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Old 28th May 2015, 8:45 am   #1
Mach One
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Default Panasonic Video Recorder Power Problem

I'd call it "modern technology", but seeing as even DVDs are no longer "modern", I hope that I am putting this in the correct department:

I have a Panasonic NV-FJ620 VHS video recorder which is not far short of 15 years old and served us well up to the mid-noughties. It then was retired into the loft and I dug it out a few weeks back to use for dubbing videos onto DVD.

It worked for a while, but I have just plugged it in and it is dead. There is power on the rear socket (measured inside) and the internal fuse is OK. Can anyone suggest which component might be an obvious one to look for to repair the unit or else it will be retired to the local dump?
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Old 28th May 2015, 10:15 am   #2
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Default Re: Panasonic Video Recorder Power Problem

Check the small electrolytic(s) in the primary of the SMPS. Also the surge limiter resistor.
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Old 28th May 2015, 11:58 am   #3
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Default Re: Panasonic Video Recorder Power Problem

Most likely the 1uF cap on primary power supply.
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Old 28th May 2015, 7:56 pm   #4
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Default Re: Panasonic Video Recorder Power Problem

Thank you to both of you for your helpful replies. I will have a poke around (!) I am aware of the high voltages present... When I am checking these capacitors would I expect a short-circuit or an open-circuit, the second of which would be difficult to check in the case of a capacitor?

I have attempted to attach a circuit diagram, but the forum has reduced its size and it is somewhat unreadable...
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Old 28th May 2015, 11:03 pm   #5
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Default Re: Panasonic Video Recorder Power Problem

You'll need an ESR meter to carry out in-circuit capacitor tests. You could just keep replacing caps until there's a response on the secondary (output side).

Be careful around the main reservoir capacitor (the big one). Anything upto 400v DC here, and it will hold its charge for a good few minutes after power-down (longer if there's no oscillation).

Also note that the PSU grounds are respective to primary/ secondary isolation.
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Old 29th May 2015, 6:14 am   #6
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Default Re: Panasonic Video Recorder Power Problem

I can't see the values but there is a chain of resistors from the negative supply to the 'start up' circuit and a couple of likely suspects on the positive side. As it stopped working abruptly it may be worth a check around these. The resevoir cap as mentioned by John can hold a nasty bite for a very long period, especially if one of those resistors is O/C. John.
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Old 29th May 2015, 6:20 pm   #7
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Default Re: Panasonic Video Recorder Power Problem

My Panasonic NVF70 ran for years and years from new and then finally failed to come back on after the mains had gone off for a few minutes one day.

In my case it was a small electrolytic capacitor in the start-up circuit on the PCB of the power supply - it was also the obvious one to pick even without any knowledge of the circuit because it was the one mounted only 3mm away from a heatsink which had obviously run quite hot, continually, for years. Heat is a terrible (electrolytic) capacitor killer.

The capacitor was practically flatlined on my V-I analyser - it had obviously failed some time before, but the mains around here is quite reliable so as long as the power stayed on, the start-up circuit wasn't needed.
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Old 29th May 2015, 6:28 pm   #8
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Default Re: Panasonic Video Recorder Power Problem

That is the one and it is 1uF 63V
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Old 29th May 2015, 6:57 pm   #9
Norman Raeburn
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Default Re: Panasonic Video Recorder Power Problem

Hi, My guess on this range of machines is the STR regulator ic, it's a common problem. Norman
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Old 29th May 2015, 7:36 pm   #10
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Default Re: Panasonic Video Recorder Power Problem

These (Sanyo?) regulators cause all sorts of strange problems when they turn faulty. In my experience, the machine will half-work.
So, for example, the clock will light up but pressing the Power button to bring the machine out of Stand By will have no effect, or the RF modulator won't work, or it'll thread a tape and then won't eject it. Really odd things like that!
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Old 30th May 2015, 6:51 am   #11
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Default Re: Panasonic Video Recorder Power Problem

1uF 400V usually, not 63V
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Old 30th May 2015, 1:19 pm   #12
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Default Re: Panasonic Video Recorder Power Problem

My fault correct cap but wrong voltage it is a few years since I last repaired one.
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Old 30th May 2015, 5:43 pm   #13
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Default Re: Panasonic Video Recorder Power Problem

I think said cap was uprated from 160V (or so) to 400V during the first production runs.

Anyway, in this more modern model, the most likely cause is the Sanken STR regulator.
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Old 2nd Jun 2015, 8:57 pm   #14
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Default Re: Panasonic Video Recorder Power Problem

Everyone seems to be thinking of the older machines from the late 80's/early 90's.

With these machines

There are two 330K resistors in the start up circuit, one or both can go o/c.

More importantly on the secondary side there are two capacitors C34 and C1260, they are 2200uF and 1000uF both 10V. Change them.
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Old 3rd Jun 2015, 11:48 am   #15
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Default Re: Panasonic Video Recorder Power Problem

Thank you to all of you for your considered replies.

Firstly, the full model number is an NV-FJ620EG-K. I believe it was the one that we bought when we were living in Germany some years ago. When we came back here, we bought the exact same UK model but we do not have that any more, unfortunately.

I can not relate any of the component identifiers to what I actually have so I am attaching some photos of the section of board concerned. I downloaded the circuit from the Internet and that is where the rather unreadable picture that I previously attached came from.

I have checked out the electrolytic capacitors on the primary side of the transformer and they seem OK as measured with my trusty Fluke DVM - they measure a varying megohm resistance as I would expect from an electrolytic. I doubt if it is a very good way of measuring them, though, of course... At least they are not short.

I think that IC1 must be the regulator that was mentioned. It and the board around it show signs of heat. Is this an easy thing to get from one of the component suppliers such as CPC?
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Old 3rd Jun 2015, 11:55 am   #16
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Default Re: Panasonic Video Recorder Power Problem

You cannot check those caps on a Fluke as it is ESR you need to read.Just change the 2 small ones on the primary side.
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Old 7th Jun 2015, 8:52 pm   #17
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Default Re: Panasonic Video Recorder Power Problem

I'm pretty sure it's the STRG regulator that usually causes this problem in machines from this generation. It is probably reasonably cheap, I think I paid 10 euro or less last time I replaced one, 1 or 2 years ago.
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Old 12th Jun 2015, 7:51 am   #18
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Default Re: Panasonic Video Recorder Power Problem

Firstly, thank you to all of you who contributed to this thread. Just to fill you in on what happened:

I took not of the advice to change the capacitors on the primary side (thank you to Michael and others...) and had partial success for a trip to Maplin and £2.50! The machine came to life!

However, as I was trying to unsolder the old capacitors, the mechanism "fell out" off the board (I now realise better how it was secured - or more accurately not secured) and although I could see power was once again there in the machine, tapes inserted were spat straight out again, apart from on two occasions when the machine played and where no video was apparent.

Now, having spent some time on this machine and having no real experience of servicing Videos or access to helpful test gear, I'm afraid I gave up at that point. In fact, I have found another working Panasonic VHS with EP for £10 at a local second-hand shop that will do the job of this one, so that's fine. Just left with a feeling of failure, but - I'll get over it!
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Old 12th Jun 2015, 6:02 pm   #19
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Default Re: Panasonic Video Recorder Power Problem

Oh well! Timing issues can be a nightmare to sort out, even for the experienced.

I'd be inclined to think that it was a dirty or misaligned mode switch from the symptoms you describe, but of course it's just a shot in the dark.
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