Hi all,
My trusty 7603 developed a fault yesterday while I was using it, and I fear that a Tek special IC has expired.
Until yesterday morning it was working perfectly. I looked away to do something else for a couple of minutes, and when I looked back the display had shrunk horizontally. It now looks like this:
Oddly the readout seems to be compressed into the left side, but the main trace is compressed into the middle. I've measured a few things around the horizontal amplifier board. The power supplies are all OK and ripple-free, and the resistor values seem plausible based on a few in-circuit checks.
Switching off the readout makes no difference (other than the readout disappearing). Pressing 'beam find' has the expected effect, and it's not stuck on.
I had a look at the waveforms going in to and out of the horizontal channel switch U510 (156-022) and, while the input (pins 2/15) looks right:
the output (pins 12/13) looks far from right:
Apologies for the lack of vertical scale on the photos: the output is at 400mV/div and the input was 100mV/div, I think.
The 'display limit command' line, which seems to bias the channel switch, is firmly at -15V as the book says it should be. I tried reseating U510 but that had no effect.
Has anyone seen a fault like this before? Should I bite the bullet and find another 156-022?
Thanks
Chris
