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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sun 03, 2015 6:47 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
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Location: Weimar, Texas
The preliminary under chassis wiring is done. Both boards are mounted. I just remembered that I still need to glue the CRT base so that's next. Things will slow down a bit now. I still haven't decided whether to strip all of the old wired off or just clean it up and reattach it.

Onward thru the fog.

Top view

Image

Bottom View

Image

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sun 03, 2015 9:22 pm 
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Posts: 2005
Location: Weimar, Texas
Front panel is on. I'll get back on it this evening and start replacing wire as needed and terminating. Getting close. The only concern I have at the moment is that when I stripped a wire from the transformer the first time I tried it the wire broke off and had "green corrosion" on it. The second one was better but there was still a hint of green. That sucks...

The fat red wire has to go. The insulation is cracked. It was laying on the CRT so I imagine heat got to it.

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Sun 03, 2015 11:29 pm 
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Location: Pocasset, Cape Cod, MA
Corrosion might be from plasticizer leaching out of the PVC.


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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Mon 04, 2015 1:06 am 
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Quote:
The fat red wire has to go. The insulation is cracked. It was laying on the CRT so I imagine heat got to it.

CRTs don't get very hot, especially the face end. I would look for another cause; or, just replace it and don't worry about it. If that is a high voltage wire, the thick insulation could be there for a reason.

Jim Mueller

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Mon 04, 2015 2:10 am 
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Joined: Dec Wed 24, 2014 7:34 pm
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Location: Weimar, Texas
Jim Mueller wrote:
Quote:
The fat red wire has to go. The insulation is cracked. It was laying on the CRT so I imagine heat got to it.

CRTs don't get very hot, especially the face end. I would look for another cause; or, just replace it and don't worry about it. If that is a high voltage wire, the thick insulation could be there for a reason.

Jim Mueller


I've never seen it light up so I have no idea what could've caused the insulation to harden and crack. It only did it where it was laying on the CRT. I moved and replaced it. It's part of the focus / intensity voltage divider. Depending on where you look on the voltage chart it's 900V to -1300V

The wire size is the same. The insulation thickness looks the same BUT I can't read the type on the wire.

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Mon 04, 2015 2:27 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2005
Location: Weimar, Texas
Progress up to now. I'm down to to the rear board / CRT and I think I'll stop for the evening. I don't want to make a mistake and fry Miss Piggy before she has a chance to light up.

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Mon 04, 2015 5:49 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
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Location: Weimar, Texas
After agonizing over the stuck rubber mounting, how to remove it, and what to replace it with it turned out to be a none event.

I found this and it worked perfectly:

Image

The CRT is mounted. There's nothing but some wiring left... and maybe a little prayer that it doesn't go up in smoke when I power it up. I'll use a dim bulb tester and the transformer secondary output is fused so I guess we'll see.

Image

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Tue 05, 2015 2:10 am 
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Joined: Dec Wed 24, 2014 7:34 pm
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Location: Weimar, Texas
There's good news and there's bad news. When I powered up thru the dim bulb tester it looked like there was a problem. And there was. I flipped it up so I could see the bottom and something was popping. One lead of a 1600V cap wasn't soldered and it arc'd when the fuse made contact. Yeah... the fuse. I think it's a slow blow fuse and it was having issues. It didn't pop but it wasn't always low resistance. It was intermittent. So... I fixed the cap issues and pulled the fuse. After checking continuity and getting good and bad readings I set my Fluke on amps and put it in series where the fuse was. Less than 1/2 an amp and all of the tubes lit up. Yay.

After about 1/2 an our of tapping on the fuse and taking resistance readings I finally got it to read a consistent 2Ω. I installed it and powered up. Tubes all lit. No trace. crap... Voltages looked good where I checked. I didn't check the 1V2 and CRT. I wasn't sure if my Fluke was good for their voltages. Then I remembered my Eico VTVM has a 0-1500V range and -1400VDC was max.

:shock: That'll make a light bulb glow bright.

I had decent readings with the Eico but one was out of range. I hauled out the 6KV probe for the Fluke and started looking around. The 1V2 looked fine. Slightly high but not way too high

The CRT... Houston... we've got a problem
Pin Chart Found
1 -1400 -1363
2 -1400 -518**
3 -1330 -919**
4 -900 -783**
5 - -
6 260 452**
7 260 443**
8 232 165**
9 290 294
10 290 294
11 - -
12 -1400 -1364

EDIT- The lower voltages on 2, 3, and 4 aren't a problem after all. The lower voltages are due to the setting of the intensity pot. Pin 9 was due to a messed up trace. Once that was fixed the voltage went from 0 to 294 which is good. There was a "spot" on the screen but it wasn't a spot. It was a ball. Horizontal and Vertical controls do not work. Focus changes it from a ball to a line. So, there's still some work to do.

If ever there was a time when I had one hand stuck in my back pocket it was this time...

All dressed up but no light in her eyes.. uh... eye...

Image

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Last edited by Mike6158 on May Thu 07, 2015 1:51 am, edited 1 time in total.

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Tue 05, 2015 6:38 am 
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Your photo shows both position controls all the way to one end. The trace is likely off the screen. Set these controls to the center of their rotation and see what happens.

Jim Mueller

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Tue 05, 2015 12:00 pm 
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Posts: 2005
Location: Weimar, Texas
Jim Mueller wrote:
Your photo shows both position controls all the way to one end. The trace is likely off the screen. Set these controls to the center of their rotation and see what happens.

