Author Topic: EEVblog #574 - NEC Analog TV IF Modulator Teardown  (Read 21312 times)

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Offline EEVblog

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EEVblog #574 - NEC Analog TV IF Modulator Teardown
« on: January 29, 2014, 01:10:55 am »
Dave looks through the documentation for the vintage 1980 NEC PCN-1205AH 5kW Analog TV Transmitter that used to transmit the CH7 TV frequency in Sydney
He then tears down the HPA-3696 IF Modulator used in the system.

 

Offline marshallh

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #1 on: January 29, 2014, 01:27:18 am »
FFFFUuuuuuuuu  :scared:
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Offline FrankBuss

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #2 on: January 29, 2014, 02:23:12 am »
Interesting teardown, thanks! The card edge connectors look exactly like the ones used on the C64, only more contacts. You can still get them at Digikey. That's the one which works perfectly for the user port: http://www.digikey.com/product-detail/en/305-024-520-202/EDC305242-ND/107508 Expensive, but good quality.
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Offline N2IXK

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #3 on: January 29, 2014, 02:39:48 am »
The fuseholder that looks like a lamp actually IS. A neon lamp that lights up when the fuse blows...

"My favorite programming language is...SOLDER!"--Robert A. Pease
 

Offline JackOfVA

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #4 on: January 29, 2014, 03:18:03 am »
1) As a guess, the SAW filter is temperature stabilized to control differential phase shift.  You really do not want the relative phase across the passband to change in color TV system as it will screw up the displayed colors. (This may be more an issue with NTSC  than PAL, however. All my limited experience is with NTSC systems.)

2) The only TV-locked frequency reference systems I'm familiar with tied to the color burst.  In the USA, network generated programming used a color reference tied to a rubidium standard, but locally originated programming used crystal based color burst. (Talking about the 1970's when rubidium standards were extremely expensive.) There were kits available that would tap into the video of a TV set and bring out the color subcarrier reference. When live (not tape delayed) network programming was being aired, this provided a stable and accurate 3.58... MHz reference tied back to a Rb standard sitting in a rack in New York or Los Angeles.  However, as technology advanced, the locally transmitted color reference was no longer tied to the network Rb standard - the exact details of the change escape me at the moment. Might have been frame buffering or the change to greater video tape use and satellite distribution instead of coaxial cable leased from the telephone companies or something else. Way too many years ago and it was not an area I worked in.


« Last Edit: January 29, 2014, 03:19:55 am by JackOfVA »
 

Offline bridgerectifier

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #5 on: January 29, 2014, 03:35:42 am »
Dave, I'm not sure the content fulfilled the expectations given by the "teaser". It's a good teardown, but certainly not your best, with respect, and I felt a bit deflated... after 3 weeks of expecting something more.

Maybe it was just me, eh.
 

Offline EEVblog

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #6 on: January 29, 2014, 04:04:44 am »
Dave, I'm not sure the content fulfilled the expectations given by the "teaser". It's a good teardown, but certainly not your best, with respect, and I felt a bit deflated... after 3 weeks of expecting something more.

Like what?
 

Offline jh15

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #7 on: January 29, 2014, 04:37:24 am »
I would like to use your video for my local SBE (Society of Broadcast Engineers) chapter meeting attraction.

Are your download video creative commons? Or do we just use the utube stuff?
tek 575 curve tracer top shape, 535 top shape, 465. 545 hickok clone, Telsa Model S,  Ohio Scientific c24P single board computer, many c-64 from my club days, Giant electric bicycle, Rigol stuff, Heathkit AR-15 receivers 2, Heathkit et 3400a trainer and interface,
 

Offline bridgerectifier

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #8 on: January 29, 2014, 04:39:39 am »
Dave, I'm not sure the content fulfilled the expectations given by the "teaser". It's a good teardown, but certainly not your best, with respect, and I felt a bit deflated... after 3 weeks of expecting something more.

Like what?

I've no idea; sorry.
 

Offline bridgerectifier

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #9 on: January 29, 2014, 04:48:52 am »
Dave, I think my expectations were possibly too high, and because I didn't know what to expect, I let *myself* down; your video is great.

