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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 4th Oct 2015, 8:58 pm   #1
alm7rom
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Default Help with National NV-780EM VHS

the problem in this video when i press vtr
its turn on for a second and off. the clock working
what the problem ...
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Old 5th Oct 2015, 12:50 am   #2
Clydeuk
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Default Re: Help with National NV-780EM VHS

Sorry don't know the model but would suggest worth checking the power supply for bad capacitors. Very common on some Panasonic units. Just a starting point maybe others can elaborate.
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Old 5th Oct 2015, 2:19 am   #3
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Default Re: Help with National NV-780EM VHS

i think it is not in the power
i have another power it's the same problem
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Old 5th Oct 2015, 4:54 pm   #4
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Default Re: Help with National NV-780EM VHS

Not sure if this model has automatic power-up when inserting a tape, but worth trying if it has. Also check the VTR switch isn't sticky or damaged; clean the mode switch; check for dry solder joints.
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Old 6th Oct 2015, 2:26 pm   #5
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Default Re: Help with National NV-780EM VHS

I have the service manual for this machine. This model has a switching power supply since it is 110-240 volt automatic. And it is a multi system too.
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Old 6th Oct 2015, 2:41 pm   #6
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Default Re: Help with National NV-780EM VHS

Try heating the power supply with a hair dryer. If the situation improves while it is hot, it has bad capacitors for sure. If the situation doesn't improve, it can still be anything.
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Old 6th Oct 2015, 4:40 pm   #7
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Default Re: Help with National NV-780EM VHS

When you press the operate button can you hear the capstan motor rotating?
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Old 7th Oct 2015, 12:15 am   #8
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Default Re: Help with National NV-780EM VHS

Yes
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Old 7th Oct 2015, 9:32 am   #9
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Default Re: Help with National NV-780EM VHS

When the capstan rotates check if the supply reel table also rotate
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Old 8th Oct 2015, 7:45 am   #10
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Default Re: Help with National NV-780EM VHS

Yes
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Old 8th Oct 2015, 9:39 am   #11
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Default Re: Help with National NV-780EM VHS

The second display below the deck (function display) works ok
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Old 8th Oct 2015, 9:04 pm   #12
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Default Re: Help with National NV-780EM VHS

Yes work but shut down in second the clock still working
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Old 8th Oct 2015, 9:49 pm   #13
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Default Re: Help with National NV-780EM VHS

Check the zener diode and the caps in the switching power supply.
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Old 9th Oct 2015, 4:19 pm   #14
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Default Re: Help with National NV-780EM VHS

Check the All Voltage in the PSU.
You need Schematic and SM of this VTR,
to check the voltage's are coeherent with the schematic.

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Old 9th Oct 2015, 10:34 pm   #15
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Default Re: Help with National NV-780EM VHS

This is a relatively early front loader from the mid 80s. D deck.
If it's the one I'm thinking of, it has a transformer PSU.

On powerup, the mech should 'shuffle' the reel idler. If this doesn't happen, then the drive belts should be replaced and the mode switch cleaned. That shoud solve this fault.
There was also a resistor of very low ohms/safety type, that used to go high, cannot recall if it was in the PSU or on the main PCB where the voltage lines come in. Will try and find some info.
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Old 10th Oct 2015, 1:51 am   #16
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Default Re: Help with National NV-780EM VHS

I think that one is on the main PCB. At least in the NV-830 and NV-850 which may be related models. R1001 or something close to that comes to mind.
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Old 10th Oct 2015, 11:10 pm   #17
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Default Re: Help with National NV-780EM VHS

You can download the service manual from here

http://freeservicemanuals.info/en/se...sonic/NV780EM/

These type of panasonic/national mechanism (D1) when the VCR operates the mechanism proceed a <<selftest>> the capstan motor rotate the suplly reel table and the loading motor make a small movement (rotation). if the self test find a failure the VCR rotate for a few seconds the capstan or the loading motor (it depends from the failure) and then turn OFF.
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Old 11th Oct 2015, 3:05 pm   #18
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Default Re: Help with National NV-780EM VHS

I believe the person who the machine belongs to has tried another power supply and still has the same fault?
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Old 12th Oct 2015, 1:11 am   #19
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Default Re: Help with National NV-780EM VHS

thank you all
I will do everything
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Old 14th Oct 2015, 4:28 pm   #20
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Default Re: Help with National NV-780EM VHS

My money is on the mode switch being faulty or having dirty contacts.
I had a lot of trouble with this series not doing its switch-on 'shuffle' and then shutting down due to the mode switch having dirty contacts. Tony
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