Jim Mueller


I took the photo before I set the controls per the manual. They are centered. I also moved them left to right, up / down per the manual and nothing showed up. Once I corrected the trace problem and had the proper voltage on Pin 9 there was a "ball" (not a dot) around the center of the screen. Focus control turns the ball into a line hand vertical / horizontal controls have no affect. More troubleshooting to come

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Tue 05, 2015 12:22 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Warner Robins, GA
Do the vertical and horizontal position controls connect in the amp stages or do they vary the voltage at the deflection plates?


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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Tue 05, 2015 11:30 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
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Location: Weimar, Texas
Tube Radio wrote:
Do the vertical and horizontal position controls connect in the amp stages or do they vary the voltage at the deflection plates?



They each control the voltage of the grid of their respective tubes

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Wed 06, 2015 1:52 am 
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Ok that means the problem is more than likely in the vertical and horizontal amp stages.


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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Wed 06, 2015 2:39 am 
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I think there are other problems as well :) The spot isn't a spot. It's about a 1/2" blob that turns into a line when I try to focus it.

I went through the resistance chart with my DMM and got some pretty off the wall readings. It makes me think that some of solder joints on some of the board mounted tube sockets are bad. The little ^ symbol means climbing rapidly.

They number left to right
V1 thru V5
V6 thru V10

V3 looks like it's in the vertical position circuit
V7 looks like it's in the horizontal position circuit


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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Wed 06, 2015 3:20 am 
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If your deflection voltages are off (two look real high) that can cause issues with focus.


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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Thu 07, 2015 2:27 am 
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Joined: Dec Wed 24, 2014 7:34 pm
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Location: Weimar, Texas
Tube Radio wrote:
If your deflection voltages are off (two look real high) that can cause issues with focus.



Found a problem and I wasn't expecting it to be where it is.

See the resistors with an inductor wound around them kind of hanging out there in the air?

Image

Schematically speaking they are L-6 with a 3.3K resistor in parallel and L-7 with a 3.3K resistor in parallel. You can clearly see Orange Orange ?????? but the coil covers the last stripe. They should be Orange Orange Red (3.3KΩ) but they read Orange Orange Black (33Ω). The parts list calls them peaking coils wound on 3300Ω resistors.

If I could get them off of the resistor they are on now I could slide them on a 3.3K resistor and all would be well. That may be my only option since paralleling a 3.3KΩ resistor around a 33Ω resistor isn't going to get me what I want and the calculator that I used to find the correct value came up with a negative value. That pretty much means it ain't happening. Any suggestions for getting that coil off of the old resistor? It looks like they painted some kind of varnish? on it.

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Thu 07, 2015 3:39 am 
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Mike6158 wrote:
Schematically speaking they are L-6 with a 3.3K resistor in parallel and L-7 with a 3.3K resistor in parallel. You can clearly see Orange Orange ?????? but the coil covers the last stripe. They should be Orange Orange Red (3.3KΩ) but they read Orange Orange Black (33Ω).

What do you mean when you say that "they read Orange Orange Black"? Did you move the coil so you can see the band, or are you saying that you measured them with a DMM and they read 33 ohms?

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Thu 07, 2015 4:33 am 
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stevebyan wrote:
Mike6158 wrote:
Schematically speaking they are L-6 with a 3.3K resistor in parallel and L-7 with a 3.3K resistor in parallel. You can clearly see Orange Orange ?????? but the coil covers the last stripe. They should be Orange Orange Red (3.3KΩ) but they read Orange Orange Black (33Ω).

What do you mean when you say that "they read Orange Orange Black"? Did you move the coil so you can see the band, or are you saying that you measured them with a DMM and they read 33 ohms?



I mean they read 33Ω. I can't see what is under the coil. I only checked them because the voltage readings for the two pins on the CRT were nearly twice what they were supposed to be.

:shock: :idea:

damn...but there's a coil in parallel with the resistor and it's going to bring the total resistance value way down... duh... with a capital D.
Obviously I type as I think it...

The inductors / resistors are probably fine and not likely to be the problem... Back to the drawing board... schematic... etc...

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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Thu 07, 2015 11:48 am 
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For the voltages that are nearly twice what they should be check the tube and circuitry around that tube those two deflection plates connect to.

For the other two deflection plates check the stages from where the position control connects all the way to the deflection plate driver tube and circuitry.


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 Post subject: Re: Knight Wideband Oscilloscope
PostPosted: May Thu 07, 2015 2:06 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2005
Location: Weimar, Texas
Tube Radio wrote:
For the voltages that are nearly twice what they should be check the tube and circuitry around that tube those two deflection plates connect to.

For the other two deflection plates check the stages from where the position control connects all the way to the deflection plate driver tube and circuitry.


I "found" the "bad resistor" (because I was looking for one I found it... funny how the brain works) when I was doing pin to pin resistance checks. For instance Pin 1 of V3 connects through a series string of chokes and resistors (plus one parallel choke resistors combo) to pin 6 on the CRT. The total appeared to be 3.3KΩ short. It's not. The 3.3KΩ resistor has a choke in parallel with it. To make a long story short- the resistance in the vertical position circuit "chain" checks out.

I have not checked the vertical gain, horizontal position, horizontal gain, or spot shape circuitry yet. Going thru these steps is good experience. I may actually understand how this thing works by the time I'm done. That's the point isn't it? I think it should be if it's not :)

BTW- I appreciate you taking the time to point me in the right direction and I appreciate Steve's gentle prod away from screwing up a perfectly good part.

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