iwatsu ss-6122 oscilloscope

[yashiro32]

Hi,

I bought a Iwatsu ss-6122 oscilloscope for a year and recently when i turned it on, i could not find the trace. I tried to adjust the vertical position knob to the highest position and i could see the trace appearing at the bottom of the screen. After that, when i adjust the vertical position knob to lower down the position the trace seems to adjust down and cannot be seen anymore. Does anyone know which parts or components of the circuit the problem lies on?

[torbjorn]

Without any specific knowledge of this specific oscilloscope, i could bet that the problem is in one half of the push-pull vertical deflection output amplifier. For exemple, a shorted output transistor, burnt-off collector resistor or something like that. Each half of this amplifier usually looks like the video output amplifiers of a tv or monitor.

[yashiro32]

Yes ,

one of the push pull transistor in the vertical deflection output amp Q34 - 2SC1412 (NPN tranistor) is damaged . As that part is obsolete, i replced it with a cross reference part - 2N5109 and the trace returned to the center of the screen .

But now, there is another problem. After i turned on the oscilloscope for around 15 -20 minutes there seems to be a double image drifting vertically up and down corresponding the trace and readings . Where could the problem be ? Could it have something to do with the Focus/Z-axis part of the circuit ?

[torbjorn]

Maybe, it could be a problem in the switching between the two vertical channels. Try switching off the other channel (or change between "alt" and "chop" mode) to see if the ghost image disappears.

Also, it is important to have good symmetry in the push-pull output stage. It is a good idea to change both transistors even if only one of them has failed, and make sure that the replacement transistors are fairly matched regarding hfe factor etc.

[yashiro32]

Does anyone have the user and service manual and the schematic diagram of this IWATSU ss-6122 oscilloscope?