Topics

Tektronix 454


erik erickson
 

Hey everyone my tektronix 454 channel two doesn't work. It worked for about 20 seconds when I reseated all the transistors and then slowly went off the screen. Sometimes it works but will always stop working within 20 seconds. The position knob would not bring it back. I'm new to this so all help will be greatly appreciated. I have the manual and I've been reading it.
Sent from my iPhone


 

Which transistors did you reseat?

Does the trace drift off screen when the input coupling is set to
ground?

Does the input response normally while it is on screen?

On Wed, 19 Jul 2017 22:06:56 -0700, you wrote:


Hey everyone my tektronix 454 channel two doesn't work. It worked for about 20 seconds when I reseated all the transistors and then slowly went off the screen. Sometimes it works but will always stop working within 20 seconds. The position knob would not bring it back. I'm new to this so all help will be greatly appreciated. I have the manual and I've been reading it.
Sent from my iPhone


erik erickson
 

Hey I'm very sorry for taking so long to respond. I've been very busy at work and in going out of town soon. I reseated the transistors on the channel 2 vertical preamp. The trace most of the time isn't on the screen so I can't be sure. I haven't seen a trace on channel two in a while. Channel one seems to work fine. Only problem is the red knob on the volts/division doesn't work.

Sent from my iPhone

On Jul 21, 2017, at 8:03 PM, David davidwhess@gmail.com [TekScopes] <TekScopes@yahoogroups.com> wrote:

Which transistors did you reseat?

Does the trace drift off screen when the input coupling is set to
ground?

Does the input response normally while it is on screen?

On Wed, 19 Jul 2017 22:06:56 -0700, you wrote:


Hey everyone my tektronix 454 channel two doesn't work. It worked for about 20 seconds when I reseated all the transistors and then slowly went off the screen. Sometimes it works but will always stop working within 20 seconds. The position knob would not bring it back. I'm new to this so all help will be greatly appreciated. I have the manual and I've been reading it.
Sent from my iPhone

[Non-text portions of this message have been removed]


Bob Groh <bob.groh@...>
 

Your problem sounds a lot like a bad capacitor - afraid I can't be more
specific that that. This hypothetical cap is building up a charge due to
leakage current and that is slowly shifting a bias someplace in the signal
chain.

Bob Groh
Blue Springs, Missouri


erik erickson
 

Thank you I will look at it tomorrow night.

Sent from my iPhone

On Aug 1, 2017, at 8:55 PM, Bob Groh bob.groh@gmail.com [TekScopes] <TekScopes@yahoogroups.com> wrote:

Your problem sounds a lot like a bad capacitor - afraid I can't be more
specific that that. This hypothetical cap is building up a charge due to
leakage current and that is slowly shifting a bias someplace in the signal
chain.

Bob Groh
Blue Springs, Missouri




[Non-text portions of this message have been removed]


 

I encourage you not to give up on your 454. It has a fabulously
bright and sharp CRT.

I have to ask some of the same questions:

1. Does the trace drift off screen when the input coupling is set to
ground?

2. Does the trace drift off screen when the input coupling is set to
DC and the input is shorted?

One thing that can cause the trace to drift off of the screen is if
the DC circuit path to the grid of V113 shown on schematic 2 is open.
This could include an open R110.

The variable control is R167 and could not cause the trace to drift
off of the CRT by itself.

What does the channel 2 INVERT switch do? It would cause problems if
the switch was bad.

Since only channel 2 is affected, the problem is on either schematic 2
or schematic 3 before the delay line driver.

On Tue, 1 Aug 2017 11:24:52 -0700, you wrote:

Hey I'm very sorry for taking so long to respond. I've been very busy at work and in going out of town soon. I reseated the transistors on the channel 2 vertical preamp. The trace most of the time isn't on the screen so I can't be sure. I haven't seen a trace on channel two in a while. Channel one seems to work fine. Only problem is the red knob on the volts/division doesn't work.

Sent from my iPhone

On Jul 21, 2017, at 8:03 PM, David davidwhess@gmail.com [TekScopes] <TekScopes@yahoogroups.com> wrote:

Which transistors did you reseat?

