Sonora 50s metal portable

[bandersen]

I stayed up late troubleshooting and it finally paid off.

First, I found this 8200 ohm power resistor was open. I cracked it open for a look inside and found a break in the wire towards one end.


The flyback was still making horrible squeals though so I fired up a scope. The waveforms are quite odd. There are bursts of 15kHz with long periods on no oscillation. Tweaking the horizontal hold and how wave shape controls improved it somewhat.


Eventually, I tracked the problem down to a bad 1N60 diode in the sync circuit. It was replaced with what I think is a 1N34.


That finally produced some HV so I hooked up the CRT. It took a long time to warm up since it's a .6A filament in a .45A string, but eventually a raster appeared.

Now I know why there was on ion trap magnet on the CRT. When it was rebuilt, they used a straight gun so it has a nice ion burn in the center


Shortly after I got the raster, I noticed a burning smell. Some sniffing led me to this fried resistor. I doubled checked my wiring and found I installed the 10uF capacitor backwards


Replacing those components gave me a stable raster so I hooked up a signal source. Clearly the horizontal is out of whack.


Fighting with the hold and waveshape controls got me a stable image. The burn isn't too noticeable if you don't think about it.

I expect the CRT would be even brighter and sharper with a proper 6.3 @ 0.6A filament supply, but I think that would also make the ion burn worse faster.


Not bad for such a simple set. Next I need to rig up some thing to hold the yoke in place. I think I can get by without the centering rings.