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Old 21st Jun 2020, 9:36 pm   #1
DMcMahon
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Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
Posts: 6,587
Default Solartron CD 1400 Oscilloscope Refurbishment

Yesterday I started checking out my recent acquisition (FOC from Atlantic 52 through "Sets, Parts and Service Information Offered") of late 60's double beam oscilloscope Solartron CD 1400, including several spare timebase plug in modules.

Its last known operational status was" There is a beam albeit a bit dim & defocussed and scans to the left of the screen".

Because it has been powered up fairly recently I dispensed with the usual safety checks and powered it up (after checking for correct fitted fuse values).

No trace/display could be obtained at all with any timebase settings, graticule lighting illuminated and after a few minutes I could smell the valves warming up.

Removed the outer cover to investigate, everything inside was heavily coated with dust and lots of fluff present. so spent quite some time removing the worst of it, will continue more cleaning as time goes on.

After cleaning the dust off three wire wound resistors on Board 1, saw that one of them looked somewhat overheated and had lost some of its enamel coating.

These resistors are R105/R106/R107 all 680 ohm 4 watts and feed the decoupled +320 volt HT supplies to the 3 timebase modules, R107 being the suspect looking one which feeds the X timebase module.

I tried to measure the 3 resistors but could not get any sensible readings (I think due to old oxidised solder joints being high resistance on the surface), so unsoldered them and remeasured, they measured OK (R106 was a little high). Refitted the resistors, but still no display, measured the voltages at the resistors and one (R107) was bad (no volts), found that the 2 tracks that the resistor was soldered to had broken away (looks like the tracks are quite fragile when disturbed).

Repaired the connections and got good voltages (around +350 volts at output of the resistors). Now have a display/trace from the upper Y module. Have some control over it, can make it into a free running spot by changing the time base speed, but Focus does not work, nor Y shift and brilliance does not work properly.

All valve and CRT heaters appear to be powering up.

So a step in the right direction but plenty to do still I think. Next I will swap over the 2 fitted Y timebase modules to see what happens. Then will go back to basics and check out properly all the numerous power supply voltages before looking at the timebase modules in more detail.

David
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