VR2414 - Possible DTF problem?

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collisr
Berichten: 44
Lid geworden op: za dec 03, 2016 8:03 pm

VR2414 - Possible DTF problem?

Berichtdoor collisr » wo apr 18, 2018 11:15 am

Hello everyone.

Thank you for your help last year in fixing my VCC machines. With your help I now have 2 working Video 2000 machines.

Last week I came across a Philips VR2414 which I wanted to rescue. I have:

- replaced the X2 mains capacitor (which had exploded!)
- cleaned the code disc, DTF contacts, tape path, capstan, video and audio heads.

But.. although the machine laces/fwd/rwd/eject all perfectly, the picture is terrible. I have a video to help show the problem: https://youtu.be/DgYpHcQ2OSI.

I believe this is the DTF circuits unable to lock onto the video track. I have tried multiple tapes and all suffer from this problem. I think you can hear the video drum actuators firing every few seconds in the video - am I right?

Any advice on what to do next would be much appreciated.

Rob

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gromsound
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Re: VR2414 - Possible DTF problem?

Berichtdoor gromsound » wo apr 18, 2018 5:31 pm

Hi Rob welcome back. It's a contageous disease this VCC bug eh?

I think you may be right blaming the DTF. Trouble with these machiens is that all boards are fixed to each other and the DTF cirquitry is spread over more then one board. so a simple swap like in the 23xxes is not possible.
of course you can try looking for leaky electrolytic capacitors (elcos) that pull signals or power to ground. check the DTF high tension too, supply might be rip.

but i might warn you from my experience, i never could repair a defective DTF in a 24xx ....
be the first one on the block! :lol:
lijdt aan AMHD - alles moet het doen

collisr
Berichten: 44
Lid geworden op: za dec 03, 2016 8:03 pm

Re: VR2414 - Possible DTF problem?

Berichtdoor collisr » wo apr 18, 2018 6:14 pm

Thanks Gromsound.

I do seem to choose the difficult ones !

Can I confirm with you that the sound I hear on the YouTube video is the DTF actuators firing? If they are working, do you agree the fault is probably in the electronics of the DTF circuits on the A610 board that is folded in 3 pieces on the VR24xx ?

Are there any measurements from the DTF contact bridge I can take to prove the reading of the DTF track is fine?

I am prepared to walk through the DTF circuit checking/changing the Elcos if we think this is the correct place to look.

I did see VCCtip 19 - based on my YouTube video, do you think this could be a cause?

Rob

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gromsound
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Re: VR2414 - Possible DTF problem?

Berichtdoor gromsound » do apr 19, 2018 4:12 pm

Hi Rob

I dont recognise the sound in your video. it almost sounds like the black plastic position lip (on top of the head) is touching the detector slit.

Are you sure your DTF ''brushes'' are making good contact? can you check the cable and the connector to those contacts. it sounds a bit like a loose bridge.
you wont measure DTF control signals on these contacts, the actual position signal is taken from the video heads (which snoop on the adjacent video tracks where the DTF info is coded in). the rotating contacts only conduct the dtf servo power (high tension) to the actuators. of course this can give info about a possible fault in teh DTF power supply but that can be measured at the supply board.

i do not see any connection to tip 19, thats just a loose cover on the head amp or a shaky scart, try hitting the top of the machine (percussive diagnostics), does that have effect?
lijdt aan AMHD - alles moet het doen

collisr
Berichten: 44
Lid geworden op: za dec 03, 2016 8:03 pm

Re: VR2414 - Possible DTF problem?

Berichtdoor collisr » za apr 21, 2018 8:27 pm

Hello Gromsound and everyone.

Today I checked further on my VR2414 DTF issue. I too cannot recognize the strange sound on my video while the tape is playing. Here is what I have done:

- I checked that the upper head drum can spin freely under the DTF bridge with the mains power unplugged - YES. ALL OKAY
- I removed the DTF bridge and checked the brushes. None are bent and are all "standing up straight". When I reconnected the bridge, it seemed that all brushes were touching the underside of the DTF bridge
- I checked the connectors from the DTF bridge to A160.DE7 with my multi-meter. No loose/broken connections.
- I swapped the upper head drum with another good video head and the same problem.

