Sony/Tek 380


Doug
 

In my case the CRT is working in that the screen is lighting up but it looks more like a flooded storage tube.
The entire screen is glowing and I can't change the brightness, let alone get a dot or a line.


Steven Bender
 

Hi Doug,

I also have a Sony/Tek 380 that shows no trace, I bought it as a cheap parts donor for my likewise no trace 335 and 336. Somewhere, someone recall mentioned his 335 having blown a Fuji 2SC3030 Darlington 900 Volt transistor in a flat TO-3P case. So, I bought a bunch of those on eBay recently its such a high voltage unit, the gain is only rated at 9! Testing one of the bunch, my little Chinese Tester said its gain was five (5). I guess, close enuf. Not sure if this part is a known failure mode in these no trace Sony/Tek 300 series sets, been to busy to attend to repairs on these units.

Hope that tidbit helps!


Steven L. Bender


 

Check the blanking.

On 4/15/2021 9:25 PM, Doug wrote:
I picked up a little Sony/Tektronix 380 Video Waveform/Vectorscope recently. It powered up but no trace,
just a faint glow on the screen. It looked to me that the X10 HV multiplier was bad so I dug out the epoxy
and made a new one. Now the glow is bright but still no trace and the brightness is not affected at all by
the intensity control or the grid bias trimmer, which leads me to believe the CRT is bad.

I have voltage on the focus grid and I tried disconnecting the H and V plates - no change

I removed the CRT to look at the insides. Nothing looks broken or out of place as far as I can tell.
The grid bias trimmer varies the heater to grid voltage from 70V to 130V with, as I said, no intensity change.
Heater is at -1950V.

Looks to me like the CRT is bad. Am I missing anything? Any suggestions?

I've posted some photos under "380".



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Doug
 

I picked up a little Sony/Tektronix 380 Video Waveform/Vectorscope recently. It powered up but no trace,
just a faint glow on the screen. It looked to me that the X10 HV multiplier was bad so I dug out the epoxy
and made a new one. Now the glow is bright but still no trace and the brightness is not affected at all by
the intensity control or the grid bias trimmer, which leads me to believe the CRT is bad.

I have voltage on the focus grid and I tried disconnecting the H and V plates - no change

I removed the CRT to look at the insides. Nothing looks broken or out of place as far as I can tell.
The grid bias trimmer varies the heater to grid voltage from 70V to 130V with, as I said, no intensity change.
Heater is at -1950V.

Looks to me like the CRT is bad. Am I missing anything? Any suggestions?

I've posted some photos under "380".