I bought an IWATSU SS-5705 40Mhz 3 channel oscilloscope for £50 from a local guy a few months ago. It was ok for the first couple of months, however I'd noticed recently that it took longer to show the traces after turned on. Today, I was working on some audio project, but left it on (no traces were being shown) and went to watch the Olympics for a good few hours. When I returned, I could not make it to show any traces any more.
My real question is - is it worth trying to repair it? My guess is that the CRT has just run out of steam and can't be helped.
![Cry :'(](https://www.eevblog.com/forum/Smileys/default/cry.gif)
The scope is relatively clean inside. I've done some visual checks, could not see any bulged caps, burnt resistors, burn mark, loosen connectors etc. nor could I smell anything burning or hear any unusual noise when it's turned on.
Unfortunately there is no traces showing at all, no flashing on the screen when turned on/off, not a glimpse of any trace even in complete darkness. Power LED is on when turned on. When a signal in connected to an input, the TRIG'D LED is turned on.
The filament of the CRT didn't seem to turn red (I'm not sure if it is supposed to), not open circuit, measured about 7ohm...
I've also tested the secondary DC supply voltage as per instructions in the service manual. All voltages (+120V, +50V, +/-10V, +5V) seemed to be ok. Also the calibration signal generator (1KHz, 0.3v square wave) is working.
My next step would be following the troubleshooting flow chart to test everything else and report back here.