Problems with my scope (Charlie) Tektronix 2225 vertical amplifier.

[The Guy]

Hi all,

I am trying to repair my scope Tektronix 2225 and I am a little lost.

 The problem it shows is that the trace from channel one is completely deflected up and can`t bring it down except with the beam find button. I`ve been measuring voltages (in red) and this is how it looks so far with a few voltages out of whack (see diagram attached). Can`t find the faulty component probably due to lack of expertise.

Appreciate any help.

Thanks.

[Armadillo]

Try taking out Q202 and Q203 and check both.

[The Guy]

Try taking out Q202 and Q203 and check both.

Hi,

I already did that, and replaced them just in case for a perfectly matched set of transistors. In fact the image I attached with the voltage readings is with the transistors already replaced. Weird.

[Armadillo]

Try taking out Q202 and Q203 and check both.

Hi,

I already did that, and replaced them just in case for a perfectly matched set of transistors. In fact the image I attached with the voltage readings is with the transistors already replaced. Weird.

Don't say the reading is still the same? If it is, then you will have to check for broken traces, from the emitter of the trainsistor Q203 to resistor R204.
Use a multimeter, check all the vicinity resistor values and traces.

Edit: Physically measure at the emitter voltage of each transistor Q203 and Q202 "at the emitters."

Q202 emitter to ground =       V
Q203 emitter to ground =       V

[Armadillo]

Let's re-focus;

Firstly let's use channel 1; Set the input to Ground, that means the input is shorted to Ground.

Adjust those center potentiometer so that the 2 voltages are about same.

Can you achieve it?

Edit: Also R145 Ch1 Gain potentiometer.
Edit: Set the Balance to Centre R107.

[The Guy]

Let's re-focus;

Firstly let's use channel 1; Set the input to Ground, that means the input is shorted to Ground.

Adjust those center potentiometer so that the 2 voltages are about same.

Can you achieve it?

Edit: Also R145 Ch1 Gain potentiometer.
Edit: Set the Balance to Centre R107.

ok will do that right away.... what should I do with that variable resistor that you circled in red (R123)?

Thank you!

[The Guy]

Let's re-focus;

Firstly let's use channel 1; Set the input to Ground, that means the input is shorted to Ground.

Adjust those center potentiometer so that the 2 voltages are about same.

Can you achieve it?

Edit: Also R145 Ch1 Gain potentiometer.
Edit: Set the Balance to Centre R107.

ok, grounded the input, centered R107, centered R123, maxed R145 and I got the 1.74V reading raised to 2.07V and 2.32V reading raised to 2.72V

I tried to fiddle around with the pots but couldn´t get them closer.

Also measured Q203 and Q202 emiters to ground and they read 2.04V

Checked continuity from both transistors to the nearer resistors all check ok.

checked the resistors in circuit and they read:

R204: 82.6 ohm
R202: 413
R203: 413
R207: 268.4
R206: 268.4
R218: 121.8
R219: 122.1
R216: 335.9
R217: 334.8
R142: 91.2
R143: 90


Thanks a bunch

[Armadillo]

Please always remember to tell me the output trace so that I can know what is happening.

Can you jumper a wire as shown in the attached and tell me that the trace return to about centre position.

If it does not, then we must be looking at the vertical output amplifier section [right side of schematic] or the tube.

If it does not, measure all the voltages at those transistors and let us know.

Take your time and be safe.

[The Guy]

Just wanted to note that right before Q104 and Q105 there already is an imbalance going on. Checked with my tester Q102 but it seems ok... measures just like Q103

[The Guy]

Please always remember to tell me the output trace so that I can know what is happening.

Can you jumper a wire as shown in the attached and tell me that the trace return to about centre position.

If it does not, then we must be looking at the vertical output amplifier section [right side of schematic] or the tube.

If it does not, measure all the voltages at those transistors and let us know.

Take your time and be safe.

Sorry. The trace didn´t come down as I performed all that. I jumpered those points as suggested and the trace did come down right to the center. I then jumpered right before  Q206 and Q207 at their bases and the trace also came down but a little above center (like 2 cm). Then jumpered right before  Q202 and Q203 also at their bases and nothing happened.

