Sony VO 9600P Umatic playback issue

[TIMTAPE]

VCR's arent my strongest point (I'm an audio tape guy mainly) although I can almost handle the VCR's mechanical side.

Generally the machine seems in good condition. I've tidied up some obvious mechanical issues such as cleaning the tape path, pinch roller, reel table surfaces etc.

I'm pretty sure the tape I am using to play back is OK. I know about sticky shed video tapes and carefully baked the moisture out of the tape before playing.

The machine only has a decent picture when in "search" mode and the front panel knob is adjusted for normal speed (but in this state it has fluttery, unstable sound but perhaps this is normal?).

"play" mode is the problem. The audio is now stable but if there is a picture at all it is blurred or smeared for the bottom third of the picture and often drops out to horizontal bands of alternating black and white. At worst there is no picture.

Seeking any pointers as to which area the fault might be in. Perhaps some faulty electro's on a particular board? Any help appreciated.

Cheers Tim

[8 Tracker]

Hi Tim,

Haven't got any U-matics, no room , but from what you describe, it could well be leaking caps. I did battle with a JVC professional VHS machine a bit back and had to change nearly a hundred of the little beasties. Any chance of a photo or three?

Mark.

[TIMTAPE]

Thanks. Happy to take photos but not sure which sections I should photograph. There are multiples boards. No obviously leaking caps but there are many of them!

Tim

[8 Tracker]

Sorry Tim, I meant a picture of the screen.

[cheerfulcharlie]

Have you made a recording with the machine? - is it the same story as your pre recorded tapes?

[TIMTAPE]

Originally Posted by 8 Tracker

Sorry Tim, I meant a picture of the screen.

Ok, I'll try and take some stills of the playback image.

[TIMTAPE]

In trying to take photo's I heard an increase in pitch in the "whine" from the mechanism when going from "search" to "play". That is the pitch is higher in "play".

I connected a CRO to the RF output and can see the same thing on the waveform. In "play" the frequency of the waveform is higher than in "search", but the actual waveform seems otherwise about the same.

Generally there is a good strong picture in "search" but in "play" it's unreliable, varying from shaky to no picture at all. That's all the photos would show.

Does that help at all?

Thanks, Tim

[TIMTAPE]

All fixed it seems.

I had a hunch it might be something to do with the RF level. I located online a rather poor but readable scan of the service manual and from that found the RF level trimpot was RV38. Opening up the machine I also noticed that trimpot RV38 was adjusted almost to the extreme clockwise position which looked suspicious. I painted white marks on the trimpot so that I could return to this setting, and then adjusted the trimmer back towards a mid position. Picture returned with full stability, colour and clarity. Problem solved. Very pleased with the result.

It seems somebody had increased the RF gain hugely which must throw out the rest of the circuitry. Does anyone have any ideas as to why anybody would do this?

Thanks for your help.

Cheers Tim

[U-matic]

Hi Tim,

I'm experiencing the same problem with a VP-7040 deck which is pretty similar to VO-9600P, except for SP and recording features. However it doesn't happen with all videotapes, I guess it would depend on allignment/back tension/tracking problem but symptoms are the same as yours. Would you take a look at this videoclip and give me your opinion?

https://www.youtube.com/watch?v=kTmZYPmIwB0

Thanks in advance.

Cheers Max

[Lodgesound]

Originally Posted by TIMTAPE

It seems somebody had increased the RF gain hugely which must throw out the rest of the circuitry. Does anyone have any ideas as to why anybody would do this?

Hi Tim;

The reason this would have been done would have been to play back Umatic tapes with the mysterious "self erasure" problem whereby the RF level recorded on the tape degrades over time to around 50% of it's original value.

We have modified machines where I work that have their RF levels deliberately offset to counter this effect when it is encountered.

There is no conclusive explanation as to it's cause.

[U-matic]

All fixed thanks to TIMTAPE's trick. I've adjusted the trimpot RV4 (VP-7040 has got a different PCB than VO-9600P, see the attached image) back towards the lowest position, at least in my case, and finally all the noise has gone! Great job mate!!!

[U-matic]

Update:

VIDEO LEVEL (RV6) and DOC (RV5) trimmers can be also regulated in order to obtain a better video performance.

[TIMTAPE]

Good to hear, U-Matic. Glad it worked in both of our cases.

Sadly I have another problem with same machine. Now there is no LED display, no response to function buttons, no eject etc.

The capstan motor runs to speed but gave a telltale sign: a ticking sound, perhaps at 1hz or 2 hz. I suspected the motor but more tests revealed the ticking seems in the power supply (all three rails: 12v unreg, 12v reg and 7v reg). It appears clearly as a blip on the CRO screen, and the capstan motor was just acting as a kind of audible transducer for it it seems. Interestingly the reel drive motor also faintly shudders in time with the pulses.

I am going to try and see if it originates in just one of the rails and is perhaps being reflected back to the other rails in the SMPS. Any suggestions welcome as I am struggling to know where to start.

Tim

[U-matic]

Bad news I see. I would replace the entire PSB, if you can find any.

I was forgetting, here are the results

https://www.youtube.com/watch?v=HNZzVS3sgC8

[U-matic]

Hi guys,

I've messed up with my VO-9600P. I must have touched something so much that now I have a pattern noise (oblique lines) on playback. Unfortunately I do not have an oscilloscope and don't know how to fix it back. Any suggestion would be greately appreciated. Thank you

[U-matic]

Hey Tim,

could you do me a favour and post (or send me) some shots of your PCB's trimmers? Thanks