Does the trace drift off screen when the input coupling is set to
ground?

Does the input response normally while it is on screen?

On Wed, 19 Jul 2017 22:06:56 -0700, you wrote:


Hey everyone my tektronix 454 channel two doesn't work. It worked for about 20 seconds when I reseated all the transistors and then slowly went off the screen. Sometimes it works but will always stop working within 20 seconds. The position knob would not bring it back. I'm new to this so all help will be greatly appreciated. I have the manual and I've been reading it.
Sent from my iPhone


erik erickson
 

The trace doesn't appear at all on channel 2. I got it to come up a few times but not lately and I don't remember what i did. And a couple times I had the cover of it and it worked for a good 10 minutes but quits again.

Sent from my iPhone

On Aug 4, 2017, at 6:18 AM, David davidwhess@gmail.com [TekScopes] <TekScopes@yahoogroups.com> wrote:

I encourage you not to give up on your 454. It has a fabulously
bright and sharp CRT.

I have to ask some of the same questions:

1. Does the trace drift off screen when the input coupling is set to
ground?

2. Does the trace drift off screen when the input coupling is set to
DC and the input is shorted?

One thing that can cause the trace to drift off of the screen is if
the DC circuit path to the grid of V113 shown on schematic 2 is open.
This could include an open R110.

The variable control is R167 and could not cause the trace to drift
off of the CRT by itself.

What does the channel 2 INVERT switch do? It would cause problems if
the switch was bad.

Since only channel 2 is affected, the problem is on either schematic 2
or schematic 3 before the delay line driver.

On Tue, 1 Aug 2017 11:24:52 -0700, you wrote:

Hey I'm very sorry for taking so long to respond. I've been very busy at work and in going out of town soon. I reseated the transistors on the channel 2 vertical preamp. The trace most of the time isn't on the screen so I can't be sure. I haven't seen a trace on channel two in a while. Channel one seems to work fine. Only problem is the red knob on the volts/division doesn't work.

Sent from my iPhone

On Jul 21, 2017, at 8:03 PM, David davidwhess@gmail.com [TekScopes] <TekScopes@yahoogroups.com> wrote:

Which transistors did you reseat?

Does the trace drift off screen when the input coupling is set to
ground?

Does the input response normally while it is on screen?

On Wed, 19 Jul 2017 22:06:56 -0700, you wrote:


Hey everyone my tektronix 454 channel two doesn't work. It worked for about 20 seconds when I reseated all the transistors and then slowly went off the screen. Sometimes it works but will always stop working within 20 seconds. The position knob would not bring it back. I'm new to this so all help will be greatly appreciated. I have the manual and I've been reading it.
Sent from my iPhone

[Non-text portions of this message have been removed]


erik erickson
 

I just checked the invert switch and when I pull it the trace flashes on the screen and then disappears instantly.

Sent from my iPhone

On Aug 4, 2017, at 6:18 AM, David davidwhess@gmail.com [TekScopes] <TekScopes@yahoogroups.com> wrote:

I encourage you not to give up on your 454. It has a fabulously
bright and sharp CRT.

I have to ask some of the same questions:

1. Does the trace drift off screen when the input coupling is set to
ground?

2. Does the trace drift off screen when the input coupling is set to
DC and the input is shorted?

One thing that can cause the trace to drift off of the screen is if
the DC circuit path to the grid of V113 shown on schematic 2 is open.
This could include an open R110.

The variable control is R167 and could not cause the trace to drift
off of the CRT by itself.

What does the channel 2 INVERT switch do? It would cause problems if
the switch was bad.

Since only channel 2 is affected, the problem is on either schematic 2
or schematic 3 before the delay line driver.

On Tue, 1 Aug 2017 11:24:52 -0700, you wrote:

Hey I'm very sorry for taking so long to respond. I've been very busy at work and in going out of town soon. I reseated the transistors on the channel 2 vertical preamp. The trace most of the time isn't on the screen so I can't be sure. I haven't seen a trace on channel two in a while. Channel one seems to work fine. Only problem is the red knob on the volts/division doesn't work.

Sent from my iPhone

On Jul 21, 2017, at 8:03 PM, David davidwhess@gmail.com [TekScopes] <TekScopes@yahoogroups.com> wrote:

Which transistors did you reseat?

