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MomPC: add video and audio outputs to Combo VCR/DCD/TV

 
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kgwbot
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Joined: 11 Apr 2009
Posts: 3

PostPosted: Sat Apr 11, 2009 11:18 pm    Post subject: MomPC: add video and audio outputs to Combo VCR/DCD/TV Reply with quote

Hello, my name is Kevin Waite, I am working on a complex project for a stroke patient. One part/phase of this project is to add a 2nd TV flat screen to their environment. Very low cost is a driving factor. The patient has a MAGNAVOX 27MDTR20/17 combo TV/DVD/VCR -- and it does not have video/audio outputs -- this sucks -- because solving this -- conventionally would mean adding a cable turner DVD recorder -- and that leaves out the VCR -- this would greatly increase complexity of the IR computer controlled efforts for MomPC.

Creating (hacking) an audio outputs is trival -- because I can tap the speaker left or right or both or tap the headphone jack..... Audio output is not my concern. . .

The video ouput is. How does one test for a video signal?

The main Tuner / VCR board found inside is a:
BTD850F01012 x4 Triple Main PCB -- the VCR box is found
above this board. I have found this board for sale as:
VHS PLAYER ASSY BTD850F01012 X4 from MAGNAVOX 27MDTR20/17
Part Type: VHS PLAYER ASSY

This board is connected to the DVD player board (or at least this 2nd "DVD" board is found under the DVD player box, see (b) below. (I have photos I can post.) These two boards are bridged (wire connected) via two 19 wired connectors labeled CN2804 CN2803

I can describe in great detail the various connections between the 4 primary circuit boards found within this 27MDTR20.

a) BTD850F01012 x4 Triple Main PCB w/ VCR drive box above
b) BTD930F01031-A DVD / power board with DVD drive box above
c) high voltage TV tube board mounted vert. on the left upper part of the
TV (looking at TV from the backside)
d) small circuit board attached to the business end of the TV tubes cathode.

This TV allows the user to select between AUX, TV, DVD, VCR -- if a DVD is started or if a tape in the VCR is started -- then the scope of TV output jumps automatically to the corresponding play beginning device either DVD or VCR.

Bottom line -- if I could find the TV signal in composite / or / s-video / or / componet form -- at any pathway within the inside of this TV -- that would allow me to hack and get my desired Video output.

There are 8 wire ribbon cables connecting these boards, and there is
a 5 wire ribbon cable going from board (a) to the business end of the cathode of the TV tube. There is a logical flow of 8 wire ribbon connectors -- I mean -- it appears that there are both DVD and VCR 8 wire ribbon connectorst going up to the vert. mounted circuit board that includes the high voltage circuits for the picture tube.

Please send me any help you know about to carry out or understand if this is impossible or not. These 8 wire ribbon cables are most likely carrying the video and possibly audio signals -- does anyone have spec sheet for these or any of these boards? If these are carying a video signal what type of video signal would it be?

Thank you in advance.

You can learn more abour MomPC at:
http://forums.trossenrobotics.com/blog.php?b=165
http://forums.trossenrobotics.com/blog.php?b=168
http://forums.trossenrobotics.com/blog.php?b=169
http://forums.trossenrobotics.com/blog.php?b=172

Sincerely,
Kevin Waite
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kgwbot
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Joined: 11 Apr 2009
Posts: 3

PostPosted: Sun Apr 19, 2009 3:07 am    Post subject: Significant progress Reply with quote

MomPC: add video and audio outputs to Combo VCR/DCD/TV

Significant progress!

Found a scope on Ebay from someone very nearby. Today I took readings from many logical locations on the Magnavox combo TV’s motherboard and came up with the following details:

Please check this web page:
http://www.kevinwaite.com/MomPC/


Before I start connecting other video equipment to jumper J1298 – if anyone out there knows about the following measured voltage increases.

J1298 (a) appears to be a composite video signal – but it also appears to be 2 times greater voltage than the input composite found on Ext. V-IN J1297. J1298 (a) carries the selected signal of DVD/VCR and TV.

The RED J1831 (and it shows more trace activity was more red is shown) (same for Green and for Blue) – these signals are about 6 times greater than the input composite found on Ext. V-IN J1297. Test points RED GREEN BLUE test points carry the selected signal of DVD/VCR and TV.

Any input or guidance – is greatly appreciated.

Thanks.

Sincerely,
Kevin Waite


The main Tuner / VCR board found inside is a:
BTD850F01012 x4 Triple Main PCB -- the VCR box is found
above this board. I have found this board for sale as:
VHS PLAYER ASSY BTD850F01012 X4 from MAGNAVOX 27MDTR20/17
Part Type: VHS PLAYER ASSY
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sun Apr 19, 2009 7:45 am    Post subject: Reply with quote

I am not a video expert so I can't really help in that department. You could look into using a voltage divider circuit to get the signal to the right level then use an old TV (look for a tube TV that most people are just throwing in the garbage) and see if you get something that is usable.

Is this project a single use project or is it something that you are thinking would be used for lots of people out there. I don't want to sound negative and discourage your progress but would this effort not tie your technology very close to an old piece of equipment.
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kgwbot
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Joined: 11 Apr 2009
Posts: 3

PostPosted: Sun Apr 19, 2009 6:25 pm    Post subject: MomPC: add video and audio outputs to Combo VCR/DCD/TV Reply with quote

Hi Alan, thanks for the info/feedback -- do you have an example of a voltage divider circuit -- one that can handle the frequencies of NTSC video -- links?

Yes -- this hack -- of this combo TV is a one-off -- not the major part of what is MomPC -- MomPC is described here:
http://forums.trossenrobotics.com/blog.php?b=165
http://forums.trossenrobotics.com/blog.php?b=168
http://forums.trossenrobotics.com/blog.php?b=169
http://forums.trossenrobotics.com/blog.php?b=172

My mom will be the first user of MomPC -- and I am enhancing her post stroke room/world/environment in all ways possible -- her combo TV not having outputs really bugged me and I pondered that maybe inside the video out was just not added -- but the signal was to be found on the main TV circuit board. This proved not to be exactly the case, but finding the composite NTSC signal post the selecting of input (VCR/DVD/TV) post me very close to making this hack good.

Thanks again.

Sincerely,
Kevin Waite
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Alan
Site Admin


Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sun Apr 19, 2009 6:50 pm    Post subject: Reply with quote

Have a look at this page for more details on how a voltage divider works
http://en.wikipedia.org/wiki/Voltage_divider

For example you would be able to cut the voltage in half by using two equal sized resistors.
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