Quote:
Originally Posted by damen
Never had much trouble with the transistors on those MAD modules. Usually the 2.2 meg resistor went bad and caused loss of the color.
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No, it was absolutely the transistor went open. The resistor still measures good (~2300k on my meter while in circuit. Close enough.) and poking the transistor casing gently with the end of a ballpoint would make the driver flicker on and off. Transistor internal failure, if I had to guess. Maybe internal junction? Solder joints on the bottom looked good.
Replacing the module brought all 3 colors back and removed the red background. Maybe red was being overdriven or out of balance because of the other driver failing.
Set looks like it might need some convergence work as well, but I'll wait until the tuner is working correctly to do that.
Color bars:
Square grid:
Dots:
As you can see, the tube seems in very good health and the picture comes in very clear - Albeit on the completely wrong channel. This is again my LCG-388 on channel 6, with the set tuned to channel 49.
Quote:
Originally Posted by zeno
When you go to UHF the VHF osc is turned off & the VHF RF amp & mixer are turned into two more stages of IF amps. This is how you can get band related fails. You should get strong snow & hiss on all channels.
Be sure the FT is actually engaging the slug in the tuner.
Its normal to be able to FT up or down & hit the adjacent channel if in the same band ( put on ch5 & tune to ch4 or 6 ).
You can try a little WD40, it can work miracles.
Video can usually be injected just after the video detector diode,
more on that later.
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On ALL UHF channels (14-83) I get a large amount of static on screen and static in the audio.
On ALL VHF channels (2-13) I get a dim gray screen and quiet static on audio. There is almost nothing visible on screen at all.
For example, to hear static through VHF, you have to turn the volume control to nearly the maximum just to hear it a few feet from the set. To hear it on UHF you can leave it very near the bottom.
When I turn the Fine Tuning knob on the VHF tuner, it turns a wheel on the back of the plate and engages a cog which turns what I'm going to guess is a potentiometer inside a metal casing. I can see and feel it turning, despite it being very light. I've sprayed both it and all of the tuner's contacts with deoxidant already, while the tuner was out of the set.
Pictured below, VHF channel 10 and UHF channel 55, picked at random.
VHF channel 10 (and all other VHF channels) are noticeably dimmer than all UHF channels. The camera is picking up far more brightness than I can see, even in a dark room. The UHF picture gives you a better idea of the huge difference between them.
Poking around with my scope on the video board, I managed to find what looks like a composite video signal on the base of Q103. Is it a good idea to inject it here, or should I look elsewhere?