Tektronix 465 w/ DM44 subject to whims.

[bd139]

Oscilloscope ownership is a hobby. I might have finished building my transceiver if I didn't have so many scopes. It's like working in a kindergarten cleaning up sick all day.

I'll start another thread on the 1740A. Rather than the switches causing trouble here it looks like the trigger is deceased. I can single sweep at any time base setting. Auto/norm have died. Hope it's not a pesky hybrid.

[tggzzz]

Oscilloscope ownership is a hobby. I might have finished building my transceiver if I didn't have so many scopes. It's like working in a kindergarten cleaning up sick all day.

Oh, but you love them all, really.

I'll start another thread on the 1740A. Rather than the switches causing trouble here it looks like the trigger is deceased. I can single sweep at any time base setting. Auto/norm have died. Hope it's not a pesky hybrid.

There are existing threads. I'd bet on something simple, maybe a switch, maybe a bias pot. In a 485 I had a resistor subtly fail in a trigger circuit; that was a pain to isolate but an easy fix.

[WaveyDipole]

For on-boards highlighted caps I can only check for shorts (AFAIK with my DMM), none is shorted, they range from several k to 77 (C1220) depending on which cap in the circuit. My tantalum caps are red ones, many having like a rubber/hard-yellow-thing o-ring on leads. No Short is the only thing I can say.

At 77 that is a very low reading for C1220 and I would suspect it of being leaky. I would de-solder or snip one end and check it again. If the reading is still that low then it needs replacing. But I would also expect R1220 (22.1ohms) to get rather hot as a result. You might want to check that it has not gone OC.

Coming back to your line voltages, it is interesting to note that your unreg line is 131v but the 55v line which is derived from a tap on the same TX winding is low. As was mentioned by db139, the 55v line is used to provide an appropriate reference voltage via a resistor divider to the op amp in each of the +15v, +5v and -8v lines. If the +55v input is low, then the voltages output on these other lines will be affected. Your measurements show that the +55v line is at 40.0v hence 72% of the expected. A quick calculation shows that +15v, +5v are exactly proportionally affected and the -8v nearly so. For the +110v line the arrangement is a little different, but that +55v is also used as a reference via VR1515 (56v) which when added provides a regulated +110v (55+56 = 111, then you also have a -0.7v drop across CR1514).

So I think it is necessary to establish why the +55v line is low.

I would suggest we first see how the replacement of the caps you have purchased goes, in particular whether replacement of C1513 makes a difference. If the line is still low after that, then the other cap to bear in mind is C1534 but you only need to de-solder one end of that and if the voltage has returned to +55v you know that it was responsible.

If we get to that point and the line is still low, then we need to start checking the voltages marked at the various reference points on the circuit around U1542A, Q1532, Q1534 and R1538 to see what we get.

But first let us know how your cap replacement went.

 

[Malefoda]

But first let us know how your cap replacement went.

Not that bad, just needed less than 10mm long extender on the 300mm diameter caps. Linked the grounds when needed. 
Power lead on... power and no smoke!
All supplies are OK, no more ripple my DMM can find, a rock solid 55.00V, the only measurement out of spec is the 110V at 114.5V when max allowed is 113.4V. Still some work?

Thank you for the helping hands, it's back from the dead 
BTW, off board C1220 is good.
The scope never really worked prior to this repair but as it seems birghter now, is the trace flashing in a centered position on power-off normal?

[bd139]

Excellent. Nice work

[WaveyDipole]

Power lead on... power and no smoke!

Great to see it working. 

All supplies are OK, no more ripple my DMM can find, a rock solid 55.00V, the only measurement out of spec is the 110V at 114.5V when max allowed is 113.4V. Still some work?

Well, that's not too far out of spec so it will probably not be much of a problem for the present, but if you want to put your mind at rest then you could try checking checking resistors R1516, R1517, R1518, R1519 in case they have drifted significantly from their values and replace any that are out of tolerance. Also check whether either Q1516 or Q1518 are leaky. Finally, the voltage at the collector of Q1518 should not be exceeding +112v. If it is, then try replacing the 56v zenner, VR1515, which was the cause of a similar problem on mine.

The scope never really worked prior to this repair but as it seems birghter now, is the trace flashing in a centered position on power-off normal?

I checked on mine and it would seem that it is not unusual to sometimes get a brief flash of the fading trace on power off, although it does not seem to happen every time. Often the trace will just fade away and disappear without a flash.

[Malefoda]

Well, that's not too far out of spec so it will probably not be much of a problem for the present, but if you want to put your mind at rest then you could try checking checking resistors R1516, R1517, R1518, R1519 in case they have drifted significantly from their values and replace any that are out of tolerance. Also check whether either Q1516 or Q1518 are leaky. Finally, the voltage at the collector of Q1518 should not be exceeding +112v. If it is, then try replacing the 56v zenner, VR1515, which was the cause of a similar problem on mine.

Ok I keep that for the next time I'll need to open it or for long cold winter night's bore, right now I can go with it