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Gabriel
Monday 6th April 2020
12:10 pm U.K.

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Dear Betamax community friends,

I am proud to share with you some experiments done on a basic but popular machine such as the Sony SL-C20. They are preliminary implementations based on Arduino.

First example is a trick for improving tape rewinding speed in machines with high mileage and worn drum assembly, causing excessive tape friction. It is a midway solution towards the Sanyo method (tape unlace during high speed transports):

https://youtu.be/6_zLcOoD-5s

Second example is the implementation of a real time counter in format hh:mm:ss instead of the classic 0000 - 9999 counter. Popular Hd44780 LCD display was used. Note that the counter is also able to count negative, show transport mode and light eight leds according to tape speed and direction:

https://youtu.be/tQtoV2q2pKQ

This third example is just a simple, quick check of the counter accuracy. It's only a basic check as the precision comes from the machine originally recording the tape:

https://youtu.be/Rm17ngiZT44

I hope you like these small experiments. Being at home for long periods is bringing me funny ideas.

Greetings from Spain,

Gabriel

Noel Higgins
Friday 3rd April 2020
1:50 am U.K.

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Kevin

Thanks! that's high praise indeed.

regards Noel

K Lambert
Friday 3rd April 2020
1:36 am U.K.

Noel:

Could'nt have put it better myself :)

Noel Higgins
Wednesday 1st April 2020
12:17 am U.K.

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Weber,

The terms used are actually back tension and forward tension. They relate to the pressure applied to the tape from the supply reel (back tension) and the take up reel (forward tension)

The capstan shafts rotational speed sets the right speed that the tape moves at in the first place. Too much back tension increases head wear.

Having the right back tension, ensures that the tape holds in position to be read by the spinning video heads as it travels over the guides that set it to travel diagonally around the video head drum assembly.

Back Tension is most often done in video machines by mechanical means such as a felt belt under tension by a spring lever arm which causes friction against the side of the supply reel mounting spindle.

For Forward Tension a similar principle supplies slippage to the drive of the forward reels mounting spindle.

What makes the Sony SLC9 special is that the both reels are controlled by steeper motors and both drive and braking resistance are managed electronically.

I hope that helps.

regards Noel

Weber1600
Tuesday 31st March 2020
11:11 pm U.K.

Seat124

Kevin

Hello, it is not very clear to me what is the rear tension, and what is the front tension.

Where is the tension measured?

Noel Higgins
Tuesday 31st March 2020
12:37 am U.K.

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Gabriel,

The last comment about cancellations during playback of the audio sweep is for when these linear stereo test tapes are played back on a mono player or stereo HiFi using the mono track.

regards Noel

Noel Higgins
Monday 30th March 2020
10:09 pm U.K.

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Gabriel,

The text below should read path alignment not patch. Before all that I clean the video and audio heads of course.

I will now email you pictures of selected pages from the Sanyo VTC M40 service and operating principles manuals

regards Noel

Noel Higgins
Monday 30th March 2020
10:03 pm U.K.

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Gabriel,

The meter I most use is a KONIG Cassette-Torque-Meter DMC 100 1 Beta. In the kit I only have the SL0003 and the SL0004.

I use a four channel oscilloscope (A Tek 7603 with two two channel plugins) which allows me to see the video waveform at the same time as I observe left and right channel audio.

The sony C9 manual treats alignment of both separately but I do it all at once.

You are correct that azimuth affect video and audio which is why I made special test tapes with different tone options and a test pattern.

I used a TTi TG230 2MHz Sweep/Function generator set up to sweep the audio range 100Hz to 10kHz (probably maximum 8kHz) at 25 times a second.

This allows me to observe the audio response of both channels at the same time as I observe the A/B wave forms from the video heads.

You are correct about the Capstan roller so I fix the first and do a patch alignment for best video first (assuming the azimuth and two other adjustments on the ACE have not been fiddled with).

I don't touch those adjustments unless I need to. The tape must be observed at the exit point to see that there is no tape curl.

