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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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10th Sep 2021, 5:26 pm | #1 |
Pentode
Join Date: Oct 2016
Location: Ware, Herts, UK
Posts: 169
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Sony AV3670 Head motor starter capacitor
Hi everyone,
Recently, my previously fine AV3670 developed a fault where intermitantly the head drum would not get up to speed causing the (usually faultless) video to disappear. I understand the head drum motor is an AC motor connected to a rather strange (at least to me) starter motor capacitor with 3 terminals (see pics) As I cannot find any direct replacement I thought I could get away with a 2.5uF 250V starter capacitor connected in series with a 1.2uF X2 capacitor but when connected up the drum no longer turns at all. I believe these capacitors in the Sony decks were known to fail after all these years. Does anyone have experience on how to replace and make the unit work again? Rob |
10th Sep 2021, 5:55 pm | #2 |
Heptode
Join Date: Jan 2007
Location: Luton, Bedfordshire, UK.
Posts: 891
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Re: Sony AV3670 Head motor starter capacitor
You'll need two motor-run capacitors with one side commoned together and connected to point (c), and the 2.5uf and 1.2uf connected to their respective positions (refer to markings on the base of the pulled capacitor). AC so no need to worry about polarity.
__________________
Regards, John |
10th Sep 2021, 6:09 pm | #3 |
Octode
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,552
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Re: Sony AV3670 Head motor starter capacitor
Are the two caps there to cater for 50 / 60 cycle operation? If so you only need one cap of 3.7 uf for UK use. (3.6 or 3.9 would probably be close enough).
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11th Sep 2021, 10:21 am | #4 |
Pentode
Join Date: Oct 2016
Location: Ware, Herts, UK
Posts: 169
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Re: Sony AV3670 Head motor starter capacitor
Thank you all.
Sounds like I wasn't completely daft. Hopefully you can see what I have done from the attached. The only 1.2uF start cap I could find was one for an electric fan - can these be combined in the way I have? As far as I can see, the head drum motor has 3 wires.
The "1.2" on the original cap appears to go to another part of the machine - possible another motor, possibly the take-up spool because now, the head drum doesn't turn at all AND the take up spool doesn't turn at all. (The supply spool and capstan still turn as before) Any ideas what I have done wrong? |
11th Sep 2021, 11:16 am | #5 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
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Re: Sony AV3670 Head motor starter capacitor
These capacitors are run capacitors, always in circuit.
Have you checked the orignal to see what capacitance(s) was/were in use when you observed the fault? John |
11th Sep 2021, 11:28 am | #6 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
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Re: Sony AV3670 Head motor starter capacitor
Looking at the schematic of a 3600 (60Hz only) machine, I'd say Barry ? in post 3 is right, and you need 3.7uF to run the head drum.
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11th Sep 2021, 12:54 pm | #7 |
Pentode
Join Date: Oct 2016
Location: Ware, Herts, UK
Posts: 169
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Re: Sony AV3670 Head motor starter capacitor
Thanks John.
Maybe I don't understand what you and Barry are suggesting. Per my previous post, the head drum motor is connected across the "common" and "2.5uF" terminals. Why would the drum want a 3.7uF starter capaciticance? What I can't unfathom is what the 1.2uF terminal is connected to. It certainly isn't the head drum motor. I too have the US model service manual and there does seem to be differences in the 3670 UK 50Hz model. |
11th Sep 2021, 12:56 pm | #8 |
Pentode
Join Date: Oct 2016
Location: Ware, Herts, UK
Posts: 169
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Re: Sony AV3670 Head motor starter capacitor
oh and the "failed" capacitor was reading 2.6uF on both "Common-2.5" AND "Common-1.2". This is what led me to conclude it had failed.
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11th Sep 2021, 1:42 pm | #9 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Sony AV3670 Head motor starter capacitor
The schematic for the CE version of the AV3620 shows the two capacitors (2.5uF + 1.2uF) connected in parallel, eg total capacitance 3.7uF.
Lawrence. Last edited by ms660; 11th Sep 2021 at 1:55 pm. Reason: extra info |
11th Sep 2021, 2:03 pm | #10 |
Octode
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,552
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Re: Sony AV3670 Head motor starter capacitor
It is common on 50 / 60 cycle equipment to switch in an additional cap for 50 cycle operation. This is in order to allow for the winding impedance at the lower frequency. The extra 1.2uf is about correct to do this on top of the 2.5uf for 60 cycle operation.
