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-   -   JVC 3320 Transport Failure (https://www.vintage-radio.net/forum/showthread.php?t=162300)

1100 man 24th Dec 2019 10:19 am

Re: JVC 3320 Transport Failure
 
Hi Peter,
I don't think there is any similarity between the 3v16 & 3v22 servo circuits. The 3v16 set up even has an extra pcb which needs a deeper rear cover to accommodate it.

Looking back over some past threads about 3v22's, drum servo problems, with similar faults to the one you describe, seem to be a common issue. The drum motor itself seems to be a common cause. It's a brushed DC motor and I assume the commutator/ brushes degrade to the point where it can't go fast enough. Might be worth checking before assuming it's an electronic fault!

In my experience, storing vcr's or almost anything for that matter in lofts, seems to almost guarantee they will be ruined! Extreme temperature turns the rubber to goo and dries out all the electrolytics. Then you get damp and mould in the winter!

Sadly I don't think I've got a manual- only a 3v16 one.

Good luck with it
All the best
Nick

peter_scott 24th Dec 2019 10:42 am

Re: JVC 3320 Transport Failure
 
Hi Nick,

I'm very much in tune with your thoughts. I had suspected the drum motor. I couldn't easily access the connections on it directly but I think I accessed the supply on the control board and it was something in the range 6 to 7 volts (I'll need to check it again.) I just didn't want to admit to myself that the motor was faulty but I'll go and solder a couple of wires onto it and check the voltage just now.

Thanks,

Peter

peter_scott 24th Dec 2019 11:13 am

Re: JVC 3320 Transport Failure
 
1 Attachment(s)
Hi Nick,

Here's what the drum motor terminals look like. The lower trace is just to point to zero volts on the scope and the upper one is at 2 volt/ div.

What do you think?

Peter

peter_scott 24th Dec 2019 11:46 am

Re: JVC 3320 Transport Failure
 
There is a capacitor or two around the drum motor drive in the 3V16 but I've yet to discover if they exist in my circuit.

peter_scott 24th Dec 2019 12:23 pm

Re: JVC 3320 Transport Failure
 
I've now changed both of the capacitors but unfortunately without any improvement.

Peter :(

peter_scott 24th Dec 2019 4:40 pm

Re: JVC 3320 Transport Failure
 
Well I think the drum motor is OK. With the odd glitch I've got it running at about the right speed with drum pulses at 25 Hz.

The breakthrough came with a tweak to the sample pulse amplitude. It's still not totally stable but appears to be a question of getting the tape path working correctly on the reference edge and without wiggling light reflections off the capstan and take-up areas and tape tension. All easier said than done. :-/

Red to black 24th Dec 2019 6:19 pm

Re: JVC 3320 Transport Failure
 
Yes the servos could be a PITA to set up on these, I probably have a service manual (paper) for this machine, I won't be able to dig it out before Christmas now though.

peter_scott 24th Dec 2019 6:40 pm

Re: JVC 3320 Transport Failure
 
Thanks Red to Black, There absolutely no urgency for this but I'd certainly like to see the schematic of the control board and maybe a bit about the path set-up.

Best wishes for a Christmas without thoughts of VCRs.

Peter.

Techman 26th Dec 2019 1:44 am

Re: JVC 3320 Transport Failure
 
2 Attachment(s)
Just been looking through my old manuals - these may be the ones you want, although one isn't very clear as the originals have been laminated, so the scanner struggled.

Techman 26th Dec 2019 1:56 am

Re: JVC 3320 Transport Failure
 
1 Attachment(s)
I've just had another go with the not so good one pressing hard down on the lid and with it showing the other end that was partially missing before, so perhaps you can work with the two. I think it's a bit clearer than the previous one.

peter_scott 26th Dec 2019 10:59 am

Re: JVC 3320 Transport Failure
 
That looks like my circuitry all right Techman and I can read them just fine. Thank you very much for this Christmas present. Very much appreciated!

Peter :):thumbsup:

peter_scott 26th Dec 2019 5:01 pm

Re: JVC 3320 Transport Failure
 
Hi Techman, Can you tell me which model your schematic is from? It is using the AN318 chip but unfortunately it is configured in quite a different way to my JVC3320.

I'm now unsure whether I have an electrical fault or a mechanical one. The drum speed is varying above and below its correct speed.

In this video the first part shows the period of the drum sensor at 5 mS/div so for the correct speed the leading edge should be at 40 mS but you can see that it varies earlier and later than this. The second part of the video shows the drum motor drive voltage. (The drum speed is of course damped by the inertia of the flywheel.)

https://youtu.be/QS1oARbcTzo

Peter

peter_scott 27th Dec 2019 12:31 pm

Re: JVC 3320 Transport Failure
 
2 Attachment(s)
Although Techman's schematic is rather different to mine it was very helpful in trying to identify the parts of my circuit. I eventually tracked it down to the limiter in the drum discriminator circuit with some help from:

https://www.americanradiohistory.com...e-Beeching.pdf

It was a leaky 10uF on the output of the limiter.

Thanks to everyone who offered help but especially to Techman.

So returning to my original problem of ghosting on a "modern" VCR I can play a 405 tape without the ghost.

Peter

Techman 15th Jan 2020 3:14 am

Re: JVC 3320 Transport Failure
 
Hi Peter. Sorry, I completely forgot about this thread, so just catching up. Great to see that you got the fault sorted in the end. The circuit I posted was from the portable version of the early piano key top loader, which I thought would be the same. If 'Red to black' happens to see this and has his copy to hand and is able to post it, then it would still be interesting to see the differences and for completion of the thread for future reference.

peter_scott 15th Jan 2020 9:36 am

Re: JVC 3320 Transport Failure
 
I am really surprised at the number of significantly different circuit versions there are for what externally look like the same VCR.

Peter

dj_fivos_sak 16th Jan 2020 1:31 pm

Re: JVC 3320 Transport Failure
 
Hi. A bit off-topic question so I apologize. What are the differences between the HR-3320 (3V22) and the HR-3330 (3V00)? I have an HR-3330TR which is multi-system (PAL, SECAM, NTSC 4.43). Was the 3320 released in the UK only with the EK model suffix?

mark2collection 16th Jan 2020 1:52 pm

Re: JVC 3320 Transport Failure
 
Quote:

Originally Posted by peter_scott (Post 1207884)
I am really surprised at the number of significantly different circuit versions there are for what externally look like the same VCR.

Peter

You're not kidding, I have the Baird version (looks standard enough) and an Akai version, where (from memory) the sys-con plus audio board are green and double sided! This being the only time I've seen double sided technology in a piano key machine.

Really must do something with these two, either enjoy them or, move them on. The Akai machine must be quite scarce(?) Cannot remember the model, begins 'VS' I think, the number 9300 rings a bell.

The Akai on occasions, unlaces whilst playing. The grease has turned to soft wax.

Mark

peter_scott 16th Jan 2020 5:06 pm

Re: JVC 3320 Transport Failure
 
Well, I can tell you that the 3330 uses an HA11711 chip in the drum servo control circuit whereas the 3320 uses AN318 an no doubt a million other differences.

Peter


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