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Originally Posted by vts1134
The heavy hitter test gear will take a few days. I have to order a probe for the scope.
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Well, while waiting for the heavy artillery, if you're game to try the 'quick & dirty' method of signal injection, here's how i would do it -
Tie onto the 6.3V heater supply just like you did earlier for the vertical, except this time put a cap in series with the clip lead. Value isn't critical, anywhere from .01 to .1 is OK. This'll give you a DC-isolated 60 cycle signal for injection.
Start at G1 of the CRT (pin 2). The raster should show a mild hum bar. Now hit the plate of the video output stage (pin 6 of the 12AU7). The same hum bar should appear. Now hit the grid (pin 7). The hum bar should show quite a bit of amplitude gain. Now hit the plate of the 1st video stage (pin 1 of the 12AU7). It should show the same amplitude gain.
Now to inject at the grid of the first video stage, it's a good idea to attenuate the signal so as to not overdrive the video stages. So let's utilize the 8.2K resistor (R27) that's already in place between the grid (pin 2) and ground. Add an 82K resistor
in series with the cap on your clip lead, so that this new resistor is now the "probe". When touched to the grid (pin 2), it's also in series with R27 and forms a voltage divider giving a little over 10X attenuation. So the grid will be seeing about .59 VAC of signal. Of course you can reduce the value of the new resistor to give less attenuation if desired. {Those two coils L10 and L11 can be considered zero ohms in this situation.}
As a precaution, i would leave the diode M4 disconnected during the procedure.
So if you lose the signal at any point while working back stage by stage, that will isolate where the failure is at.
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Pin 7 on the 12AU7 was the only voltage that was a good bit off of spec. It is supposed to read -.2vdc, it actually reads -.57.
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That doesn't mean anything since that's a very high impedance point, and the original meter probably loaded it more than the new meter you're using.
oc