open, or some trouble with this line (the circuit/switch for the AUTO/Manual are inoperative?). Certainly one function corresponds (the one making GND connection) to basically near 0V on the cathode of D608. Then the cathode of D609 will presents very low voltage I suppose. Unless...
The cathode of D609 is connected to another thing in the circuit, or is only to Q613?

[vol.2]

Originally Posted by Alex KL-1

Also makes wonder if D608 are not resistive or open, or some trouble with this line (the circuit/switch for the AUTO/Manual are inoperative?). Certainly one function corresponds (the one making GND connection) to basically near 0V on the cathode of D608. Then the cathode of D609 will presents very low voltage I suppose. Unless...
The cathode of D609 is connected to another thing in the circuit, or is only to Q613?

I can say at least that switching Auto/Manual control does indeed still switch the control mode. The horizontal size doesn't work at all, but the position controls all work somewhat. The vertical position "works," but it shows up in the wrong spot (too far down).

The cathode of D609 (right side) goes only to the base of Q613, nowhere else. It's at 2.7V. The collector of Q613 is supposed to be 6.5V, but it's 0V, the emitter of Q613 is grounded.

The other cathode touches Q615 and IC602/604, but that voltage is correct.

The anode goes to the switch between GND/Open and the two resistors that connect it to the 5.5V rail.

The main problem I'm seeing is the lack of 6.5V on Pin 1 of IC604. That bad logic sees the circuit between it and the other two diode arrays, IC250 and IC302 incorrect. But I don't know if the problem comes from D609 side or IC250/IC302 side. Can bad voltage(s) on output side of those ICs cause cascade failure back towards D609?

You can see that lack of 6.5V on the circuit to the right of IC604 has a lot of problems for the logic. It flips the logic level on 5 Darlington pairs inside IC250 and 4 pairs inside IC302.