1979 Hitachi (NP9X-L chassis)

[Dreamsbeard]

Good afternoon guys,

I picked up this 19'' 1979 Hitachi this morning. At first, all three guns where barely registering on the CRT tester, but after a soft clean and balance they came back to life...and pretty strong also!

I couldn't believe how bright and sharp the picture was! This one is a keeper for sure.

A few things I would like to know : if you look at the third picture , you'll see that in the top of the picture there are white lines, those line slowly disapear when the tv warms up (takes about 2 mins), could those be related to bad caps?

Also, in great contrast scenes (or when there is subtitles) the television emmits a "loud" buzzing sound. No matter of much I calibrate the channel 3, I can't get rid of it. Is there a way to eliminate that buzz?

Thanks!

[Electronic M]

Those lines are the closed captioning data. If you can see them your vertical is underscaning and needs to be adjusted or fixed.

The buzz is often a function of the signal fed in to it, and often is hard/impossible to fix...Unless it is AC filter buzz.

[Dreamsbeard]

Humm well the picture is from a DVD, do those have close captionning? Its strange because they disapear after a while. Maybe an element comes back to spec after being on for a while and then the lines fades...just a theory.

[dr.ido]

When the lines at the top of the screen go away has the picture height increased (and pushed the lines outside of the visible area)?

Those lines look like Macrovision or some other data inserted in the vertical blanking period. If the you're signal source is a DVD player a copied DVD will not have the Macrovision protection on it. If you're signal source is a cable box it's more likely to be data rather than Macrovision protection - here the cable co only turned on Macrovision for PPV. Some channels did insert data (usually during commercials) that a couple of my sets had trouble with.

If the lines stay the same (at least for the first 2 minutes while they're there) with different signal sources marginal caps in the vertical section are certainly possible. I'd look at the small electrolytics (under 100uF) first. When I was doing a lot of these I could probably guess which pin of the vertical IC (at least for a few common types) it could be hanging off, but I doubt I remember it now.

I've experienced the buzzing (especially around text) with various sets, but I've never found a definite solution. I did find it didn't occur with over the air broadcasts (not that helps anymore) - only the output from other sources. My solution back in the day was to turn the TV volume down and run the audio from the VCR/etc through the stereo.

[Dreamsbeard]

Originally Posted by dr.ido

When the lines at the top of the screen go away has the picture height increased (and pushed the lines outside of the visible area)?

Those lines look like Macrovision or some other data inserted in the vertical blanking period. If the you're signal source is a DVD player a copied DVD will not have the Macrovision protection on it. If you're signal source is a cable box it's more likely to be data rather than Macrovision protection - here the cable co only turned on Macrovision for PPV. Some channels did insert data (usually during commercials) that a couple of my sets had trouble with.

If the lines stay the same (at least for the first 2 minutes while they're there) with different signal sources marginal caps in the vertical section are certainly possible. I'd look at the small electrolytics (under 100uF) first. When I was doing a lot of these I could probably guess which pin of the vertical IC (at least for a few common types) it could be hanging off, but I doubt I remember it now.

I've experienced the buzzing (especially around text) with various sets, but I've never found a definite solution. I did find it didn't occur with over the air broadcasts (not that helps anymore) - only the output from other sources. My solution back in the day was to turn the TV volume down and run the audio from the VCR/etc through the stereo.

No, the picture does not change size, it's widescreen all along, I will do some more testing and i'll get back to you on that one. As for the caps, that was my first assumption. That set is 35 years old, so at one point those caps are all going to go bad and create a lot of weird problems. As soon as I get an soldering iron I'll start changing them.

As for the buzzing, pretty much all my tv's do it, but this one is consistently louder than the others. It's weird, I can't imagine a tv going out of the production line like that...but as you said, in 79 most of the tv's source where from "air transmission" so maybe tvs where not designed with other sources in mind, and that might be the problem. Maybe a different RF modulator would do the trick...?

[zenith2134]

I have a very similar TV in my basement storage area. I see yours, too, has the ST button (signal tracker). They are good TVs with great CRTs in my experience. On some of my tube-fired sets, a thorough line-up of the IF section can and did totally remove the audio noise when lettering appears in the picture. On later sets, it has been less of an issue for me, but perhaps the same procedure would work?

