EEVblog #381 - How Do Ultrasonic Delay Lines Work?

How do glass ultrasonic acoustic delay lines work? The kind used in PAL video recorders.
This is Part 3 of the Sony CCD Video 8 Camcorder Teardown.

Delay line info:

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[RandomNullpointer]

@22:01 I saw one of these glass delayers 30 years ago, and I never found out what it was. Today I'm celebrating this knowledge, thanks to you, buddy :)

[metaforest]

Didn't see any comments about the transducers on the edge of the glass so I'll comment.   If you look closely where the bond-wires are connected, you will see two conductive layers stacked on top of each other.  Between them is a piezo film.  The piezo material is sandwiched between the conductors which are stepped to expose them as pads for the bonding wires.  When the conductive layers are energized they cause the piezo film between them to flex.  This flexing sets up a vibration in the glass plate's edge that propagates down the acoustic waveguide.  The features bonded to the face of the glass plate as Dave describes form the acoustic path.  When the wave-front hits the far end  of the waveguide it flexes the receiving transducer (which to my eye) appears to be identical to the transmitting side.  The glass itself is not piezo material.

[whitcwa]

The camea's delay line is used to increase horizontal resolution. Delayed video is subtracted from undelayed video and the difference is amplified and added back to the undelayed video. Other cameras use 1H delays to increase vertical resolution.
The VCR uses the delay line for dropout compensation. When the signal off the tape dropped below a usable level, the previous 2 lines of video could be switched in place of the bad video. Most tape dropouts are much shorter than 2 lines. 
The 2 inch quad VTR's used delay lines which were approx 6 inch (150mm) rods of quartz.

[crumplezone]

1985 was a great year, and that service manual is a thing of beauty.

[vjk]

I love those old service manuals. Back in the days when things were built to be repaired..

[ChipGuy]

Hi Dave, i was a Service Manual writer once at TELEFUNKEN Germany. It takes about 1 full month of work just to make a service manual for a CD player, when the schematics have already been done. It would certainly take 5 people 3 months to make this elaborated manual from that Sony cam.

[neail]

Thank you very much, I know it's 10 years, yet that thumbnail helped me to find out.

Marvelous piece of engineering, and thanks for the explanation, I was fascinated when I had my self one, disassembling a TV (broken) was absolutely astonished then, as you showed the tranceducers I noticed them too but never thought conversion to sound and manipulation inside a circuitry was ever an option.

I did almost forgot untill today. Thankyou.

[EEVblog]

Yes, I wanted to do a follow-up video this one.

[dorbie]

On the CCD, there's obviously the color bayer pattern, but above this there is a layer of micro-lensed material. This serves a couple of potential purposes, it can act as an anti-alias filter to mitigate Moire patterns, this means it is a spatial domain Nyquist frequency pass band filter for light (although it won't be as soft as it needs to be for marketing reasons) Bandwidth in the spatial domain here is limited by the CCD pixel density. It also helps gather light into the photoreceptor wells to make the CCD more efficient. I suspect the optical effect you are seeing is refraction and internal reflection on this micro-lens layer.

[treborrrrr]

This video just blew my mind a wee bit. Being fairly young (30ish) and not having dealt with electronics much more than the small amateur tinkering with MCUs I do at home I had never seen this type of physical interaction between components before. Sending signals through a piece of glass/crystal to slow it down, man, that's (in lack of a better word) fucking cool. Sometimes it makes me sad how everything these days is so "simple".

[EEVblog]

No such thing as the next level, just continuous improvement, I still lean new stuff every day after 30+ years of doing electronics. Read and hang out in a forum like the EEVblog forum and you'll learn a lot.

[oldevil]

"I could scroll through this all day long, I love it!" Haha you are are really something, these phrases makes me come back every time and watch your videos, keep up the good work!

[azyfloof]

I've seen those glass delay lines in all sorts of old equipment like VCRs and televisions. Been tearing stuff down for about 25+ years now! It's amazing seeing how stuff's changed.
I always wondered what the black resin patterns on the side of the crystal were, and always just assumed they were "standoffs" to stop the crystal touching the inside of the case.

[brianharper]

Just came across this. Excellent video Dave, haven't seen one of those in over 30 years. Used to work at the Philips plant in Blackburn, UK some 30+ years ago there we made the glass delay lines for use in tv's, bring's back a lot of memories.

[DanielGBenesScienceShows]

Absolutely wonderful peek into the inner workings! Your passion for how things work and teaching spirit are a great gift to all of us. Learning that a glass delay line device existed more than fulfilled my goal of learning something new everyday. Keep 'em coming!

[andy]

Absolutely incredible! I was given a somewhat earlier black and white camcorder with a shoulder-strap recorder unit separate from the camera. Absolutely incredible piece of tech.  

[whitcwa]

Sony still makes great service manuals for their pro video gear. They also offer maintenance training in their CA and NJ facilities. I have been to 2 two-week courses, and the manuals for each filled three big binders. They are also available in searchable electronic format- thank goodness!

[Orionrobots]

There's got to be some great learning to be had by looking at the waveforms there - more so having the gear and probing at the points, and correlating activities with the service manual. I am now eyeing up any vintage gear in our flat to try and find service manuals - though I doubt any will come close to that beauty.

[whitcwa]

The filter is definitely a Bayer filter.
Pro NTSC cameras used glass(quartz) delay lines for the vertical detail circuit. The 168nS delay line is for horizontal aperture correction which is pretty much the same thing as horizontal detail. In detail circuits delayed and undelayed video are subtracted to create a signal which represents the high frequency components of the video. It is then added back to the video for a sharper picture.
VTRs used glass delay lines for dropout compensation.

[elboa]

Worked on these on a daily basis, back then. The grim reality was if you could not fix it under about 2 hours tops it wasn't viable. However I never seemed to get tired of that moment when, YES! I've fixed it. Regards...