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Old 27th Apr 2021, 4:58 pm   #21
dj_fivos_sak
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Default Re: JVC HR3330 Lower Drum Issue

No worries. I actually have a working HR-3330TR which is the multi system version, pictured here. I replaced all the belts 5 or 6 years ago and it's been working pretty flawlessly ever since.

Fivos
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Old 27th Apr 2021, 5:32 pm   #22
G6ONEDave
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Default Re: JVC HR3330 Lower Drum Issue

Do check that the correct bearing number is 6202, as that's a number from memory and might not be the one you need for your model. There is a whole range of bearings in that style but at least they are marked with a number to make finding a replacement easier. I would go for the higher speed rated ones / longest life if possible and match the cover material as well. Some covers are metal whilst others are plastic and then there are open types.
Good luck in finding the exact type needed.

Dave
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Old 29th Apr 2021, 11:15 pm   #23
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Default Re: JVC HR3330 Lower Drum Issue

Well I've spent quite a lot of time on this HR3330EK so far but it's a long way from working. Here's a summary of where I am.

With the help of the manual kindly shared by Fivos, I tried to set up the capstan servo. The 2.51MHz oscillator (pin 4 of IC4) is running at the correct frequency but the rectangular waveform at pin 3 of IC4 is running at 7.85KHz instead of 1.867KHz. There is no trapezoid waveform at TP11 but adjusting R66 does vary the capstan motor speed. The trapezoid waveform should be derived from the capstan pick up pulse but I'm guessing that as the reference pulse is occurring approximately 4.2 times too often it's effectively flattening the top of the waveform continuously. I am able to set the capstan speed to produce capstan pick up pulses at a frequency of 3.7Hz but the servo is not locked.

IC4 could be faulty but my money is on a cap. Unfortunately the circuit diagram for the Audio/Servo board is missing from the manual but Practical Television gives a good explanation of the circuit. I might be able to reverse engineer the circuit diagram from the board layout.

Moving onto the drum servo this appears to be working ok. The drum pick up pulses are very uneven in amplitude but this is to be expected with one of the flywheel magnets having a chunk missing. Fortunately the following Drum Flip Flop Out signal is a healthy 10V in amplitude.

The real issues though are the noisy drum bearings and lack of output from the drum assembly. Putting a probe on pin 41 or 51 of the Pre/Record Amp board, as suggested in the manual, produces significant bursts of noise on both TP6 (FM luminance) and TP7 (AM chroma) so it would seem that either the rotary transformer is faulty or the video heads are worn out.

I think this is going to be a back burner project. Before I strip the lower drum down I should try to get the capstan servo working correctly. I did find the associated IC (MSM5816) still available from a supplier located in Madrid.
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Old 30th Apr 2021, 11:04 am   #24
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Default Re: JVC HR3330 Lower Drum Issue

Quote:
Originally Posted by dj_fivos_sak View Post
No worries. I actually have a working HR-3330TR which is the multi system version, pictured here. I replaced all the belts 5 or 6 years ago and it's been working pretty flawlessly ever since.

Fivos
In the words of Lennon and McCartney, 'It's a clean machine'.

Thanks again for the service manual. Maybe the missing circuit diagram for the audio/servo board was providence telling me to give up.
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Old 30th Apr 2021, 11:15 am   #25
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Default Re: JVC HR3330 Lower Drum Issue

Quote:
Originally Posted by G6ONEDave View Post
Do check that the correct bearing number is 6202, as that's a number from memory and might not be the one you need for your model. There is a whole range of bearings in that style but at least they are marked with a number to make finding a replacement easier. I would go for the higher speed rated ones / longest life if possible and match the cover material as well. Some covers are metal whilst others are plastic and then there are open types.
Good luck in finding the exact type needed.

Dave
Yes thank you G6GONEDave. I will take the old ones out before trying to order replacements. I'm still a little puzzled by the sudden loss of output from the heads? There doesn't seem to be any vertical free play in the shaft and barely room for a sliver of writing paper between the edge of the upper and lower drum. I'll inspect the rotary transformer carefully when I strip it down. Do you think it's advisable to pre-load the bearings a little before tightening the bottom collar?

I might treat my HR3300 to a new head drum and put the known good one from that in the HR3330.
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Old 3rd May 2021, 8:58 am   #26
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Default Re: JVC HR3330 Lower Drum Issue

If you find that IC3 is faulty (upD4011C) you can replace it with a cmos 4011 chip but not the 4011B. The 4011B is buffered, whereas the original is not and the internal diodes within a buffered type might upset the circuit.

Info for others reading this, the sine waveform coming from the capstan pick up head is 0.1 volt peak to peak, as measured on an oscilloscope with the probe set to x10. I am guessing that when the probe is set to x1 the sinewave is attenuated too much for stable operation in the control circuit. This is from a pencilled note in my manual on page 10-10/circuit 10-11.

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Old 3rd May 2021, 10:38 am   #27
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Default Re: JVC HR3330 Lower Drum Issue

Quote:
Originally Posted by G6ONEDave View Post
If you find that IC3 is faulty (upD4011C) you can replace it with a cmos 4011 chip but not the 4011B. The 4011B is buffered, whereas the original is not and the internal diodes within a buffered type might upset the circuit.

Info for others reading this, the sine waveform coming from the capstan pick up head is 0.1 volt peak to peak, as measured on an oscilloscope with the probe set to x10. I am guessing that when the probe is set to x1 the sinewave is attenuated too much for stable operation in the control circuit. This is from a pencilled note in my manual on page 10-10/circuit 10-11.

