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Old 9th Jul 2020, 4:32 pm   #1
BlackStudio
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Default VCR Panasonic NV-7200

Hello all,

I come to ask for your help because I am faced with a problem that I cannot solve.
I work on a VHS VCR Panasonic NV-7200 and I could see that this device has already been treated several times in this forum, so I tell myself that you may be able to help me.
When I got this VCR, it was not working.
I worked on it a lot and I did the following:

I replaced:
All belts
The pitch roller
Primary ans secondary Idler Clucth

I cleaned:
The mechanical compartment and all the rest of the VCR.
All heads

I checked:
The power supply and the output voltages.

After having done all this work, the VCR is gone and works quite well with a beautiful image and a clear sound.
The only problem is that i stops alone at random.
It can operate for 3 hours non-stop or 1 minute and return to stop mode.
This problem occurs indifferently in play and rec mode, rew, FF review ans cue mode.
To date, I have not been able to determine whether the failure is mechanical or electronic.
Thank you for all the help you can give me.

Laurent
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Old 10th Jul 2020, 6:05 pm   #2
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Default Re: VCR Panasonic NV-7200

Hi,
Please check that the counter memory is not set first.
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Last edited by Red to black; 10th Jul 2020 at 6:12 pm.
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Old 10th Jul 2020, 8:45 pm   #3
BlackStudio
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Default Re: VCR Panasonic NV-7200

Thank you for your answer.
The counter memory is not switched on. It is therefore not because of the counter that the VCR stops.
Do you know if there are rotation sensors on this model and where are they?
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Old 10th Jul 2020, 10:31 pm   #4
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Default Re: VCR Panasonic NV-7200

Found these. Hope they might be of some use to you, and others:

Panasonic NV7000:

Switches off after playing for a few seconds (OK in ffwd/ rew); pinch roller not engaging: Loading belts.

Stops after 35 minutes; capstan slows down - if put in pause runs OK without sound: IC6403 overheating (4049) - replacement cured fault.

No play - 12v supply reads high: Q1501 s/c, check Q1001/2, and D1101/2.

Panasonic NV7200:

Goes into still-frame at beginning/ end of cue/ review: Check mode switch and loading belts.

Laces up then unlaces about one second later: Replace supply spool defective magnet.

No play - (intermittent) tape loads then unloads: Dirty contacts on cassette detect leaf switch.
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Old 11th Jul 2020, 5:49 pm   #5
BlackStudio
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Default Re: VCR Panasonic NV-7200

Hi John,
Thank you for this faults list.
In play mode, the "play solenoid" is well engaged and does not move. The new belts are tight.
The cassette switch is clean and tight when a cassette is present. I do not think it is involved
I noticed something lately. When the fault occurs and the VCR switches to stop mod by itself, the "playe solenoid" is actuated several times, 3x see 4x ??
That is to say that when the stop is sent, it engages again up to 4x in a row before the mechanics goes into stop mod definitively.
I do not understand this problem and I do not know where to look!

For the NV-7200's faults, I don't think I can use them for my research. The 7000 and 7200 are VCR which share the same mechanics but the electronics are very different. I will have to be able to compare the diagrams to see.
Friendly.
Laurent
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Old 11th Jul 2020, 9:48 pm   #6
John123
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Default Re: VCR Panasonic NV-7200

Try lacing up the deck by hand just to make sure it's completing the full sequence. Could be a bad solenoid coil, or dry joints. First, try another thorough clean of the cassette and mode switches. The latter, especially. Use a good quality electrical contact cleaner that's safe on plastics.

Also, be careful as the deck may be light sensitive! Place the top cover back on and see if there's any difference.
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Old 18th Jul 2020, 1:07 am   #7
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Default Re: VCR Panasonic NV-7200

Hi. I recently worked on a similar one (NV-7500) where the play idler wasn't making a good enough contact with the take-up reel table and that caused the machine to intermitently stop during play/record after a few seconds or even after an hour or so. Replacing a couple of levers that control the play idler and the pinch roller cured the problem.
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Old 18th Jul 2020, 8:55 am   #8
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Default Re: VCR Panasonic NV-7200

Hi Laurent,

It's been a while since I worked on these, having left Panasonic back in '94. From memory:-

Solenoids re-firing is usually a worn or dirty mode-switch. If you do remove it, make sure it goes back in the exact place. (I cannot remember the alignment procedure for these). Best to place a mark on the switch and chassis to aid refitting.

Other possibles for stopping at random, the counter has a hall-effect sensor, the worm drive could be gummed up causing slow rotation of the counter, the machine cannot see the right number of pulses, & stops.

Another possible, if this machine is fitted with a photo-sensor just after the pinchroller/capstan, and the take-up spool slows up, the resultant 'tape loop' will stop play/record.

Personally (& if not currently done), I'd remove supply/take-up spools, service the shafts & bearings, remove the counter & service, clean the mode switch. Before you remove the supply reel, place a mark on the back tension band, marking its location by the retaining screw, and have some contact adhesive ready, just in case the felt band drops off.

It's worth playing some music before dismantling, try violin or sine wave and listen for wow & flutter, as a worn/dirty mode switch causes the loading motor to shuffle in playback, which makes the pinchroller tension 'bounce' on the capstan. You won't see the effect, but you will hear it with slow/steady music. That said, you may be able to see the loading motor 'shaking its wheel' in playback/record.

Gummy grease can cause wow/flutter too, especially true of the capstan itself, but have a listen before digging in too deep.

All good fun.

Mark
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Old 29th Jul 2020, 5:58 pm   #9
BlackStudio
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Default Re: VCR Panasonic NV-7200

Hey guys,
I was away from home for a few days, so I didn't work on the VCR anymore.
When I get back, I'm going back to work.
Thank you all for these new faulty lists.

For dj_fivos_sak:
I replaced the idler, all the belts and the pinch roller with new Panasonic parts. I watched the mechanics running from above and below for hours.
I found no misfiring or slippage. Everything is in order.

For Mark
I recently checked the correct setting of the mechanics with the service manual and everything is in place. The switch select mode is clean and OK.
On this VCR, there is no hall effect sensor on the tape counter. It's a simple counter with the possibility of memory position "0000".
There is also no photo sensor after the pinch roller and capstan.
However, there is a rotation sensor on the left take up reel. If it doesn't rotate for 4 seconds, the VCR stops. OK
I have already dismantled the 2 take up reel to do a good cleaning and a light greasing of the axles.
The back tension band is probably the original part. I couldn't find a new replacement part so I left it in place. I don't think it's responsible for the untimely stops.
I knew the trick of playing a cassette recorded with classical music to detect the rotation of the pinch roller or capstan. Unfortunately I only have cassettes recorded with rock music and it seems to be fine.
While I'm writing this post, the NV-7200 is working and not a problem.
This VCR is a mystery ...
If you have other ideas, don't hesitate.
Thanks again for your help.
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