Sorry if I offended you mate - that wasn't what I meant to do :)
« Last Edit: January 29, 2014, 04:50:27 am by bridgerectifier »
 

Offline hikariuk

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #10 on: January 29, 2014, 04:54:17 am »
Well there's a good chunk of my work-from-home Thursday gone.
I write software.  I'd far rather be doing something else.
 

Offline GeoffS

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #11 on: January 29, 2014, 05:02:06 am »
Dave, I think my expectations were possibly too high, and because I didn't know what to expect, I let *myself* down; your video is great.

Sorry if I offended you mate - that wasn't what I meant to do :)

It's good to occasionally see a teardown of such high end equipment from 30 years ago. All good solid construction, metal not plastic. And not a microporocessor in sight! I'd have liked to see a tear down of the power output section but ...
Reminds me of some of the stuff I used to work on many, many years ago.
 

Offline bridgerectifier

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #12 on: January 29, 2014, 05:07:26 am »
Dave, I think my expectations were possibly too high, and because I didn't know what to expect, I let *myself* down; your video is great.

Sorry if I offended you mate - that wasn't what I meant to do :)

It's good to occasionally see a teardown of such high end equipment from 30 years ago. All good solid construction, metal not plastic. And not a microporocessor in sight! I'd have liked to see a tear down of the power output section but ...
Reminds me of some of the stuff I used to work on many, many years ago.

I totally, completely agree. I could EASILY never see another consumer product taken apart, especially anything Apple - SO SO SO SO BORING!

I could easily repair oscilloscopes and tear them down for fun, no problems - especially CROs :D
 

Offline darrell

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #13 on: January 29, 2014, 05:11:40 am »
I'm surprised you didn't comment on the seriously blackened PCB for the SAW oven controller. That seems like poor design when the pass transistor could have been heat sunk to the aluminum block, saving power. Perhaps, with supply voltage variation, that would have caused problems for the control loop.

I tore down an old rubidium frequency standard and it used a pair of transistors as the heater. They were acting as a current sink from the supply voltage. The controller board on that one was inside the oven and was brown from 20 years of 100 degree C operation. One of the older Rb standards would make a great teardown video, but you'd have to read up on the physics of it to get the commentary right.
 

Offline jh15

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #14 on: January 29, 2014, 05:12:54 am »
And you have to know your stuff on b'cast commercial equipment. . Repair techs today do card or even box  level, not t-shoot to component level. Think of some tech today reading a script... "if IF modulator faulty, toss and replace with new".

Not to mention the safety instincts you must have around that power and voltage. Maybe a rubber skull cap near the widow stick in the old days.

And... how could one possibly think of a major station off the air in pre-internet times.
« Last Edit: January 29, 2014, 05:19:59 am by jh15 »
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Offline EEVblog

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #15 on: January 29, 2014, 05:14:54 am »
I'd have liked to see a tear down of the power output section but ...

In case it wasn't clear enough, teardowns on the other two bits will follow...
The intention was to show all 3 briefly, but you know who takes always works out...
 

Offline EEVblog

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #16 on: January 29, 2014, 05:17:12 am »
Are your download video creative commons? Or do we just use the utube stuff?

They are not creative commons, but you can of course use the youtube stuff.
 

Offline jh15

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #17 on: January 29, 2014, 05:22:28 am »
Darn..

And here is.... stall  the IF... stall modulator... stall reload page, connection lost...
tek 575 curve tracer top shape, 535 top shape, 465. 545 hickok clone, Telsa Model S,  Ohio Scientific c24P single board computer, many c-64 from my club days, Giant electric bicycle, Rigol stuff, Heathkit AR-15 receivers 2, Heathkit et 3400a trainer and interface,
 

Offline GeoffS

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #18 on: January 29, 2014, 05:29:14 am »
I'd have liked to see a tear down of the power output section but ...

In case it wasn't clear enough, teardowns on the other two bits will follow...
The intention was to show all 3 briefly, but you know who takes always works out...

The power section with the 5KW power tube? I didn't think you could fit that bit in your hatchback  :)
 

Offline Skimask

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #19 on: January 29, 2014, 05:40:49 am »
The wife caught me watching this particular tear-down.  I say caught because generally I try to not subject her to this sort of wonderful torture.
Told her she should be happy I don't get a Chromecast or plug a PC into the TV in the living room 'cause when (notice I say 'when' and not 'if) I do, this is the sort of thing we'll be watching the majority of the time.

