Topics

465 with V scale issue

Nick Scalfaro
 

My Oscope issue starts like a lot of other stories. I bought a 465 off
Ebay.

It needs new feet that I'll probably make, and the V scale reads about 22%
of what it should. Vpp for the 300 mv calibrator is 65 mv (21.6%). Vdc
for a 10V input is 2.2 V. Both channels. Take the exact number with a
grain of salt. As everyone including me (now) knows, the gain can't correct
that much. But I tried. I've learned a lot in the past week. The Oscope
works reasonably well except for the aforementioned issue and a ground
short on the channel 2 input that makes it think it always has a 10x Tek
probe installed. Since that doesn't affect anything other than which light
bulb is lit, I'm pretty pleased with my buy thus far. The Oscope didn't
come with probes. I bought some cheap ones off Amazon, but verified it
isn't the probes with a P3010 I borrowed from work.

Would I be correct in thinking I have an issue with a reference voltage
coming out of the PSU?

Nick

 

Grab a service manual (recommend artekmedia.com) and start reading.

You should first open it up and check all the low voltage power supply levels and ripple.

The capacitors (electrolytics) are all many decades old so that would be the first thing to rule out.

Where about do you live in MD? I am in Forest Hill if you are near there.

Regards,
Tom

----- Original Message -----
From: Nicholas Scalfaro nwscalfaro@... [TekScopes]
To: TekScopes@...
Sent: Tuesday, May 23, 2017 10:28 PM
Subject: [TekScopes] 465 with V scale issue



My Oscope issue starts like a lot of other stories. I bought a 465 off
Ebay.

It needs new feet that I'll probably make, and the V scale reads about 22%
of what it should. Vpp for the 300 mv calibrator is 65 mv (21.6%). Vdc
for a 10V input is 2.2 V. Both channels. Take the exact number with a
grain of salt. As everyone including me (now) knows, the gain can't correct
that much. But I tried. I've learned a lot in the past week. The Oscope
works reasonably well except for the aforementioned issue and a ground
short on the channel 2 input that makes it think it always has a 10x Tek
probe installed. Since that doesn't affect anything other than which light
bulb is lit, I'm pretty pleased with my buy thus far. The Oscope didn't
come with probes. I bought some cheap ones off Amazon, but verified it
isn't the probes with a P3010 I borrowed from work.

Would I be correct in thinking I have an issue with a reference voltage
coming out of the PSU?

Nick

Nick Scalfaro
 

Tom,
I'm way south of you down around La Plata. Can an Oscope be used to check
the ripple on itself? I've got this Oscope and a pretty good Fluke DMM.

Nick

On May 23, 2017 10:54 PM, "'Tom Miller' tmiller11147@...
[TekScopes]" <TekScopes@...> wrote:



Grab a service manual (recommend artekmedia.com) and start reading.

You should first open it up and check all the low voltage power supply
levels and ripple.

The capacitors (electrolytics) are all many decades old so that would be
the first thing to rule out.

Where about do you live in MD? I am in Forest Hill if you are near there.

Regards,
Tom


----- Original Message -----
From: Nicholas Scalfaro nwscalfaro@... [TekScopes]
To: TekScopes@...
Sent: Tuesday, May 23, 2017 10:28 PM
Subject: [TekScopes] 465 with V scale issue

My Oscope issue starts like a lot of other stories. I bought a 465 off
Ebay.

It needs new feet that I'll probably make, and the V scale reads about 22%
of what it should. Vpp for the 300 mv calibrator is 65 mv (21.6%). Vdc
for a 10V input is 2.2 V. Both channels. Take the exact number with a
grain of salt. As everyone including me (now) knows, the gain can't correct
that much. But I tried. I've learned a lot in the past week. The Oscope
works reasonably well except for the aforementioned issue and a ground
short on the channel 2 input that makes it think it always has a 10x Tek
probe installed. Since that doesn't affect anything other than which light
bulb is lit, I'm pretty pleased with my buy thus far. The Oscope didn't
come with probes. I bought some cheap ones off Amazon, but verified it
isn't the probes with a P3010 I borrowed from work.

Would I be correct in thinking I have an issue with a reference voltage
coming out of the PSU?

Nick

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

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




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

Tom Gardner
 

On 24/05/17 04:04, Nicholas Scalfaro nwscalfaro@... [TekScopes] wrote:

I'm way south of you down around La Plata. Can an Oscope be used to check
the ripple on itself? I've got this Oscope and a pretty good Fluke DMM.
Sometimes a scope can be used to diagnose itself.

In this case simple DMM measurements would be
sufficient, obviously set to AC ranges when measuring
ripple.