[Dreamsbeard]

Originally Posted by zenith2134

I have a very similar TV in my basement storage area. I see yours, too, has the ST button (signal tracker). They are good TVs with great CRTs in my experience. On some of my tube-fired sets, a thorough line-up of the IF section can and did totally remove the audio noise when lettering appears in the picture. On later sets, it has been less of an issue for me, but perhaps the same procedure would work?

Interesting, but I'm going to show my inexperience here and ask : what is the IF section , and more importantly how can I align it (or at least try to)?

Yes the "AFC" button, it's really handy to fine tune the channels, and my channel 3 is tune exacly as it should , thanks to it. Too bad the plastic channel label are all over the place and that the unused original label are missing.

[zenith2134]

The IF is the intermediate frequency section of the receiver, whereby the carrier signals sent out by the transmitting station (or other analog RF source) are demodulated, mixed, and converted into baseband signals which the rest of the TV's circuitry can work with. For instance, an NTSC signal is 6MHz wide, per VHF or UHF channel. In that allocated bandwidth lies the color subcarrier which is extracted from the station carrier, along with the sync pulses, sound, and actual video information.

What I was suggesting in my earlier post is to attempt an alignment of the Sound IF section, which sometimes contains adjustable coil for the trap or an additional discriminator coil.

To perform this procedure, you typically require some test gear, consisting of an sweep/marker-generator, a suitable oscilloscope (dual-trace is preferred), and the original documentation specific to your set. It really does help, IMO, to have the original documents, since they often outline the exact curves you are seeking to replicate, and a bunch of other test data.

[Findm-Keepm]

What is the model number? Hitachi service data that I have is by model, not chassis. Should be a CTXXXX model number. Hitachi sets of that vintage had a pretty good AGC action, and it may be as simple as backing off of the AGC control. Too early of a set to have a jungle chip, so it's likely an easy fix for the buzz.

Lemme know the model and I'll see if I have a copy of the service data, archived by Hitachi in TIFF format.

Cheers,

[Dreamsbeard]

I think it is a CT-1905, I say "think" because the number on the back says CT-969...but that's the Canadian model number of course.

[dr.ido]

The size increase I was referring to may only be enough to just push the lines off the top of the screen. Faulty capacitors (and other components) can change in value as the set warms up. This can cause the vertical height to change as the set warms up.

The intercarrier buzz may have been present even on a broadcast signal if the set is out of alignment. The problem is that now there are no analog broadcasts to serve as a known good reference signal. In the past if the set was fine with broadcast signals I left the alignment alone - "if it ain't broke don't mess with it".

Try another source if you can. A different modulator, VCR, even a Nintendo if you have one. If all your sets are buzzing it's more likely your modulator is out of alignment (or overloading) than all your sets are out of alignment. Trying a different source (ideally one that you know isn't using Macrovision, close captioning or other data) will also determine the source of the lines.

Some modulators do have adjustments. Easier to tweak the modulator once than to do it to every set.

[Findm-Keepm]

Originally Posted by Dreamsbeard

I think it is a CT-1905, I say "think" because the number on the back says CT-969...but that's the Canadian model number of course.

I've got two versions of the CT-969 manual in TIFF format, one is English, the other is bilingual French/English (de Aout 1979). PM me your email address so I can send both to you.

AGC control is off pin 12 of the HA11215A IC (may be a HA11215F in your set). R210, a 5K pot is the AGC. Rock it slightly CCW when you have buzzing to see if it helps. The little mickey-mike (1, 2.2uf and 4.7uf) electrolytics around the Video AGC chip were known to cause some problems like streaking, negative video, crappy sync, AGC overload and so on, so a recap of those might be of some help. GE used the same IF/Video AGC chip as their part number EP84X139 on some chassis, and the same caps were always bad - Marcon branded, and we replaced them as a preventative measure to avoid callbacks. IIRC, about 6 or 7, all hanging off pins of the chip.

Cheers,