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-   -   NV-FS200 spots on bright white scenes (https://www.vintage-radio.net/forum/showthread.php?t=181110)

willow5 14th Jun 2021 9:30 pm

NV-FS200 spots on bright white scenes
 
2 Attachment(s)
Hello all, I have painstakingly replaced the capacitors in the PSU, TBC and Sub-Luminance / Chrominance boards but still have an issue with colour spots on some extremely bright white scenes.

I have tried playing the same tape on other machines but am not convinced that the spots are present on other machines (Mitsubishi HS-M1000 for example but only composite output, not S-Video like the FS-200 so perhaps I am not comparing apples with apples).

It is extremely hard to spot these errors on still images or even computer monitors but they are very visible when I play the mpg files back on a big screen.

Can anyone kindly shed any light on this issue ? I attach 2 stills (one from the Mitsubishi HS-M1000 (slightly dull) and one from the FS200 (brighter image) but even then, it is extremely hard to see the spots on these stills).

Perhaps in connection with this issue is that the reds are too red and there appears to be some colour bleeding / blue haze. Not sure if this is related to the same issue or a red herring. Otherwise I am very happy with the quality of this machine as you can compare from the 2 stills I attach.

I would be happy to share the video clips with anyone interested in helping.

Many thanks

Andrew2 14th Jun 2021 10:23 pm

Re: NV-FS200 spots on bright white scenes
 
Can I ask what TV you are using for display? It's not a CRT by any chance is it?

willow5 14th Jun 2021 10:33 pm

Re: NV-FS200 spots on bright white scenes
 
No, it is a LCD TV which is HD compatible

rambo1152 14th Jun 2021 10:33 pm

Re: NV-FS200 spots on bright white scenes
 
I think we need to see the video.

willow5 14th Jun 2021 10:37 pm

Re: NV-FS200 spots on bright white scenes
 
Sure, how can I share as each clip is around 100Mb ?

Cobaltblue 15th Jun 2021 5:30 am

Re: NV-FS200 spots on bright white scenes
 
Most folks seem to use youtube to share video or you could try something like drop box.

Cheers

Mike T

HamishBoxer 15th Jun 2021 6:58 am

Re: NV-FS200 spots on bright white scenes
 
Could be head earthing.

rambo1152 15th Jun 2021 12:27 pm

Re: NV-FS200 spots on bright white scenes
 
Quote:

Originally Posted by HamishBoxer (Post 1382738)
Could be head earthing.

I wondered if it was "comet tails" due to that.

willow5 15th Jun 2021 7:52 pm

Re: NV-FS200 spots on bright white scenes
 
Hi all, here is a short clip of the white spots. You will have to view on a regular TV rather than through a laptop to experience the spots

Eagle eyes will need to pay attention to the bright white scenes. Feedback welcome

Edit - it seems YT have "optimised" the video so I will try another source here:

https://we.tl/t-F0tvAuV9Hu

willow5 17th Jun 2021 10:52 pm

Re: NV-FS200 spots on bright white scenes
 
I checked the head earthing and cleaned the strap but the problem persists.

I am now convinced that there is a bad cap or few caps elsewhere. Does anyone have a good understanding of the circuitry on these units and could point me in any sort of direction where to look other than the sub-boards which I already re-capped?

Could it be the head amp or main PCB ?

HamishBoxer 18th Jun 2021 6:54 am

Re: NV-FS200 spots on bright white scenes
 
Trying to think whether the head drum or motor assembly can cause this.

murphyv310 18th Jun 2021 9:00 am

Re: NV-FS200 spots on bright white scenes
 
Hi.
If this is a standard VHS machine it's pretty normal. The chrominance bandwidth is restricted on VHS and remember so is luminance, this purely down to a decrease in definition. Re the spots.... No idea unless we see a video. Post it to YouTube and put the link up here.

willow5 18th Jun 2021 12:37 pm

Re: NV-FS200 spots on bright white scenes
 
Hi, I understand but this is not happening with other players (Mitsubishi HS-M1000 for example). Maybe you missed the link but here it is:

https://we.tl/t-F0tvAuV9Hu

John123 18th Jun 2021 1:15 pm

Re: NV-FS200 spots on bright white scenes
 
Perhaps try scrutinising the luma/ chroma/ HQ circuits again, especially if they have any of those ceramic thick-film units with surface mount electrolytics on them.

willow5 18th Jun 2021 1:20 pm

Re: NV-FS200 spots on bright white scenes
 
Thanks John, I am not familiar with the ceramic thick-film capacitors. I only replaced the electrolytic ones. What do the thick-film capacitors look like and can I test them with an ESR ?

John123 18th Jun 2021 2:56 pm

Re: NV-FS200 spots on bright white scenes
 
1 Attachment(s)
Sorry, I meant the PCB modules the capacitors are physically mounted to. These mini-modules are made of a ceramic type material. The surface-mount electrolytic capacitors themselves are the silver can-type, mounted directly onto the modules.

As you can see in the attached example, the four in the middle of the photo have leaked. I'm not sure if your machine has this exact same module, or ones like it, but definitely something to look out for.

[Picture pulled from this post]

rambo1152 18th Jun 2021 8:06 pm

Re: NV-FS200 spots on bright white scenes
 
I can see what I think are VideoCrypt artefacts on the L & R extremities, but other than that the picture looks pretty good to me.

What you are seeing may possibly be a consequence of some "improvements" to the VHS standard collectively called "VHS HQ". If I remember correctly one of the things it did was to take liberties with the luminance level and pre/de-emphasis and although it succeeded in making the picture subjectively sharper, it seemed to me to be a bit of a fudge that would inevitably lead to compatibility issues between machines.

I would not bet money on there being an actual fault that can be fixed.

its ur aerial 19th Jun 2021 4:27 am

Re: NV-FS200 spots on bright white scenes
 
I have looked at the Video on the PC Monitor, and apart from the VideoCrypt could honestly not really see a issue, I would totally agree with Graham G3ZVT, it may well be a fault that's not fixable.
As you have checked the Upper drum earthing, a stab in the dark would be the the Drum Motor, but remember VHS and VHS HQ was always a compromise .
Ken G6HZG . VMARS

murphyv310 19th Jun 2021 7:50 am

Re: NV-FS200 spots on bright white scenes
 
Hi.
I have to agree with Graham and Ken. I think you may be expecting more than the machine can produce. If a customer brought in a machine like that for repair if it performed well on a soak test it would be sent back NFF.
In those days spending days on a machine for an alleged fault you'd most likely get a warning of wasting company time.

I remember one customer measuring every square on the test card and if they differed by any more than 1 millimetre he would demand a new set, and then go through the same again.
Often in VCRs and TV sets of the time there were compromises made.
Splashes on screen are generally earthing or the signal level off tape being slightly low, this could be the heads themselves too, slightly low record level or even incompatibility between different machines, some of these things can be difficult to resolve and remember if there are too many drop outs due to low signal the drop out compensator will struggle.
Again in IMHO that picture looks pretty good to me.

willow5 19th Jun 2021 8:06 am

Re: NV-FS200 spots on bright white scenes
 
Thanks both. Please note, in order to see the artefacts I am referring to, you must watch it on a TV as opposed to a monitor as these artefacts can only be seen there


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