Just watch the maximum DMM voltage, which probably
rules out directly measuring the -2.5kV cathode voltage.
However, since you have a decent trace, there's no
indication that is a problem.

Albert Otten
 

Hi Nick,

I refer to the B250000-up manual here.
When power supply voltages are fine (checked as suggested by others) you might proceed with following the amplification from stage to stage. First decide whether the fault is in the Vertical Switching <3> or in the Vertical Output Amplifier <4> or in the Delay Line between these two. You can use the 300 mV pp calibrator signal as input to CH1 (or CH2), CH1 set for 5 mV/div. Then at <3> TP322 and TP324 check that the voltage swing is 150 mV pp (waveforms 25 and 26). Then at the bases of <4> Q4402 and Q4412 check that the voltage swing is 75 mV pp (waveforms 27 and 28).
When all measured with the DMM (DC blocked), the ratio of these 3 voltages should be 1 : 1/2 : 1/4. A fault of a factor 22% will be seen immediately. If your DMM frequency response doesn't go to 1 kHz, then apply a 50 or 60 Hz signal of about 300 mV pp to the input of CH1 in stead of the calibrator signal.

Albert

 

It is a good idea to start by checking the low voltage power supply
outputs for level and ripple which can be done with just a voltmeter
but I suspect the problem is in the vertical amplifier chain after the
vertical channel switch.

Albert posted a great detailed suggestion for how to proceed.

Do the vertical position controls move the traces over the full
vertical range of the CRT?

When the calibrator waveform is displayed, does changing the vertical
position cause the displayed trace to compress toward the top and
bottom of the screen?

What serial number is your 465 and is the vertical CRT amplifier board
discrete or integrated?

My guess is that you will find an open resistor between the emitters
of one of the transconductance stages which should be easy to repair.
Albert's directions should lead you right to it.

On Tue, 23 May 2017 22:28:26 -0400, you wrote:

My Oscope issue starts like a lot of other stories. I bought a 465 off
Ebay.

It needs new feet that I'll probably make, and the V scale reads about 22%
of what it should. Vpp for the 300 mv calibrator is 65 mv (21.6%). Vdc
for a 10V input is 2.2 V. Both channels. Take the exact number with a
grain of salt. As everyone including me (now) knows, the gain can't correct
that much. But I tried. I've learned a lot in the past week. The Oscope
works reasonably well except for the aforementioned issue and a ground
short on the channel 2 input that makes it think it always has a 10x Tek
probe installed. Since that doesn't affect anything other than which light
bulb is lit, I'm pretty pleased with my buy thus far. The Oscope didn't
come with probes. I bought some cheap ones off Amazon, but verified it
isn't the probes with a P3010 I borrowed from work.

Would I be correct in thinking I have an issue with a reference voltage
coming out of the PSU?

Nick

Nick Scalfaro
 

Dave,

The Oscope loses the trigger on the 300 mv calibrator signal when the
entire trace is in the bottom third of the CRT. It can show an AC signal
across the full display. The waveforms do not distort vertically.

Serial number has been lost to history unless it's inside somewhere as
well. The 2 white boxes on the rear panel that presumably are supposed to
have the model and SN info are completely blank.

Dunno if it's integrated or discrete yet. Three kids and work have kept me
from opening it up to do any diagnostic work.

On May 24, 2017 2:21 PM, "David @DWH [TekScopes]" <
TekScopes@...> wrote:



It is a good idea to start by checking the low voltage power supply
outputs for level and ripple which can be done with just a voltmeter
but I suspect the problem is in the vertical amplifier chain after the
vertical channel switch.

Albert posted a great detailed suggestion for how to proceed.

Do the vertical position controls move the traces over the full
vertical range of the CRT?

When the calibrator waveform is displayed, does changing the vertical
position cause the displayed trace to compress toward the top and
bottom of the screen?

What serial number is your 465 and is the vertical CRT amplifier board
discrete or integrated?

My guess is that you will find an open resistor between the emitters
of one of the transconductance stages which should be easy to repair.
Albert's directions should lead you right to it.

On Tue, 23 May 2017 22:28:26 -0400, you wrote:

My Oscope issue starts like a lot of other stories. I bought a 465 off
Ebay.

It needs new feet that I'll probably make, and the V scale reads about 22%
of what it should. Vpp for the 300 mv calibrator is 65 mv (21.6%). Vdc
for a 10V input is 2.2 V. Both channels. Take the exact number with a
grain of salt. As everyone including me (now) knows, the gain can't
correct
that much. But I tried. I've learned a lot in the past week. The Oscope
works reasonably well except for the aforementioned issue and a ground
short on the channel 2 input that makes it think it always has a 10x Tek
probe installed. Since that doesn't affect anything other than which light
bulb is lit, I'm pretty pleased with my buy thus far. The Oscope didn't
come with probes. I bought some cheap ones off Amazon, but verified it
isn't the probes with a P3010 I borrowed from work.

