Portacolor dead IF, am I on the right track?

[AlanInSitges]

This is a different Portacolor than the one with the wiggles FYI. It's another NTSC set, nothing weird or European about it.

White screen, no sound, no static changing channels, nothing. Varying AGC has no affect. I can inject video at the test point right after the video detector and get an image. I have tried to inject IF at various places along the IF strip with a makeshift output from my Philips pattern generator but honestly don't know if it's working or not, so not really a reliable indicator. I've swapped out both of the IF tubes with no change.

Checking voltages I came across something that seems off; I'm not sure if I understand the circuit correctly so hopefully one of you can tell me if I'm on the right track. To set the mood: 270V B+ is exactly 270V.

The plate and screen of V3B 2IF measure 270V, and the grid measures 137V, just as the Sams indicates. However the cathode and suppressor grid are both about 20% high at 155V. Incidentally, plate and screen of V3A 1IF are also high at 155V. Cathode is about 300mV and grid is pretty much 0, varying a few mV.

So.

Tracing the current flow through this part of the circuit, it seems that we start with 270V on the bottom of T152, through the transformer, to the plate of 2IF, through the tube to the cathode, over to the bottom of T151, through that transformer and to the plate of the 1IF, through that tube to the cathode and then finally to ground via R155, essentially stacking the two IF tubes like a voltage divider to get the 135V they need to do their thing. It seems to me that based on this understanding, and the voltages I have measured, the circuit should be more-or-less working. The fact that everything in the voltage divider part is high makes me wonder why, it seems like if the 1IF weren't conducting (due to 0V grid) that could explain the higher voltages everywhere else.

My questions are:

1. Do I understand what's going on in the circuit correctly?
2. Could the lack of slightly-positive 1IF G1 explain the higher voltages?
3. Could that be the cause if my dead IF strip?

And a bonus question:

* How does one troubleshoot an IF problem like this without a known working IF source?

Thanks as always!