Does the trace drift off screen when the input coupling is set to
ground?

Does the input response normally while it is on screen?

On Wed, 19 Jul 2017 22:06:56 -0700, you wrote:


Hey everyone my tektronix 454 channel two doesn't work. It worked for about 20 seconds when I reseated all the transistors and then slowly went off the screen. Sometimes it works but will always stop working within 20 seconds. The position knob would not bring it back. I'm new to this so all help will be greatly appreciated. I have the manual and I've been reading it.
Sent from my iPhone


erik erickson
 

Also just found out trace appears if I leave invert switch halfway out but no functions work when the trace appears.

Sent from my iPhone

On Aug 4, 2017, at 6:18 AM, David davidwhess@gmail.com [TekScopes] <TekScopes@yahoogroups.com> wrote:

I encourage you not to give up on your 454. It has a fabulously
bright and sharp CRT.

I have to ask some of the same questions:

1. Does the trace drift off screen when the input coupling is set to
ground?

2. Does the trace drift off screen when the input coupling is set to
DC and the input is shorted?

One thing that can cause the trace to drift off of the screen is if
the DC circuit path to the grid of V113 shown on schematic 2 is open.
This could include an open R110.

The variable control is R167 and could not cause the trace to drift
off of the CRT by itself.

What does the channel 2 INVERT switch do? It would cause problems if
the switch was bad.

Since only channel 2 is affected, the problem is on either schematic 2
or schematic 3 before the delay line driver.

On Tue, 1 Aug 2017 11:24:52 -0700, you wrote:

Hey I'm very sorry for taking so long to respond. I've been very busy at work and in going out of town soon. I reseated the transistors on the channel 2 vertical preamp. The trace most of the time isn't on the screen so I can't be sure. I haven't seen a trace on channel two in a while. Channel one seems to work fine. Only problem is the red knob on the volts/division doesn't work.

Sent from my iPhone

On Jul 21, 2017, at 8:03 PM, David davidwhess@gmail.com [TekScopes] <TekScopes@yahoogroups.com> wrote:

Which transistors did you reseat?

Does the trace drift off screen when the input coupling is set to
ground?

Does the input response normally while it is on screen?

On Wed, 19 Jul 2017 22:06:56 -0700, you wrote:


Hey everyone my tektronix 454 channel two doesn't work. It worked for about 20 seconds when I reseated all the transistors and then slowly went off the screen. Sometimes it works but will always stop working within 20 seconds. The position knob would not bring it back. I'm new to this so all help will be greatly appreciated. I have the manual and I've been reading it.
Sent from my iPhone


Roger Evans
 

Probably with the switch half way out each pole of the switch is open circuit. Do you have any way of checking Q164 and Q174? You can do basic open circuit and short circuit checks with just a multimeter.

Roger


 

On Fri, 4 Aug 2017 18:34:48 -0700, you wrote:

I just checked the invert switch and when I pull it the trace flashes on the screen and then disappears instantly.
On Fri, 4 Aug 2017 18:36:33 -0700, you wrote:

Also just found out trace appears if I leave invert switch halfway out but no functions work when the trace appears.
That probably means that the problem is to the left of the invert
switch. When it disconnects the emitters of Q184 and Q194, then the
differential signal is basically zeroed going to the CRT.

What I would do is measure the various emitter and collector voltages
going back toward the input as shown on the schematic. The emitter of
Q134, Q164, and Q174 are especially important. This should show the
point at which there is a problem.


 

One easy approach to isolate the bad section of the amp is to short like parts on opposite sides of the vertical amp.Take a jumper wire & short the transistor cans to each other.If the trace centers up, then move the short one stage closer to the input & repeat the shorting process.When you get to the stage where the short does not return the beam to the vertical center, that is where the problem is.Those transistors are probably socketed . . . . swap them & see if the problem moves in the opposite direction (Watch the beam finder lamps).Return them to their original sockets so you can minimize the recalibration.
You can also use the invert switch; if the trace moves to the opposite direction, then the problem is prior to the switch.
 HankC, Boston WA1HOS