[Armadillo]

Jumper Base of 202 and base of 203

[The Guy]

Jumper Base of 202 and base of 203

Sorry I just edited my post above.... that´s what I did 

[Armadillo]

Ok tell me about the 2 Transistors you used and base, emitter and collector.... I just make sure we level ground.

Edit: Please jumper base of Q202 and Q203 and then measure the voltages;

Q202:
base
Collector
Emitter

Q203:
base
Collector
Emitter

[The Guy]

Sorry, what do you mean? I took the transistors from another Tek 222five that I have for parts (bad CRT). They didn´t center when jumpering at their bases before the swap... Though I´m not sure if I swapped both of them to be honest. I took 4 transistor in total from both scopes and I just choose the ones that did read the closest.

[The Guy]

Ok tell me about the 2 Transistors you used and base, emitter and collector.... I just make sure we level ground.

Edit: Please jumper base of Q202 and Q203 and then measure the voltages;

Q202:
base
Collector
Emitter

Q203:
base
Collector
Emitter

Alrighty... I´m on it

[Armadillo]

Previous voltage don't look right.

If Q207 is not conducting, then you should be reading one side as negative volt. [the 0.56V is not right].
Please confirm that there is -8.6V1 voltage.
Take out Q207 and check that the transistor is OK.
Then re-measure the blue circle voltage.

[The Guy]

Damn, the trace did came down two centimeters above center... but i took the measurements anyway. With their bases jumpered they read:

Q202

Base: 3.01V
Collector: 4.98
Emitter: 2.25

Q203

Base: 3.01V
Collector: 5.28
Emitter: 2.25

Will continue jumpering down stream till I find the culprit.

[Armadillo]

 

[The Guy]

Previous voltage don't look right.

If Q207 is not conducting, then you should be reading one side as negative volt. [the 0.56V is not right].
Please confirm that there is -8.6V1 voltage.
Take out Q207 and check that the transistor is OK.
Then re-measure the blue circle voltage.

Those -8.6 are from r215 and c215 junction and it reads ok... it´s there. At the base of Q207 there is 7.8V now

If you notice after DL224 there should be 0V along the lines... not sure if that explains those 0.56V

[The Guy]

Why are you laughing 

Alright Continued jumpering downstream. Jumpered at the base of Q104 and Q105 and the trace centered (almost)
then jumpered at the emitters from Q102 and Q103 and nothing happened.

[Armadillo]

Good progress I would say;

Then start measure voltages around that 102 and 103.

I was laughing because you must have kick started something that revert the voltages... 

Edit: Take out Q102 and Q103 to check. Since near the input, may have been over-voltage by former user.

[The Guy]

Good progress I would say;

Then start measure voltages around that 102 and 103.

I was laughing because you must have kick started something that revert the voltages... 

Edit: Take out Q102 and Q103 to check. Since near the input, may have been over-voltage by former user.

Alright... Lol.... i dunno what happened.... it just happened

K will take out those transistors but it will take some time, its fiddly.

[Armadillo]

Good progress I would say;

Then start measure voltages around that 102 and 103.

I was laughing because you must have kick started something that revert the voltages... 

Edit: Take out Q102 and Q103 to check. Since near the input, may have been over-voltage by former user.

Alright... Lol.... i dunno what happened.... it just happened

K will take out those transistors but it will take some time, its fiddly.

Make sure the X1 and X10 supply to Q102 and Q103, there are the 8.6 and -8.6 volts.... clean those contacts....

Take your time, no hurry. enjoy.

[The Guy]

Alrighty... took em out and they read (DMM negative probe to base with the selector switched to diodes):

Numero 1: 0.778v base to emitter; 0.769v base to collector.

Numero 2: 0.781v base to emitter; 0.773 base to collector.

changing the DMM negative probe to either the emitter or the collector all combinations read zero.

x1 (-8.58v).and x10 (8.68v) voltages are there.

[Armadillo]

changing the DMM negative probe to either the emitter or the collector all combinations read zero.

Are you saying they are shorted?