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

[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.