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

[The Guy]

I am going to drop a bomb right here... one of the other 222five that has both channels working reads exactly the same as all this last measurements!!! Now, THAT´S weird.

one thing I just found out is that with the beam finder pushed the vertical position control does not change the trace, but in channel 2 with the beam finder pressed it does vary the trace position. Channel 1 position pot does vary resistance tho.

[Armadillo]

I am going to drop a bomb right here... one of the other 222five that has both channels working reads exactly the same as all this last measurements!!! Now, THAT´S weird.

one thing I just found out is that with the beam finder pushed the vertical position control does not change the trace, but in channel 2 with the beam finder pressed it does vary the trace position. Channel 1 position pot does vary resistance tho.

Resolve C8, C31, R31. [Update your voltage measurements as you did before].  Let's not take your other unit into this comparison. After you repair this unit, then you can take this unit as reference to repair the others.   


 

[The Guy]

I am going to drop a bomb right here... one of the other 222five that has both channels working reads exactly the same as all this last measurements!!! Now, THAT´S weird.

one thing I just found out is that with the beam finder pushed the vertical position control does not change the trace, but in channel 2 with the beam finder pressed it does vary the trace position. Channel 1 position pot does vary resistance tho.

Resolve C8, C31, R31. [Update your voltage measurements as you did before].  Let's not take your other unit into this comparison. After you repair this unit, then you can take this unit as reference to repair the others.   


 

ok... replaced them parts and nothing happened. I went ahead and replaced the whole attenuator board with one from another scope and though the traces were completely out of the screen I could actually move channel 1 trace with the vertical position knob with the beam find button pressed. Then  put back the original board because I still want to repair it.

Voltages are the same.

[The Guy]

I think we need to concentrate on the fact that the vertical control doesn´t work at all with this attenuator board. I´m still stuck tho.

[Armadillo]

Readjust R33 so that the voltage at base of the U30 comes close to zero.
And please redo the voltage measurement as you did before, so that we can see the outcome.
Intention to follow the spec on the manual as close as  possible.

So with the capacitors out of the circuit, what is the measurement value of it?

[The Guy]

Readjust R33 so that the voltage at base of the U30 comes close to zero.
And please redo the voltage measurement as you did before, so that we can see the outcome.
Intention to follow the spec on the manual as close as  possible.

So with the capacitors out of the circuit, what is the measurement value of it?

Both measured 1nF and infinite resistance

[Armadillo]

Readjust R33 so that the voltage at base of the U30 comes close to zero.
And please redo the voltage measurement as you did before, so that we can see the outcome.
Intention to follow the spec on the manual as close as  possible.

So with the capacitors out of the circuit, what is the measurement value of it?

Both measured 1nF and infinite resistance

if you read earlier post, if it leak onto the pcb, you need to seriously solve the problem first. Otherwise, it will be a ghost hunt. Seriously speaking.

[The Guy]

Readjust R33 so that the voltage at base of the U30 comes close to zero.
And please redo the voltage measurement as you did before, so that we can see the outcome.
Intention to follow the spec on the manual as close as  possible.

So with the capacitors out of the circuit, what is the measurement value of it?

Both measured 1nF and infinite resistance

if you read earlier post, if it leak onto the pcb, you need to seriously solve the problem first. Otherwise, it will be a ghost hunt. Seriously speaking.

I replaced them... no leak. they´re ok.

Attached are the updated voltages.

I just discovered that if I short pin 7 with pin 13 of U30 the trace centers and I can actually move it with the vertical control like if it were perfectly normal... with the beam find button pushed!

[The Guy]

By infinite resistance i mean that the capacitors read open when measuring their resistance.

[Armadillo]

By infinite resistance i mean that the capacitors read open when measuring their resistance.

Did you try to adjust R33?

[Armadillo]

Please measure the voltages around the 2 FETs.
The voltage at the base of U30 is too high.

Edit: remember to ground Channel 1.

[The Guy]

By infinite resistance i mean that the capacitors read open when measuring their resistance.

Did you try to adjust R33?

Yes I zeroed it.

[Armadillo]

Yes I zeroed it.

But your measurement showed 1.4V?

[The Guy]

Please measure the voltages around the 2 FETs.
The voltage at the base of U30 is too high.

Edit: remember to ground Channel 1.

Which FETs? code please....

I just jumpered R13 to get it out of the circuit and the voltage at R14 rose a little... not sure if that means anything. What´s the base from Q13A?

[The Guy]

Yes I zeroed it.

But your measurement showed 1.4V?

Yeah... but thats for R29 instead of the -0.8v in that node

[The Guy]

at U30´s pin10 there is zero volt.

[Armadillo]

Yes I zeroed it.

But your measurement showed 1.4V?

Yeah... but thats for R29 instead of the -0.8v in that node

Question: if the emitter is 1.4V what should be the base voltage of the Transistor?  And you should not be getting 1.4V at the emitter when the transistor is OFF, right? because R22 is connected to minus -8.6V.

Can you probe the PCB for leakage conductive path as earlier post described. Ghost hunt.

