Tektronix 465 (S/N B276519)
I am trying to get an old Tek 465 working. I have been able to get Ch-2 working but Ch-1 will only show the trace at the very top of the display when using Beam Finder. Using the service manual, O-scope troubleshooting guide and forums I think I have isolated the problem to the Ch-1 Preamp section.
I have performed the following:
- checked DC voltage and ripple on all rails minus 2k rail all rails DC values were good. Ripple less than 4 mVAC RMS except 110V rail was 11 mV RMS (55 mVAC p-p) and had an unusual blip (see pic below). not sure if this is normal.
- used the Common-mode technique on TP322 and TP324. this moved the trace to the vertical center of the display (per the troubleshooting guide this indicates that the problem is in a stage prior to the Vert. Switch. section, which also tracks with the fact that CH-2 works but CH-1 does not).
- used the Common-mode technique on TP141 and TP147. This had no effect.
- checked DC values at the following test points:
- TP322: +0.6135VDC
- TP324: -0.8034VDC
- TP326: +1.6321VDC
- TP141: +8.529VDC
- TP147: +7.975VDC
- re-seated the following transistors:
I am at a loss on how to narrow it down further. Any suggestions on what to check next?
SIDE NOTE: I can see the Trigger level as expected when pressing Beam Finder and Trigger View, but I noticed that the trigger level pot is inverted (turning it "-" raises the trigger level and vice versa) on both channels. Is this normal behavior? I am inexperienced with analog scopes.
I can see the Trigger level as expected when pressing Beam Finder and Trigger View, but I noticed that the trigger level pot is inverted (turning it "-" raises the trigger level and vice versa) on both channels. Is this normal behavior? I am inexperienced with analog scopes.
Not really helpful but I happened to have a plugged in 465 next to me. This is normal
with DC coupling.
Since you have one channel working you can use it for comparison troubleshooting. Set both channel 1 and 2 to the identical setting on volts/div. Apply identical signal, such as the calibrator, to both channels. Trace the signal on both channels through the vertical circuits until you come upon a difference. That should be the area of the defect.