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Hi Everyone!
Thought I'd give an update on how the restoration is going! Very frustrating to say the least. There are so many out of tolerance resistors that I've had to swap out. Still no big improvement.. I think I'm starting to focus on things that aren't the real fault here.
My biggest issue I think is some incredibly high B+ in some circuits. I have an extra 30 volts on the cathode of the 5u4 rectifiers but I don't think thats something I can fix and I doubt that's the real issue. I managed to get the plate voltages in the horizontal osc sections within normal but V16 6SJ7(2nd sync clipper) plate voltage is 340 volts! Sams says 250V. 80 volts high. The screen voltage is a bit less. That explains my limited range of sync both vertical and horizontal. I have some sync so its partially working.
A more confusing issue is in my V7 6AL5 dc restoration. The cathode on pin 1 has 20 volts on it! It does vary with the brightness control but only from about 30 volts to 20. Sams says .4 with all controls set at minimum. There are only two resistors there R47 and R48 I replaced the 470K one but the 150K only tested 10 K higher. I doubt very much that it threw it off that much so I left it. The caps have already been replaced and are wired correctly. Pin 2 on the CRT should only have 1.1V but its right there at 20V. Which explains why the picture lacks contrast.
The contrast control only has a small range where the sync falls into place and there is a picture. The screen blanks out when the contrast control is less than a 1/4 and washes out again when set more than halfway. To get any sync its set about 1/3 from minimum. I have to imagine that the way the contrast control varies the gain the IF tubes are not being cutoff correctly.
I am really running out of ideas here. Tomorrow I will write down the plate and screen voltages and see if I can come to some kind of conclusion. I know I'm not far off from having this project complete as everything is nearly working..... Its just not quite there yet..
My B&K 1077B arrived yesterday. Broken.... Poor packing. The fuse holder on the back was broken off and the Horizontal output tube departed the socket and smashed around. Lots of glass shards to clean out inside. Now I am waiting for a new tube and fuse holder. Seems the CRT survived.
Thanks for reading! My brain feels mushy after so many resistance and voltage checks this afternoon. I should have saved myself time and wrote down the voltages on paper today instead I'll recheck them tomorrow.
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Matt Davala
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