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Old 22nd May 2020, 10:20 pm   #70
staticmind
Tetrode
 
Join Date: Sep 2019
Location: Aalborg, Denmark
Posts: 97
Default Re: B&O Capri 606 TV (17") restoration

Ok with an 1N4007 and a 15 Ohm dropper, I have about 180V on b+, but it didn't solve anything, as you also suggested much earlier.

Disconnecting C69 did nothing to the voltages. It might be my hearing, but when it is disconnected I don't hear the line whistle.

I did measure out voltages of the 3x EF80 in the image IF section, they seem about right. As I have no signal integrity to worry about, the most important measurements would be from the last EF80 (no 3.). On the anode, I have about 185V.

I have spent some hours analysing the "output stage" of the image IF, and how it affects g1 of PCL84.

In the 971H97, only AC is coupled by a coil/transformer, so the anode voltage passes through the coil and 10 kOhm resistor to g2, so I actually don't see how it can affect g1 of PCL84.

As I see it, the ONLY way to affect g1 of PCL84 is by voltage rail +a, going through the 1.8M resistor to the pot, then through resistor 67, the combined resistor/coil 66, then to can 971H77, where it goes to resistor/coil 65 and then to g1 of PCL84.

However, in 971H77, it also passes to resistor/coil 63 and down into 971H97 and forwarded through the video detector diode RL41.

When I measured RL41 last time, I did detect the correct forward voltage, but also a higher voltage when measured in the opposite direction. What bugs me about this is that if the diode conducts in the other direction to, DC can pass through "backwards" though the circuit if you know what I mean.
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