B&K 1077B "Vintage TV" Questions

[Chris K]

OK don't beat me up for this! The thread probably belongs in the "Diagnostic Equipment" category but the issue with my 1077 has to do with the picture I get on the CRT. It's supposed to be an ultraviolet color but on first power up and after recapping, cleaning and messing with the vertical controls, there is no change and the screen looks like the mess in the picture.

Someone has been in here because a number of resistors have been changed including 2 that are listed at 1 meg in the schematic (R-52 and R-53) replaced with much lower value resistors...in the 47 kohm range.

I have a lot of troubleshooting to do but I can use some advice on where to start. I think this is a vertical issue correct? Has anyone else had this problem? From what I've been able to see, most of these work straight away and only need some caps and adjustments. I guess I'm just so lucky eh?

Thanks

[old_coot88]

Did you replace the main filter caps? If that severe distortion of the raster wasn't locked to powerline freq, it would be a "crawling hourglass" caused by B+ ripple.

[Chris K]

Originally Posted by old_coot88

Main filter cap(s) shot, causing that severe distortion of the raster. It would be a "crawling hourglass" if the vert sweep wasn't locked to powerline freq.

Thank you but I've changed the main filter caps...a 4 part can that I used an Adapt-A-Cap base on and 4 new Nichicon capacitors. I also changed the 2 elecrtolytics on the sweep board. The caps you see in the picture have not been changed but I don't think they have anything to do with main filtering.

[bandersen]

Looks like the horizontal freequency is off. Have you tried making any adjustments?

[Chris K]

Originally Posted by bandersen

Looks like the horizontal freequency is off. Have you tried making any adjustments?

Not to the horizontal, I've just moved the vertical size and vertical linearity pots. I think the horizontal frequency is supposed to be 15.75 Khz.

[Chris K]

HORIZ FREQ—Adjust for 15,750 Hz. This can be done by connecting an oscilloscope adjusted to 7875 Hz. horiz sweep to point M on the sweep printed circuit board, adjust R54 for 12 pulses. Refer to Fig. 16 waveform chart.

This is what is in the service manual but unfortunately it does not have the waveforms it refers to. I'm not sure I understand the instructions anyway...when I use my scope to measure a frequency, I just hook on the probe and press auto!!!

[Electronic M]

What I do to set horizontal frequency on TV (should also apply here) is hook my scope to the composite output of a DVD player or DTV box adjust the horizontal time scale control of the scope for 2-4 cycles of the H sync pulse on screen, count how many graticule marks are between the leading edges of 2 adjacent peaks....Once I have done this I don't touch the horizontal control of the scope or auto scale...Then I connect the scope to the horizontal osc in the TV, adjust the vertical scale of the scope to compensate for the amplitude difference, and adjust the TVs osc adjustment so the peaks of the osc have the same spacing on the graticule as measured earlier with composite video from a digital reference source. Most TVs I do this with are dead nuts in sync from warm up with no further adjustment.

[Chris K]

Originally Posted by Electronic M

What I do to set horizontal frequency on TV (should also apply here) is hook my scope to the composite output of a DVD player or DTV box adjust the horizontal time scale control of the scope for 2-4 cycles of the H sync pulse on screen, count how many graticule marks are between the leading edges of 2 adjacent peaks....Once I have done this I don't touch the horizontal control of the scope or auto scale...Then I connect the scope to the horizontal osc in the TV, adjust the vertical scale of the scope to compensate for the amplitude difference, and adjust the TVs osc adjustment so the peaks of the osc have the same spacing on the graticule as measured earlier with composite video from a digital reference source. Most TVs I do this with are dead nuts in sync from warm up with no further adjustment.

Thanks Tom…that’s graduate school stuff for me but your instructions are very detailed so I might be able to do this. I’ll give it a shot later tonight. In the meantime keep them comments comin’!!!

[jr_tech]

Originally Posted by Chris K

HORIZ FREQ—Adjust for 15,750 Hz. This can be done by connecting an oscilloscope adjusted to 7875 Hz. horiz sweep to point M on the sweep printed circuit board, adjust R54 for 12 pulses. Refer to Fig. 16 waveform chart.

This is what is in the service manual but unfortunately it does not have the waveforms it refers to. I'm not sure I understand the instructions anyway...when I use my scope to measure a frequency, I just hook on the probe and press auto!!!

Early scopes had the horizontal sweep “calibrated” in frequency instead of time. With a more modern scope, you would measure about 63.5 microseconds for one complete horizontal cycle. The “12 pulses” might be a miss print, I think it should be “2 pulses”

What scope do you have?

jr

[Chris K]

Originally Posted by jr_tech

Early scopes had the horizontal sweep “calibrated” in frequency instead of time. With a more modern scope, you would measure about 63.5 microseconds for one complete horizontal cycle. The “12 pulses” might be a miss print, I think it should be “2 pulses”

What scope do you have?

jr

The one I have from the 1077 era is an HP 54600B 100MHz

[jr_tech]

Originally Posted by Chris K

The one I have from the 1077 era is an HP 54600B 100MHz

I’m thinking that the scope is at least 10 years newer than the B&K. Horizontal sweep is expressed in time rather than frequency.

If you set the scope sweep time to 20 microseconds per division and connect the vertical input to point “M” on the B&K, how many complete waveforms do you observe?

jr

[Chris K]

Yeah the scope is from the late 1990s. Sorry about that and I can vary the sweep time.

But I think full disclosure is necessary here. If I'm a novice with electronics, I'm even more rudimentarily acquainted with the oscilloscope. The extent of my abilities and to understand instruction are limited to looking at discrete frequency waveforms and that's about it. Having shopped for a sweep generator for TV alignment, I know what that does...sweeping through a frequency range over and over again as it generates a signal but I don't know anything about oscilloscope "sweeping" looking for signals. I guess I need to do more remedial reading and study.

[zeno]

MOST of the time......
Waveforms in manuals show 2 complete cycles. Some newer scopes
@1975 + have a setting for it like the Sencore. It may be called
line & field or TV hoz & TV vert on the time base SW.
Wave forms are pretty generic. If you can look at them on a running set
with manual it would help you a lot. Then write down the time base.
And dont forget the isolation transformer !

73 Zeno
LFOD !

[Chris K]

Yes the B&K and the HP Scope are on separate isolation transformers.

[Notimetolooz]

Yes, many earlier sources of service data assumed you would be using the older type of scope that had a horizontal (time) drive that was based on the frequency of a free running oscillator. That would often quote a scope sweep of 7875 for the scope horizontal signal. I suppose for convenience they also assumed that you would want two cycles of the monitored signal on the screen.
Maybe those scope often had distortion at the start and end of a horizontal sweep. This causes confusion today with modern scopes.

Another complication you should be aware of is that the exact TV horizontal frequency standard was changed in about 1954 when the color standard came out. The color system used a color carrier reference of 3.58 some MHz. The vertical and horizontal TV frequencies were slightly changed so that they would be obtained from dividing down the color carrier frequency. So the vertical frequency became slightly less that 60Hz and the horizontal frequency became a bit lower than 15750. From that time even Black and White TV broadcasting used the newer frequencies. The only place this makes any difference is color TV AND modern sources of video. You couldn't see the difference in frequency on an (analog) oscilloscope.
I'm not sure about the 1077 (there were at least two versions) but earlier B&K model generators of this type had a vertical frequency derived from the 60Hz power.

Here is a good video introductions to oscilloscopes.
https://www.youtube.com/watch?v=KYEMPm0c9kY