Tektronix 465B - help needed -> fixed!

[Rerouter]

not so much for the procedure, but isocol branded isoproply you get at chemists has so far never left any residues for me,

from memory it involves wetting a sheet of something with it, then sliding in and out underneath the contacts to clean them, perhaps someone else can fill that in...

[nomad86]

Yep, read around a bit more and that sounds like the accepted process. A bit of paper with isopropy alcohol on it GENTLY rubbed between the contacts. I have a some isocol on hand so I will give it a go. Thanks Rerouter.

Another question, if I do the following:
- hook up the calibration signal output into the A trigger input
- set the A trigger switch to EXT
- set the VERT MODE switch to A TRIG VIEW
what should I see on the trace?

I am currently seeing just a plain line. Note that I can get the square wave from the calibration output to display without any worries when input into CH1 or CH2. I then leave the time base and the volts/div at the same settings when I follow the above steps.

My understanding was that it takes the input given by the trigger selector and displays it without any amplification so what I see (just a line) is correct. But the operators manual procedure for Basic Timing Check makes me think I should see the same signal as if i plugged it into CH1 or CH2. I am confused...

EDIT: Figured it out. I will write up my findings just in case someone else needs it. The input into A TRIGGER EXT should be displayed the same as if it is fed into CH1 or CH2 except with a constant vertical scale of 0.1V/DIV (as stated on the front panel). You can't adjust this scale although you can adjust the overall vertical position with the A TRIGGER SLOPE knob. This is probably obvious to anyone who has a working 465B. The reason I was only getting a single straight line for a trace was that the two connectors (J7535 & J7524 on schematic for A & B trigger generators, this is missing from most manuals off the net, find it at http://bama.edebris.com/manuals/tek/465b/ under "465bMissingPages.pdf") were not seated correctly. The wire end was out to the side of the connector assembly rather than in the socket and so no signal was getting through. Simply re-seat these connectors and you're good to go!

[scatterandfocus]

I got a 465B recently with exactly the same symptoms, showing similar voltages, and sure enough C4331 is shorted  just the same.  When the scope arrived it showed a trace, although not a good one.  After the next power cycle it showed exactly as nomad86 described.  Good work  nomad86, SeanB!  I was holding off a bit on ordering a bunch of components until after I got a chance to open this thing up and look at the voltages just in case the problem was only a failed component that I could track down.  And then I ran into this thread while searching on the low voltage at the +55V test point and other off voltages at the nearby test points.  So hopefully swapping out that cap will get the 465B back up.

[scatterandfocus]

I borrowed a 100uF 20V electrolytic cap from a broken battery charger, and I got a beam and a trace!  Woo ha.

I think this thing is going to have some other issues though.  The display seems to have alot of flicker, the beam is a little off kilter, and the beam trace seem a little fuzzy and noisy.

Edit:  The flicker was due to the holdoff setting.  The kilter seems ok after adjusting the trace rotation.  Maybe the slightly fuzzy/grainy trace is normal on this scope?  I have seen some people mention that the 465B doesn't have the sharpest trace.

[james_s]

Does the fuzzy trace clean up if you set the inputs to Gnd? My 465B doesn't have the sharpest trace I've seen but I wouldn't call it fuzzy either.

[scatterandfocus]

Does the fuzzy trace clean up if you set the inputs to Gnd? My 465B doesn't have the sharpest trace I've seen but I wouldn't call it fuzzy either.

It doesn't change anything when doing that.  Rather than fuzzy, I would better describe it more as the trace being thick and having soft edges, in comparison to a Hitachi that I have.  I think it is functioning as it should be, and it is not a big deal.  There was some good discussion on trace sharpness here:  https://www.eevblog.com/forum/repair/tektronix-465b-repair-97327/

This is a hell of a cool old scope for a beginner to tinker with.

[james_s]

I can pull my 465B out and get a few pictures of the trace later if it would help. I agree it's a lovely old scope and an iconic classic, first "modern" scope I owned and I still hold onto it because the XY mode blows away that on my DSO. Also sometimes it's just fun to use an old analog scope. The fact that it's almost as old as I am and still a useful instrument says something about the design.