Looking for circuit to keep Zenith DTT901 on constantly? - AVS Forum
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post #1 of 23 Old 06-14-2009, 04:30 PM - Thread Starter
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Looking for circuit to keep Zenith DTT901 on constantly?

When the power button on a Zenith DTT900/901is pushed it momentarily shorts a 3-volt line, which causes the box to power up.

I am looking for a simple circuit that can be added so that the box will power its self up when ever it is plugged in.
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post #2 of 23 Old 06-14-2009, 08:07 PM
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I'm not going to answer your question because I Don't know but suggest an alternative (although perhaps I misunderstood the goal). Why not set the autooff option to "off" so once you push the power button to turn it on, it stays on until you turn it off?
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post #3 of 23 Old 06-14-2009, 08:24 PM
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I believe he has something like a power strip with numerous things on it, and wants this box to turn on with everything else when the strip is powered up..

First, that is a scanned key, and all other keys (On the box) will become inoperatable once you hold it.
So what you choose to do will need to one-shot, then release if you want to use other buttons on that box.

It may also negate the use of remote control functions too as they share the same command structure elsewhere.

Try holding the "on" button on the box while plugging it in,
and while still holding it try to change channel with your remote after it finishes it's self-initiating startup procedure.
You may not be able to use the remote either.

That would rule out the simple option of simply dropping a drop of solder across those contacts (Like some others here have done on other models).

If I still had one here, Id give you an exact answer, I moved on to the CM-7000's

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post #4 of 23 Old 06-14-2009, 09:16 PM - Thread Starter
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WeThePeople you sir are correct as usual.

I have an old TV that uses a power on relay and will remember its power on state when unplugged. If I can find out how to make a Zenith CECB act the same way I can just run an extension cord type power switch and turn them both on and off using 120-volts. It will be the same as turning them on and off with a light switch. Not only will this prevent wasted standby juice but protect from lighting damage when not in use.

I found a way to do this with an Artec T3AP using a small cap but it uses a 6-pin power up chip that was easy to find. With the cap added to the circuit the T3AP will power its self up when plugged in but can still be powered off with the on/off switch or remote.
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post #5 of 23 Old 06-14-2009, 09:46 PM
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Then you'll simply need to incorporate a transistor's emitter/collector across those scanned X and Y matrixes (The two contacts on that "on" button),
with a resistor from the base from one of the contacts,
through a very small electrolytic capacitor that will charge biasing the base into turning the transistor on until the cap is charged and ceases to hold the transistor in the forward conduction part of it's operating curve.

But this is the hard way.

When all is said and done on an X/Y matrix scanned keypad set,
a signal wire will leave the main board heading to the supply board to turn it on. You might want to look for that and work a simpler solution.

Again, I would just shoot a schematic to you, but I no longer have one of those models anymore.

Could another technician with one of these take a peek for Ron?

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post #6 of 23 Old 06-15-2009, 05:16 AM
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Maybe not the answer you want, but a box like the CM-7000 remembers what state it was in when it was unplugged and goes back to that. For example if the box was ON and then unplugged, when it was plugged back in it would return to ON, it it was OFF it would stay off when power returned.
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post #7 of 23 Old 06-15-2009, 02:33 PM
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Quote:
Originally Posted by ron350 View Post

Looking for circuit to keep Zenith DTT901 on constantly?.

I have a cable headend using these, the headend tech tells me you can solder a jumper across the on/off button and the box will return powered on.

I just tested this, it works fine if you want to leave the box on the same channel all the time and the osd on....
And, as we the people says, pushing another key does indeed then turn the box off.

BTW, I have a friend at LG in engineering, he tells me they aren't releasing schematics for the 900/1.

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post #8 of 23 Old 06-15-2009, 03:22 PM
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One should also consider a cheap UPS, I have one use where the 901 and the DVD recorder are on a cheap 250va UPS I got for $19 on sale.

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post #9 of 23 Old 06-15-2009, 05:14 PM
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TY Bob,
I suspected that would do fine.
Seeing as going to the box to push the on button is the (Original) issue,
I strongly suspected the lack of usability of other buttons woukld not be an issue.

Does the remote still work though?

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post #10 of 23 Old 06-15-2009, 06:03 PM
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Quote:
Originally Posted by WeThePeople View Post

Does the remote still work though?

Didn't try remote..especially since OSD did not go away when power button is held.I wonder if the 900 is different under these conditions? I suspect that it will NOT work tho. In speaking with my bud at LG,I explained to him the need for a locked-down box for MATV and other specialty (recording) usage. His comment was they aren't making any money on this box and basically did it to placate the powers that be, and that these boxes are a one-time item.

