Quick update! (I gotta go in a moment!)

Just to say that yesterday I performed a cleaning of the commutators of the head drum motor (something that has given me good results in the past :D). I also cleaned the heads carefully, and the contact plates on top of the head drum, the audio and eraser head and part of the tape path.

Result: EXACTLY the same image!!

I started changing other PCB, one by one, with the other (almost)identycal machine: same results!! (at least it was useful to test that the other machine components are ok... or they have the same fault - the Ablaufsteuerung, which also I reconstructed with conductive paint and shown no F when aborting playing, and has the hour static, has been proven to work appart from that!).

So now I'm almost sure the problem is mechanical and is located somewhere in the tape path... I suspect it's on the capstan because, as I noted before, I "dissolved" part of its magnet when cleaning it with alcohol - the towel got stained with black from it!
Also I touched with my fingers the "tensor" part, to apply more or less, and the changes in the image were not significant, so another part which I was suspecting of is discarded!

Tried too different arrangements for the mounting plate of the capstain, without noticeable changes...

The sealings in the screws are not broken, so that part, at least, is as it came from the factory...

I tried with different tapes, and I already knew of the bad quality of some manufacturers, remember I reported about bad experiences when using Agfa? So no, that's not the case...



PS: have yet to test the constant tension in the capstan...

Then it looks like the video heads are at their end of life!
Perhaps, the DTF-voltage is not correct or even missing, then the "Dynamic Track Following" system cannot operate correctly.

And also, as I have already written, the capstan motor can have a fault! I would change it for testing...
How is the image of a standing picture ("Pause")?
And how is the image in fast forward and back search mode?

I don´t believe in a damaged Capstan. But one thing can appear: One or both capstan bearings are worn. This must be heard in a rough sound, and the image must be clear in "pause" mode.

Best regards,
stego

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Hi Stego!

I'm about to upload a video of how it looks to youtube. In the meantime:

- Picture looks the same in pause mode than in normal mode.
- The same applies to fast forward, reverse and slow mode. Fast forward seems to be the worst playing mode, with kind of "start-stop" pulses, not continuous smooth run, and also it reflects in the sound of the head drum when rotating.

- Otherwise, if it wasn't for that and the lack of color, image would be really clear! Almost no white spots and the remaining image looks crisp and clear, considering how old the tape is!

By the way: this drum is smooth, with no concentrical stripes. Why is this?? I've seen both versions; in fact, I own two machines without the stripes. I read somewhere that they allow for better adherence of the trape to the drum... Do you consider that drums with stripes offer better image quality??

Oh, and another detail: here it goes a picture on how the contacts of the drum motor were before cleaning: really dirty, even with green oxid? stains... Too bad that image quality didn't improve after cleaning them!

Here is the vid!

http://www.youtube.com/watch?v=nKtBuHXYs90

Also it don't appear in the video (have to record another one!! :hammer), but after some time playing, the image will lose stability and start jumping, displaced about one fourth from the bottom and compressed on top!

The vertical bars, obviously are synchronous with, and have a frequency of some harmonic of, the H-deflection.
I guess, that the DC-supply of some preamplifier and/or the PLL is contaminated with too high a ripple voltage from either the switching power supply or the motor regulator.
This ripple voltage can the be seen as the brightness modulation and it also prevents the PLL from lock, resulting in no colour.

As usual, this might be the result of some dried out filter capacitors.


[ Diese Nachricht wurde geändert von: perl am 27 Aug 2011 22:17 ]

I don't think that the stripes on the drum affect the image quality, they rather prevent the tape from having contact to the drum which would eat the tape due to the friction - om nom nom...

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[ Diese Nachricht wurde geändert von: ElektroNicki am 27 Aug 2011 23:15 ]

Hi Perl!

Great reply! It sounds very instructive, but... unfortunately, I've swapped all the modules of the machine with the ones from an (almost)identycal machine I'm 99'99% sure they're ok (I saw it working for a while until I ruined it breaking something in the -probably- mechanical part of the tape mechanism and it had crisp image and brigth colors) and the results are the same! I even exchanged the power supply. The rubber part on top of the head have been proved not no need that precision since I exchaanged my homemade one for the one I had in an intact Interfunk 2x8 and the results where the same...

