DVD Recorders in the A/V room

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russellhltn
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Postby russellhltn » Mon May 14, 2007 1:25 pm

Transformer: If it was one side of the secondary, the circuit would go from full-wave to half wave rectification and would cause a more ripple then the designers intended.

Diode: If it failed open, the power supply would again become a half-wave rectifier. The one I worry about is if the diode shorted and took out the transformer.

Capacitor: Quite possible. Although failure of capacitors running at 60 Hz aren't very common. (Switching power supplies are another story.)

Regulator: With a voltage regulator, there is no need to filter the DC down to pure DC. One only needs to keep the minimum instantaneous voltage from going under the regulator's minimum input voltage. If the regulator shorted out, it would cause an overvoltage to the rest of the modulator, but it would also pass on more hum then normal.

I hadn't thought of the over current, but that's also a possibility.

So, anything is possible. I'll just have to dig in and see what is wrong. However right now I'm packing to go on vacation so it might be awhile before I get to dig in.

skiptaylor
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Postby skiptaylor » Mon May 14, 2007 2:19 pm

rmrichesjr wrote:An open in one leg of the transformer's secondary winding or an open in one of the two diodes might cause hum by increasing the ripple voltage, but only if the design had _VERY_ little voltage drop across the regulator or a rather large intended ripple voltage across the capacitor. Another possible cause of the hum might be some other component (maybe not in the power supply section) pulling excessive current, but that would be accompanied by said component getting unusually hot, perhaps glowing red or letting out some quantity of smoke. A short across part of the transformer secondary might reduce voltage enough to cause hum, but the transformer would get much warmer than usual. Looking at the voltage across the capacitor should go a long way toward revealing the true culprit. Better yet, if you have two units of the same brand, would be to compare voltages and waveforms between the two units.


I think I know what's causing the problem, it's been overheated. I'm unfamiliar with the temperature level of the equipment, but the DVR396 is almost too hot to touch. It's right below the Pico modulator and heat does rise.

Someone has the rack in this area set this way:

Blonder-Tongue Modulator for Ch# 3
Pico Modulator for Ch#6
DVR396
Sanyo VHS Recorder stacked on
Sanyo VHS Recorder sitting on
shelf

I've suggested the DVR 396 be separate from the other components due to the heat it's giving off. Should they be THAT warm? The stake building stays in the low 70's most of the time. There is NO ventilation for the closet that I can see (who designed these?). There's another rack across from this one that's locked that houses all the audio amplifiers and transmitters. I've no key to that so I can't mess with it (their loss!).:D

I've called the local FM group and told them what's wrong. If they can't fix it, I guess I'll have to get out my gear and go do it myself. :eek:

Skip

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Postby russellhltn » Mon May 14, 2007 6:41 pm

avskip wrote:I think I know what's causing the problem, it's been overheated.


Maybe. In our rack (which has side vents) the modulators are all stacked together, but are separate from sat receiver and other items. I don't think the modulators are that warm and I think the survivor has been toward the top of the stack.

skiptaylor
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Postby skiptaylor » Mon May 14, 2007 11:10 pm

RussellHltn wrote:Maybe. In our rack (which has side vents) the modulators are all stacked together, but are separate from sat receiver and other items. I don't think the modulators are that warm and I think the survivor has been toward the top of the stack.
I guess I wasn't really plain enough in what I typed. It was all correct in my head when I typed it. ;)

What I meant was that the sat receiver seems to be really hot. The other components don't seem to have a large amount of heat except those close to the sat receiver.

We have side vents also.

I guess I'll see what they wind up fixing or replacing.

Skip

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Postby russellhltn » Tue May 15, 2007 1:58 am

avskip wrote:I guess I wasn't really plain enough in what I typed. It was all correct in my head when I typed it. ;)


No, I understood what you said. Heat dissipation is a valid concern when stacking. The receiver seems to run warmer then I'd like. It uses some small fan that I wonder when it will choke on the dust. (Seems like fan reliability is inversely proportional to the size of the fan. ;) ) Running 24/7 it's got to be collecting dust.

But I don't think heat is a primary factor in the failure of the modulators. If only one channel has hum bars in the video, then it has to be the modulator since it's the same video feed for all channels. The audio feed is what's different.

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Postby thedqs » Wed May 16, 2007 8:52 pm

rmrichesjr wrote:An open in one leg of the transformer's secondary winding or an open in one of the two diodes might cause hum by increasing the ripple voltage, but only if the design had _VERY_ little voltage drop across the regulator or a rather large intended ripple voltage across the capacitor. Another possible cause of the hum might be some other component (maybe not in the power supply section) pulling excessive current, but that would be accompanied by said component getting unusually hot, perhaps glowing red or letting out some quantity of smoke. A short across part of the transformer secondary might reduce voltage enough to cause hum, but the transformer would get much warmer than usual. Looking at the voltage across the capacitor should go a long way toward revealing the true culprit. Better yet, if you have two units of the same brand, would be to compare voltages and waveforms between the two units.


Great points and thanks for the corrections.
- David

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Postby skiptaylor » Fri Jun 01, 2007 2:51 pm

In all my looking I've only found 3 current models of DVD recorders that have an internal hard disk (DVR).

Thus far are a Sony model (very expensive), Pioneer and Philips. I don't recall all the model numbers, but I have noticed that the only one I seem to find available to purchase is the Philips and that's at Walmart!

Is there something I'm unaware of that's coming down the line to replace these units? Is the lack of product presence only because of their pricing?

Is recording direct to a blank DVD really THAT reliable?

I"m puzzled, but that's normal anymore.

Regards,
Skip

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thedqs
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Postby thedqs » Fri Jun 01, 2007 4:10 pm

My sister recently purchased the Toshiba DVD recordered that doesn't have the internal drive, but recording straight to DVD instead of hard drive doesn't improve the realiability just that you can at least preview the program before commiting it to disc. All the same options of titling the show, splitting it up into chapters, etc were available. If you really want a hard drive feel without the hard drive expense then just buy a few DVD-RW and record onto those. That way it is the same as having a 4.7 GB hard drive (except after 1000 or so re-records you have to replace the disc).
- David

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Postby rmrichesjr » Fri Jun 01, 2007 5:18 pm

avskip wrote:...
Is recording direct to a blank DVD really THAT reliable?
...


thedqs wrote:My sister recently purchased the Toshiba DVD recordered that doesn't have the internal drive, but recording straight to DVD instead of hard drive doesn't improve the realiability just that you can at least preview the program before commiting it to disc. All the same options of titling the show, splitting it up into chapters, etc were available. If you really want a hard drive feel without the hard drive expense then just buy a few DVD-RW and record onto those. That way it is the same as having a 4.7 GB hard drive (except after 1000 or so re-records you have to replace the disc).


I thought Skip's point was that recording straight to _only_ a DVD _reduces_ the reliability. When recording to hard disk on a decent system, there's very little probability of an I/O error causing loss of the content. When recording only to a DVD, if the DVD becomes a coaster, you just lost the content. If I were recording important one-of-a-kind content without a hard disk, I'd want two DVD recorders working in parallel and a VHS for good measure.

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Postby russellhltn » Fri Jun 01, 2007 6:16 pm

rmrichesjr wrote:If I were recording important one-of-a-kind content without a hard disk, ....


I'd find the manufactor's list of recommended media and use only that. In a ideal world, all blank media will work. But the truth is it's better to stick to the media the manfuactor actually calibrated the unit for.

I think the lack of hard drive in burners are because for most people who want that function they buy dedicated DVRs.


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