VA62 barsweep

[JohnCT]

So yesterday an old friend long retired from the business stops in for a visit. I haven't seen him in a few years and almost didn't recognize him with his long hair. Can't wait to get *my* mullet chopped off..

So he said he had something in the car that I might want. It's a VA62. Sure Tony, I'll take that! He also said he had a picture tube restorer and is going to drop that off. It's probably a B&K 467 (I have three of those now) but it might be a Sencore as well. Anyway.

I have a VA48 that's partially functioning, so this was nice to get. This one is *well* used, but I tried it out and everything works except the built in DMM, which reads either zeros or some random number. It does say "DC" or "PP" as required by the function switch, but doesn't read. Not a problem as everything else works.

But I'm intrigued by the bar sweep. I scoped the output of the bar sweep function at the video output jack and found each of the ten stops is virtually flat from .5 to 4.5mhz.

I've heard that Sencore used to say that an IF alignment could be done by watching this bar sweep waveform at the video detector, and not using the shaped curve with markers. Has anyone tried this?

John

EDIT: I don't think there isn't a switch or control that isn't flaky. I spent about a half hour constantly pushing and rotating every movable item to get it to settle down some. I have a Sencore Z LC75 that I bought new in 1985 and use it every day, and the controls are perfect. This might have sat for a decade or two before I tried it yesterday.

[old_tv_nut]

Have never tried to do IF alignment on a bar sweep (multiburst, as it is also called). Probably OK for the overall shape at 1 MHz and above, and sound traps could be adjusted based on the 4.5 MHz burst. However, the 0.5 MHz response is affected by the slope around the video carrier and it's hard to tell what you're doing there because you get energy from both the upper sideband and the vestigial sideband. Could result in some video smears, even though the amplitude of the 0.5 MHz is OK. But then, a customer who doesn't know all this may not complain about minor smearing, having seen ghosts that are worse.

[Notimetolooz]

The VA62 is good for a lot of things but aligning the IF is something it isn't that good for.

[JohnCT]

Originally Posted by Notimetolooz

The VA62 is good for a lot of things but aligning the IF is something it isn't that good for.

Just intrigued by the prospect of the alignment procedure. I remember at a VA48 seminar when those were new the field rep ran the IF slugs all the way in on a TV (don't recall what kind but it was a color portable) and did the alignment with the bar sweep and a scope. I wasn't paying particular attention as the coffee and donuts were being put out (and I was like 16 at the time) but he had it done in about 10 minutes, and the picture looked fine.

The reason I asked is that I know there's a mod developed by two gents from this forum for the 62 that will let it get into the 25mhz region where I have a 1951 TV that could use a touch up. I have a B&K 415 that we bought new, but that doesn't do anything but 45mhz.

John

[JohnCT]

Originally Posted by old_tv_nut

Have never tried to do IF alignment on a bar sweep (multiburst, as it is also called). Probably OK for the overall shape at 1 MHz and above, and sound traps could be adjusted based on the 4.5 MHz burst. However, the 0.5 MHz response is affected by the slope around the video carrier and it's hard to tell what you're doing there because you get energy from both the upper sideband and the vestigial sideband. Could result in some video smears, even though the amplitude of the 0.5 MHz is OK. But then, a customer who doesn't know all this may not complain about minor smearing, having seen ghosts that are worse.

Good info. Thanks.

John

[zeno]

Was that seminar at the Sheraton inn Boxboro Ma. ? Was there &
we bought the package. I liked Sencore stuff. Looked nice & was
geared to the TV biz. Anyhows they used a Zenith CC2 (19EC45 etc)
for the demo & did the IF's in jig time. Only beef with Sencore was it
wasnt as reliable as others. Cold joints under harmonica connectors & bad CRT cables on testers. And they did not give anything away !

73 Zeno
LFOD !

Originally Posted by JohnCT

Just intrigued by the prospect of the alignment procedure. I remember at a VA48 seminar when those were new the field rep ran the IF slugs all the way in on a TV (don't recall what kind but it was a color portable) and did the alignment with the bar sweep and a scope. I wasn't paying particular attention as the coffee and donuts were being put out (and I was like 16 at the time) but he had it done in about 10 minutes, and the picture looked fine.

The reason I asked is that I know there's a mod developed by two gents from this forum for the 62 that will let it get into the 25mhz region where I have a 1951 TV that could use a touch up. I have a B&K 415 that we bought new, but that doesn't do anything but 45mhz.

John

[JohnCT]

Originally Posted by zeno

Was that seminar at the Sheraton inn Boxboro Ma. ? Was there &
we bought the package. I liked Sencore stuff. Looked nice & was
geared to the TV biz. Anyhows they used a Zenith CC2 (19EC45 etc)
for the demo & did the IF's in jig time. Only beef with Sencore was it
wasnt as reliable as others. Cold joints under harmonica connectors & bad CRT cables on testers. And they did not give anything away !

73 Zeno
LFOD !

No, it would have been in CT, maybe Meriden or Waterbury.

You're right; Sencore was never shy about charging for anything they sold. It was before my time, but Sencore had a horrid reputation for quality earlier - like the 60s and 70s. I remember a few comments from seasoned techs at those seminars. They got their act together later.

My Z meter was trouble free from 1985 until early this year, when it started getting slow to acquire a number and drifted. I used a handheld ESR meter to pick off the worst offenders and it's been running perfectly since. Some day I'll recap it.