 :-+ Thanks Dave.  I get to spend more time in my shop now that she knows what really goes on out here! :-+
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

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Offline nitro2k01

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #20 on: January 29, 2014, 06:03:06 am »
The sha in kinsekisha is just a suffix, that is used when addressing companies. The Japanese have a lot of suffixes in their language.
Whoa! How the hell did Dave know that Bob is my uncle? Amazing!
 

Offline speffex

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #21 on: January 29, 2014, 06:15:25 am »
Hi, Dave.. I remember those old Philips capacitors. I think (under the shrink wrap) they were ribbed- not for pleasure, but to increase the surface area so that they'd heat up less with a given ripple current. Cool cap = long life cap. Cheers!
 

Offline EEVblog

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #22 on: January 29, 2014, 06:53:36 am »
The sha in kinsekisha is just a suffix, that is used when addressing companies. The Japanese have a lot of suffixes in their language.

Ah, that explains it! thanks.
 

Offline takotako

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #23 on: January 29, 2014, 09:19:42 am »
The sha in kinsekisha is just a suffix, that is used when addressing companies. The Japanese have a lot of suffixes in their language.

Not in this case, sha is an integral part of the name of Kinsekisha Laboratory (*see the attachment for the Japanese if you're interested, sha is underlined). Kinsekisha Laboratory is present-day KYOCERA Crystal Device Corporation.

Just a little more info since Kinseki was mentioned. They're all the same company. Founded in 1941 as Kinsekisha Laboratory, the crystal business division of Kinsekisha Jewelry. Became an independent company in 1950. Changed their name to Kinseki in 1980. Became a Kyocera subsidiary in 2003 and changed their name to Kyocera Kinseki in 2004. Changed their name again in 2012 to the current Kyocera Crystal Device Corporation.
« Last Edit: January 29, 2014, 11:50:46 am by takotako »
 

Offline vk6zgo

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #24 on: January 29, 2014, 09:34:59 am »
That frequency stability isn't bad considering the resultant output is a 6.25MHz wide signal at VHF.(horses for courses)
TV Receiver local oscillator stability wouldn't be near that good.

The frequency reference from the TV signal was based on the idea that the difference frequency between the Vision Carrier & Colour Subcarrier remained stable,no matter how much the Vis carrier,or Rx local oscillator drifted (one of the strong points of full carrier modulation systems).

The very pretty Transmitters from the French company LGT had a facility to lock the Vision & Sound Carriers to the TV line sync frequency.

It may have been something to do with SECAM,but we never used it in this country.
Their Carrier oscillator/video & Sound modules were tiny & crammed enough,without additional stuff which did nothing.

Working on an NEC was a dream after trying to find your way around an LGT,with their horrible,inadequate"Franglish" manuals.

Re the VSB filter:


Back in the "Dream Time",the first TV Transmitters were High Level Modulated.
(Actually the PA stage was grid modulated)

Most of the VSB shaping was done after the TX output using a "Filterplexer".
I say "most",as we would tune the PA to minimise the LSB.
If you put a wideband signal into the Filterplexer,most of the power from the LSB would be used up making the unbalance load hot.

After the advent of IF modulation,the first VSB filters used at IF frequencies were LC types.
Such filters are expensive,need individual adjustment,& often additional correction circuits.

It's too long ago,but I'm pretty sure the early (mid '60s) NECs used LC filters.
I'm not so sure about LGT,Thomson,& Siemens,but I think the latter did.

SAW filters were a great innovation,as they had the same transit time for all frequencies,& once they were manufactured,they needed no further adjustment.
The "oven-ising " would seem to be "gilding the lily" a bit,but NEC Engineers were "the real thing",& I defer to their wisdom!

Re some of the "special components":

NEC were also a major supplier of Communications equipment,including much of the Microwave Broadband Network installed by Telecom Aust in the 1970s/80s.
A lot of stuff is re-useable in both fields.
 

