[ARC Tech-109]

No the schematic doesn't reflect the same voltages as the T933 uses the 6LM8 for a video amp and my T940 uses a 6MU8. The DC bias from the brightness pot is present. My T940 print isn't nearly good enough for a photograph.

So the replacement tuner arrived late Saturday afternoon and installed without a problem but now I'm chasing down another that really has me scratching my head. Tuner has two B+ sources, #1 is the +130V source derived from R240 which is an 8200 ohm 1W on the supply divider board and this feeds the plate circuit of the 6HQ5 RF amp, the other is B+ #2 which is 140V supply that feeds the 6HB7 mixer/osc and gets dropped further to run the UHF tuner when selected. I'm finding +235 volts on the #1 B+ source and it seems to be from a lack of loading, the resistor itself checks good on the meter at 8225 ohms. I've swapped three known good 6HQ5 triodes and nothing changes, these are the ones that have the cathode tied to pins 2 & 7 via thin ribbon inside and are easily damaged by careless testing. I know everyone is passing a signal as I'm feeding in a known good IF signal into the UHF port of the VHF tuner and selecting UHF and if I feed from the UHF tuner I get plenty of mixer noise which is not present on any of the VHF channels.
This is a known good tuner so I' at a loss with this. My test IF signal is from a 80's vintage Panasonic 11" color on an iso trans and what I see on this set is perfect, I tapped the IF out of this tuner and feeding a dedicated jack I use for testing.

The original issue with the tuner was an accidental contact of the AC terminal of the little fuse block near the IF input with the tuner IF cable and that popped a number of parts in the tuner, thankfully another member was able to send me a spare replacement. The IF cable is good showing continuity and no shorts, it's passing the test IF to the chassis IF strip and all is well but it's like the RF osc is dead or way off frequency due to the elevated voltage which itself doesn't make sense. All the grounds are good and the AGC bias is right on the mark at 0.45v. According to the schematic the signal path in UHF starts at the little RCA jack on the side and is then coupled thru the RF amp thru the turret, from there it's coupled to the mixer (pentode side) of the 6HB7 which is acting as a second IF amp before it makes its way down the IF strip to the detector. IF AGC action is good and I can easily push that to an overload or cutoff so there's plenty of signal making its way thru and I know the Panasonic IF is spot on as they use a SAW filter to set the response and the magnavox matches this.

I'm at a total loss to why the tuner B+ one isn't being loaded down by the RF amp. Gone thru three known good 6HQ5 triodes and no changes.