With my 901 that is on UPS and left on the same channel all the time, it occasionally will lock up putting the blue garbage text on screen others have described. At that point, it's pull the plug time.

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post #11 of 23 Old 06-15-2009, 06:59 PM
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Quote:
Originally Posted by bdfox18doe View Post

Didn't try remote..especially since OSD did not go away when power button is held.

Sounds like a one-shot circuit like requested could be of value elsewhere then. I take it the OSD is not on the output your using for the headend feed then? Sure would suck to redistribute that OSD full time in an MATV enviroment.

Quote:
Originally Posted by bdfox18doe View Post

In speaking with my bud at LG, I explained to him the need for a locked-down box for MATV and other specialty (recording) usage. His comment was they aren't making any money on this box and basically did it to placate the powers that be, and that these boxes are a one-time item.

I fully understand the placation issue. But that they didn't provide commercial firmware to address this issue tells me LG/Zenith/Insignia consider these consumer toy-level units. I did find a site that held schematics for all thet were required to pass FCC ATSC tesing for the CECB certification. I found it doing some intricate boolean expression googlin' one day. Sad they won't release them.

I am however horrified that a properly engineered commercial grade rack mount ATSC unit with proper heatsinking, rack cooling integration, and power management is not being used in the field as a matter of course (Can you say Highland Cable, Etc.).
Just wow.

I can understand using CECB's in economy-sensitive MATV redistribtion installs though.

Quote:
Originally Posted by bdfox18doe View Post

With my 901 that is on UPS and left on the same channel all the time, it occasionally will lock up putting the blue garbage text on screen others have described. At that point, it's pull the plug time.

Slight line glitches were notorious to the unit I had. My storage scope caught them, and they were fairly minimal considering all.

I used large electrolytic capacitors on the first 900 unit
(before my UPS/901 setup next) to negate the Central Point Electriciy
grid switching dropout here in Houston just before dawn
and any ole time mid afternoon very single day.

Even the switching time on consumer grade UPS's were a problem with this unit, although all other equipment on it had no issues with them here.

It never locked up after that.
I thought it PSIP info errors at first BTW.
Of couse I never did put the cover back on either
until I returned it for a 901, so maybe it was a heat issue...

A simple two component solution is an optocoupler.
Emittier.Collector acros the power button pads,
Electrolytic cap through internal LED to ground from B+.

The charge surge from a power supply buss through the cap would provide a quick "Closure" of the power button path upon initial AC supply connection until the cap was charged and released the closure condition.

That is, if the the unit was ready for it...

The CM-7000 as example does a POST (Power On System Test) indicated by the red LED until it goes orange and awaits a power button press to display green for ON.
So it would have to be determined that the 901 would be ready for that power button pseudo-press right away upon power application.

Then again, like Jjeff said, the CM-7000 remembers It's last power state (Amoungst other things) in non-volitile memory.

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post #12 of 23 Old 06-16-2009, 04:33 AM
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Quote:
Originally Posted by WeThePeople View Post


I am however horrified that a properly engineered commercial grade rack mount ATSC unit with proper heatsinking, rack cooling integration, and power management is not being used in the field as a matter of course (Can you say Highland Cable, Etc.).
Just wow..

I thought the same thing, but then the cable guy told me that all the commercial demods he had tried were not as sensitive as the 901. They're way out of our coverage area, so he's lucky to be getting a signal at all.

Of course, I do have one commercial demod that doesn't have proper heatsinking, rack cooling integration..and requires a fan on it.

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post #13 of 23 Old 06-16-2009, 06:39 PM
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Quote:
Originally Posted by bdfox18doe View Post

....Of course, I do have one commercial demod that doesn't have proper heatsinking, rack cooling integration..and requires a fan on it.

LOL, will manufactures ever learn...

If anyone wants to send me a 901 for a bit,
I'll noodle out a simple two to three piece add-on using only what is available from Radio Shaft so everyone has fair access to the solution.

It will retain the remote control, and not keep the OSD on all the time.

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post #14 of 23 Old 06-16-2009, 10:10 PM - Thread Starter
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Thanks WeThePeople just had to find the right optocoupler.

I was having intermittent luck with a P621 and tried a P627 and it works. Just had to add a 10K bleed resistor across the cap so the cap would discharge.

Similar to a degauss circuit on a TV that fires a relay but the cap bleeds down through the relay windings.

Edit

Thanks again.
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post #15 of 23 Old 06-16-2009, 10:28 PM
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Knew it would be simple Ron.

when you get a chance,
scribble it out and post it here for Bob, his tech friends, and others whom may benifit by duplicating it too.

If you need a pic, the 901 threads are full of them near the beginning of each thread when oogling the insides satisfied curiosities of what was in the newer unit (replacing the non-APT 900).

