Scopex 14D-10

[trickyhicky270]

Hi all
I recently purchased an old Scopex 14D-10 from the mid 1970's from a car boot sale, paid next to nothing for it so wasn't expecting much as it was filthy dusty and looked like it hadn't been used in years. I got it home plugged it in and it worked OK, so I gave it a good clean up and put it away (in the house in the warm). A couple of weeks ago I went to use it and the dot on the screen got bigger and bigger to the point were after 5 minutes it was just a solid block of green light on the screen about an inch high accompanied by a buzzing noise on pressing the "locate" button. Everything thing else seems to work Ok, X and Y position, registers an input on the screen from A and B input but the trace is so big you just can't tell what it is.
I downloaded a copy of the repair manual from another thread on this forum and have just spent most of a week swapping electrolytic caps and trying in vane to get the voltages down to somewhere near normal, were I should be getting +200V my meter (set on 1000 volts!) is going off the scale to the point were last night I burned 2 resistors out in it....
The back of the CRT is glowing bright orange and TR259, TR256,R181, R182, R184 and R186 are all to hot to touch in less than a minute. The buzzing noise (locate button)has gone away since I changed the caps but if anything the dot/trace on the screen has got bigger.
I am hoping someone can help me out here as it seems a shame to bin it, although I am a little outside my "comfort zone" with the high voltages inside this thing. I only normally tinker with mobile phone, laptops and the like

 

[alec_t]

I've got a Scopex 4S-6. Its power supply is a linear type with only one winding giving > 200V. Don't know if the power supply is similar to yours but if so it suggests there's a short somewhere between the high voltage winding and elsewhere; or perhaps shorted primary-winding turns thus increasing the transformer ratios.

 

[dr pepper]

If you have a meter check the esr of the power supply electrolytics, in fact all the electro's.

 

[Wolfe]

Could you repost the repair manual please?

I've just dug a scopex 14d-10 out.
Checked the BF858 I thought was faulty but it tested as to diodes ok.
Turned it on; nothing on the screen but s smudge bottom right when you press locate.
Therefore dot off the screen.
Retested the two heatsunk BF858s, one now had 1.8v as a VBE, all other 4 BF858s where 0.7.
Changed transistor, I now have a waveform.
But it's on the right and sweep doesn't work.
So I spent an hour on the web and ended up here.
Then I followed the circuit again. No schematic.
Sweep pot ok, goes into a quad switch ic ok.
Then goes via an MPS6518 to a BF858.
The timebase signal goes to the other BF858 next to it.
Looks like one horizontal plate is sweep, and the other is timebase.
The MPS6518 is short.
I'll order one.

Would still like a manual to calibrate unit.

Is yours working yet?
All my high voltage readings on these BF858 devices where 180V
Centre screen typically 90V but essentially whenever the two plates are equal.
Also unit has +/-15V to the inputs of that helps.

 

[alec_t]

Welcome to ETO, but note that this thread is 7 years old so the thread starter may not be back.