Tektronix TAS 250 +145 V power supply repair and partial schematic

[octillion]

I fixed an issue with an out-of-spec +145 VDC supply in a Tektronix TAS 250, which I'll share here in case it helps anyone else.  A service manual, schematics, and BOM were never released for this or the sister TAS 220, only adjustment procedures.

It's a budget scope, I wouldn't ever pay money for one (I found it in the trash), but functions well enough for most uses once it is working and tuned up.  The plastic used to make the knobs is absolute garbage, and will spontaneously fall apart without ever being touched.  If you want to have a laugh, do an image search for TAS220 or TAS250, and notice that 99% of the images have at least one knob missing or replaced with a substitute.  This guy made 3D printed knobs for the variable knobs, and released the design files: https://www.thingiverse.com/thing:2209012

I was making replica knobs for a few other items, so ended up making all new knobs for this oscilloscope.  Attached are one of the few TAS 250 images with zero missing knobs, but they are all replicas (only the buttons are original, which don't spontaneously disintegrate).  The knobs are a little darker than original as I was color matching for the other knobs I was making.

Symptoms:
The screen intensity was too high, and the beam retrace was visible (especially at the fastest time divisions).  At 0.1 us/Div, the main beam and retrace had equal brightness, making it hard hard to distinguish the two, and the image would distort when moving the horizontal position left and right.  At the fastest time divisions, the cursor display had a significant amount of noise.  Focus and astigmatism were sub-optimal, but not bad.

Resolution:
Replaced C605 (1 uF 200 V), which was leaky and caused the +145 V supply to regulate around 130 V.

Casual inspection of C605 could easily miss this fault, as an LCR meter measured 0.974 uF with a Q of 25 at 120 Hz.  DC resistance measured with a DMM fluctuated between 12.5 - 13.5 MOhm, but when measuring leakage current at high voltage, the DCR dropped below 1 MOhm, which is sufficiently low to bring the circuit out of spec.

Circuit notes:
Partial schematic attached.  A bridge rectifier charges a 47 uF 350 V capacitor to about 210 volts (this is not shown in the schematic, but it connects to the double up and double down arrows).  The positive end is the +145 V supply rail, and the negative end gets regulated through Q601 to ground, referencing the -12 V supply.