Help with National NV-780EM VHS - UK Vintage Radio Repair and Restoration Discussion Forum

alm7rom · 4th Oct 2015, 7:58 pm

the problem in this video when i press vtr
its turn on for a second and off. the clock working
what the problem ...

Clydeuk · 4th Oct 2015, 11:50 pm

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, 1:19 am

i think it is not in the power
i have another power it's the same problem

John123 · 5th Oct 2015, 3:54 pm

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, 1:26 pm

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, 1:41 pm

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, 3:40 pm

When you press the operate button can you hear the capstan motor rotating?

alm7rom · 6th Oct 2015, 11:15 pm

Yes

vhs doctor · 7th Oct 2015, 8:32 am

When the capstan rotates check if the supply reel table also rotate

alm7rom · 8th Oct 2015, 6:45 am

Yes

vhs doctor · 8th Oct 2015, 8:39 am

The second display below the deck (function display) works ok

alm7rom · 8th Oct 2015, 8:04 pm

Yes work but shut down in second the clock still working

dj_fivos_sak · 8th Oct 2015, 8:49 pm

Check the zener diode and the caps in the switching power supply.

Libratron · 9th Oct 2015, 3:19 pm

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, 9:34 pm

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, 12:51 am

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, 10:10 pm

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, 2:05 pm

I believe the person who the machine belongs to has tried another power supply and still has the same fault?

alm7rom · 12th Oct 2015, 12:11 am

thank you all
I will do everything

boxdoctor · 14th Oct 2015, 3:28 pm

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

4th Oct 2015, 7:58 pm	#1
alm7rom Triode Join Date: Sep 2015 Location: Al-Kharj near Riyadh, Kingdom of Saudi Arabia. Posts: 38	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 ...

4th Oct 2015, 11:50 pm	#2
Clydeuk Hexode Join Date: Mar 2012 Location: Liverpool, Merseyside, UK. Posts: 430	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.

5th Oct 2015, 1:19 am	#3
alm7rom Triode Join Date: Sep 2015 Location: Al-Kharj near Riyadh, Kingdom of Saudi Arabia. Posts: 38	Re: Help with National NV-780EM VHS i think it is not in the power i have another power it's the same problem

5th Oct 2015, 3:54 pm	#4
John123 Heptode Join Date: Jan 2007 Location: Luton, Bedfordshire, UK. Posts: 717	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. __________________ Regards, John

6th Oct 2015, 1:26 pm	#5
dj_fivos_sak Heptode Join Date: Mar 2015 Location: Lefkada, Greece Posts: 796	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.

6th Oct 2015, 1:41 pm	#6
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 3,108	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.

6th Oct 2015, 3:40 pm	#7
vhs doctor Pentode Join Date: Oct 2011 Location: Athens, Greece. Posts: 130	Re: Help with National NV-780EM VHS When you press the operate button can you hear the capstan motor rotating?

6th Oct 2015, 11:15 pm	#8
alm7rom Triode Join Date: Sep 2015 Location: Al-Kharj near Riyadh, Kingdom of Saudi Arabia. Posts: 38	Re: Help with National NV-780EM VHS Yes

7th Oct 2015, 8:32 am	#9
vhs doctor Pentode Join Date: Oct 2011 Location: Athens, Greece. Posts: 130	Re: Help with National NV-780EM VHS When the capstan rotates check if the supply reel table also rotate

8th Oct 2015, 6:45 am	#10
alm7rom Triode Join Date: Sep 2015 Location: Al-Kharj near Riyadh, Kingdom of Saudi Arabia. Posts: 38	Re: Help with National NV-780EM VHS Yes

8th Oct 2015, 8:39 am	#11
vhs doctor Pentode Join Date: Oct 2011 Location: Athens, Greece. Posts: 130	Re: Help with National NV-780EM VHS The second display below the deck (function display) works ok

8th Oct 2015, 8:04 pm	#12
alm7rom Triode Join Date: Sep 2015 Location: Al-Kharj near Riyadh, Kingdom of Saudi Arabia. Posts: 38	Re: Help with National NV-780EM VHS Yes work but shut down in second the clock still working

8th Oct 2015, 8:49 pm	#13
dj_fivos_sak Heptode Join Date: Mar 2015 Location: Lefkada, Greece Posts: 796	Re: Help with National NV-780EM VHS Check the zener diode and the caps in the switching power supply.

9th Oct 2015, 3:19 pm	#14
Libratron Pentode Join Date: Jun 2011 Location: San Martino di Lupari, Veneto, Italy. Posts: 195	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

9th Oct 2015, 9:34 pm	#15
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 6,183	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. __________________ Regards, Ben.

10th Oct 2015, 12:51 am	#16
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 3,108	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.

10th Oct 2015, 10:10 pm	#17
vhs doctor Pentode Join Date: Oct 2011 Location: Athens, Greece. Posts: 130	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.

11th Oct 2015, 2:05 pm	#18
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 7,729	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? __________________ G8JET BVWS Member and V.M.A.R.S

12th Oct 2015, 12:11 am	#19
alm7rom Triode Join Date: Sep 2015 Location: Al-Kharj near Riyadh, Kingdom of Saudi Arabia. Posts: 38	Re: Help with National NV-780EM VHS thank you all I will do everything

14th Oct 2015, 3:28 pm	#20
boxdoctor Heptode Join Date: Sep 2010 Location: Ripley, Derbyshire, UK. Posts: 773	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 __________________ The job "couldn't be done". He didn't know that, So he did it.