Video input mod and vertical poor interlacing

[old_tv_nut]

Poor interlace results when horizontal sweep waveforms bleed into the vertical sync section. Because of the high currents and voltages in the H sweep, this means that grounds are critical. Many sets have questionable interlace under normal use without added circuits, but adding a baseband video input may have created a ground loop for horizontal sweep currents/voltages.

It may help to do some trial-and-error experimentation of where the added video input circuit is grounded, but there is no guarantee.

[Alex KL-1]

Originally Posted by old_tv_nut

Poor interlace results when horizontal sweep waveforms bleed into the vertical sync section. Because of the high currents and voltages in the H sweep, this means that grounds are critical. Many sets have questionable interlace under normal use without added circuits, but adding a baseband video input may have created a ground loop for horizontal sweep currents/voltages.

It may help to do some trial-and-error experimentation of where the added video input circuit is grounded, but there is no guarantee.

Thanks! This makes sense, considering that some of these things have very simple and critical circuits (to reduce costs etc), not always optimized or routed.

I will play with grounding, routing and with sync separator too, in one particular 10" portable I'm restoring/modding that have horrific vertical interlace. Perhaps it will behaves a little better.

And perhaps will better for me to having only moderate expectations when injecting direct video of course.... hehe

[Alex KL-1]

Originally Posted by Alex KL-1

Thanks! This makes sense, considering that some of these things have very simple and critical circuits (to reduce costs etc), not always optimized or routed.

I will play with grounding, routing and with sync separator too, in one particular 10" portable I'm restoring/modding that have horrific vertical interlace. Perhaps it will behaves a little better.

And perhaps will better for me to having only moderate expectations when injecting direct video of course.... hehe

I played with this Philco 10" set, first trying to add some shield for the vertical oscillator, since it is located just below the flyback transformer
This not helped much (but I don't removed it), so I decide to play with circuit.
After changing the grounding of vertical sync filter, from ground to +B (due to reference of oscillator input), and changing the input from sync separator from the original video output tap to a exclusive video buffer, then the vertical sync and interlace becomes very good; so good that the range of adjustment to sync become uncritical and I can easily adjust.
To be true, the major difference was when I changing the Vsync filter, so I presume that the ripple induced by the H switching was intruding into the oscillator, upsetting it.

[Alex KL-1]

By the way, I observed the interlace in my TV's and made some ranking of interlace smoothness-:
Using my most picky device for interlacing (my PC):

#My homemade TV with TDA9373 processor (Philco programmed, 2005): the best so far. Zero interlace troubles. But I made it with shields in critical areas, and is a IC with logic and PLL's.

#Sony TV-700U (1966): Impressive. So simple circuit, but very easy to achieve the interlace point, and very stable. Not needed to change the control anymore. But again, Sony put the flyback inside a shield, maybe for not frying the signal Ge transistors. This confirms the H pulse interfering with V sync, in lesser set's without shielding or good layout.

#Toshiba TS-207 (1987): with TDA2578. Good, but become sensitive ater 30 minutes or more, and not interlaces more. ******

#10" Philco portable (1976): Good after changes. Perhaps better than the Toshiba.

#Telefunken TV-231 (1964): originally horrible; good after vertical mods.

#Telefunken TV-472V (1978): discrete vertical stages. Picky for interlace, but relatively stable when one achieve the point. I don't played with it yet.

******NOTE: in fact, probably my PC become lazy with interlace after some time, but the good TV's yet interlace properly.
The worst TV's didn't interlace with any modern device, not only my PC (like original tube Telefunken or original Philco portable).