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?   

[The Guy]

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

Are you saying they are shorted?   

I guess not... there is infinite resistance the other way around

[Armadillo]

Can you insert the transistors back, then measure the voltages around Q102, Q103, Q104 and Q105?

[The Guy]

Sorry had to go to the supermarket 

ok... installed them back and the voltages are:

Q102
Base: 4.37V
Emitter: 5.1V
Collector: -3.1V

Q103
Base: 4.37V
Emitter: 4.8V
Collector: -7.8

Q104
Base: -3.1V
Emitter: -3.78V
Collector: -0.3V

Q105
Base: -7.85V
Emitter: -8.56V
Collector: -0.3V

[The Guy]

Well, damn... I just discovered that the problem actually comes from the vertical attenuator preamp!!

It´s caos voltage-wise. Check schematic attached with recommended voltages and actual voltages in red.

If i jumper CH1+ with CH1- right after U30 the trace appears on the screen! I replaced U30 just in case and nothing changed.

I´m thinking maybe Q13 is screwed? Whatcha think?

[The Guy]

Sorry.... two voltages were swapped in the schematic above. Here they are corrected.

[tautech]

Don't go pondering why the voltages you measure and those on the schematic don't agree.....Schematic DC voltages are only valid when the scope is set in a specified mode. RTFM. 

Place it in XY mode and as the SM spec's and start at the V plates to check for balance and go from there...either backward or from the inputs. DMM is all you need to start with, use of another scope is later on if the DC voltages can't agree with the schematic in XY mode.

[The Guy]

Don't go pondering why the voltages you measure and those on the schematic don't agree.....Schematic DC voltages are only valid when the scope is set in a specified mode. RTFM. 

Place it in XY mode and as the SM spec's and start at the V plates to check for balance and go from there...either backward or from the inputs. DMM is all you need to start with, use of another scope is later on if the DC voltages can't agree with the schematic in XY mode.

Thanks, will do.

I measured another 222five and the voltages were very near the values per the schematics. Both scopes were set up the same.
What worries me is those 2.6V instead of zero right below R14. That´s very suspicious... I say something´s wrong right there.... How would you explain that voltage otherwise?

Thank you! 

[The Guy]

In XY mode the trace is completely deflected to the right side. It only appears on the screen if I push the beam find button.

[Armadillo]

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.

Well, damn... I just discovered that the problem actually comes from the vertical attenuator preamp!!

It´s caos voltage-wise. Check schematic attached with recommended voltages and actual voltages in red.

If i jumper CH1+ with CH1- right after U30 the trace appears on the screen! I replaced U30 just in case and nothing changed.

I´m thinking maybe Q13 is screwed? Whatcha think?

So what happened that you did for Q102 and Q103? Need to uncover something, otherwise might just miss something important. Can we say dirty contacts? or measurement error?

[Armadillo]

Sorry.... two voltages were swapped in the schematic above. Here they are corrected.

C8 looks suspicious. Then adjust R33 to try bring the Pin 7 and Pin 13 equal.

[Armadillo]

In XY mode the trace is completely deflected to the right side. It only appears on the screen if I push the beam find button.

If you like it on the right side to solve the vertical problem.

[The Guy]

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.

Well, damn... I just discovered that the problem actually comes from the vertical attenuator preamp!!

It´s caos voltage-wise. Check schematic attached with recommended voltages and actual voltages in red.

If i jumper CH1+ with CH1- right after U30 the trace appears on the screen! I replaced U30 just in case and nothing changed.

I´m thinking maybe Q13 is screwed? Whatcha think?

So what happened that you did for Q102 and Q103? Need to uncover something, otherwise might just miss something important. Can we say dirty contacts? or measurement error?

...this is so weird... if I place a jumper before R100 and R101 the trace appears BUT if I jumper AFTER R100 and R101 (between R100-R101 and Q102-Q103) nothing happens.

[Armadillo]

...this is so weird... if I place a jumper before R100 and R101 the trace appears BUT if I jumper AFTER R100 and R101 (between R100-R101 and Q102-Q103) nothing happens.

Let just move forward to C8 and R33 as suggested above.     

[The Guy]

...this is so weird... if I place a jumper before R100 and R101 the trace appears BUT if I jumper AFTER R100 and R101 (between R100-R101 and Q102-Q103) nothing happens.

Let just move forward to C8 and R33 as suggested above.     

Nope... R33 doesn´t change a thing. Hmmmm.... this doesn´t smell good.

[Armadillo]

...this is so weird... if I place a jumper before R100 and R101 the trace appears BUT if I jumper AFTER R100 and R101 (between R100-R101 and Q102-Q103) nothing happens.

Let just move forward to C8 and R33 as suggested above.     

Nope... R33 doesn´t change a thing. Hmmmm.... this doesn´t smell good.

Is the C8 OK ? When you adjust R33, did the wiper voltage changed? Are you able to adjust it to 0 volt?

Edit: Check R22, R23, R29. With R22 powered to minus, you can adjust to negative voltage if you want.

[The Guy]

With R33 maxed i get 8,7V before R32. 4.38V after R22 and 0.091V after R30!!! Is R30 Broken?

[Armadillo]

With R33 maxed i get 8,7V before R32. 4.38V after R22 and 0.091V after R30!!! Is R30 Broken?

Lucky if the resistor is broken.    otherwise U30 internal shorted but not common.
Let us know the good news.   

Edit: Check C31!
Edit: otherwise change CA3102E.

[The Guy]

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

[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.

[The Guy]

With R33 maxed i get 8,7V before R32. 4.38V after R22 and 0.091V after R30!!! Is R30 Broken?

Lucky if the resistor is broken.    otherwise U30 internal shorted but not common.
Let us know the good news.   

