EEVblog #574 - NEC Analog TV IF Modulator Teardown

[EEVblog]

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.

[marshallh]

FFFFUuuuuuuuu 

[FrankBuss]

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.

[N2IXK]

The fuseholder that looks like a lamp actually IS. A neon lamp that lights up when the fuse blows...

[JackOfVA]

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.

[bridgerectifier]

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.

[EEVblog]

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?

[jh15]

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?

[bridgerectifier]

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.

[bridgerectifier]

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

[hikariuk]

Well there's a good chunk of my work-from-home Thursday gone.

[GeoffS]

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.

[bridgerectifier]

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

[darrell]

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.

[jh15]

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.

[EEVblog]

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...

[EEVblog]

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.

[jh15]

Darn..

And here is.... stall  the IF... stall modulator... stall reload page, connection lost...

[GeoffS]

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 

[Skimask]

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!

[nitro2k01]

The sha in kinsekisha is just a suffix, that is used when addressing companies. The Japanese have a lot of suffixes in their language.

[speffex]

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!

[EEVblog]

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.

[takotako]

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.

[vk6zgo]

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.