Offline mikeselectricstuff

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #25 on: January 29, 2014, 12:02:17 pm »
Maybe the reason for using a TCXO rather than an OCXO is that there is no warm-up time - for broadcast gear you want to be able to swap stuff out quickly in case of a fault - you don't want to have to wait for an oven to stabilise.
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Offline Galaxyrise

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #26 on: January 30, 2014, 04:13:45 pm »
Getting all that scanned in looks like it could be quite a project! I'm definitely interested in the oven controller schematic, though.
I am but an egg
 

Offline brabus

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #27 on: January 30, 2014, 06:20:01 pm »
Ladies, just one question, why everybody is like: "Oh, Dave, you should have said that and that", "Dave, you should have done more", blah blah blah... :blah:

You know what? Next time YOU go to the TV transmitter station, provide something interesting to teardown, and say whatever you want!
Sorry but I can't stand futile criticizing.



On my side, I can only say: GOSH.  :clap: :clap: :clap: AWESOME piece of engineering, wish I could smell that '80s essence...
You lucky 'astard, Dave! ;D :-+ Go ahead with the other two puppies!  :-+
 

Online firewalker

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #28 on: January 30, 2014, 07:23:00 pm »
You should really call them and ask about the dust thing.

Alexander.
Become a realist, stay a dreamer.

 

Offline SeanB

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #29 on: January 30, 2014, 07:50:18 pm »
SAW filter heating is simple, it is a crystal, and with temperature changes the dimensions change and the passband and rejection drifts, and the ripples in response vary up and down. Keeping at a constant temperature means the output filtering can be adjusted to handle the ripple and attenuate it. At the receive end the drift can be a lot worse as it has little visible effect, and the AFC will tend to compensate a lot for the drift.  At the transmitter end if it drifts it will drop out of the SAW filter ranges on some receivers and give rise to vision on sound or sound on vision as the filter drifts and the transmit frequency varies. Your transmitted signal has to be good enough so that a broadcast quality picture can be received on any good set. Most sets are far from that, but you will get a good number of very good receivers and the viewers of those will be the most critical of the broadcast quality. The whole chain is only as good as the worst part, and you really want the customer end to be that.

Dust is easy, you have HEPA filtering of the air coming in, and positive pressure inside the whole facility. Note the doors coming in are at least 3 sets of double doors with sealing strips on the sides, and this allows the area to be kept dust free, along with having dirt trapping mats on all entrances. Major source of dust is then the people.

Like the 4 trim cuts on that power heater resistor, all done so as to make the trim even out to a constant heat per segment. Nice work on that one. Also remember using those TO66 heatsink adaptors for TO39 packages as well. They are pretty expensive, costing a lot more than the transistor itself.
 

Offline jippie

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #30 on: January 31, 2014, 06:11:57 am »
What is a "pedestal clamp"? Eg. @ 0:52:33.

 

Offline vk6zgo

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #31 on: January 31, 2014, 10:01:04 am »
What is a "pedestal clamp"? Eg. @ 0:52:33.


The short intervals of blanking level (PAL) or black level (NTSC) before & after the Sync Pulse in the  Composite Video signal are collectively known as the "Pedestal".

"Keyed Clamping" is a DC restoration technique which  produces a narrow pulse from the sync pulse.
This is then delayed in time until it is coincident with the "back porch",where a switch (classically a diode bridge,or,as in this case,a FET) is turned on by the pulse,returning the signal line to zero volts,or whatever voltage you wish to clamp the signal blanking (PAL),or black level (NTSC) to.

This can be used to remove such signal perturbations as hum,loss of DC component following  an AC  coupled Amplifier,etc.

With colour TV,care must be taken that the clamp does not distort the colour burst.

 

Offline ram

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #32 on: January 31, 2014, 11:03:57 am »
dave scanned documentation please it really helps in my under graduation programme studies
 

Offline jippie

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #33 on: January 31, 2014, 02:02:07 pm »
What is a "pedestal clamp"? Eg. @ 0:52:33.


The short intervals of blanking level (PAL) or black level (NTSC) before & after the Sync Pulse in the  Composite Video signal are collectively known as the "Pedestal".

For a moment I thought you meant the front and back porch until I read:

This is then delayed in time until it is coincident with the "back porch",

But I get the essence of what you wrote, thnx!
 

