Fix the bending and waving images when playing beta and VHS tapes on your old TV

[Electronic M]

Originally Posted by jmetal88

Where do you live?

Seriously? Check the upper right corner of any post I make right below 'join date'.

The suburbs here are reasonably affluent. The thrifts are usually FLOODED with old VHS decks. I've bought 7 SVHS decks in the last two years and passed on some. I've scored 4 Betamax decks in the last year or so as well. In that time I've also scored 5 DVD recorders one of which also functions as a DVR.

There are also a lot of elderly folks here who are a source of tube gear. I've lost count of the number of tube radios and stereo consoles I've seen in garage sales and thrifts.

[jmetal88]

Originally Posted by Electronic M

Seriously? Check the upper right corner of any post I make right below 'join date'.

The suburbs here are reasonably affluent. The thrifts are usually FLOODED with old VHS decks. I've bought 7 SVHS decks in the last two years and passed on some. I've scored 4 Betamax decks in the last year or so as well. In that time I've also scored 5 DVD recorders one of which also functions as a DVR.

There are also a lot of elderly folks here who are a source of tube gear. I've lost count of the number of tube radios and stereo consoles I've seen in garage sales and thrifts.

Yeah, I realized you had your location listed right after I posted. XD
I didn't go back and edit it though, as I felt that removing that question would make my statement less effective, haha.

I used to find a lot of cool stuff in thrift stores when I lived in Fargo (that's where I got my SelectaVision video disc player with 20 or so movies for $20), but around here you only get clothes and kitchen stuff.

[jmetal88]

Dang it, I really want a TBC, now. And also an S-VHS machine and a SuperBeta Hi-Fi, haha. The thrift stores around here don't really have anything cool (though I guess I should check the one by the recycling center sometime, as I often ignore that one), but sometimes the pawn shops have nice stuff. I wouldn't expect the pawn shops to sell me anything that could be used as a TBC for less than $50, though.

[jmetal88]

Surprise, surprise! I went to a pawn shop today, and they sold me a DVD recorder for $15!

Actually, I'm not sure it's a DVD recorder -- it says it's a Digital Media Recorder on the front panel, but it does have a DVD drive, so I'm kind of assuming it would record to that by default rather than to the USB port on the front panel. I do NOT know if it has a TBC, but I thought $15 was worth the risk. It does have a component output, so at the very least it would have to have some kind of transcoder for the video inside.

EDIT: Huh. The damn thing's a DVR. I opened it because the DVD tray wouldn't open (even though the machine powered up and seems electronically intact), and found a 40GB hard drive inside.

EDIT 2: It does have some sort of TBC, but not a very good one. It works well for 'normal' video, but I tried running a tape of '80s music videos through it, and when they have sections of the screen that are blacked out next to sections that have a full picture, there's still some pretty funky bending going on.

EDIT 3: I've figured out what it is. This crazy thing has some sort of automatic brightness control or something. It seems to be constantly adjusting the picture to maintain a consistent black level, which is honestly kind of annoying on my main CRT, and is probably the cause of the funky distortion I'm seeing on my 1959 Zenith. It's still not a bad purchase for $15 though, and I'll probably start using it to record some of my TV shows (since my VCR is honestly terrible at it -- it probably needs a cleaning, badly).

[NJRoadfan]

Originally Posted by jmetal88

EDIT 3: I've figured out what it is. This crazy thing has some sort of automatic brightness control or something. It seems to be constantly adjusting the picture to maintain a consistent black level, which is honestly kind of annoying on my main CRT, and is probably the cause of the funky distortion I'm seeing on my 1959 Zenith. It's still not a bad purchase for $15 though, and I'll probably start using it to record some of my TV shows (since my VCR is honestly terrible at it -- it probably needs a cleaning, badly).

It likely doesn't have a TBC. The brightness thing is likely overzealous Marcovision protection kicking in.

[jmetal88]

Originally Posted by NJRoadfan

It likely doesn't have a TBC. The brightness thing is likely overzealous Marcovision protection kicking in.

No, it's doing this while watching regular TV stations. The effect is actually far less pronounced when watching tapes.

You're probably right that it doesn't have a TBC, though. I think what the passthrough feature is actually doing is digitizing the video, writing it to memory, then playing back whatever is written in memory.

[old_tv_nut]

C106 and R156 are the main AFC loop filter components, in conjunction with R155.

I would try reducing the size of C106 first. How much is hard to say, but try 1/3 the size (about .05) first and see what you get. The bending should extend less down into the picture, but if it gets squiggly, then you need to play with the damping resistor R156.

This kind of modification is actually easily made by "decade box engineering." if you are observant. If you have a switchable capacitor box and a switchable resistor box, just substitute them for the C and R in the circuit, start with them set for the schematic values, and then note the effects of changing the values. It's wise to shut off the set before changing the switches, as you may have infinite resistance and infinitesimal capacitance between switch positions.

If you don't have decade boxes, the next easiest experimentation is substituting parts using clip leads - be careful that the connections are secure!

[maxhifi]

Thank you!! This is exactly what I will do, very appreciated advice!

[maxhifi]

Changed C106 to 0.047 and problem is a little better but far from watchable. In other words the bending did extend less far down and I did get squiggly. Going to have to get an assortment of capacitors and resistors and dig into this farther. Luckily havibg C106 at 0.047 does not affect anything with a dvd signal so the TV is still absolutely watchable. I am getting fast at pulling the chassis!

[old_tv_nut]

Originally Posted by maxhifi

Changed C106 to 0.047 and problem is a little better but far from watchable. In other words the bending did extend less far down and I did get squiggly. Going to have to get an assortment of capacitors and resistors and dig into this farther. Luckily havibg C106 at 0.047 does not affect anything with a dvd signal so the TV is still absolutely watchable. I am getting fast at pulling the chassis!

Yep, that's squiggly! But you can see that you could zero in on the correct values pretty quick if you had a variety handy to try.

[maxhifi]

Okay so I took the cop out solution - stopped by a thrift store today while doing something else and picked up a lite-on dvd writer for $9.99 CDN. Ran through that the picture is perfect. I still would like to make it work properly but the urgency is gone.