TP1801 measures 5.69V (SM says should be 5.7V)
TP1805 measures 1.74V (SM says should be 1.8V)
So maybe, as David says, that sugggest the (main) problem is not earlier in the z-axis signal chain?
Is the filament open or shorted to the cathode?
Measuring across the cathode (3KV TP) and one side of the heater I get about 100K.
Is the CRT filament drawing current?
Do you mean the heater?
Measuring across R1887 (the 16 ohm resistor in series with the heater) I get about 1.6V RMS.
Here is a photo of the signal at TP1876. Following the SM, I adjusted it's DC level to 9V (with intensity all the way down). In the photo it looks like 10V, but that's due to camera angle/tilt and difficult-to-read resolution.
I've added two additional horiz times so that you can see the actual shape of the waveform, in case that might be significant.
The photos were taken before adjusting the gain. I have to turn R1810 almost all the way CCW to reduce it down to the 74V peak the SM directs.
Is there a relatively easy but definitive way to test whether the CRT is good or not? I don't want to spend time tweaking things if the CRT isn't good.
BTW- access to the CRT on the R7903 is difficult, because the connections are below the z-axis board, and one needs to (evidently) unplug the connectors in order to remove the z-axis board. I haven't yet figured out the location of the deflection plates connectors.
Also, BTW- I'm using one of the military (grey) Fluke 27/FM's, which are reputedly true-RMS. Of course that doesn't mean I alway know how to use it properly.
Thanks,
Keith Ostertag