Offline jnissen

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #34 on: January 31, 2014, 04:35:35 pm »
30 minutes of reading from a manual! If YouTube has specs on how many folks fast forwarded through your first 30 minutes I bet it would be high!  :-DD
 

Offline JoannaK

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #35 on: January 31, 2014, 04:57:27 pm »
30 minutes of reading from a manual! If YouTube has specs on how many folks fast forwarded through your first 30 minutes I bet it would be high!  :-DD

Well.. I didn't. I don't know what it tells about me, but I watched it entirely.  ???

Of course it would be nicer to read the copy of the manual at the same time as the Dave talks about it, but it's not mandatory.
 

Offline N2IXK

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #36 on: January 31, 2014, 05:44:03 pm »
I watched the whole damned thing, as well.  :-+

As far as what else could have been shown, how about firing the system up, applying audio and video signals, and showing the output on a spectrum analyzer and a TV set?

Signal tracing the video through all the processing and correction stages (and tweaking the trimpots) would be neat, too, but probably a bit too much for most viewers.
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Offline EvilGeniusSkis

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #37 on: January 31, 2014, 05:53:34 pm »
Dave, @1:00:00 I think the caps are hexagonal so that they tessellate(fit together better).
 

Offline FrankBuss

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #38 on: January 31, 2014, 07:04:47 pm »
30 minutes of reading from a manual! If YouTube has specs on how many folks fast forwarded through your first 30 minutes I bet it would be high!  :-DD
Youtube has such a statistic, it is called "Audience retention", but only the uploader has access to it (for one of my videos:
). I admit, I skipped the manual reading as well. Might be interesting to see the curves for this video :)
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Offline jippie

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #39 on: January 31, 2014, 07:19:39 pm »
30 minutes of reading from a manual! If YouTube has specs on how many folks fast forwarded through your first 30 minutes I bet it would be high!  :-DD

Dave might have hidden a secret give-away somewhere half way the manual reading for all you know ;) I know I carefully viewed the entire video :)
 

Offline david77

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #40 on: January 31, 2014, 07:30:40 pm »
I also watched Dave reading from the manual, I love this kind of technical documentation. The manuals for analogue broadcast equipment are especially interesting, it's fascinating to see how the engineers went to town on stuff where money was no object.
 

Offline Rasz

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #41 on: January 31, 2014, 08:34:13 pm »
Dave, I'm not sure the content fulfilled the expectations given by the "teaser". It's a good teardown, but certainly not your best, with respect, and I felt a bit deflated... after 3 weeks of expecting something more.

Like what?



30 minutes of reading from a manual! If YouTube has specs on how many folks fast forwarded

as a matter of a fact they do have this data :) I dont know if they share it with content creators, but they do collect it.
DASH
http://en.wikipedia.org/wiki/Dynamic_Adaptive_Streaming_over_HTTP
lets them know which parts of the video you request + YT player pings back which parts you actually watched.

edit:
Youtube has such a statistic, it is called "Audience retention", but only the uploader has access to it (for one of my videos:
)

ha :)
« Last Edit: January 31, 2014, 08:44:42 pm by Rasz »
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Offline Towger

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #42 on: January 31, 2014, 10:06:14 pm »
It really needs to be fired up one last time.
 

Offline vk6zgo

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #43 on: February 01, 2014, 01:04:25 am »
What is a "pedestal clamp"? Eg. @ 0:52:33.


The short intervals of blanking level (PAL) or black level (NTSC) before & after the Sync Pulse in the  Composite Video signal are collectively known as the "Pedestal".

For a moment I thought you meant the front and back porch until I read:

This is then delayed in time until it is coincident with the "back porch",

But I get the essence of what you wrote, thnx!

Yes,the "Pedestal" is the  front & back porches,so clamping on the back porch is "Pedestal" clamping.

"Pedestal" is an old term,which is apparently more used in Japan than elsewhere.

I think it originated in the UK or USA---looking at an inverted sync pulse it looks a bit like a monument mounted on a Pedestal,so  that's probably where the name came from.

It is easier to generate the clamp pulse & delay it a few microseconds to clamp on the back porch,than to clamp sync tips (which is done),as that requires either a very fast clemp pulse generator to clamp on the same sync pulse.,or a very long delay(64uS),so as to clamp on the next pulse.
The front porch duration is quite short,& I have never seen any attempt to clamp there.
 