A quick check of the tape staying flat during review and preview modes first is good as this checks capstan roller and capstan perpendicular alignment.

Best response is usually obtained using video drum exit guide (ACE entry guide) to flat top video exit waveform, then ACE exit guide to peak highest frequency response and get equal left right audio level.

I usually check the left and right channel level and phase by using a 3kHz or higher tone and overlaying the two wave forms. (channels observed using chop mode not alternative)

I hope that not too confusing.

The audio sweep shows cancellations at some frequencies if the azimuth is out.

regards Noel

Gabriel
Sunday 29th March 2020
7:52 pm U.K.

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Noel,

Thanks a lot for reporting your experience regarding tape tension among different machines.

One remark is that the original Sony SL-0003C tape also allows for simultaneous readings on both back and forward tape tension (I have them three: the SL0003, SL0003C and SL0004).

The C9 is a very special special machine. The fact you measure phase difference on L and R channels is smart and quite interesting. Are you using a scope for that (2ch + lissajous pattern) or use a more specific device such as an audio analizer?

There is also a concern I have while servicing machines and adjusting azimuths, tilts, heights and guides: sometimes you are altering the factory alignment, which is normally the best "balanced" one. The element to blame for these adjustments is mostly a worn pinch roller. Do you agree with this or are there any other factors behind that? (Consider you are not replacing any mechanical element).

Not to mention the previously fiddled "hit and miss" attempts from people with no knowledge or means for that... A nightmare to adjust betas.

Greetings,

Gabriel

Noel
Friday 27th March 2020
5:28 am U.K.

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Kevin,

I agree about head wear but 35gm is a safe setting for normal Sony mono machines ( SLC30, 34, 35 etc) and I find most need to be adjusted up to 35 from about 25 to 30gm as the spring has lost tension over time.

The tape tension gauge I am using is an aftermarket one. I do have a SONY set of gauges but have not used those because mine measures forward and back tension at the same time.

Given that the linear stereo machines ar only using a third of the tape surface that a mono machine uses I think the tension has to be optimum. Definitely higher.

You can also notice tape wear(condition) by a drop of in sound in the right channel (I think it was) from tape damage or stretching as that track sits at the edge of the tape.

regards Noel

K Lambert
Thursday 26th March 2020
7:49 pm U.K.

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Hi Noel.

Good info.

The back tension for the C9 is 45-48gm .I try to set the ones I work on to the lower spec. For obvious reasons(head life).

If no tape guage then that is a unique way to see.

I also didn't find the cassette tray obscured everything on the Slc0003 gauge just some.

The SLHF950 is 40 -48gm.

The rest seem to be 31 - 35gm.

..Kevin

Noel
Thursday 26th March 2020
5:53 pm U.K.

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Kevin and Webber,

Some information which may help.

My tape cassette with the back tension meter in it cant be read while in the SLC9 but back tension for the SLF1 is the same high 45gm versus 35gm for normal machines so I developed other ways to set it.

I have noticed that the back tension setting on the SLC9 whilst critical, can best be judged by its effect on wow and flutter and also the frequency response and level of the sound.

I have test tapes with both a full swept audio frequency response which I can observe on a CRO and also section with just 1kHz tone.

(On an SLC9 I use the 1kHz tones to determine correct azimuth alignment by checking the phase of the tone in each channel is the same and also that their levels are similar.)

With swept frequencies or the 1kHz tone - If you have too little back tension the high frequencies drop off first, then the overall level.

With the 1kHz tone - If you start to get the tension too high you get increased wow and flutter. Far too much tension causes picture issues as well as the tape tends to pull off its correct path on the guides whilst going diagonally around the video heads.

Good luck?

regards Noel

K lambert
Wednesday 25th March 2020
12:37 pm U.K.

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Weber1600:

You really need the back /forward tape tension cassette to get that setting perfect. Only THEN will you know for sure if that is causing your current issues.

The Sony breed are very particular with these settings, especially on the C9.

..Kevin

Weber1600
Tuesday 24th March 2020
11:29 pm U.K.

