Electronics 32 VTC-202

Hello All! My subject flew off. Flew after I soldered the boards in an attempt to get rid of this “floating” glitch - from time to time the frames began to run. Well, I soldered it, turned it on: no green color. I started digging. On board video channel there is such a place: 510 Ohm┌───┬─────┬──+11.9V ┌─────────────────────────────┐ █ █20KOhm│ │ │ █ █ ┌──┘ └────┐ 100 Ohm └───┴─╫─┼──┤kt315 kt315├─┬─████─┬────┐ 2.2uF █ └>─┐ ───<┘ │33nF │33nF│ █20KOhm│ green ═╪═ ═╪═ │ │ │ green ─┴─ ─┴─ │ ─┴─ │ on board - - - - - - - - - -│- - └──────> ────┐ │ | kinescope ├─┬─████─┬────┤ | ───<┘ │ │ │ | red ═╪═ ═╪═ │ | ─┴─ ─┴─ │ | ────┐ │ | ├─┬─████─┬────┤ |┌ KS133A ───<┘ │ │ └───┤<├─┐ blue ═╪═ ═╪═ | │ ─┴─ ─┴─ | ─┴─ | - - - - - - - - - - - - That is, three channels: R, G, B are completely identical. Each of them includes KT315 with a common base. The signal arrives at the emitter and leaves the collector. Bases connected to the zener diode. From the collector the signal is fed to the last stage of the amplifier (also 315 with a common emitter) and goes to the connector to the kinescope board.So: R and B are fine, but green comes to the emitter, and from the collector doesn't go away. Replacing the transistor did not give anything, replacing the next one too, checking for breaks and shorts showed that everything is in order, checking all the parts between the collector of the first transistor and the base of the second showed that all values correspond to the diagram. Base potentials of the first transistor for all channels are equal. I was already scratching my head, but then kind people advised me to measure the currents. I measured it: there is no base current. Attention question: why? What else should I check? I no longer have my own ideas. Best regards, Dmitriy.

Hello Dmitriy! 09 Jun 03 12:02, Dmitriy Nesmachny -> All: DN> My subject flew away. Flew after I soldered the boards in an attempt DN> will get rid of such a “floating” glitch - from time to time frames will run DN> started. Well, I soldered it, turned it on: no green color. Became DN> dig. There is such a place on the video channel board: DN> 510 Ohm┌───┬─────┬──+11.9V DN> ┌─────────────────────────────┐ █ █20KOhm│ DN> │ │ █ █ ┌──┘ DN> └────┐ 100 Ohm └───┴─╫─┼──┤kt315 DN> kt315├─┬─████─┬────┐ 2.2uF █ └>─┐ DN> ───<┘ │33nF │33nF│ █20KOhm│ DN> green ═╪═ ═╪═ │ │ │ green DN> ─┴─ ─┴─ │ ─┴─ │ to board DN> - - - - - - - - - -│- - └──────> DN> ────┐ │ | kinescope As far as I understand, you don’t have an oscilloscope?!... try changing places green (coming to the kinescope board) for example with red.If the red disappears, treat the Conder 2.2 microfarads. (well, if not, what is the most probably in your situation - dig a kinescope board.) in general, you can poke a voltmeter between 2.2 microfarads <-> 315 - if visible there is no effect - compare the potentials of the 2nd transistor with similar channels and check whether the 33H condensers are shorting, but if there are, measure them (for a short time!) under power on the Conder, while staring at the monitor - if the visible effect manifests itself in any form;) again, dig Conderah! Bay W.B.R. rNd [Team: X-Tension] [FREE]