Would I be correct in thinking I have an issue with a reference voltage
coming out of the PSU?

Nick

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

Albert Otten
 

Nick, the S/N should be at the front panel, below the two bottom/rightmost BNC connectors. Do a picture search in Google for "Tektronix 465" and you will see lots of examples.
Albert


---In TekScopes@..., <nwscalfaro@...> wrote :


Serial number has been lost to history unless it's inside somewhere as
well. The 2 white boxes on the rear panel that presumably are supposed to
have the model and SN info are completely blank.

Fabio Trevisan
 

Hello Nick
If the serial number is missing on the front panel, there's a chance that
the same is marked (with sharpie pen) on the back of the aluminum chassis,
behind the back plastic panel (that covers the FAN and supports the rear
BNC plugs).
On mine (a 464, not exactly same model as yours), I found recently the
serial number hand-written there, in big numbers (you can't miss it,
although part of it may be covered by the fan rotor itself).
Rgrds,
Fabio

2017-05-25 0:25 GMT-03:00 Nicholas Scalfaro nwscalfaro@...
[TekScopes] <TekScopes@...>:



Dave,

The Oscope loses the trigger on the 300 mv calibrator signal when the
entire trace is in the bottom third of the CRT. It can show an AC signal
across the full display. The waveforms do not distort vertically.

Serial number has been lost to history unless it's inside somewhere as
well. The 2 white boxes on the rear panel that presumably are supposed to
have the model and SN info are completely blank.

Dunno if it's integrated or discrete yet. Three kids and work have kept me
from opening it up to do any diagnostic work.

On May 24, 2017 2:21 PM, "David @DWH [TekScopes]" <
TekScopes@...> wrote:



It is a good idea to start by checking the low voltage power supply
outputs for level and ripple which can be done with just a voltmeter
but I suspect the problem is in the vertical amplifier chain after the
vertical channel switch.

Albert posted a great detailed suggestion for how to proceed.

Do the vertical position controls move the traces over the full
vertical range of the CRT?

When the calibrator waveform is displayed, does changing the vertical
position cause the displayed trace to compress toward the top and
bottom of the screen?

What serial number is your 465 and is the vertical CRT amplifier board
discrete or integrated?

My guess is that you will find an open resistor between the emitters
of one of the transconductance stages which should be easy to repair.
Albert's directions should lead you right to it.

On Tue, 23 May 2017 22:28:26 -0400, you wrote:

My Oscope issue starts like a lot of other stories. I bought a 465 off
Ebay.

It needs new feet that I'll probably make, and the V scale reads about
22%
of what it should. Vpp for the 300 mv calibrator is 65 mv (21.6%). Vdc
for a 10V input is 2.2 V. Both channels. Take the exact number with a
grain of salt. As everyone including me (now) knows, the gain can't
correct
that much. But I tried. I've learned a lot in the past week. The Oscope
works reasonably well except for the aforementioned issue and a ground
short on the channel 2 input that makes it think it always has a 10x Tek
probe installed. Since that doesn't affect anything other than which
light
bulb is lit, I'm pretty pleased with my buy thus far. The Oscope didn't
come with probes. I bought some cheap ones off Amazon, but verified it
isn't the probes with a P3010 I borrowed from work.

Would I be correct in thinking I have an issue with a reference voltage
coming out of the PSU?

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



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

Nick Scalfaro
 

The serial number is B295060. That seems fairly high so hopefully I've got
a newer model.

On May 25, 2017 9:19 AM, "Fabio Trevisan fabio.tr3visan@...
[TekScopes]" <TekScopes@...> wrote:



Hello Nick
If the serial number is missing on the front panel, there's a chance that
the same is marked (with sharpie pen) on the back of the aluminum chassis,
behind the back plastic panel (that covers the FAN and supports the rear
BNC plugs).
On mine (a 464, not exactly same model as yours), I found recently the
serial number hand-written there, in big numbers (you can't miss it,
although part of it may be covered by the fan rotor itself).
Rgrds,
Fabio

2017-05-25 0:25 GMT-03:00 Nicholas Scalfaro nwscalfaro@...
[TekScopes] <TekScopes@...>:



Dave,

The Oscope loses the trigger on the 300 mv calibrator signal when the
entire trace is in the bottom third of the CRT. It can show an AC signal
across the full display. The waveforms do not distort vertically.