[The Guy]

Question: if the emitter is 1.4V what should be the base voltage of the Transistor?

zero i guess

And you should not be getting 1.4V at the emitter when the transistor is OFF, right? because R22 is connected to minus -8.6V.

with channel 1 grounded all should be pretty balanced and within spec i think.

Can you probe the PCB for leakage conductive path as earlier post described. Ghost hunt.

Sorry I don´t know what you mean by that... which post? can you give me the reply number please?

Could you also explain to me how Q13 works please? Do pins 5 and 6 have continuity?

[Armadillo]

C8 measures 83nF in circuit and 101Kohm resistance so I guess it´s not shorted.

Take it out of the circuit and changed it. It became a Resistor.
It should be 1000uF.

Edit: if defective out of circuit, then also change C31, might as well. Visual any leak onto the board. This area is crucial, it at the mouth of the amplifier. Wash and Scrup, Scrup, Scrup it if sign of leak. Put meter to 2M ohm range and touch the pcb board at non conductive part of that area, it should be infinity ohm.

[Armadillo]

Question: if the emitter is 1.4V what should be the base voltage of the Transistor?

zero i guess

And you should not be getting 1.4V at the emitter when the transistor is OFF, right? because R22 is connected to minus -8.6V.

with channel 1 grounded all should be pretty balanced and within spec i think.

Can you probe the PCB for leakage conductive path as earlier post described. Ghost hunt.

Sorry I don´t know what you mean by that... which post? can you give me the reply number please?

Could you also explain to me how Q13 works please? Do pins 5 and 6 have continuity?

No, the base should not be zero volt. The Transistor is OFF, So I am suspecting U30.
Just measure the voltage of the 2 FET on the Pins 1,2,3 and 5,6, 7, otherwise swop a known good one and swop a known good U30 to expedite matter.

https://www.allaboutcircuits.com/textbook/semiconductors/chpt-5/meter-check-transistor-jfet/

[The Guy]

Question: if the emitter is 1.4V what should be the base voltage of the Transistor?

zero i guess

And you should not be getting 1.4V at the emitter when the transistor is OFF, right? because R22 is connected to minus -8.6V.

with channel 1 grounded all should be pretty balanced and within spec i think.

Can you probe the PCB for leakage conductive path as earlier post described. Ghost hunt.

Sorry I don´t know what you mean by that... which post? can you give me the reply number please?

Could you also explain to me how Q13 works please? Do pins 5 and 6 have continuity?

No, the base should not be zero volt. The Transistor is OFF, So I am suspecting U30.
Just measure the voltage of the 2 FET on the Pins 1,2,3 and 5,6, 7, otherwise swop a known good one and swop a known good U30 to expedite matter.

https://www.allaboutcircuits.com/textbook/semiconductors/chpt-5/meter-check-transistor-jfet/

But at pin2 U30 the voltage is 0V as per schematic.

I already replaced U30 for one from a working scope.

Alright.. Fet voltages:

pin1 : -8.38V
pin2 : 2.6V
pin3 : -8.58V

pin5 : 2.99V
pin6 : 7.9V
pin7 : 3.64V

[The Guy]

Damn man... You really have a patience made out of gold. Thanks a lot for sticking in! 

[Armadillo]

Question: if the emitter is 1.4V what should be the base voltage of the Transistor?

zero i guess

And you should not be getting 1.4V at the emitter when the transistor is OFF, right? because R22 is connected to minus -8.6V.

with channel 1 grounded all should be pretty balanced and within spec i think.

Can you probe the PCB for leakage conductive path as earlier post described. Ghost hunt.

Sorry I don´t know what you mean by that... which post? can you give me the reply number please?

Could you also explain to me how Q13 works please? Do pins 5 and 6 have continuity?

No, the base should not be zero volt. The Transistor is OFF, So I am suspecting U30.
Just measure the voltage of the 2 FET on the Pins 1,2,3 and 5,6, 7, otherwise swop a known good one and swop a known good U30 to expedite matter.

https://www.allaboutcircuits.com/textbook/semiconductors/chpt-5/meter-check-transistor-jfet/

But at pin2 U30 the voltage is 0V as per schematic.

I already replaced U30 for one from a working scope.

Alright.. Fet voltages:

pin1 : -8.38V
pin2 : 2.6V
pin3 : -8.58V

pin5 : 2.99V
pin6 : 7.9V
pin7 : 3.64V

Please confirm per attached.

[Armadillo]

Please confirm Q13A Pin 7 voltage, you measured 3.64V? Please double confirm.
Cannot be for n channel JFET.

Edit: Please take out your attenuator assembly, otherwise 77mA flow across R7.

[The Guy]

Please confirm Q13A Pin 7 voltage, you measured 3.64V? Please double confirm.
Cannot be for n channel JFET.

Edit: Please take out your attenuator assembly, otherwise 77mA flow across R7.

yep... pin 7 voltage reads 3.7V
Pin 2 also 2.6V

Sorry man... you got me there. How do I take out the attenuator assambly and where is it located? Cant find it.