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-   -   Help with National NV-780EM VHS (https://www.vintage-radio.net/forum/showthread.php?t=120045)

alm7rom 4th Oct 2015 8:58 pm

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 ...???

Clydeuk 5th Oct 2015 12:50 am

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.

alm7rom 5th Oct 2015 2:19 am

Re: Help with National NV-780EM VHS
 
i think it is not in the power
i have another power it's the same problem

John123 5th Oct 2015 4:54 pm

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.

dj_fivos_sak 6th Oct 2015 2:26 pm

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.

Maarten 6th Oct 2015 2:41 pm

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.

vhs doctor 6th Oct 2015 4:40 pm

Re: Help with National NV-780EM VHS
 
When you press the operate button can you hear the capstan motor rotating?

alm7rom 7th Oct 2015 12:15 am

Re: Help with National NV-780EM VHS
 
Yes

vhs doctor 7th Oct 2015 9:32 am

Re: Help with National NV-780EM VHS
 
When the capstan rotates check if the supply reel table also rotate

alm7rom 8th Oct 2015 7:45 am

Re: Help with National NV-780EM VHS
 
Yes

vhs doctor 8th Oct 2015 9:39 am

Re: Help with National NV-780EM VHS
 
The second display below the deck (function display) works ok???

alm7rom 8th Oct 2015 9:04 pm

Re: Help with National NV-780EM VHS
 
Yes work but shut down in second the clock still working

dj_fivos_sak 8th Oct 2015 9:49 pm

Re: Help with National NV-780EM VHS
 
Check the zener diode and the caps in the switching power supply.

Libratron 9th Oct 2015 4:19 pm

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.

Libra

ben 9th Oct 2015 10:34 pm

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.

Maarten 10th Oct 2015 1:51 am

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.

vhs doctor 10th Oct 2015 11:10 pm

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.

HamishBoxer 11th Oct 2015 3:05 pm

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?

alm7rom 12th Oct 2015 1:11 am

Re: Help with National NV-780EM VHS
 
thank you all
I will do everything

boxdoctor 14th Oct 2015 4:28 pm

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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