John

[zeno]

Used to see a lot of Conn techs at Boxboro, Marlboro, Worcester, & especially
Springfield of course. I had a 40 hr job & when not there I contracted other
shops. I went to every seminar I could. One cat I never worked for but he
paid me to go to an RCA seminar so he could keep his warranty status.
I always took 2 sets of training manuals & my regular job loved it.
Those TM's were worth there weight in gold with the rapid evolution of
SS sets. Ah the good old days.

73 Zeno
LFOD !

[Electronic M]

Originally Posted by JohnCT

Just intrigued by the prospect of the alignment procedure. I remember at a VA48 seminar when those were new the field rep ran the IF slugs all the way in on a TV (don't recall what kind but it was a color portable) and did the alignment with the bar sweep and a scope. I wasn't paying particular attention as the coffee and donuts were being put out (and I was like 16 at the time) but he had it done in about 10 minutes, and the picture looked fine.

The reason I asked is that I know there's a mod developed by two gents from this forum for the 62 that will let it get into the 25mhz region where I have a 1951 TV that could use a touch up. I have a B&K 415 that we bought new, but that doesn't do anything but 45mhz.

John

A few years ago there was a thread here on VK where someone found a way to successfully heterodyne down the output of a 415 to do 25MHz IF alignment....it was all external equipment that could be removed easily to switch between the two IF frequencies.

[JohnCT]

Originally Posted by zeno

One cat I never worked for but he
paid me to go to an RCA seminar so he could keep his warranty status.
I always took 2 sets of training manuals & my regular job loved it.
Those TM's were worth there weight in gold with the rapid evolution of
SS sets. Ah the good old days.

73 Zeno
LFOD !

Yep. RCA training manuals were exceptionally written. I've been throwing stuff away the last few years and a lot of those went out. I should see if anyone wants any of these before the next purge.

The theory of those TVs was given in great detail. Even the full service manuals of later RCAs like the 169 series has about 10 pages of theory before the schematics. A schematic only shows so much, but without the theory, the protocol of the software and the communications between all the ICs is something that required explanation.

Originally Posted by Electronic M

A few years ago there was a thread here on VK where someone found a way to successfully heterodyne down the output of a 415 to do 25MHz IF alignment....it was all external equipment that could be removed easily to switch between the two IF frequencies.

I saw that, but to be honest, I don't have a clue what that stuff is or how to connect it!

John

[JohnCT]

The point is moot anyway. While the bar sweep on this example works, the 3.5mhz bars are jibberish. Sometimes it looks like a tight checkerboard and other times it's just a green band. All the others on either side work. Strangely, scoping the bar sweep at the video output shows full amplitude at the 3.5 mhz band, but no lines.

So I'll add this one to the storage pile along with a VA48 that has no bar sweep at all.

The good news is that my buddy stopped back with a BK freq counter, another 467 CRT tester with a crapload of sockets, and an old variac (non isolated). I've got some friends who can use those at least. He said he might have some more stuff as well.

John

[old_tv_nut]

Originally Posted by JohnCT

The point is moot anyway. While the bar sweep on this example works, the 3.5mhz bars are jibberish. Sometimes it looks like a tight checkerboard and other times it's just a green band. All the others on either side work. Strangely, scoping the bar sweep at the video output shows full amplitude at the 3.5 mhz band, but no lines.

John

This sounds to me like the "3.5 MHz" is really close to color subcarrier, at least sometimes. If it's supposed to be stripes (locked to the horizontal rate), it should be possible to trouble shoot why it's not locked.

[JohnCT]

Originally Posted by old_tv_nut

This sounds to me like the "3.5 MHz" is really close to color subcarrier, at least sometimes. If it's supposed to be stripes (locked to the horizontal rate), it should be possible to trouble shoot why it's not locked.

I didn't get more specific because I don't have the schematic for the 1100 board, which is NOT included in the service manual I borrowed from a friend who has a VA62 that purportedly works , but I think you're on the money.

Anyway the 3.5 is not just close to the chroma subcarrier, it's 3.579mhz... The button is marked 3.5, but the block diagram that I have shows the actual frequency as 3.579. Why the front panel isn't marked 3.6mhz instead of 3.5mhz I don't have a clue.

I mentioned everything else is working and it seems to be, but the dot and crosshatch patterns, while crisp and clean, show a slight color to them. The color can be removed by pushing a combination of the Interlace adder and VIR adder buttons (I don't recall which one is in, out or both in). I think what's going on is that chroma is leaking in one of the switching ICs and clashing with the 3.58 from the multiburst generator.

The other possibility I suppose is that the green bar is normal when the 3.58 button is pushed, but I don't have the owner's manual, and I have a sneaking suspicion that might turn out to be the case. Maybe I'll drag it back out and try it with the color control turned down.

Also, when scoping the multiburst pattern, the amplitude of the 3.58 signal is the same amplitude as the others, but no lines can be discerned when expanded out using the delayed sweep- just jibberish is seen.

The service manual shows component level detail of every board except the 1100 board which is block diagram only, so I put it in storage.

I may try to figure out the downconverting add-on to the B&K415 for 25mhz IF sweeping.

John

EDIT: I forgot to add that the VA48 I also have has a completely non-functioning bar sweep section, but that also shows some color bars in the crosshatch, so maybe that's normal for these animals.


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