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Old 24th Oct 2021, 6:02 pm   #21
frsimen
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Default Re: Tek 2215. Vertical Amplifier Issues.

I don't suppose that many people know, as they won't have tried running this type of 'scope without the tube. The main problem will be doing it safely with the EHT lurking. EHT will jump a long way, so I wouldn't be keen to work on it in this fashion. If the EHT lead comes in contact with anything, you'll have even more problems to deal with.

There is still a lot you can do without powering the scope up. You have proved that the lower half of the circuitry isn't working, while the upper half is. Why not try some in circuit resistance measurements on the transistors in the Y amp circuit, moving back from the output stage one stage at a time. Measure base to emitter both ways base to collector both ways and collector to emitter. Compare the measurements of transistors in the lower half of the circuit with their partners in the upper half of the circuit

If the components are good, the results should be similar between the upper half and the lower half of the circuit. If you find a significant difference, you have found an area with a fault. You can then investigate more closely.

One final thought. Is this 'scope a type with plug in transistors? If it is, just make sure that they are all plugged in properly.

Paula

Last edited by frsimen; 24th Oct 2021 at 6:05 pm. Reason: Added the words "in circuit"
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Old 24th Oct 2021, 7:14 pm   #22
M3VUV51
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Default Re: Tek 2215. Vertical Amplifier Issues.

No it's all soldered through hole on a double sided PCB, maybe I should hook the EHT to the CRT then test voltages?
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Old 24th Oct 2021, 8:18 pm   #23
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Default Re: Tek 2215. Vertical Amplifier Issues.

Is the vertical amp accessible with the CRT installed? Seems to me you should be able to track down the fault pretty quickly by comparing voltages on the two halves of the differential amplifier as Paula suggested.
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Old 25th Oct 2021, 6:29 am   #24
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Default Re: Tek 2215. Vertical Amplifier Issues.

You can test the vertical circuit with the CRT removed, but as mentioned you have very high voltage present. Isolate it and your fine.

Andy.
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Old 25th Oct 2021, 6:57 am   #25
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Default Re: Tek 2215. Vertical Amplifier Issues.

Well I hooked up the EHT to the CRT and moved the whole lot to one side, here's a few readings I took on Q387's base. I get 8.8V, it should be 2.6V! R290 wiper measures as follows, fully CW=3.44V, fully CCW 3.4V, R190 is fully CW 3.4V, fully CCW 3.4V. Don't know if this helps?
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Old 25th Oct 2021, 11:08 am   #26
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Default Re: Tek 2215. Vertical Amplifier Issues.

Quote:
Originally Posted by Diabolical Artificer View Post
Hard to read the voltages but it looks like you should have +4v on one plate and - 49v on the other.

Good luck, Andy.
Clean/readable schematic shows +9V and -9V.

David
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Old 25th Oct 2021, 11:12 am   #27
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Default Re: Tek 2215. Vertical Amplifier Issues.

Quote:
Originally Posted by M3VUV51 View Post
Well I hooked up the EHT to the CRT and moved the whole lot to one side, here's a few readings I took on Q387's base. I get 8.8V, it should be 2.6V !, R290 wiper measures as follows, fully CW=3.44V, fully CCW 3.4V, R190 is fully CW 3.4V ,fully CCW 3.4V. Don't know if this helps?
The 8.8V on Q387 base is probably the full -8.6V (2) DC supply voltage so possibly indicating that Q387 is not conducting/is turned off, so I would recommend checking the components around Q387.

David
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Old 25th Oct 2021, 11:21 am   #28
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Default Re: Tek 2215. Vertical Amplifier Issues.

Quote:
Originally Posted by M3VUV51 View Post
R290 wiper measures as follows, fully CW=3.44V, fully CCW 3.4V, R190 is fully CW 3.4V ,fully CCW 3.4V. Don't know if this helps?
Are you indicating that adjustment of the two vertical position controls are having no effect on their wiper voltages?

David
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Old 25th Oct 2021, 4:03 pm   #29
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Default Re: Tek 2215. Vertical Amplifier Issues.

Just use the position control as you did before to monitor for voltage change on Q376 and Q386
If Q376 base changes but Q386 does not then trace back through the circuit by looking for change on base of Q350, Q335, Q331.
If Q386 changes but Q376 does not then trace back on the other path Q360, Q345, Q341.
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Old 25th Oct 2021, 11:11 pm   #30
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Default Re: Tek 2215. Vertical Amplifier Issues.

Quote:
Originally Posted by DMcMahon View Post
Quote:
Originally Posted by M3VUV51 View Post
R290 wiper measures as follows, fully CW=3.44V, fully CCW 3.4V, R190 is fully CW 3.4V ,fully CCW 3.4V. Don't know if this helps?
Are you indicating that adjustment of the two vertical position controls are having no effect on their wiper voltages?

