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Old 7th Jul 2020, 4:51 pm   #1
peter_scott
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Default Panasonic NV-FS90B dead

My trusty FS90B has been completely trouble free since I bought it new many years ago but when I came to switch it on today it was completely dead.

I do have a service manual for it but wondered if complete deadness was a common problem that someone can lead me direct to the faulty component.

Both fuses in the power supply are intact.

Thanks,

Peter
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Old 7th Jul 2020, 5:10 pm   #2
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Default Re: Panasonic NV-FS90B dead

Not sure if this applies to yours Peter but on many N.P. recorders a dried up 1uf 450v cap on the primary side of the power supply was a very common failure causing the no start up fault. Worth a look. John.
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Old 7th Jul 2020, 5:30 pm   #3
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Default Re: Panasonic NV-FS90B dead

Thanks John, Can you see it on this diagram?

There's one across the bridge output and another running across the top of the Auto Volt Selector on the diagram.


Peter
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Old 7th Jul 2020, 6:15 pm   #4
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Default Re: Panasonic NV-FS90B dead

Close-up.
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Old 7th Jul 2020, 6:18 pm   #5
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Default Re: Panasonic NV-FS90B dead

Beat me to it,1uf in psu normally in start up circuit I think,certainly primary side ,unless you are very unlucky then the unobtainable i.c.Possibly that auto volt selector one,if in doubt swap them both.350/400Volts rating I believe.
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Old 7th Jul 2020, 6:24 pm   #6
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Default Re: Panasonic NV-FS90B dead

Thanks to both you Hamish and John.

I don't really need auto voltage selection so I guess I could lose that if the IC is faulty and unobtainium.

Peter
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Old 7th Jul 2020, 7:08 pm   #7
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Default Re: Panasonic NV-FS90B dead

C1109 Peter. Might be worth checking the four resistors for value while you have it out but the 1uf 400V is a classic. John.P.S. Watch out for a charged up main cap...
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Old 7th Jul 2020, 7:52 pm   #8
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Default Re: Panasonic NV-FS90B dead

A very useful reminder John. I could easily have gone ohms probing in there without discharging C8. It had a very healthy charge on it. Even after a few discharge shorts I was getting some very strange readings on my digital ohmeter. Reading something sensible in one direction and 5M ohms the other way around.

Reverting to an old analogue meter showed 56k for R2 and R3 (both ways) and 300k for R23 and R24. I can't actually see in to read the bands on R23 and R24 so I'll just assume they made an alteration from the 470ks on the schematic. I'll order up a 1uF 400 volt for C9 and if that doesn't fix it I might just try hard wiring the transformer primaries in series.

Many thanks again to you and HB,

Peter
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Old 7th Jul 2020, 11:10 pm   #9
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Default Re: Panasonic NV-FS90B dead

C1109. The IC is not actually an auto voltage selector, it's just the switching power supply power chip.

The secundary electrolytics can also be on their way out. Make sure to use low ESR types such as Panasonic FM or FR for thosee.
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Old 7th Jul 2020, 11:29 pm   #10
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Default Re: Panasonic NV-FS90B dead

Thanks Maarten, I'll keep that in mind.

Peter.
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Old 8th Jul 2020, 4:41 pm   #11
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Default Re: Panasonic NV-FS90B dead

IIRC there's a 20v zener in the secondary that can also cause issues. If that's the case, you'll sometimes hear a tell-tale 'chirp' from the PSU (when powered from cold).

I agree with Maarten, secondary electrolytics are very suspect given the age of these decks. Going forward, blanket replacement is probably your best option.
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Old 8th Jul 2020, 4:52 pm   #12
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Default Re: Panasonic NV-FS90B dead

Quote:
Originally Posted by Heatercathodeshort View Post
Watch out for a charged up main cap...
A hefty voltage sitting on the mains input smoothing cap and waiting to bite you is usually one of the tell-tales for a start-up circuit fault, since if the switching regulator never starts up, it won't discharge the capacitor when the mains is removed.

Although, sometimes there will be high value resistors across the cap to discharge it gently anyway.
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Old 8th Jul 2020, 6:27 pm   #13
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Default Re: Panasonic NV-FS90B dead

I haven't heard a chirp on start-up but all comments gratefully received. Now awaiting delivery of 1uF 400v electrolytic.

Thanks,

Peter
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Old 8th Jul 2020, 7:45 pm   #14
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Default Re: Panasonic NV-FS90B dead

Also, the cause of the 18V/20V zener in the secundary giving problems (not present in all models, I think) could be bad regulation caused by secundary capacitors going bad.

Replacing C1109 is a good first step in any case, though.
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Old 8th Jul 2020, 8:21 pm   #15
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Default Re: Panasonic NV-FS90B dead

I think I'm gaining a better understanding of this circuit now.

Thanks,

Peter

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Old 8th Jul 2020, 11:02 pm   #16
Norman Raeburn
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Default Re: Panasonic NV-FS90B dead

I found with these if the 20v zener has gone itís the 47uf in the primary that causes it. Hopefully you wonít need to bother with thus as the 1uf cures it 90% of the time. An esr meter is very handy when working on these. Good luck Peter. Norman
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Old 9th Jul 2020, 6:52 am   #17
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Default Re: Panasonic NV-FS90B dead

Thanks Norman, I see the 47uF you are referring to. I don't have an ESR meter and also have a rather poor record with them, having killed one for just the reason that HKS reminded me to avoid earlier in this thread.

Peter
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Old 11th Jul 2020, 12:01 pm   #18
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Default Re: Panasonic NV-FS90B dead

Very many thanks to all who responded to this help request. Replacing C9 with a new 1uF 450 volt part restored the FS90B to full working again.

Peter
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Old 11th Jul 2020, 2:50 pm   #19
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Default Re: Panasonic NV-FS90B dead

That's good.

I had an FS88B which is very similar and found it thoroughly excellent.

David
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Old 11th Jul 2020, 2:53 pm   #20
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Default Re: Panasonic NV-FS90B dead

Yes, it's a nice machine and certainly worth repairing.

Peter
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