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CJVx 06-29-2019 02:20 PM

Recommendations on tuning up my TV
 
4 Attachment(s)
I did the normal replace all the capacitors etc. about 10 years ago to get this thing up and running. Used it for a bit until the broadcast stopped. I have just outfitted my house with an agile modulator so getting back into operating this tv. Please look at the screenshots, it appears to have the picture shifted a bit to the left, horizontal stability is very touchy, I am getting lines when the scenes fade out. Any recommendations on where to start? Thanks

It’s a 1948 Philco

Notimetolooz 07-01-2019 10:00 AM

Those lines are retrace lines. At the end of a frame scan the electron beam returns to the beginning. Normally the set should have a blanking signal that is sent to the CRT to turn off the beam during this time. It could be that the set doesn't like the way the modulator puts out the sync signals.
Post the TV model number and/or the schematic. Did you replace resistors also? Do you have some test equipment?

old_tv_nut 07-01-2019 10:19 AM

If your signal is modulated correctly (have you checked another TV?) then the combination of low contrast and touchy sync could be an AGC/IF gain issue.

Edit: Is this a set where the contrast control is actually an IF gain control? I see the last two pictures look like normal contrast, so I take back my comment.

CJVx 07-03-2019 09:14 AM

It is a Philco 48-1001 model. The TV worked decently on analog broadcast back before they cut it off in 2009. I think after that i only turned it on a handful of times to make sure it still "fired up".

Now that i have the modulator set up, I have been operating this TV more frequently. I have other TV's that pick up the modulator's signal and they display nice clear pictures, but they are newer, 1970's being the oldest I've tried so far.

The contrast is not low on normal operation, its just when the picture fades out during darkening of the scene or transitions to other scenes, the retrace lines are shown. The picture is relatively clear, with the major problems being a touchy horizontal stability and some sort of picture shift to the left. I don't recall changing any resistors during the initial repair years ago. I'm going to get the chassis out, dust it off etc. and try to find the SAMS i bought for it back then to get started.

old_tv_nut 07-03-2019 10:22 AM

Just looked at the schematic - seems like the DC restorer is not working.

CJVx 07-03-2019 10:36 AM

Thanks for the tip. Did this set even have DC restore, or is this something I should add.

old_tv_nut 07-03-2019 11:21 AM

You can get the schematic off of the earlytelevision site:
http://www.earlytelevision.org/tv_sc...ms_philco.html

It definitely has a DC restorer section with a dedicated tube.
I think the sync pulling is likely to be a separate problem, but check it out.


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