Offline vk6zgo

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #44 on: February 01, 2014, 01:10:51 am »
I watched the whole damned thing, as well.  :-+

As far as what else could have been shown, how about firing the system up, applying audio and video signals, and showing the output on a spectrum analyzer and a TV set?

Signal tracing the video through all the processing and correction stages (and tweaking the trimpots) would be neat, too, but probably a bit too much for most viewers.

Dave doesn't have the mixer (upconverter) so nix on the TV set,but he could do the rest.
But---Guys,we have to remember Dave's got a life outside letting us "perve" on interesting Electronics! ;D
 

Offline dave_k

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #45 on: February 01, 2014, 10:02:24 am »
It really needs to be fired up one last time.

Gee, I'm tempted to fire up the old Ch 7 transmitter one last time into a test load. It would be interesting to see if it all works properly after sitting for 8 weeks with no power!
 

Offline vk6zgo

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #46 on: February 01, 2014, 10:29:11 am »
It really needs to be fired up one last time.

Gee, I'm tempted to fire up the old Ch 7 transmitter one last time into a test load. It would be interesting to see if it all works properly after sitting for 8 weeks with no power!

It's an NEC,Dave,------of course it will!

What I liked when we installed the second 13kW Tx at TVW7,was that our test results were exactly the same as those achieved by the last test at the factory before they pulled it apart for delivery.

With most other Manufacturers you have to adjust them on arrival to get them into spec!
 

Offline aroby

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #47 on: February 04, 2014, 04:16:09 am »
Great teardown.

How would the manufacturer go about testing something like this?   The debugging must have been horrendous.  Today you can use  computer simulations, back 35 years ago, how would this be done?
 

Offline coppice

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #48 on: August 09, 2014, 04:46:41 pm »
1) As a guess, the SAW filter is temperature stabilized to control differential phase shift.  You really do not want the relative phase across the passband to change in color TV system as it will screw up the displayed colors. (This may be more an issue with NTSC  than PAL, however. All my limited experience is with NTSC systems.)

2) The only TV-locked frequency reference systems I'm familiar with tied to the color burst.  In the USA, network generated programming used a color reference tied to a rubidium standard, but locally originated programming used crystal based color burst. (Talking about the 1970's when rubidium standards were extremely expensive.) There were kits available that would tap into the video of a TV set and bring out the color subcarrier reference. When live (not tape delayed) network programming was being aired, this provided a stable and accurate 3.58... MHz reference tied back to a Rb standard sitting in a rack in New York or Los Angeles.  However, as technology advanced, the locally transmitted color reference was no longer tied to the network Rb standard - the exact details of the change escape me at the moment. Might have been frame buffering or the change to greater video tape use and satellite distribution instead of coaxial cable leased from the telephone companies or something else. Way too many years ago and it was not an area I worked in.

1. Piezo materials for saw filters are not the most temperature stable in the world. They are often temperature controlled, typically by peltier devices.

2. Rhubidium locking for TV signals was really important in the 1960s, 70s, and into the early 80s, as changing the frame rate or frame phase of a signal was really hard. Large studio complexes had a room full of coax cables of different lengths, and other forms of delay line. Those gave you the various delays needed to perform frame phase adjustments. The atomic clock ensured the frame phase slewed so slowly it didn't matter. As people like Quantel massively brought down the cost of frame stores, and frame rate adjustment, the need to atomic locking went away.

There was never a need for an accurate carrier frequency for TV transmitters. TCXOs were normal for setting the carrier frequency. They can give you something like 1in 10^7 without any warmup time, which is goo d enough. The ones in this unit must have been made just prior to the switch to digitally controlled TCXOs.
 

Offline vaualbus

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Re: EEVblog #574 - NEC Analog TV IF Modulator Teardown
« Reply #49 on: October 27, 2015, 09:06:25 pm »
I'd have liked to see a tear down of the power output section but ...

In case it wasn't clear enough, teardowns on the other two bits will follow...
The intention was to show all 3 briefly, but you know who takes always works out...

So they other module will come.... Almost two yaers after no more video on any of them.......
Also you never scanned the schematics!
 


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