|
The weirdness was the wrong value resister in disguise causing the Chroma, blanking and AGC issues and this is where I mistook the problem as being a misaligned IF strip that came from a T933. The AGC overloading was causing the strange response so I attempted to counter these and made things worse. I then went to replace all the resistors on the IF board along with by pass caps then during the alignment phase grazed the IF cable from the tuner against the little fuse block next to the input jack on the chassis and smoked the tuner. Two months later I have the front end out of a T933 and while double checking things came across the rogue resistor, once that was replaced along with the damaged AGC pot everything started to work correctly leaving me with the task of cleaning up the mess I made.
This all started years ago when I attempted to resurrect the old family set using NOS parts I had cleaned out of a storage room working at a Motorola service center. We had hundreds of those resistor kits in the little file drawers along with more in little jars and on tape & reel, I was the service manager at the time and tasked with the decision making... the decision was made to bypass the dumpster and load most everything in my truck. We had just a few weeks to clear out some 40+ years of history as the depot was closing and lease was done, once the test equipment and other capital assets were removed I got the word out to the ham radio community and they picked the place clean over a weekend.
So during the attempt at replacing all of the resistors in the set I managed to break the original IF strip thru sheer clumsiness and made the decision to go with composite video, with the push to digital and impending demise of analog broadcast this seemed like a good alternative and I worked out a few circuits but a few bad real estate moves followed by a divorce that traded me in for a younger model forced the set into a large refrigerator box and into the barn for long term storage. That was 20 years ago.
Now the goal is to un-modify the set and bring everything back to the way it was in 1970... well the TV chassis anyway. I replaced the original amp many years ago with a Heathkit AA-100 I picked up at a hamfest around 1985 and modded the receiver section for stereo TV audio adding one of those stand alone Recoton "FRED" MTS decoders picking the 4.5 SIF up using a loop.
As it stands at the moment I have a good response curve on the IF strip, not stellar and the task for the afternoon is to get this squared away and move onto the lack of vertical height. The 1K-3W resistor for the plate side of the 6GF7 is on the mark and DC values are within tolerance, the tube itself is new from the carton and I've sub'd in a few others with the same results. I have not checked the boost B+ as of yet but it might be a bad boost rectifier as it still has the original selenium on the board.
Once this gets straightened out it's onto a convergence board issue that has the R/G tilt not responding, I've only replaced the diodes on the board so far as I don't need perfect convergence at the moment. We'll get there.
|