I have been looking at the service manual and will be diving deeper next week. For now, 2 questions:

Q1) I wish to prove that the actuators are not to blame. Have you ever swapped a VR2324 or VR2350 tape unit into a VR24xx. On first look the connections are the same - only the DTF and Servo boards on the VR23xx are under the tape deck and the VR2414 are behind the tape deck in a chain of 3. IS THIS CORRECT?

Q2) I have seen a DTF check procedure in the Service manual, but it is in dutch. Could you translate for me? (Google Translate isn't good at this). And offer any advice on whether this is a useful procedure?

=======================
Service Manual 6.8
DTF Test
- Stop een cassette in het apparaaat en spoel de band een stuk vorruit
- Druk de toetsen "record" en "down" beide tegelijk in.
- Sluit het apparaat aan op de netspanning (POR)
- Service status op het klokdisplay
- Druk de "bandteller reset" toets in.
- Bandteller indicatie op het klokdisplay
- de DTF uP7210 levert een zaagtand spanning op de uitgang van de Digitaal Analloh Concert (DAC, 13-7230)
- Controleer met een oscillograaf de amplitudes van de zaagtand op de punten zoals in fig. 6.2 is aangegeven.

Opmerking
De amplitude van de zaagtand op de uitgangen van de actuator eindversterkers is afhankelijk van de instelling van 3306 (ACTA 1) en 2226 (ACTA 2). Voor de juiste instelling van 3306 en 3336 wordt verwezen baar de electrische instellingen van print A610 op biz. 5-22

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Dominic
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Re: VR2414 - Possible DTF problem?

Berichtdoor Dominic » zo apr 22, 2018 10:40 am

By the way, did you check the slipring contacts of the DTF for wear or oxidation? I've had a few 3rd generation machines with silver plated contact fingers which were actually totally black from silver oxide which is a bad conductive material.

Translation of the DTF test procedure:

DTF Test:
- Put a cassette in the machine and wind the tape forward a bit
- Disconnect the mains
- Push the "record" and "down" buttons simultaneously and hold while connecting the mains again
- Service status appears on the clock-display
- Push "counter reset"
- Tape counter indication appears on the clock-display
- The DTF processor uP7210 now puts a sawtooth voltage on the DAC (DAC 13-7230)
- Check with an oscilloscope the amplitude of the sawtooth signal on the points given in figure 6.2

*Note:

The amplitude of the sawtooth voltage on the output of the actuator amplifier is depending on the setting of 3306 (ACTA1) and 2226 (ACTA2).
For the correct settings of 3306 and 3336 see the chapter "electrical settings of board A610" on page 5-22.
Een ieder die zich aanpast aan de geest van de tijd, raakt zijn persoonlijkheid kwijt.

collisr
Berichten: 44
Lid geworden op: za dec 03, 2016 8:03 pm

Re: VR2414 - Possible DTF problem?

Berichtdoor collisr » zo apr 22, 2018 4:05 pm

Thanks Dominic.

Yes, I did have to (gently) clean the DTF contacts/brushes. As you say, they were black on the tips, but now they are silver and shiny after cleaning with iso-propyl alcohol.

Thanks for the translation. I would have thought I could measure the actuator voltages without going into this test mode, but I will try and see if the correct power is getting to the brushes. If not, I guess i have to trace back from plug DE7 and see if anything obvious has broken. There appear to be a few elco caps in that area - maybe they have gone high ESR?

Will update the forum with any progress.

Rob

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gromsound
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Re: VR2414 - Possible DTF problem?

