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  #16  
Old 06-21-2013, 10:59 AM
jmetal88 jmetal88 is offline
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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.
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  #17  
Old 06-21-2013, 04:47 PM
jmetal88 jmetal88 is offline
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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).

Last edited by jmetal88; 06-22-2013 at 01:48 AM.
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  #18  
Old 06-22-2013, 09:20 PM
NJRoadfan NJRoadfan is offline
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Quote:
Originally Posted by jmetal88 View Post
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.
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  #19  
Old 06-23-2013, 12:59 AM
jmetal88 jmetal88 is offline
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Originally Posted by NJRoadfan View Post
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.
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  #20  
Old 06-23-2013, 09:58 PM
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Electronic M Electronic M is offline
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Quote:
Originally Posted by NJRoadfan View Post
This. A proper TBC will solve any viewing issues with old TVs and lead to higher quality video output as well. A great overview is found here: http://www.digitalfaq.com/forum/vide...time-base.html

When I do captures for DVD transfers, I usually use a SVHS VCR with a line TBC (true Time-base correction) to correct horizontal jitter and an external full-frame TBC (really just a frame sync/buffer as my unit does little jitter correction) to clean up the sync (front/back porch, color burst, etc) and output proper RS-170a to the capture card. It also provides a stable continuous sync signal to prevent frame dropping.

A popular DVD recorder with pass-through TBC is the Panasonic DMR-E10. Some of the JVC DVHS machines also have pass through TBC functionality as well.
I'd love to have a professional one, but I could not even afford a 20$ used pro unit at a ham fest a week back(low on my priorities compared to caps for my restorations).

I always thought of a TBC as only cleaning synch issues and not the video that makes it to the screen...That site stretches the definition I've always had of a TBC.

I mostly use a Toshiba D-VR5 for elimination of flag waving/ bends at the top of the screen on my tube sets. I feed it S-video from my JVC HR-S3912U SVHS-ET deck(the Toshiba is a VCR/DVD recorder, but I don't like or use the tape section of it). I also have a Panasonic DMR-E80H that may have a TBC, but the current state of my system wiring prevents me from easily testing that.

I do have a NEC brand DS8000U mkII SVHS deck with a three setting "Digital NR" that improves video noise issues(I can't find any info about this deck online). It does get motion issues at it's highest setting, but the lower settings seem to get the job done without doing that to an objectionable or noticeable extent.

I almost never transfer video tape to digital formats...As I prefer to watch my tapes on a CRT TV with a tape deck(In fact aside from my computers, which I rarely watch video on, I only use CRTs for the video I watch). Also most of my tapes are first gen time-shifts made on decks I still own and keep working, so anything more than synch correction is not all that noticeable or important to me.
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Last edited by Electronic M; 06-23-2013 at 10:08 PM.
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  #21  
Old 11-08-2014, 07:41 PM
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maxhifi maxhifi is offline
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Encountering issue on my ctc-38. Played one tape without an issue then the next one had massive bending at the top, tried a third and same thing. Horizontal AFC circuit is a bit different than the zenith earlier in this thread - any ideas which parts to mess with ?
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  #22  
Old 11-08-2014, 10:34 PM
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old_tv_nut old_tv_nut is offline
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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!
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  #23  
Old 11-09-2014, 01:06 AM
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maxhifi maxhifi is offline
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Thank you!! This is exactly what I will do, very appreciated advice!
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  #24  
Old 11-09-2014, 01:04 PM
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maxhifi maxhifi is offline
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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!
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Last edited by maxhifi; 11-09-2014 at 01:29 PM.
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  #25  
Old 11-09-2014, 03:07 PM
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maxhifi maxhifi is offline
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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.
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  #26  
Old 11-09-2014, 08:18 PM
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old_tv_nut old_tv_nut is offline
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Quote:
Originally Posted by maxhifi View Post
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.
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