VA62 barsweep

[JohnCT]

Originally Posted by old_tv_nut

This sounds to me like the "3.5 MHz" is really close to color subcarrier, at least sometimes. If it's supposed to be stripes (locked to the horizontal rate), it should be possible to trouble shoot why it's not locked.

I didn't get more specific because I don't have the schematic for the 1100 board, which is NOT included in the service manual I borrowed from a friend who has a VA62 that purportedly works , but I think you're on the money.

Anyway the 3.5 is not just close to the chroma subcarrier, it's 3.579mhz... The button is marked 3.5, but the block diagram that I have shows the actual frequency as 3.579. Why the front panel isn't marked 3.6mhz instead of 3.5mhz I don't have a clue.

I mentioned everything else is working and it seems to be, but the dot and crosshatch patterns, while crisp and clean, show a slight color to them. The color can be removed by pushing a combination of the Interlace adder and VIR adder buttons (I don't recall which one is in, out or both in). I think what's going on is that chroma is leaking in one of the switching ICs and clashing with the 3.58 from the multiburst generator.

The other possibility I suppose is that the green bar is normal when the 3.58 button is pushed, but I don't have the owner's manual, and I have a sneaking suspicion that might turn out to be the case. Maybe I'll drag it back out and try it with the color control turned down.

Also, when scoping the multiburst pattern, the amplitude of the 3.58 signal is the same amplitude as the others, but no lines can be discerned when expanded out using the delayed sweep- just jibberish is seen.

The service manual shows component level detail of every board except the 1100 board which is block diagram only, so I put it in storage.

I may try to figure out the downconverting add-on to the B&K415 for 25mhz IF sweeping.

John

EDIT: I forgot to add that the VA48 I also have has a completely non-functioning bar sweep section, but that also shows some color bars in the crosshatch, so maybe that's normal for these animals.


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