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Chemistry Electronics Services
ARCHIVE OF REPAIR TRICKS, USEFUL INFO, ETC.



Repair CRT display, Philips TEM CM100 CM200 Electron Microscope


Electron microscope CRT display with crazy distortion. Can't read menu for pushbuttons!


Fortunately this one has schematics for the small PCB that drives the monochrome picture tube. It's a TEA2037A sweep generator, LM1881 synch seperator, and LM1201 video amp. The ribbon cable fits a 26pin gold pcb edge-connector, see schematic link below. Orient the connector by finding +12V supply pins on one edge of the connector, pins 1 and 2 being on opposite sides. NTSC video input is then pin 11, with grounds on 9,10, on 12,14,16, also 22,24,26. Normal behavior: it initially draws 2amps at +12V, decreasing rapidly to 0.8Amps.


We had a video source; an old IR camera with NTSC output jack. The crazy distortion in displayed raster was both in transients in the vertical sweep, also as large blotches of video-blanking. Accidentally I found that the CRT monitor worked perfectly at 13VDC supply voltage, but giving the distorted raster at 12.9V and below. (Note that without a video feed, the vertical deflection becomes very small.)


The cause was one dead, dried out electrolytic capacitor, C2; the 150uF 16V filter on the +10V supply, on pin 16 of U1 the TEA2037A chip. (This capacitor is located right against the chip, next to pin16.) Also a similar capacitor was nearly dead but still functional, C21 100uF 50V on the flyback xfrmr.


Replacing these caps put everything back to normal. The same symptoms still appear, but only if the supply voltage is decreased down to +11.1V


LINKS



Created and maintained by Bill Beaty.



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