Have to discover yet if the PLL is in a module PCB or if it is in the motherboard (something I haven't tested yet for errors)

ElektroNicki, thanks for the info, too! I thought it was the opposite, that is, the stripes would creat a kind of "empty" space that could "suck the tape to the drum...

[ Diese Nachricht wurde geändert von: Perepandel am 28 Aug 2011  8:27 ]

Perls explanation may hold some kind of truth, but on a diffrent machine and definitely not in this case!

The vertical bars we see are caused by the "Umlaufende Drop-Out-Kompensator" circuit (round-trip-drop-out-compensation) doing what it is supposed to do; repeat the last non-noisy scanline read off the tape OVER AND OVER until another non-noisy scanline can be read from the tape.
And since one single scanline is repeated multiple times, the contoures present in this single line blend into vertical lines.
Color is lost, since the color signal is NOT passed through the drop-out compensator, which btw only has a 2,5MHz Bandwith.
Which scanline is repeated depends on the moment the noise level exceeds the noisekiller threshold (i.e. YAD on the Video module).- So what we see may not necessarily be a line of the picture, but a line of some test- or videotext-signal that normally resides outside the visible area of the screen.
And of course you may lose tracking and drum/capstan lock, since with V2000 both is derived from the video-signal itself and not from separately recorded sync tracks.

Zitat :

but after some time playing, the image will lose stability and start jumping, displaced about one fourth from the bottom and compressed on top!

The effect that the picture shifts vertically is also caused by the drop-out compensation. If the signal from the heads is noisy and unreadable during the vertical sync pulse or even during many frames, the picture would jump or eventually roll vertically. To circumvent this problem the feature "V- und Y- Eintastung" - luma and vertical sync insertation has been added.
Basically V-sync pulses derived from the Drum/Servo speed loop are added as soon as the dropout compensation strikes during the v-sync or persists multiple frames.
Of course if dropout compensation persists for too many frames, the speed loop will drift from the previously locked speed and default to a more free running state, until a decent signal can be read, which then restores the speed lock.

My hunch; you have multiple major faults in the tape path alignment and/or worn heads.
Sorry to say so: Without oscilloscope and scanning the RF Signal read off the tape and extensive knowledge of the tricky uncommon insides of these machines, there is NO chance to get this fixed. Maybe you can get hands on english service manuals or someone to translate the german manuals uploaded somewhere on the net. Because all of what was explained before is at great lenghts explained in the Service manual.
I fear that in the long run, you may make things only worse by fiddling/cross-changing modules between multiple machines. Hope you won't end up with all machines trashed.

Zitat :

I've seen both versions; in fact, I own two machines without the stripes. I read somewhere that they allow for better adherence of the trape to the drum... Do you consider that drums with stripes offer better image quality??

With VHS some sources claim that videoheads with grooves are said to produce a bigger and more stable air cushion between the tape and the rotating part, thus minimizing tape abrasion, friction and drag on the drum motor. OTOH it is stated that once these grooves get clogged up it is exactly the opposite.
But what you do not want at all with either VCR - be it VHS, Hi8, V2000 etc is the tape sticking or getting sucked onto the rotating upper drum. The ONLY part of the rotating drum that is supposed to touch the tape are the videoheads themselves.
If you want to see what happens, when tape gets sucked onto the rotationg drum, get your hands onto a junk(!!!!) machine and an old tape, sprinkle even a miniature drop of water onto the tape where it enters the rotating drum and watch mayhem happen.
So much for better adherence...

Ok, this is becoming very interesting... Onnanokodesu explanation is very technical and well-explained, it is clear that he knows what he is talking about...

Nevertheless, I'm suspecting that the problem is from a different origin. I believe in some misalignement, don't want to think of worn heads yet . I thought about an electrical problem due to the loss of stability after some time playing. With worn heads, I thought, the problem would appear from the beginning... (but, after Onnanokodesu explanation I've understood it is not necessarily tht way).

I have the service manual; I've already translated parts of it with Google translator :D, somewhat enough for me to understand something and be able to do further test.

