Panasonic VCR NV-L20 PSU goes on and off - UK Vintage Radio Repair and Restoration Discussion Forum

vhs doctor · 23rd Sep 2018, 11:42 pm

Hi

I have a panasonic NV-L20. The VCR had leaky electrolytic capacitors in the secondary side of the PSU. I have replace all the electrolytic capacitors with new capacitors also i resoldered all the pcb. The VCR now have clock and power on but when the PSU works under load goes instantly off and on (ex when you select a function REW PLAY etc).

I have measure the fusible resistors and the are OK i have also replace the STK regulator but nothing changes. The fault seems to be created from the primary side. In the primary there is a zener D6 (orange-white-white) according to the manual the zener is MA4030.

Does anyone know the value of the zener or have any expirience in this specific fault?

Thank you

ben · 24th Sep 2018, 3:14 pm

I vaguely recall on the multivoltage version of one of this era of Pannys a small sub pcb in the PSU can with a low value electrolytic which dried out and gave exactly these symptoms. Hopefully someone else on here will have a better memory of it than me!

Red to black · 24th Sep 2018, 7:43 pm

Quote:

Originally Posted by vhs doctor

Does anyone know the value of the zener or have any expirience in this specific fault?

D1006 MA4030L is a 3 Volt Zener

vhs doctor · 24th Sep 2018, 10:18 pm

Thank you for your answers and for your help.

SteveCG · 27th Sep 2018, 11:01 am

Are the primary side electrolytics alright? In particular, are they soldered to the board properly? I had a computer psu which showed similar loading problems where there was crack around the soldered connections of both the two primary electrolytics.

vhs doctor · 27th Sep 2018, 3:13 pm

All capacitors was leaked in secondary side. I have already replace them with new ones. I have also resoldered the pcb.

Heatercathodeshort · 27th Sep 2018, 7:54 pm

Out of the blue. Is there a 1uf 450v on the primary side? This used to give a lot of trouble after a power break. John.

HamishBoxer · 27th Sep 2018, 8:00 pm

They are fitted to most NatPan,s and they are fine till you turn the power off.

Sorry,I have doubled up!

vhs doctor · 27th Sep 2018, 10:22 pm

For everyone who have panasonic VCR with this specific power supply (VEP 01379 or smilar) and want to restore or operate them

This type of power supply (such as NV-L20/L25) you can find it in most panasonic NV-Jxx, NV-Lxx and on the early NV-SDxx (such as NV-SD30/40 etc) in the later models of sd series i think 1995 and then panasonic had change the psu unit.

The problem is created from the electrolytic capacitors especially in secondary side. The capacitors due to temperature and from years became leaky. You can notice a liquid "coating" on the components side. In some cases this luquid and the fumes of this create rust on the case of the PSU. The typical sympton is that the VCR is dead no clock. You can also have problem in capstan motor (usually lack of torque) or operation with no display.

One more problem (and the most serious for me in my opinion) is that the capacitor liquid is corrosive. It corrodes the other components such as resistors ceramic capacitors etc) and also destroy the protective coating of the PCB line. From green became black).

What to do in this case

1. Remove the PCB from his case
2. Take notes where each electrolytic capacitor located and his value. Desolder and remove all the electrolytic capacitors. It is useful to have the service manual.
3. Remove also the STK regulator and the SMPS tranformer ( be extremely care not to brake the ferrite core.
4. Clean very well both sides of the PCB with a flux remover or a PCB cleaner.
5. Replace all the electrolytic capacitors do not measure them. For the main capacitor "it has unusual values" in primary side (snap-in type) you can use the Rubycon QXW series you can find also and equivalents and from other companies.
6. Observe and check the other components in PCB ceramic capacitors, resistors, small diodes etc could be destroyed or corroted. The result is O/C or short circuit components replace them if you measure fault.
7. Install the new capacitors.
8. Resolder all the PCB.
9. Clean and the old and install new thermal paste on STK regulator
10.Clean very well the outer case and install the board.

In general do not store or operate these panasonic machines with faulty capacitors.

I hope in the future to make a complete quide with photos.

dj_fivos_sak · 30th Sep 2018, 6:36 am

Some Panasonic models with switching power supplies from the early-mid 80s had a serious problem where when the capacitors on the primary side dried up, the oscillator couldn't change the frequency and the output voltage just kept going higher and higher until the machine completely blew up, even though the optocoupler was lightning at full brightness. They fitted zener diodes in later machines to prevent that.

