It will stay stuck on either 4 or 6 for a while, and then work fine. The only remaining problem to solve is an intermittent in the 2nd digit from the right in the phase display. After the great cleaning, powered it up, and there it is, working fine. With a last cal date of 1989, I wouldn't be surprised if it had sat unused for a decade or two before I got it. This thing is in meticulous condition inside. At this point it was clear that there were intermittent contacts between the boards and their edge connectors, so I pulled each one and cleaned the gold fingers and the sockets too. Signal paths checked out OK, so I troubleshooted the A/D boards, didn't find anything wrong, plugged them back in, and the levels are now in the ballpark but phase is off. Checked the levels on each channel and they were not even close. Pulled the board, examined it, didn't see anything obvious, plugged it back in, powered it up, and now the display is working, though some digits drop in and out at random. Went through the troubleshooting tree, found an out-of tolerance frequency on the clock board (A32). Replaced it, and the choke that precedes it (which is what burned), and it powered up again, display still frozen. I guess such things are to be expected when a unit has sat untouched in the garage/warehouse for over a decade. A week or so later, after moving the inputs from the rear to the front panel, moments after powering it up again, smoke started pouring out of a board in the test channel analog card cage. As I mentioned last post, after getting the power supply up, the displays were frozen. Performance-wise, they really are quite good. I used this combo (not these exact units) for a number of years back in the 80's and 90's and this brings back some good memories. And here it is in all its glory, a 99.9% functional 3570A, sitting atop the world's fugliest 3330B.
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