Berichtdoor gromsound » zo apr 22, 2018 4:54 pm

Have you ever swapped a VR2324 or VR2350 tape unit into a VR24xx. On first look the connections are the same - only the DTF and Servo boards on the VR23xx are under the tape deck and the VR2414 are behind the tape deck in a chain of 3. IS THIS CORRECT?
Never tried that (normally a dead 24xx will go into the bin) but i think it might work. all core deck parts are the same, you may run into trouble with some connectors for audio which exist in 3 different flavours along the series. but that is not important for your experiment.

but i bet you that the DTF circuit is defect (parts scattered along the three boards) since the head drum itself proved not to be the problem. my best guess stays: leaking elcos to ground in the DTF circuit. maybe you can check all test voltage levels in the diagram along the way and find the position where it goes wrong.
i never had the patience to do so for a lowspec 24xx machine :? found another one that worked for the collection.
Laatst gewijzigd door gromsound op ma apr 23, 2018 3:56 pm, 1 keer totaal gewijzigd.
lijdt aan AMHD - alles moet het doen

collisr
Berichten: 44
Lid geworden op: za dec 03, 2016 8:03 pm

Re: VR2414 - Possible DTF problem?

Berichtdoor collisr » zo apr 22, 2018 6:43 pm

I will try that Gromsound and let you all know.

I am still learning with these machines and am finding that when they are working, they all have different abilities to play very old VCC tapes.

I have a VR2324, VR2334 and (no laughing) a Grundig Super 2x4 which all work now. I do find that some very poor tapes still play in the Grundig but produce only a screen of snow on the Philips. I suspect this is the back tension on tapes which have "curved" over time but the Grundig tends to play anything (which is useful for transferring very bad tapes). I think the picture quality is best on my VR2334.

I would like to understand whether the VR24xx gives me any further options for transferring my many many video 2000 tapes.

mae
Berichten: 3458
Lid geworden op: zo nov 17, 2013 2:42 am

Re: VR2414 - Possible DTF problem?

Berichtdoor mae » zo apr 22, 2018 10:10 pm

The VR24xx series is mostly historically important because it was a cost down development by the Krefeld design team and may have been designed with VHS in mind (to have some electronic and case parts in common so both could have been produced alongside - which only happened for a very short while and not in the way Philips had envisioned it only a few years before). I don't know whether this cost down principle has a positive, negative or neutral impact on picture quality and tape compatibility, it could go either way.

P.S. Could I have your full model number and serial number for my other topic please?

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gromsound
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Re: VR2414 - Possible DTF problem?

Berichtdoor gromsound » ma apr 23, 2018 3:55 pm

Yes possibly the Ghhrundigghh has the best tape-drum contact because it laces up beeeehta style (C-loading) which no Philips vcc does. But in a 20xx you can very simply increase tape tension with the sliding detector base plate on the left side (close to the erase head). Just make a small mark where the original position was. you can feel with a finger (nail) against the loose tape loop to get an impression of the tape tension. also you can hear it from the sound of the tape against the spinning drum. and watch the image change (or not).

the 24xxes have no special ''talent'', they are just stripped down and repackaged 23xxes. image quality should be the same (when new!) because all important parts regarding that aspect are the same. you may after decades finds some difference but that is not systematically i think. might be due to wear so try to find one with as less running time as possible. and that may well be a late one like a 24xx...

My experience: i have only one 2414 which gives an unbelievable sharp image, kept it just for the head disc (it's the rebadged Erres model). this one could probably be the least used vcc i have. pity they have no hour-counter in the computer like later VHS ones.
lijdt aan AMHD - alles moet het doen

collisr
Berichten: 44
Lid geworden op: za dec 03, 2016 8:03 pm

Re: VR2414 - Possible DTF problem?

Berichtdoor collisr » ma apr 23, 2018 7:58 pm

Hi Mae,

Unfortunately, the sticker on the back of my VR2414 had been removed when I received the machine. Is this the only place to find the information? I recall the N1502/1700/1702 had additional stickers inside the machine.

Rob

mae
Berichten: 3458
Lid geworden op: zo nov 17, 2013 2:42 am

Re: VR2414 - Possible DTF problem?

Berichtdoor mae » di apr 24, 2018 12:22 pm

On the VR2414 this is the only place as far as I know.

Gromsound is probably right in his analysis that the better picture quality in his case is just because of a low operating hours count. I should study the VR2414 some more.


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