Seat124

K lambert

With a tape in play mode, I have turned the RV002 potentiometer in both directions of rotation, on the one hand, the tape increases in tension, turning the potentiometer in another direction, the tape loses tension.

But unfortunately the image on the TV screen is still black.

The counter does not work in play mode, and in Rec mode it does not work.

The rest of the functions are correct, just like previous weeks.

Gabriel
Tuesday 24th March 2020
10:55 pm U.K.

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Kevin, Noel,

Thanks a lot both of you for offering me the scans for Sanyo M40. Incidentally, I was finally able to find some schematics which, with some patience will show me a clue. At least, now I know the test points locations and their related signals. My guess points out towards some chroma modulation subcircuit in the record signal path as it -seems to- be stucked at a particular frequency (grey). But this could be due to one million reasons. This beaty will need some hours of testing, oscilloscope and care.

Side note about Sanyos: I was recently working on a VTC-M20 from a customer and I was amazed the good picture this machine was giving just by cleaning the tape path and adjusting a bit the dropout compensator after changing all the belts. Even with factory capacitors the image was superb. I didn't remember these M series were so good.

Talking about the lockdown: here in Spain we are facing serious problems. We are suposed to be quarantined at home during one full month. You can only go out for some very specific reasons and the police are continuously controlling people's moves. Sad but necessary. This is a good time for reading and pleasing activities at home. Not many testing tools at home so I will only spend some time with basic checks.

All my best wishes for all you and your families. Please take lots of care and, as always, stay tuned.

Gabriel

K lambert
Tuesday 24th March 2020
9:23 pm U.K.

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Hi Gabriel:

Yes I have to MINT condition VTC M40 's in black for my own light use for any beta hi-Fi tapes and the odd recording too.

I have never seen that issue. I did sort one out for a guy that had black and white playback and tuned out to be a crystal that was faulty. Took some finding too.

You won't cure that with any of the settings or switches on the front.

I do have the service manual for this model but not in PDF.

I could scan a few pages and send them to you if you like.

What areas did you require as these later manuals were not as detailed as say the VTC 5000 and 6500 ones were which is a shame.

Noel:

Things are not too bad in the area of Suffolk where I live and as well as my normal job outside (which has'nt been affected ) I am still repairing and servicing beta and VHS with the odd V2000,Umatic and Betacam for others.

learning new things as I go.

So this 'lock down' hasn't really affected me at all. My family are also not too affected either which is a relief.

I hope others who post here and their families hav'nt been badly affected either?

..........................Kevin

Rich
Tuesday 24th March 2020
9:29 am U.K.

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Hi Noel,

Those scan pictures would be very welcome indeed! Many thanks.

My email is now showing if you click on my name.

Thank you,

Rich.

Noel
Monday 23rd March 2020
9:32 pm U.K.

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Kevin,

How are you and your family holding up with the situation going on in UK? Still fixing machines?

It seems to me that those with a home hobby might be better placed for boring wait of self imposed isolation.

For some - what better time to do digital transfers of VHS and Beta tapes.

I for one never seem to get around to that.

regards Noel

Noel Higgins
Monday 23rd March 2020
5:50 am U.K.

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Rich,

I have photographed the exploded parts diagrams for both and the numbers are similar but slightly different - though they look the same except I notice the head motor of the C6 does not have shielding wrapped around it.

C7 head assembly is DSH-08A-R whereas the C6 shows DSH-08R

Gabriel,

I have service manuals and circuits for the Sanyo VTC40 and VTC50 models but I would not know where to start with the problem you have indicated.

Either of you can email me if you want pictures sent.

regards Noel

Rich
Saturday 21st March 2020
12:49 pm U.K.

Thanks, Gabriel,

I'll try to find the service manual online for the C6 mk1 and cross reference the head assembly. I'm crossing my fingers that it's the same for the C7 as the C7 needs a new videohead (which I have a few) but no eccentricity gauge to use when replacing it.

Cheers

Rich.

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