Dave
Useful tip thanks Dave. I had been using a x1 probe so will re-measure everything using x10 in future. The capstan pulse looks solid enough on mine though. It's the division from the Xtal oscillator that is wrong. I've even tried the age old wet finger to try and coerce it into the correct division. Hopefully changing IC4 and some of the caps will get it working again.

Last edited by hillsrob; 3rd May 2021 at 10:53 am.
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Old 6th May 2021, 3:53 pm   #28
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Default Re: JVC HR3330 Lower Drum Issue

I made a little progress today. First of all thanks to G6ONEDave for supplying a spare MSM5816 and a copy of the circuit diagram for the AUDIO SERVO board.

Having changed IC4, I'm now getting the correct capstan waveforms i.e. 2.51MHz sine wave on IC4-pin 4, 1.87KHz rectangular waveform on IC4-pin 3 and a trapezoid waveform that I can adjust to get a flat top of 75mS duration. See attached photos.


The audio sounds to be at the the right pitch although the pinch roller needs a little pressure by hand to prevent wow on the sound.

A new problem has come up though. No rewind. The Rewind key trips out immediately it is pressed.

One question for some of you with experience of these machines. On replacing the AUDIO SERVO board, should the 2 sprung loaded levers pass through the lugs at the ends of the slide switches or just locate and push on the ends of them?
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Old 6th May 2021, 4:48 pm   #29
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Default Re: JVC HR3330 Lower Drum Issue

If the spring loaded levers have 'L' bends where they meet with the switches, I would expect them to locate into the slotted holes on the end of the switches. Otherwise the levers could prevent the switches from going fully into the operated/non operated position, depending which way round the switch is being controlled.

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Old 6th May 2021, 5:51 pm   #30
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Default Re: JVC HR3330 Lower Drum Issue

Quote:
Originally Posted by G6ONEDave View Post
If the spring loaded levers have 'L' bends where they meet with the switches, I would expect them to locate into the slotted holes on the end of the switches. Otherwise the levers could prevent the switches from going fully into the operated/non operated position, depending which way round the switch is being controlled.

Dave
I checked the manual which just says make sure the levers are fully left before replacing the board. They seem to operate ok and return under their own spring pressure. The levers are slightly cranked over so it would be quite a fiddle to locate them in the eyes at the end of the switches. They have eyes at both ends so I guess they are quite generic in design. I won't know for sure if the switches are working properly until I do some of the setups that require both record and playback. I can for now check that the record light comes on in record mode. I'm just pleased that the MSM5816 replacement has fixed the capstan servo issue.
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Old 6th May 2021, 8:54 pm   #31
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Default Re: JVC HR3330 Lower Drum Issue

I suddenly realised that the cause of no rewind was that while handling the machine I had inadvertently pressed both the memory search and counter reset buttons. It wouldn't rewind because it was at the search found position!
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Old 6th May 2021, 10:00 pm   #32
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Default Re: JVC HR3330 Lower Drum Issue

I can scan you the audio/servo circuit if you want. I have the paper manual for the Ferguson 3V00.

Edit: Never mind, I see you've already been supplied with one. If you need any other bits scanning I can do.

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Old 6th May 2021, 11:00 pm   #33
hillsrob
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Default Re: JVC HR3330 Lower Drum Issue

Quote:
Originally Posted by birksholt View Post
I can scan you the audio/servo circuit if you want. I have the paper manual for the Ferguson 3V00.

Edit: Never mind, I see you've already been supplied with one. If you need any other bits scanning I can do.
Thanks for the kind offer. I have the paper manual for the Akai VS-9300G/EK which is a clone of the JVC HR3300. Fivos shared the complete JVC HR3330 manual with me but unfortunately the schematic for the AUDIO SERVO board was missing. G6ONEDave kindly scanned that for me so I'm all set thank you.
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Old 8th May 2021, 4:41 pm   #34
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Default Re: JVC HR3330 Lower Drum Issue

Now getting back to the lower drum. I need to replace the bearings and quite likely the upper head drum. Before that I want to be sure that the drum servo is working correctly as far as in can in record and playback mode. I carefully studied the description given in Oct 1981 edition of Television - VCR Servicing part 2 by Mike Phelan. I have already mentioned that one of the ferrite magnets on the drum flywheel has quite a chip taken out of it! (see photos) As a result it's not possible to get a balanced -0.6v pair of pulses at IC pins 2 and 28. Furthermore the rectangular bistable output at pin 23 (TP7) was at a frequency of approximately 12.5Hz when it should be 25Hz. Adjusting R23 it was possible to force a switch to approximately 25Hz but the signal was quite erratic probably due to the now amplified noise on the good magnet signal. The trapezoid waveform was similarly erratic in frequency and shape but the reference pulse from control head was at least visible on the trace.

So I decide my next step is to try to replace the ferrite magnets. I measured the good one and it was 2mm in diameter. It protrudes about 1mm from the flywheel so I have ordered a pack of these. https://www.first4magnets.com/circul...379|ps_1_16690

I realise that I will need to work out which is N and which is S. I'm thinking I will break the existing ones up in situ and depending on the fit secure the replacements with a dab of Araldite or something similar.
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Old 15th May 2021, 11:15 pm   #35
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Default Re: JVC HR3330 Lower Drum Issue

Yesterday I replaced both magnets on the drum flywheel. The drum pulses are now balanced and the bistable output is good. (see photos)

The tape speed is still fluctuating though due to poor pinch roller performance. This is causing an erratic trapezoid on playback. The trapezoid is stable on record with a video signal as input. On playback there is no output from the head drum and, as already discussed, the drum bearings are shot.

The next stage is to replace the pinch roller and check the drum servo performance on playback. Then I will attempt to replace the drum bearings and finally the head drum.
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