Doodlin' on top of an existing board shot pic might provide a better visual aid to those not fully schematic-literate here, that can still solder.

For the record, many pieces of equipment in the marine electronics arena that I have worked on have opto-isolator's on as many input wires as possible due to the enviroment being rich with outrageous levels of RF interference (Like ubber-wattage single sideband radio's, and VHF radio's with linear amplifiers way above what the FCC would tolorate on land...).

Thats why the opto idea came quick...

For those that want to start familierizing yourself with this IC,
here is the (TLP627-x) PDF Datasheet from Toshiba's own site.

Note, it comes in multiple segments in 8 and 16 DIP packages,
not just the single segment in the 4 pin DIP offering ...

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post #16 of 23 Old 06-16-2009, 11:26 PM - Thread Starter
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No wonder the P627 conducted so well it is a darlington with a damper diode.

Strange I cannot find an optocoupler on RadioSkacks page or in their last catalog? They used to sell a 6-pin optocoupler part #276-134?

They still sell the small relay radioshack #275-232 @$2.99.
http://www.radioshack.com/product/in...ductId=2062478
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post #17 of 23 Old 06-17-2009, 01:53 AM
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Yeah, they were only $1.99 too.

The Shaft used to carry a lot of good discreet components and custom IC's.

Now all they have is a lousy page and a half HERE.

$3.49 will get you a Matching Pair of IR-LED and IR-Transistor you could connect by heatshrink tubing I suppose...

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post #18 of 23 Old 06-17-2009, 03:45 AM
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Quote:
Originally Posted by ron350 View Post

Guess such a simple circuit was beneath them. LOL

Some of us have better things to do with our time. But I will pass your data on to my cable buddies up in yonder boondocks. Thanks!

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post #19 of 23 Old 06-17-2009, 05:46 AM
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Quote:
Originally Posted by WeThePeople View Post

...I can understand using CECB's in economy-sensitive MATV redistribtion installs though.

...the CM-7000 remembers It's last power state (Amoungst other things) in non-volitile memory.

Sorry if I am repeating something that may have been already posted in the CM7000 thread or elsewhere, but I've bought and installed close to 100 CM7000s in MATV headends, and have discovered that the most recent few dozen are "stubborn" when I try to disable the 4 hour shutoff. I go into the menu and navigate to the disable screen, it forewarns me that I am about to become an energy waster and a blight on society and asks me if I want to proceed, I proceed anyway and uncheck the two boxes, and then I exit, thinking my power-down problems are solved. I can even go back into the menu and confirm that those two boxes are still unchecked. But four hours later, the box will go off again, as the checks in those boxes have been retored. I then have to repeat the process, but it seems to "take" the second time around.

I don't have enough time to test some boxes side by side to see if I can fare better by exiting the disable screen by using "exit" rather than "menu". From now on, I'm going to have to set up these boxes in my shop and confirm that the 4-hour auto power-down problem has been solved before I deliver them to any hotels where they won't report that they have shut off until an angry guest calls the desk in the evening.
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post #20 of 23 Old 06-17-2009, 06:10 AM
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ron350 and wethepeople could make a nice profit selling modified 901's for just this purpose. If LG would take the time to modify the software, and have a
nice 1RU rack kit they'd sell a ton of them for MATV. But they did not seem interested when I mentioned that to them.

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post #21 of 23 Old 06-17-2009, 06:28 AM
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They're probably more interested in selling the over-priced/underperforming flat screen televisions.

I saw a news segment last week where some big city was recycling televisions for free and the yard in the background must have had 20-30 pallets stacked with 27" televisions wrapped with shrink. I wonder how many of those sets were perfectly usable.
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post #22 of 23 Old 06-17-2009, 08:15 AM
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Quote:
Originally Posted by AntAltMike View Post

.....and have discovered that the most recent few dozen are "stubborn" when I try to disable the 4 hour shutoff. I go into the menu and navigate to the disable screen, it forewarns me that I am about to become an energy waster and a blight on society and asks me if I want to proceed, I proceed anyway and uncheck the two boxes, and then I exit, thinking my power-down problems are solved. I can even go back into the menu and confirm that those two boxes are still unchecked. But four hours later, the box will go off again, as the checks in those boxes have been restored. I then have to repeat the process, but it seems to "take" the second time around.

The test is positively draconian in nature to determine this.

Accept the non-green scorns and uncheck/accept the change.
Once out of all menu's, UNPLUG IT.

This will tell you if was ever written to the non-volitile flash memory the first place.
Or if their newer ROM's firmware coding update is reverting your choice.

Let us know, thanks.

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post #23 of 23 Old 06-17-2009, 08:18 AM
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Quote:
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.....I wonder how many of those sets were perfectly usable.

All of them...

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