David
they do have an effect but change then seem to go up and down from 3.4v then back to 3.4v,hard to describe,if that makes sense?
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Old 26th Oct 2021, 6:16 am   #31
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Default Re: Tek 2215. Vertical Amplifier Issues.

Quote:
they do have an effect but change then seem to go up and down from 3.4v then back to 3.4v,hard to describe,if that makes sense?
It doesn't.
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Old 26th Oct 2021, 8:11 am   #32
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Default Re: Tek 2215. Vertical Amplifier Issues.

the voltages on the vert position pot wipers is as follows fully ccw=3.6v,halfway point =1.2v,fully cw =3.6v,hope that clears things up.
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Old 26th Oct 2021, 9:30 am   #33
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Default Re: Tek 2215. Vertical Amplifier Issues.

The position was working OK in post #11, I think we are descending a rat hole. R290 is Channel 2 position and the wiper is connected to -8.6V via a resistor so the results are quite reasonable.

Post #11 also established the fault is on one half of the vertical differential amplifier. You need to set the scope up as channel 1 only and use the channel 1 position control for tests and work back through the vertical amplifier as suggested in post #29.
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Old 26th Oct 2021, 9:32 am   #34
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Default Re: Tek 2215. Vertical Amplifier Issues.

the voltages on the vert position pot wipers is as follows fully ccw=3.6v,halfway point =1.2v,fully cw =3.6v,there are no bad conections.
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Old 26th Oct 2021, 9:36 am   #35
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Default Re: Tek 2215. Vertical Amplifier Issues.

ive ordered a hot air station and some mini grabber probes so should be able to test voltages on the transistors without shorting things using those,or remove them to sest out of circuit when they arrive,im sure its gonna be a transistor shorted.
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Old 26th Oct 2021, 8:39 pm   #36
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Default Re: Tek 2215. Vertical Amplifier Issues.

If you have a "shorted" transistor, you WILL find it with a DVM on low ohms or diode test. EASY, no need for soldering station yet, only when you locate the shorted transistor. Unless it is something else.
Some logic and manual study needed before you kill the whole thing completely.
PJL, we don't have that sort over here, we only have "long tails", but they do have holes.
Les
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Old 26th Oct 2021, 9:09 pm   #37
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Default Re: Tek 2215. Vertical Amplifier Issues.

It might be worth trying the beam locate to see what that does to the plate with 20V on it. If it has no effect then it is likely to be one or both of the output pair on that side.
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Old 27th Oct 2021, 7:17 am   #38
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Default Re: Tek 2215. Vertical Amplifier Issues.

From what I posted in post #16....

Quote:
I also see the V driver stage is connected to the beam finder button, so what happens if the beam finder button is pressed? It should center your trace in the center of the CRT. If it doesn't something else to investigate.
I sense the OP is floundering and out of his depth. I and others have offered detailed advice, which I suspect isn't being fully taken on board.

m3vuv51 You've checked some voltages, this indicates a fault around Q386/387. You now need to find out why they aren't working correctly. Forget random testing of transistors, you have to understand the circuit, or least have a rough idea how it works. Therefore if a voltage reading is wrong, why is it wrong? READ THE MANUAL, vert amp circuit description especially. Also thread's like these need reading, and re-reading, then take notes,then off to the bench to try suggestions and checks..

Andy.
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Old 27th Oct 2021, 11:10 am   #39
dave cox
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Default Re: Tek 2215. Vertical Amplifier Issues.

My guess is that Q387 is not the culprit.

The +9V on the base of Q387 is consistent with the 20V you found on the vertical plate, assuming that's the one connected to Q387's collector!

why ?

If you look at the marked voltages around Q387 you see -4.3V, +2.6V & +9V - the resistors R386 / R387 are causing that 1:1 split in voltage with Q387's base (should be +2.6V) sitting 1/2 way between -4.3V and +9V ,nearly (*). In the same way 9V is 1/2 way to 20V making me think its working just fine.

My next measurements would be on Q360 / Q350 bases ...

dc

PS
(*) Is that 'cascode like' circuit just spreading the miller capacitance between 2 devices to get a faster slew rate ?

Last edited by dave cox; 27th Oct 2021 at 11:15 am.
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Old 27th Oct 2021, 11:26 am   #40
M3VUV51
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Default Re: Tek 2215. Vertical Amplifier Issues.

well just an update,the deflection plate with the fixed voltage on it goes from 18v that doesent alter with the pos pot,but drops to 13v with the beam finder pressed.
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