Philco Safari Vertical Foldover issue

[goat1981]

Cool. Thanks for the reply. I'll check some voltages this weekend.

Are there any specific resistors I should check the values on? Specifically those that may affect the vertical height or linearity?

Thanks again for your help.

Originally Posted by Electronic M

I'd check voltages at the transistor pins with the set at reduced ans normal voltages and compare to what the schematic specifies.

Word to the wise whenever at all possible read the value off the original part you are replacing in the set, and NOT the schematic....I've blindly followed sam's and got bit by their numerous typos a few times, and now take all sam's data with a grain of salt.

[Electronic M]

Originally Posted by goat1981

Cool. Thanks for the reply. I'll check some voltages this weekend.

Are there any specific resistors I should check the values on? Specifically those that may affect the vertical height or linearity?

Thanks again for your help.

R75-R80 would be prime suspects, but I'd check every vertical resistor (including the pots), and the synch resistors (since the bias of the synch sep affects current flow through the vert osc transformer primary and the osc stage).

Voltage differences (and if you have an oscilloscope, waveform differences) in the vertical stage should help you localize the problem

[goat1981]

Excellent! Thank you for the starting point.

I appreciate your help.

[goat1981]

Hello, everyone,

I have had time this past weekend to look further into the Safari vertical distortion issues. Thanks to Tom (Electronic M) for supplying me with a spare sweep board to check for incorrect resistor values (and spare parts).

I was actually hoping that I made a mistake somewhere when replacing resistors (doing this originally because of the distortion issues), but I couldn't find any incorrect values when comparing with the unmodified sweep board and the SAMS.

I tried slightly increasing the value of the non polar capacitors C15 and C17 (see attached schematic), and this actually improved things a bit. I increased C15 from 7mfd -> 10mfd, and C17 from 5mfd -> 6.8mfd. My reasoning was that the original capacitors were a bit high in value to begin with. After doing this modification, there is no more foldover.

However, the vertical linearity is still not correctable with the controls. Please see attached pictures -- this is the best I can do. The top and bottom are pinched and the middle is a bit bloated. I checked all resistors, capacitors, and controls in the vertical circuits, and all are within spec. I also did DC voltage measurements on the transistors in this circuit, and this is where issues came up....

The voltages around the vertical oscillator (X14) were fine -- pretty much what the SAMS specifies. However, the vertical output transistor (X15) had values that were off, specifically on the emitter.

Here are the readings on X15:
B: -.89v (SAMS specifies -.7v)
C: -3.7v (SAMS specifies -4.5v)
E: -.7v (SAMS specifies -.1v) -- !!?

Is it possible I have a bad vertical output transistor that's working but not to its full potential? I have checked every other component in that circuit and am at a loss. There seems to be a replacement transistor out there -- the NTE 121 -- but it's relatively expensive, and am not sure it would work correctly. Anyone have experience with this transistor? Any other thoughts?

Thanks for your help in fixing this TV. I really would like to get it working optimally.

[goat1981]

For some reason I can't get the screen shots to post with the correct orientation. Please orient 90 degrees to the right.