23rd Sep 2018, 11:42 pm	#1
vhs doctor Pentode Join Date: Oct 2011 Location: Athens, Greece. Posts: 173	Panasonic VCR NV-L20 PSU goes on and off Hi I have a panasonic NV-L20. The VCR had leaky electrolytic capacitors in the secondary side of the PSU. I have replace all the electrolytic capacitors with new capacitors also i resoldered all the pcb. The VCR now have clock and power on but when the PSU works under load goes instantly off and on (ex when you select a function REW PLAY etc). I have measure the fusible resistors and the are OK i have also replace the STK regulator but nothing changes. The fault seems to be created from the primary side. In the primary there is a zener D6 (orange-white-white) according to the manual the zener is MA4030. Does anyone know the value of the zener or have any expirience in this specific fault? Thank you

24th Sep 2018, 3:14 pm	#2
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Panasonic VCR NV-L20 PSU goes on and off I vaguely recall on the multivoltage version of one of this era of Pannys a small sub pcb in the PSU can with a low value electrolytic which dried out and gave exactly these symptoms. Hopefully someone else on here will have a better memory of it than me! __________________ Regards, Ben.

24th Sep 2018, 10:18 pm	#4
vhs doctor Pentode Join Date: Oct 2011 Location: Athens, Greece. Posts: 173	Re: Panasonic VCR NV-L20 PSU goes on and off Thank you for your answers and for your help.

27th Sep 2018, 11:01 am	#5
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: Panasonic VCR NV-L20 PSU goes on and off Are the primary side electrolytics alright? In particular, are they soldered to the board properly? I had a computer psu which showed similar loading problems where there was crack around the soldered connections of both the two primary electrolytics.

27th Sep 2018, 3:13 pm	#6
vhs doctor Pentode Join Date: Oct 2011 Location: Athens, Greece. Posts: 173	Re: Panasonic VCR NV-L20 PSU goes on and off All capacitors was leaked in secondary side. I have already replace them with new ones. I have also resoldered the pcb.

27th Sep 2018, 7:54 pm	#7
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Panasonic VCR NV-L20 PSU goes on and off Out of the blue. Is there a 1uf 450v on the primary side? This used to give a lot of trouble after a power break. John.

27th Sep 2018, 8:00 pm	#8
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,935	Re: Panasonic VCR NV-L20 PSU goes on and off They are fitted to most NatPan,s and they are fine till you turn the power off. Sorry,I have doubled up! __________________ G8JET BVWS Archivist and Member V.M.A.R.S

27th Sep 2018, 10:22 pm	#9
vhs doctor Pentode Join Date: Oct 2011 Location: Athens, Greece. Posts: 173	Re: Panasonic VCR NV-L20 PSU goes on and off For everyone who have panasonic VCR with this specific power supply (VEP 01379 or smilar) and want to restore or operate them This type of power supply (such as NV-L20/L25) you can find it in most panasonic NV-Jxx, NV-Lxx and on the early NV-SDxx (such as NV-SD30/40 etc) in the later models of sd series i think 1995 and then panasonic had change the psu unit. The problem is created from the electrolytic capacitors especially in secondary side. The capacitors due to temperature and from years became leaky. You can notice a liquid "coating" on the components side. In some cases this luquid and the fumes of this create rust on the case of the PSU. The typical sympton is that the VCR is dead no clock. You can also have problem in capstan motor (usually lack of torque) or operation with no display. One more problem (and the most serious for me in my opinion) is that the capacitor liquid is corrosive. It corrodes the other components such as resistors ceramic capacitors etc) and also destroy the protective coating of the PCB line. From green became black). What to do in this case 1. Remove the PCB from his case 2. Take notes where each electrolytic capacitor located and his value. Desolder and remove all the electrolytic capacitors. It is useful to have the service manual. 3. Remove also the STK regulator and the SMPS tranformer ( be extremely care not to brake the ferrite core. 4. Clean very well both sides of the PCB with a flux remover or a PCB cleaner. 5. Replace all the electrolytic capacitors do not measure them. For the main capacitor "it has unusual values" in primary side (snap-in type) you can use the Rubycon QXW series you can find also and equivalents and from other companies. 6. Observe and check the other components in PCB ceramic capacitors, resistors, small diodes etc could be destroyed or corroted. The result is O/C or short circuit components replace them if you measure fault. 7. Install the new capacitors. 8. Resolder all the PCB. 9. Clean and the old and install new thermal paste on STK regulator 10.Clean very well the outer case and install the board. In general do not store or operate these panasonic machines with faulty capacitors. I hope in the future to make a complete quide with photos. Last edited by vhs doctor; 27th Sep 2018 at 10:39 pm.

30th Sep 2018, 6:36 am	#10
dj_fivos_sak Heptode Join Date: Mar 2015 Location: Lefkada, Greece Posts: 969	Re: Panasonic VCR NV-L20 PSU goes on and off Some Panasonic models with switching power supplies from the early-mid 80s had a serious problem where when the capacitors on the primary side dried up, the oscillator couldn't change the frequency and the output voltage just kept going higher and higher until the machine completely blew up, even though the optocoupler was lightning at full brightness. They fitted zener diodes in later machines to prevent that.