Author Topic: Tektronix 2215 repair attempt and SM accuracy  (Read 268 times)

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Online giosif

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Tektronix 2215 repair attempt and SM accuracy
« on: April 11, 2021, 01:08:18 pm »
Hello,

I recently bought a Tektronix 2215 (non A) analog oscilloscope in a rather dirty and non-working condition.
First thing I did was to take it apart and check for any obvious issues and good thing that I did: the RIFA caps "feature" had struck once again and the X cap had blown its guts.
I replaced that, as well as other Y RIFAs present in the power supply.
I also replaced as many of the electrolytic caps that I could (still need to order a few more odd value ones).

In any case, I put the scope back together and the problem I'm seeing is that there is no horizontal sweep: with no signal, I get only a dot.
If I put in a signal, I can see a vertical line, which means vertical deflection works.
If I change the vertical or horizontal positions, the "trace" moves accordingly, so I think that's further confirmation that vertical deflection is fine, but also that horizontal deflection works (to some degree, at least).

So, next thing I did was to check for the horizontal sweep signal on A12 board (i.e. R631), but there was nothing there.
I then traced the signal using the Sweep generator & logic page from the SM all the way back to U603 on the A10 (main) board.

Now, the strange part is that, according to the SM, the signal at "hexagon" number 3 should be a 3 Vpp square wave while, at the same time, they say that signal is coming from Q492 in the Trigger section.
If I then check the schematics for Q492, it says the output of Q492 should be about 2.8V, which is what I'm seeing.
So, which one is correct?
Furthermore, the schematics for the Sweep generator shows pin 4 of U603 to be connected to the same signal from Q492 as pin 11 but, measuring on my scope, I see pin 4 is actually tied to GND (as well as pins 2 and 3), while pin 11 is indeed tied to Q492.
And not to mention the schematics for the Trigger section specify the output of Q492 would go to U630, which doesn't exist (most likely a "typo" for U603).

So, right now, I am not sure where to look and where I should see the horizontal sweep sawtooth signal being generated.
Any suggestions, please?

Thanks!
 

Offline highpower

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Re: Tektronix 2215 repair attempt and SM accuracy
« Reply #1 on: April 11, 2021, 06:29:08 pm »

Furthermore, the schematics for the Sweep generator shows pin 4 of U603 to be connected to the same signal from Q492 as pin 11 but, measuring on my scope, I see pin 4 is actually tied to GND (as well as pins 2 and 3), while pin 11 is indeed tied to Q492.
And not to mention the schematics for the Trigger section specify the output of Q492 would go to U630, which doesn't exist (most likely a "typo" for U603).


Yes. Noted in the Manual Change Information at the back of the service manual.
 

Online giosif

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Re: Tektronix 2215 repair attempt and SM accuracy
« Reply #2 on: April 11, 2021, 08:43:34 pm »
Ah. Didn't think of checking that.
Thank you!

Anyone who could confirm, please, if the signal coming out of Q492 should be a square wave signal?
 

Online giosif

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Re: Tektronix 2215 repair attempt and SM accuracy
« Reply #3 on: April 24, 2021, 09:01:17 pm »
Just an update on this: after going through different parts of the manual and checking some more, I think I found the source of the problem - Q630B JFET in the Miller sweep generator section of the A12 board is dead.
The challenge is this JFET and Q630A are a matched set, so I need to find a new pair.

If anyone happens to have one such matched set or an otherwise spare A12 with Q630A and Q630B in working state, I would be interested.

Thanks!
 

Offline jdragoset

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