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Old 16th Nov 2018, 3:24 pm   #1
collisr
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Default Alignment (Head?) issues with a Panasonic AG 7350

On a different topic... I undertook a challenge to rescue a "broken" AG 7350 that was given to me earlier this year.

The first problem was "ERR 6" on play which was down to one of the screws on the reel servo board had cracked the PCB causing no back tension. This was fixed by adding one jumper to the PCB to bridge the gap.

On power up, the head hours are saying "2" - so possibly this was a factory fault and the machine had hardly been used.

So.. to the outstanding problem. As pictures 1 and 2 show - playback is pretty nasty with lots of interference and grain throughout. Tracking appears to work but the picture does not get any better than this. The video heads look intact and have been cleaned - as has the ACE head. Sound is perfect. I noticed that in pause and jog/search mode (picture 3), the picture is much clearer/sharper and the interference is diminished. On some frames, the noise is completely gone.

Any ideas? It's possible the machine had been "messed with" before I got it. I have the service manual and scope/tools to tune, but not used to servicing this model.

Rob
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Old 16th Nov 2018, 4:22 pm   #2
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

I once had a Sanyo VTC-5000 Betamax machine on which I fiddled with the tape guides. It gave almost exactly these symptoms: awful 'tracking bars' across the picture, but picture search wasn't bad at all. I never did manage to get it right again...

Chris
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Old 16th Nov 2018, 6:41 pm   #3
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

Tape guides on vcr's should in 99.9% of cases never be touched.i too have seen this happen ,whereby some think moving these outward will help the tape move better no doubt.... WRONG. It just put's out the tape path alignment with the heads and servo's. Hence the 'horrible noise and bad tracking'

Rob:
I have service a lot of Panasonic AG5260's and 4700's and similar that utilise the 'K' deck.
Those issues you have I've not seen.It could be excessive wear to one or maybe both normal play heads. The reason you have a better picture with the jog/shuttle is it more than likely utilises a different head for those modes to make things clearer.
Is the Hi-Fi OK?
That usually goes before the picture ones do.
Does the tape appear to be seating nicely around the head drum with no gaps or tape curl to the two guides each side?
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Old 16th Nov 2018, 9:31 pm   #4
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

You may also want to check the back tension too.

.Kev
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Old 17th Nov 2018, 12:47 am   #5
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

To me, that looks like leaky caps in the luminance/Chroma circuits. These Panasonic are known for having SMD caps in these circuits that go bad.

Fivos
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Old 17th Nov 2018, 7:25 pm   #6
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

SMD caps ,the absolute WORST....Give me good quality electrolytic types every time
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Old 17th Nov 2018, 9:53 pm   #7
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

Quote:
Originally Posted by collisr View Post
On power up, the head hours are saying "2" - so possibly this was a factory fault and the machine had hardly been used.
Hi Rob,
We used to service these machines occasionally along with the more usual timelapse VCR's that we did.
Depending on the make, hour counters can just roll round to zero again once they have clocked up whatever their maximum hours are. I would very much doubt if this machine has only seen 2 hours use! As part of a full service including new heads, we would always reset the hour counter to zero.

That looks to me like very worn heads. Different heads are used for pause & slow, hence in picture 3, you have output from both heads albeit with a noise bar.

Even in the '90's, heads were eye wateringly expensive for these. I seem to recall a full 10,000 hour service cost the customer about £400!

Cheers
Nick
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Old 18th Nov 2018, 3:42 am   #8
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

As I first suspected.
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Old 18th Nov 2018, 2:32 pm   #9
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

Hi all,

I can understand why Nick would think it's worn heads - he may be right (and I didn't know you could reset the hours during a service), but I suspect it may be something else.

https://youtu.be/VqmcWn-4XQ8

... shows a video of 2 tapes (the first one pre-recorded, the second from the TV). This machine also suffers from "no counter" for the first 15 mins or so, after that point tracking can make the picture slightly better.

To Fivos' earlier idea, I swapped the 3 video boards (inc. Y & Chroma) and Head Amp with known working ones and that didn't make any difference, so still think it's somewhere on the syscon/servo board. Maybe I'll swap this out for a known good one and see where that gets me.

Rob
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Old 19th Nov 2018, 12:22 am   #10
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

Hi Rob,
Having watched your video, I am even more convinced that there is very little output from either standard play head.

If there are no control pulses coming from the audio/ control head, the tape counter won't count and the capstan servo won't lock. This will lead to regular periods of complete snow as both the Ch1 & Ch2 heads completely miss their respective tracks.

It would appear this is exactly what is happening in the video. However, if it was just a servo or control pulse fault, the picture in between the periods of snow would be perfect. As it isn't, either there is minimal signal coming from the heads, or it's getting lost in either the rotary transformer or the head amp.

I don't know if the still/ search pair of heads share the same head amp with the standard play heads- you would need the circuit to find that out. The fact you have already changed the head amp PCB would suggest the fault is not in that area.

Let's hope I'm proved wrong and the heads are blameless!

Good luck
Nick
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Old 19th Nov 2018, 6:18 pm   #11
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

Thanks Nick - I'll update the forum once I know for sure.

BTW - If you are correct - why would the still/search heads wear at a different rate to the "normal" video heads? If there is life in the still/search heads, could I swap the solder points over so the normal PLAY mode uses the search/still heads?


R.
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Old 19th Nov 2018, 11:12 pm   #12
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

Quote:
BTW - If you are correct - why would the still/search heads wear at a different rate to the "normal" video heads? If there is life in the still/search heads, could I swap the solder points over so the normal PLAY mode uses the search/still heads?
Hi Rob.
Sadly, you couldn't use the 'still' heads in normal play as the azimuth and head width will be wrong and you would get a noise bar at the top and bottom of the picture. That's why they use a different pair of heads for still/ search.

As heads wear, they become more prone to clogging and reduced output. The wear rates will never be identical for every head on the drum, especially as the still/ search heads will be a different width to the standard play heads and will therefore wear at a different rate.

All the best
Nick
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Old 23rd Nov 2018, 5:46 pm   #13
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

Hi Nick,

Quick update. Fixed the CTL pulse problem - that was a faulty elco (C44 3.3uF/50v) in the syscon board. But... as you suspected, the picture is still crappy. I would like to conclude it is worn-out video heads, but one curious point:

- When cleaning with strips of "airmail paper" soaked in Iso-Propyl Alcohol, I get loads of black smears left on the paper - even after 15-or-so attempts - much more than I would usually expect when cleaning video heads.
- Also - all the heads are very clearly felt through the paper - i.e. they protrude a lot. I thought worn heads would not be felt as easily.

Sadly, the cleaning does not appear to be making much difference, so I am about to (reluctantly) admit you were right, but any views on the "muck" released when cleaning the heads? Even now, I can still get more and more black muck of them.

Rob
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Old 24th Nov 2018, 12:16 pm   #14
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Default Re: Alignment (Head?) issues with a Panasonic AG 7350

Rob

You couldn't let me have a few sheets of "airmail" paper? They are so thin on the ground as to be almost unobtainable!

All joking aside, black residue from ferritte heads seems strange. I've used your cleaning technique many times and the pattern of contamination shown on the paper is a good indication of where the problem lies and how difficult it will be to resolve.

With worn heads, oxide from the tape will soon contaminate them again and reduce output but usually this can be often cleaned off and the cycle will be repeated.

However, the heads leave a clearly seen dark line on the paper when dirty not a smear as described. Any chance of a photo of the "smear test". Whoops, I mean airmail paper after being used to clean the heads.
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