Zenith OTA STB (trouble displaying ABC 720P) (1 Viewer)

[MikeSno]

I recently purchased a used Zenith HDV420 High Def Ota Set Top Box. The unit works great displaying NBC CBS PBS 1080I broadcast on my Mitsubishi WS48311. The Mits does not display 720P but the Zenith STB should upconvert it to 1080I. The display with ABC is out of sync. The picture stutters and stalls and is not watchable. It even does this if you display it via Svidio 480I. Has anyone had this problem before or have any solutions? I have a feeling the only solution would be a set that displays 720P. Any help would be greatly appreciated.

Mike

 

[Steve Schaffer]

I would very strongly suspect that you have a reception problem with that ABC station rather than a problem with upconversion/downconversion. Having had ota HD reception for over 2 years and my share of problems, what you describe sounds just like weak signal or multipath problems. Try checking the signal meter for that ABC station. I know that box has a signal meter as I once owned one. Check your owner's manual as my memory isn't good enough to tell you exactly how to bring up the meter.

If the meter is in the "normal" to "good" range you should be getting enough signal strength, however if the meter jumps around a lot you have too much multipath for the box to get a good bitstream. Try re-aiming the antenna.

In all my experience and research at this and AVS forum on HD set top boxes I've never read of one having a problem with scanrate conversion causing your reported symptoms, I'm virtually certain you have a reception problem with that one station.

I've also had the same picture "stalling" problem when the station's encoding equipment was on the fritz.

You might try posting an inquiry in the Local HD reception forum over at AVS forums, putting your location and the ABC stations call letters in your header--others in your area can report as to whether they are also having problems with that particular channel so as to eliminate the broadcaster as the source of the problem.

 

[MikeSno]

Thanks for responding Steve. Unfortunately, that is not the issue. I have a strong 93% signal and I receive ABC non-high def broadcasts perfectly. I also get the signal perfect on my RCA DTC100 high def receiver. Thanks again for your help...it is very much appreciated.

Mike

 

[Steve Schaffer]

Mike,

Since you mention such a high signal strength it may be a case of too strong a signal. This can cause the box to confuse a reflected (multipath) signal for the main one and cause the problems you're having.

The difference in signal strength between the main signal and any reflected signals has to be more than 15db for the box to effectively reject the multipath signal. I've had instances where I got better reception of some stations at much lower signal strengths than others with much higher ones. A Hughes E-86 I had would pixellate like crazy with my local ABC station at a 90% signal strength, but be solid as a rock with a strength of only 40.

The 420 is a very sensitive box, probably more so than the DTC-100. The manual for the 420 I had for a while stated that a too-strong signal can actually create reception problems. The one I had came with a signal strength attenuator to be put inline with the cable from the antenna in order to correct the overstrong signal.

Radio Shack sells a variable attenuator that has helped some people with this problem. If your box didn't come with the fixed attenuator this may be of help to you.

I had good reception with my 420. I did return it because I wanted a DirecTV capable receiver with good local ota reception to replace the Hughes which was lousy ota. The 420 and the then available Sony HD-200 had the same ota tuners, so I bought the 420 for "triesies" intending to return it for the HD-200 if it's ota tuner solved my local reception problems, which it did.

Sorry to sound like I'm beating a dead horse, just thought of the attenuator thing after my last post and thought it might be of some help.

The LG-mfg boxes (Zenith, Sony, Hughes HTLD) have about the best local ota tuners available now.

Your box may indeed have a 720p to 1080i conversion problem, but if it does it's a malfunction in that one box and not a characteristic of the model in general.

 

[John S]

I use the same Zenith 420 midel STB and do not have any issues with ABC and 720p and it upconverting it to 1080i for display on my Philips.


You may have good signal, but I'll bet your getting a bad reflection from somewhere along the way.

 

[MikeSno]

John,
If I were getting a bad signal, why would the picture be fine during non high def broadcasts?

Thanks
Mike

 

[Steve Schaffer]

Mike,

Do you get a solid picture from the ABC HD channel when they are broadcasting upconverted non-hd programming? If so, the problem is not in the box's 720p/1080i conversion.


Digital broadcast channels don't switch from one scanrate to another depending on whether the content is actually HD.
When the program being broadcast on a 720p HD channel is not true HD, the station puts black bars on the sides or in a few cases stretches the image and broadcasts the picture as a 16/9 720p image.

For example, my ABC affilliates HD channel is 30.1 (actually broadcast on VHF channel 9). 30.1 is 720p all day every day 24hrs. When not broadcasting a true HD program the station upconverts the analog broadcast to 720p and puts black bars on the side, so even though the program is not HD, the signal is still 720p and my box still has to convert it to 1080i.

If you are getting a good picture from that channel when the program is not in HD, but a bad picture when the program is HD, the problem is with your local station's ability to pass the HD signal from the network. As long as it's the channel that broadcasts HD, it's broadcasting in 720p all the time, even when the program is not HD, and thus your 720p/1080i conversion is ok.


If that channel is bad all the time, there are any number of possible reasons why it's bad and your other HD channels are ok, the least likely of which is your box's 720p/1080i conversion.

 

[MikeSno]

Steve,
I will do some more checking. I really don't think it is a problem with the broadcast because my RCA High Def Receiver has a perfect picture. I know the Zenith Box has a better receiver. It holds other stations much better. I live 50 Miles from the station. The only other difference between my ABC Channel is ,it is broadcast via VHF. All my other high def channels are UHF

Thanks for all your input.
Mike