Snagged a 475A for spares/repair that looks like it lost a fight with a hammer.
Was labelled 110V and had no plug on the end of it, so I wired up a plug and switched it to 230V as I’m in the UK.
1.5A fuse on the back of the thing was blown out and blackened so I replaced it with a 3A fuse (smallest I had to hand, apparently 700mA fuses aren’t a thing).
It’s a rackmount unit so I coaxed it out of the casing and put it on my bench upside down so I could probe the power supply.
before powering it up I took a look at the insides and noticed the vertical section had all the jumpers disconnected (some ripped out), and one of the jumpers was misrouted, so I assume this has already had someone noodling about inside of it.
Once powered on all of the voltages are within tolerance except unregulated 50V which was quite high at 65V, but regulated 50V was within fine so I assume it’s not an issue as the unregulated line is only used for the “low line” sensor on the front.
It powers up, CH1 and CH2 uncal lights come on, and there’s no beam.
I hit the beam finder and I get an off-centre dot that I used the horizontal adjustment knob to move into the middle, but it was still off vertically.
Hooking up CH1/CH2 to the CAL output (1kHz 300mV pk-pk, only have a DC multimeter and it reads approx 300mV so I assume it’s working) and I still only get a dot with the beam finder. Oddly if I change the TRIG settings I can get a single dim vertical line to appear (see picture).
I made a new slider for the power switch today, as it had been lost in the melee, and turned the scope on after flipping it upright, lo and behold there’s a single bright dot in the centre of the screen, without needing to hit the beam finder!
But when I do hit the beam finder it simply shifts the dot vertically by approx two scale divisions. I cant tell what the volts/div setting is currently as the dial is destroyed, but rotating the knob had no effect on the movement.
An accidental bump later and the dot goes, however the entire screen is slightly lit up. Repeated bumping can change between these two states.
With the now-upright oscilloscope, I noticed odd behaviour when adjusting the horizontal position of the beam. Turns out it’s not a dot but a line that changes length with the horizontal adjustment knob, video of this can be provided.
I’m lacking experience in debugging scopes, and having checked out the stickied post which has an excellent looking pdf on debugging tek scopes linked on sphere.bc.ca, I am led to believe there is most likely a problem with the horizontal section from the symptoms I had when the scope was upside down (no beam, dot on beam finder). However, the righted scope seems to have different issues which have me stumped (temperamental dot).
When I first took a look at it, one or two of the wires inside were disconnected and there was a solder joint snapped off that connected two grounds (CHB and the vertical section). Clearly this scope has been through hell, but does it sound like given a few weekends and some TLC it could be brought back to life?
I have pictures and video of pretty much everything with the scope so far, so I'll attach them once I figure out a sane way to embed them in this post.