Motorola 9T1 60 Hz Hum and Horizontal Pulling
 

Hi Guys,

I've been restoring a 9T1, TS-18A chassis, and it's been going pretty well but now I'm stuck. I've recapped all the poly and electrolytic caps, rebuilt the ballast, replaced the selenium diodes and performed an alignment. Alignment tried to kick my ass but I've got a pretty good waveform, aligned audio and video and a pretty good picture. BUT (and you knew there was going to be a "but") I've got a 60Hz horizontal hum moving up the picture which affects momentarily sync when it gets to the top of the picture.

I've tested and swapped tubes without a noticeable change. I've started to swap out cathode and heater bypass capacitors but so far after replacing about 5 of them, no joy. Should I continue swapping bypass caps?

How about the few mica caps in the horizontal sweep circuit? I've read that they can be troublesome and in watching banderson's 7VT1 videos, he swapped them all out with what appears to be a modern mica cap. My trouble is the highest rating I can find is 500 or 1000V stuff. The originals are 2000V.

Easy, right? You guys can probably do this in your sleep.

Thanks in advance, Scott

Look for (read that as "reflow with a big high wattage iron") bad ground solder joints. I've heard of that causing similar issues in other electrostatic deflection Motorolas.

Thanks Tom. I’ll look for bad grounds. Any thoughts on replacing the mica caps?

I only change them if they test leaky or off tolerance. Just radios in Canada might stock higher voltage micas. Some may criticize the practice (I sure will if the right part is affordable and easy to find), but in a pinch get 2 1000V micas at double the capacitance of the original and place them in series the series pair will be effectively equivalent to the original. Another option might be NP0 temperature stable ceramic caps.