Tektronix 2213 - Auto Intensity not working

[dan3460]

Still working on this thing. It seems to have very little control over the intensity of the beam. Manual here:
http://www.hellspark.com/dm/ebench/tools/Analog_Oscilliscope/tektronix_2213_service.pdf

Working on "Auto Intensity and Z Axis <6>".

Probing for signal 18 (pin 11 U825) I get something similar but a lower top voltage around .8v.
Signal 19 (pin 1 U835) no signal, steady .9V.
Signal 20 (pin 7 U835) some kind of signal, but I think is leakage from other part of the circuit. Voltage -1.2v Attached picture.
Signal 21 (R856) Similar signal to the chart, a little higher voltage 32V, the "SWP Z-AXIS Signal" is at 20V.

I suspecting U825 (there are signs that was previously changed as the solder is a different color) by following the schematics I should have some kind of signal on pin 14,3 and 4, definitely on 4 as this feeds one of the opamps on U835. Should I replace U825?

[moya034]

U825 may indeed be bad, but if it has already been replaced once, I'd like to know why two have failed in the same unit. Perhaps a resistor or capacitor near it has also failed?

I'll be following along with interest... I have one of these scopes myself I picked up cheap at a hamfest. It has an issue with channel 2 that I have to troubleshoot one of these days. Perhaps a calibration procedure too.

[dan3460]

Thanks for the answer, this is a scope that I bought on ebay and I will be giving it to a kid that is learning electronics. I already solved a problem with channel 2. You can see the problem on this same forum.