Man, THIS has 'un really got you Buffaloed..No pun intended, either..

Heh :D

It's snowing out like crazy, the wife was working most of the night, my Mouser order for DuMont and Halolite parts didn't show, so I had nothing else to do anyway. Besides which, this is extremely valuable experience that I'm getting :)

This l'il guy's a 7", correct ? Never understood how those worked, anyway... They look like they're missin' about half the parts..

What did you measure on pin 5 of V13B?

Maybe it's time to ohm out T2. Sams says 50 ohms primary, 150 ohms secondary. Interestingly Sams shows the same part number used for both horizontal and vertical blocking oscillator transforms(T2,T3). That makes it easy to compare windings.

Any chance there's an adjustable core down inside the top hole of T2? Sams doesn't mention it, but I just noticed the hole in the Sams top of chassis photo.

15K *not* 20K? My Sams sez it should be 20K... In-circuit measurement should not make any difference, as it appears that the pot is isolated DC wise from any shunting paths. What does the pot in the "parts set" measure?

jr

Nah, no such luck. I'll ohm that out next.

One thing I should note. It looks like T4 was replaced at some point in time with something that was a little larger than the original. I decided to ohm that out first. Should be 250 ohms on the primary, and 200 on the secondary. I've got 225 on the primary and 190 on the secondary. Dunno if that could be a contributing factor.

I'm getting 16K on the pot on the parts set.

I'm getting 44 and 142 out of T2. This one I tested in circuit, which I don't usually do. It's just a PITA getting in there to unhook a side, but I will if I gotta :)

Going on the assumption that the H frequency is too high (rather than too low), you could experiment with slowing it down by subbing a couple of values.
The 10K resistor.. try something like 15K, 18K, or 22K
The .01 cap.. increase value by adding something like .002, .0033, or .0047 across it.

If this improves things, while not "fixing" it, it'd at least tell you it's moving the frequency in the right direction (ie., down).

Is it safe to assume we don't have a scope at the scene of this repair?

This set is certainly being a little stinker. :yes:

I have a Hickok 505A scope, but I don't think it's up to par yet. I threw some caps in it a few months back, but never finished the job because I was informed that this scope was useless without external sweep and RF generators.

I subbed in a 20 K resistor. No change.

I added .0047 across the .01 cap. No change.

Man, this is really a tough dog. Should I start scouring Craigslist for a scope?

In-circuit measurement *should* be ok... I don't see an obvious DC path that would affect the reading other than the two 39K resistors, which would only slightly lower the readings. What does the vertical transformer measure? How about the transformers in the "parts set"?

jr

Yesss!!!!!
 

Decided to swap the horizontal sweep transformer out of the parts set, and looky what I got!!!!

Obviously, it's not done, but I'm a HECK of a lost closer than I was! :banana:

Now the weird part was that the readings on the transformer that was in the set weren't far off spec, but it was some replacement that was larger than the original. I figured that maybe it was wound different or something, causing the issue. Bingo!!!

Now, to fix the vertical issue and the lousy focus. At least it's nice to end tonight on a win....sort of :)

Glad you got it working. :thmbsp:

Oh, and you should have another backup in the spare vertical osc transformer. At least Sams calls them the same part number, which seems a little weird.

Good thing you made mention of that. I tested and replaced 3 of the resistors in the focus circuit, one of the 2.2 M was open. Powered up the set, no raster, and the transformer I just installed was starting to brown up. In all fairness, that transformer that I installed looked like dried out garbage, but it ohmed out fine.

Guess that's next on the list.

Checked the transformer. Now I see why there was black tape on the one I removed.....seems that something happened to this transformer when I went to relocate the chassis ground (it was clip leaded for the test). Move the wire one way, open. Move it another, it's in spec, move it another, and it's WAY high.

Yep, transformer time.

New transformer installed, and with the resistors I replaced, she's making a pretty nice picture. Sound is good too :)

The only thing that I have to address is the vertical height. Not ideal, but may not be noticeable once in the cabinet. Still, going to check all the resistors in the circuit to see where we're at. Of course, I still have to tweak the linearity, but I'm pretty pleased so far!

Pretty pretty pretty!

Here's a video of where we're at now. I replaced a 10M and a 100K resistor that were about 30% high. Pulled in the picture somewhat better:

http://www.youtube.com/watch?v=r0MsL...ature=youtu.be

Still as you can tell, it's got slightly insufficient height. I had to adjust the linearity to compensate for it to get (close to) a full raster. The 6SL7 tests like new. I figure this is some type of low emission in the vertical output circuit, and the only component I can think of in there that I haven't changed or tested is a 100 PF cap.

Or am I being too picky? :dunno:

You should be able to get the picture more linear than that... Are the voltages ok? Do you have other 6SN7s and 6SL7s to swap? (sometimes a tube test does not tell the whole story).... Once, in one of these sets I mixed up the 6SN7 and 6SL7 and the set worked *almost* ok, but had height problems.

jr

I admit that right now with the set working somewhat decently, I'm starting to get lazy, and I don't wanna go back and test voltages :D . No other way though.

I have a boatload of 6SN7s, I should have some 6SL7s here too. I'll take time to do that tomorrow....I noticed that the horizontal width control has a flat spot big enough to drive a car through, and the flat spot is right where it should be, so I'll test the one out of the parts set and swap it over.

New weird issue with the Admiral, after about 6 hours of use. Getting intermittent blanking of the horizontal sweep. Linearity's not perfect I know, but here's a video. I'm almost thinking that the used horizontal sweep transformer that I installed is starting to give way.

http://www.youtube.com/watch?v=wWhXO...ature=youtu.be

To follow up, for the first 20 minutes the set is on, this blanking is not evident.

Seems to start after the set has been on for about 20 minutes.

I would also check the video, perhaps there is a noisy resistor in the video amp. Perhaps check for HV arcing as well? IMHO, the horizontal is looking nice and stable.
jr

Look closely at the blanking. It almost looks like the scan lines are getting folded together.....for lack of better phraseology.....

So there are little "step function" jumps in the vertical position as the tube is scanned? Noisy resistors? Dirty vertical position pot?
jr

I replaced almost all of the resistors in the vertical section, but there were a couple that I had to rob out of the parts chassis because I didn't have suitable replacements. Hm.

Other than testing the resistor to see if it's in spec, how does one spot a "noisy" resistor?

That description almost makes me think line pairing. Does it look like every other scan line is missing when this happens? I can't really detect what you're describing from watching the video.

Since the problem occurs after the set is "warmed up", perhaps blasting suspect components with "circuit cool" might reveal the source of the problem.
jr

Often some judicious poking and prodding (with an insulated tool), tapping tubes (including the CRT neck) will reveal an intermittent component.
Freez Spray ("circuit cooler") can be useful if the condition is heat related.

The set's now in the hands of my friend Al, in MD. It's generally been performing well for him, other than that intermittent raster issue.

Since Al is pretty handy and not a stranger to the soldering iron (and loves this stuff), I suggested that he replace the remaining resistors in the sweep circuits.

I probably would have, but ran out of time......he was in to visit family for Christmas :)

Resistors ordered.

ID, Snip, solder. Repeat! :D