Many machines have this type of arrangement in order to reduce the manufacturing differences for equipment sold in different territories. |
11th Sep 2021, 4:27 pm | #11 |
Pentode
Join Date: Sep 2011
Location: Coventry, West Midlands, UK.
Posts: 211
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Re: Sony AV3670 Head motor starter capacitor
Don't forget Japan itself has 50Hz mains in the east and 60 Hz mains in the west, so a dual cap. wouldn't seem an "odd" solution.
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11th Sep 2021, 4:33 pm | #12 |
Octode
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,552
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Re: Sony AV3670 Head motor starter capacitor
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11th Sep 2021, 5:17 pm | #13 | |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Sony AV3670 Head motor starter capacitor
Quote:
If your machine is definitely 50Hz then as others have explained according to the schematic both capacitors should be paralleled together to give a total of 3.7uF The 1.2 terminal side of the 1.2uF would normally go to a 50/60Hz mains frequency selector switch (typically in most machines) which when switched to 50Hz effectively connects it to the 2.5uF terminal. Have you measured the capacitance across the 2.5uF since replacing it ? David Last edited by DMcMahon; 11th Sep 2021 at 5:29 pm. Reason: Typo correction |
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11th Sep 2021, 9:49 pm | #14 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
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Re: Sony AV3670 Head motor starter capacitor
As a double-check that we're all convinced they should be parallelled: if you multiply 2.5 by (60/50)^2, (i.e. keeping the same resonance in the quadrature winding), you get 3u6.
John |
12th Sep 2021, 7:53 pm | #15 |
Pentode
Join Date: Oct 2016
Location: Ware, Herts, UK
Posts: 169
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Re: Sony AV3670 Head motor starter capacitor
John/David - thanks. I think I need to trace where the 1.2uF terminal does connect to. A 50/60Hz selector switch sounds reasonable.
If this is indeed correct - and the fault is that the machine needs 3.6uF to drive the start-up of the head drum, what would that mean for the 50/60Hz selector feed wire. i.e. If I connect the motor red/black wires to the terminals of a 3.6uF starter cap, would I leave the frequency selector wire unconnected? Surely that wouldn't have a complete circuit? |
12th Sep 2021, 8:20 pm | #16 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
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Re: Sony AV3670 Head motor starter capacitor
You can trace it out, but unless you plan at some point to use the machine on a 60Hz supply, the wire is kind of redundant, so can be insulated and tucked away. BTW, it's a run capacitor, always in circuit!
John |
12th Sep 2021, 8:22 pm | #17 |
Pentode
Join Date: Oct 2016
Location: Ware, Herts, UK
Posts: 169
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Re: Sony AV3670 Head motor starter capacitor
Thanks John. I will revert once I have tried a few things out.
I may be able to get a lot of these old beasts working, but my actual understanding of electronics is very poor (as you can probably tell). |
12th Sep 2021, 8:30 pm | #18 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Sony AV3670 Head motor starter capacitor
It is slightly strange that the schematic does not show the 50Hz/60Hz selection switch ? the 1.2uF could connect elsewhere but does not seem likely. I have not seen the rest of the schematic (from what has been posted here) to see if it might show a connection to the 1.2uF somewhere else.
I personally would remove wire that connects to the 1.2uF capacitor and just connect that end of the capacitor to the 2.5uF terminal, to connect them in parallel (to give 3.7uF) and then retest to see what happens. David |
12th Sep 2021, 8:30 pm | #19 |
Pentode
Join Date: Oct 2016
Location: Ware, Herts, UK
Posts: 169
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Re: Sony AV3670 Head motor starter capacitor
oh and just to check , as there doesn't seem to be such a thing as a single 3.7uF start/run cap widely available, I am perfectly fine to wire my 2.5 and 1.2 caps (from post 4) together in parallel and solder the head drum motor across the combined replacement aren't I?
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12th Sep 2021, 9:45 pm | #20 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
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Re: Sony AV3670 Head motor starter capacitor
Yes.
David |