Now I was taking a look at it to try to find some hint. BTW, I even removed the modulator/tuner module to discard any interference from there, with no luck. Then I was already thinking of messing with the "kopfverstärker" (head amplifier), which is almost the only part I haven't checked yet (along with the "auxiliar" or "standby" netzeil -power supply-) and looks consistent with the problem.

But first I've stopped on page 88, which I'm attaching and talks about the "Wechsel des Optokopplers - Kopfrad lagengeber" ("Change of the optocoupler - head wheel position sensors").

Well, the screws on the tape run haven't been touched; they still have the blue paint intact to indicate they're still "sealed" as they were when the machine came out from the factory... But the ones marked with "3" and "5" have signals of manipulation!!

I'm going to adjust them and give some feedback on the results. On the meantime, I'm attaching another vid, in where I captured the effect of the image after one or two minutes playing. And here it goes an interesting thing: after the displacing of the image to the top, there is a strip at the bottom without the vertical bars! I'm pointing to it with my finger.

http://www.youtube.com/watch?v=ZrW3r5tDBco

PS: the "jumping" on the image on "real life" is not as severe as in the video. It's being exagerated due to the refresh of the screen (it's a CRT one).

[ Diese Nachricht wurde geändert von: Perepandel am 28 Aug 2011 21:38 ]

Well, I´m afraid, that this what onnanokodesu wrote, ist true (and I have guessed even before watching the youtube video): The video heads are worn or defective!

Because V-2000 has it´s sync-signals recorded also with the video signal, the fault causes the DTF system to get out of control. The video heads do not deliver a clean signal, and all of the signal stages get out of control.

You need to change the video head drum.

For further repair, a oscilloscope is neccessary. The head switch-over moment must get alligned, the head drum height (with the thin washers on the head drum spindle) must get alligned and at last, the DTF voltage must get checked for a constant run over the whole period of a head rotation.
Also, you need a control cassette. The best would be the original "Bandlauf-Kontrollcassette" Philips/Grundig for the Video-2000 system. But, unfortunately, this cassette is not avilable since many years.
Then, a very good recorded cassette would do a good job for allignment (but not 100 %).

Best regards,
stego

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Ok, I'm giving up. I'm following onnanokodesu and Stego advice. The manual adjustment of the "Kopfrad lagengeber" has given no noticeable improvements. I could put my other non-functioning 2x4 head drum in this machine (which I know is OK), but I have no oscilloscope and, as far as I know, they are very expensive, so I don't know if I'm going to invest in one.

Can anyone tell me if one of those homemade oscillators for PC, based in soundcards, could do the job? (it seems its biggest disadvantages are that the maximum frequency would be about 20000 Hz and maximum voltage input around 1.7 V)

If this is not possible, then I think I would try to revive that other machine that has good video heads.

This is a bit sad
Anyway, many thanks for helping and for the great info!

Zitat : if one of those homemade oscillators for PC, based in soundcards, could do the job? (

Perhaps you mean "Oscilloscopes"?
Don't waste your time with that.
You can use them for estimatimg the FFT or the THD of sine signals, but they have a strange phase response and, even at 1kHz or so, they will very heavily distort the shape of an impulse.

P.S.:

Offtopic :

onnanokodesu hat am 28 Aug 2011 13:51 geschrieben : Perls explanation may hold some kind of truth, but on a diffrent machine and definitely not in this case! Na, wenigstens hat mich Melli dieses Mal nicht gleich in der Luft zerrissen.

[ Diese Nachricht wurde geändert von: perl am 29 Aug 2011  4:16 ]

Hello Perepandel,

for a first testing another head drum, you can take the head drum of another machine, inserting it into this one machine. The only thing you must be careful: don´t loose or damage one of the very thin washers on the head drum axle!

You take the whole numbers of washers from the "giving" machine and install the head drum into your "defective" machine (Normally there are 3 washers, but depending on the tolerance of production, there can be also only two or even four washers).

Even without calibrating the head drum or the head switch-over moment, a picture must been imaged on the tv screen! It may be, that the picture is in a too high or low position, but that doesn´t matter, it´s only a test!

Don´t forget to clean the bulit-in head drum to wipe away any fingerprints!

Be careful not to touch the two magnetic heads on the drum!
The changing of the head drum is shown in the service manual.

Good luck and best regards,
stego

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