Edit: Check C31!

Holy sh*t!!! C31/R31 junction to chassis measures 0ohm!! but to its lead that is supposed to be connected to ground it measures 98ohms

[Armadillo]

With R33 maxed i get 8,7V before R32. 4.38V after R22 and 0.091V after R30!!! Is R30 Broken?

Lucky if the resistor is broken.    otherwise U30 internal shorted but not common.
Let us know the good news.   

Edit: Check C31!

Holy sh*t!!! C31/R31 junction to chassis measures 0ohm!! but to its lead that is supposed to be connected to ground it measures 98ohms

Resolve C8, C31, R31.

[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.

[The Guy]

Will do... but tomorrow. It is super late here...   

What about those 2.6V right below R14? How do you explain that?

[Armadillo]

Will do... but tomorrow. It is super late here...   

What about those 2.6V right below R14? How do you explain that?

Because C8 became a Resistor.

Edit: I was watching the Dawn of the Dead just now, so I should say..... C8 became a Zombie.... LOL .

[tautech]

Will do... but tomorrow. It is super late here...   

What about those 2.6V right below R14? How do you explain that?

Because C8 became a Resistor.

That'll stuff that whole area up.
Better change the one on the other channel too.

[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.

[The Guy]

ohhh got it....  the volts/div mechanism.... How do i take it out?

[Armadillo]

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.

[Armadillo]

Please don't mix match.. otherwise troubleshooting become exponentially bizarre !   hahaha ha LOL 

[The Guy]

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.

Yeah... but what i did there is actually to replace the whole board... the whole circuit board. the whole thing but only for a brief moment to see what happened.

[Armadillo]

The voltage at the JFET is not right.

For capacitors from 1000uf to 1nf and no leak? You mean the oil evaporated away? unlikely LOL.
So either leak onto PCB, Ghost hunt or attenuator problem.

[The Guy]

The voltage at the JFET is not right.

For capacitors from 1000uf to 1nf and no leak? You mean the oil evaporated away? unlikely LOL.
So either leak onto PCB, Ghost hunt or attenuator problem.

If  I put ch1 in DC mode and measure dc voltage at the probe input I get 2.4VDC not so in ch2 But that´s probably coming from pin7 in Q13...

[The Guy]

I doubt its the caps because I changed them for the ones from a working unit....

[Armadillo]

The voltage at the JFET is not right.

For capacitors from 1000uf to 1nf and no leak? You mean the oil evaporated away? unlikely LOL.
So either leak onto PCB, Ghost hunt or attenuator problem.

If  I put ch1 in DC mode and measure dc voltage at the probe input I get 2.4VDC not so in ch2 But that´s probably coming from pin7 in Q13...

Could be possible, then change new nfet for Q13A.   

[Armadillo]

I doubt its the caps because I changed them for the ones from a working unit....

At least you should have measured the capacitance and ESR before plugging it in?

[The Guy]

I doubt its the caps because I changed them for the ones from a working unit....

At least you should have measured the capacitance and ESR before plugging it in?

I dont know how to measure ESR... I just started a year ago building guitar amplifiers, and when I started I didn´t knew the difference of positive voltage and negative (not kidding), so this is rocket science to me Lol

[The Guy]

Screw it, I´m gonna change that Q13 and see what happens.

[tautech]

I doubt its the caps because I changed them for the ones from a working unit....

At least you should have measured the capacitance and ESR before plugging it in?

I dont know how to measure ESR... I just started a year ago building guitar amplifiers, and when I started I didn´t knew the difference of positive voltage and negative (not kidding), so this is rocket science to me Lol

Measure, check, verify or you'll end up just chasing your tail.
Methodical processes need be employed....

[Armadillo]

I doubt its the caps because I changed them for the ones from a working unit....

At least you should have measured the capacitance and ESR before plugging it in?

I dont know how to measure ESR... I just started a year ago building guitar amplifiers, and when I started I didn´t knew the difference of positive voltage and negative (not kidding), so this is rocket science to me Lol

You got good soldering and desoldering skills I would say..... I think you are pretty good at electronics .. at the very least you have the courage to hands-on...

[The Guy]

I doubt its the caps because I changed them for the ones from a working unit....

At least you should have measured the capacitance and ESR before plugging it in?

I dont know how to measure ESR... I just started a year ago building guitar amplifiers, and when I started I didn´t knew the difference of positive voltage and negative (not kidding), so this is rocket science to me Lol

You got good soldering and desoldering skills I would say..... I think you are pretty good at electronics .. at the very least you have the courage to hands-on...

I`m a high end jeweller by day and amp builder by night... I know how to work with tiny stuff 

Damn... how do I desolder the fet.... that`s a hard one

[The Guy]

Yep.... it is the fet. Took it out, tested it and there is conductance between pin 7 and pin six... it should read open.

[The Guy]

IT Wooooooooooooooooooooooooooooorksssssssssssssssss!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 

Yeeeehaaaaw!

[The Guy]

Thanks Armadillo! You`ve been most helpful 

I hope to have the opportunity to give you a hand as well someday.

Now I need to calibrate this thing because it`s a mess. Volts x10 in channel 1 is completely out of whack.

Hopefully there won`t be no more surprises.

 

[Armadillo]

Congratulation!................................................................................................
You did it..

 

[The Guy]

Congratulation!................................................................................................
You did it..

 

Yeah man... we did it!! I already calibrated it (well, almost. Need a time mark generator) and it works like a charm.

https://youtu.be/vE4YOKN6nac

[tautech]

Mr Dean and Ben next.

[The Guy]

Mr Dean and Ben next.

Yessir! Tomorrow I start bringing Mr. Dean back to life! ...screwed up power supply I guess.

 

[Armadillo]

Looks like new. Great Job!