Just got a KCS-96 chassis set

[Aperna1985]

Hey guys so I've been trying to selectively recap this set, to try and learn, the symptoms of failures in each of the sections. Right now I fully recapped PC 103. However I still can't pass a signal to the picture tube. Also I've lost a little bit of vertical deflection since the recap.

In addition to recapping PC-103 I have replaced C63, C64, I've replaced all three sections of C1, c116, c117, and c118. Out of all these caps only C62,C63, C65,c116, and 1 section of C1,were bad. The rest tested good surprisingly but I didn't want to have to unsolder the boards again if I didn't have to.


I'm going to recap the vertical board today, to hopefully fix the issue with the vertical deflection. What's sad is before I recapped board pc103 and replaced the filter caps I actually had full deflection but couldnt pass an image through the TV. I don't know if maybe it's just coincidental and capacitors are failing on the vertical board. I also tested coil number 50 and it tests at 7.5 ohms.


I tried putting a signal in on the 6aq5 on pin number one and couldn't get an image on the screen, then I tried pulling V6 the third video If and putting a signal in on pin number seven and still couldn't pass a signal. My Heath kit signal generator only puts out about 1.5 volts in the video setting is it just not enough to pass through? I also tried putting the lead from the heath kit directly to pin number two of the picture tube and that didn't do anything either.

I'm not sure what to make of all this, it seems to me if I could pass a signal over pin 1 of the video output it should display on the screen. I tried removing V6 to try and keep the IF from sending a signal in and over powering my signal. What am I missing?

[old_tv_nut]

When no signal goes through, it's a clear indication that SOMETHING is wrong, but not much help in determining WHAT. The next thing I would do is check voltage readings to try to isolate the problem area.

[Yamamaya42]

if you wish to try to feed in video, the best place to try is point C, on the SAMS, right after the video det, feeding into the grid of the video amp.

[Yamamaya42]

You mentioned L50, but what about the others?
L47,L48,L49? Everything in that area, if you put a 1.5 signal at the grid of V7, (point C) and got no reaction on the screen, with known good tubes and bias within spec, you have a problem from point C to the control grid of the CRT, this will also kill sound, if the video amp has no signal on the plate to give to the sound IF.

[Aperna1985]

Originally Posted by Yamamaya42

You mentioned L50, but what about the others?
L47,L48,L49? Everything in that area, if you put a 1.5 signal at the grid of V7, (point C) and got no reaction on the screen, with known good tubes and bias within spec, you have a problem from point C to the control grid of the CRT, this will also kill sound, if the video amp has no signal on the plate to give to the sound IF.

I only looked at l50 because I was trying to figure out the path from the video output tube directly to the picture tube. I figured if it's not passing from there to there it had to be a problem in either the capacitor or that coil. Is this flawed thinking?

Also I'm going to try the video amp just to see. I was doing only the video output V8

[Yamamaya42]

Be meticulous, starting from the det V6 to the CRT V20, check every coil and resistor, it could be any number of things. I normally take a green marks all ink marker, and put a little green dot on things that check 10-15% to what they should, and think about replacing parts that don't.

[Aperna1985]

Originally Posted by Yamamaya42

Be meticulous, starting from the det V6 to the CRT V20, check every coil and resistor, it could be any number of things. I normally take a green marks all ink marker, and put a little green dot on things that check 10-15% to what they should, and think about replacing parts that don't.

Okay, so I shouldn't be trying to move back from the CRT I should be trying to move towards it when I'm troubleshooting? I was thinking start at the closest point to the crt and inject a signal if it works there l move back one section and do it again until it doesn't work.

[Yamamaya42]

Work in sections, you know you have HV, sweep, V+H, but going on that you had no results putting in a singal at point C, and going on the assumption that signal was good, and put in correctly, there should have been a reaction if the circuit was working from point C to the CRT, so there must be a fault.
In order to input a signal at the CRT, you need a negative signal at 50v PtP, only a few video equipment can do that, so it's best to work from the lower end and check things over.

[Electronic M]

If you happen to have an audio generator or a low frequency RF generator with several volts of output you could that as a signal generator. It won't put out a standard pattern but you'll get black and white patches (whether they form spots or bars depends on the instantaneous frequency difference between them and the sweep). Hell, if the set isn't hot chassis you could capacitively couple 6.3v from the heater into the video amp grid....if the hum bar gets through you know that the amp is passing signal.
There's no perfect substitute for the right test equipment but if you're smart and desperate enough there's often some workable options.

[Aperna1985]

Originally Posted by Electronic M

If you happen to have an audio generator or a low frequency RF generator with several volts of output you could that as a signal generator. It won't put out a standard pattern but you'll get black and white patches (whether they form spots or bars depends on the instantaneous frequency difference between them and the sweep). Hell, if the set isn't hot chassis you could capacitively couple 6.3v from the heater into the video amp grid....if the hum bar gets through you know that the amp is passing signal.
There's no perfect substitute for the right test equipment but if you're smart and desperate enough there's often some workable options.

Originally Posted by Yamamaya42

Work in sections, you know you have HV, sweep, V+H, but going on that you had no results putting in a singal at point C, and going on the assumption that signal was good, and put in correctly, there should have been a reaction if the circuit was working from point C to the CRT, so there must be a fault.
In order to input a signal at the CRT, you need a negative signal at 50v PtP, only a few video equipment can do that, so it's best to work from the lower end and check things over.

I do have a BK1077B that I just restored, I'm just a little nervous about blowing it up. I was reading in the manual that it has a negative signal generator, would that put out enough? I was using the Heathkit because it's a little more disposable....

[Yamamaya42]

I'm not sure that the BK1077B can put out a 50v PtP signal however, the best way IMOH, is to start from V6, and check that all is OK in the path to the CRT, (coils , resistors ) , you will most likely find tired / worn resistors, especially the lower resistance ones on the cathodes, they love to go up in value, making the tube work very poorly.

I have seen this a lot in sets of this era.

[Electronic M]

On most sets if brightness isn't set too high you can get a faint image (or contrasting nonsense as it probably won't be synced) injecting at the CRT with max amplitude from the video output of a B&K 1077.

The 1077B has a large high voltage cap on its video output jack to protect it so it should be fine. The 1077 is a fairly rugged piece of gear intended to be miss-connected occasionally.

[kf4rca]

Don't forget an open trace on the PC board. I once saw a guy replace 5 chips on a Beta deck (broadcast version) and it turned out to be an open trace on the PC board.
A real simple video generator can be found here:

http://pa2rf.blogspot.com/2013/08/di...generator.html

I've made several and they work well for analog tv's and monitors.

[Aperna1985]

Just wanted to follow up guys, I'm not done with the vertical board unfortunately the RCA schematic is wrong, shockingly enough to Sam's is right. You would think RCA would know what was in their TV. I ordered off the RCA parts list so I didn't order a .068 capacitor for the board. Interestingly enough though so far every cap has been open in the vertical section. Literally not one good one. I'm surprised I didn't have a collapsed vertical.

[jr_tech]

Sounds unusual... how are you testing the caps?

jr