Tektronix TDS754D color CRT adjustments

[eKretz]

I recently picked up a TDS754D from a fellow member here and it had a very dim CRT. I've adjusted the brightness and contrast per the SM but this has revealed or created a focus issue. The display is sharp in the center but soft around the edges. Has anyone got any experience dialing in the focus on one of these?

[NavyBOFH]

If that's the case you want to go back and check the cathode/anode/grid voltages if you have the right equipment (or if there are test points available). Whenever I've had to repair anything with a CRT I've noticed those issues like you're describing coming down to a bad power supply or driver. The CRT itself could be showing its age as well...

[eKretz]

 Found some info from TekScopes Yahoo group that ID'ed some of the pots controlling focus so I set up my two 754's next to each other so I could drive the troublesome CRT with the other scope - as a troubleshooting measure and so I could make adjustments without having to remove the CRT from the chassis.

The 754A has a very sharp display with no issues, the 754D has the soft around the edges issue. When I drove the D's CRT with the A's board, it still had the same soft focus around the edges, so it seemed very unlikely to me that it was related to power supply issues.

At this point I set up the composite display pattern and started tweaking focus pots. After about a half an hour worth of dialing center, horizontal and vertical focus pots I got it about as good as it's going to get. It is much improved but still just a tad soft at two of the extreme opposite corners. It's pretty much invisible unless you're looking for it, so I'm happy with where it's at now.

Thanks go to TekScopes and Andy who I PM'ed for some info regarding the pots and ID'ing which does what.