Serial number has been lost to history unless it's inside somewhere as
well. The 2 white boxes on the rear panel that presumably are supposed to
have the model and SN info are completely blank.

Dunno if it's integrated or discrete yet. Three kids and work have kept
me
from opening it up to do any diagnostic work.

On May 24, 2017 2:21 PM, "David @DWH [TekScopes]" <
TekScopes@...> wrote:



It is a good idea to start by checking the low voltage power supply
outputs for level and ripple which can be done with just a voltmeter
but I suspect the problem is in the vertical amplifier chain after the
vertical channel switch.

Albert posted a great detailed suggestion for how to proceed.

Do the vertical position controls move the traces over the full
vertical range of the CRT?

When the calibrator waveform is displayed, does changing the vertical
position cause the displayed trace to compress toward the top and
bottom of the screen?

What serial number is your 465 and is the vertical CRT amplifier board
discrete or integrated?

My guess is that you will find an open resistor between the emitters
of one of the transconductance stages which should be easy to repair.
Albert's directions should lead you right to it.

On Tue, 23 May 2017 22:28:26 -0400, you wrote:

My Oscope issue starts like a lot of other stories. I bought a 465 off
Ebay.

It needs new feet that I'll probably make, and the V scale reads about
22%
of what it should. Vpp for the 300 mv calibrator is 65 mv (21.6%). Vdc
for a 10V input is 2.2 V. Both channels. Take the exact number with a
grain of salt. As everyone including me (now) knows, the gain can't
correct
that much. But I tried. I've learned a lot in the past week. The
Oscope
works reasonably well except for the aforementioned issue and a ground
short on the channel 2 input that makes it think it always has a 10x
Tek
probe installed. Since that doesn't affect anything other than which
light
bulb is lit, I'm pretty pleased with my buy thus far. The Oscope
didn't
come with probes. I bought some cheap ones off Amazon, but verified it
isn't the probes with a P3010 I borrowed from work.

Would I be correct in thinking I have an issue with a reference
voltage
coming out of the PSU?

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


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



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

 

On Wed, 24 May 2017 23:25:33 -0400, you wrote:


The Oscope loses the trigger on the 300 mv calibrator signal when the
entire trace is in the bottom third of the CRT. It can show an AC signal
across the full display. The waveforms do not distort vertically.
Under what conditions does this happen? Single or dual trace? Trigger
source?

The NORM trigger source is from just after the vertical channel switch
before the delay line and vertical CRT amplifier. If this is
occurring with the NORM trigger source, then this points to a problem
between the channel switch and delay line driver.

Does changing the trigger source to channel 1 or 2 fix the triggering?
When one channel is displayed, switching the trigger source between
that channel and NORM should not change anything.

I have to ask this gain; do the vertical position controls move the
traces over the full vertical range of the CRT?

On Thu, 25 May 2017 11:37:23 -0400, you wrote:

The serial number is B295060. That seems fairly high so hopefully I've got
a newer model.
That makes it a late 465 which is good because we have documentation
for it but it still could have either a discrete or integrated CRT
amplifier.

Nick Scalfaro
 

On May 28, 2017 8:32 PM, "David @DWH [TekScopes]" <
TekScopes@...> wrote:



On Wed, 24 May 2017 23:25:33 -0400, you wrote:

The Oscope loses the trigger on the 300 mv calibrator signal when the
entire trace is in the bottom third of the CRT. It can show an AC signal
across the full display. The waveforms do not distort vertically.
Ok so looking at a line voltage through my variac there is a good bit of
flicker. Indeed the waveform peaks are flattened a bit. 10 Vac yields
6.4 Vpp both channels. And again adjusting the trace down looses trigger (
light goes out, multiple traces). Switching the lower source switch (below
source light) from NORM to CH1or CH2 does let it find a trigger though it's
still flickering.


Under what conditions does this happen? Single or dual trace? Trigger
source?

Single and dual, though CH2 is worse



I have to ask this again; do the vertical position controls move the traces
over the full vertical range of the CRT?

No, now that I've carefully looked at it. It goes much further up than
down. However with a Vac source the sinusoid will go off screen vertically
both ways.


On Thu, 25 May 2017 11:37:23 -0400, you wrote:

The serial number is B295060. That seems fairly high so hopefully I've got
a newer model.
That makes it a late 465 which is good because we have documentation
for it but it still could have either a discrete or integrated CRT
amplifier.




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

 

I think the triggering problem is an illusion. When the position
control is at an extreme, it will cause triggering to fail anyway but
at that point the trace will be off of the screen.

The lack of full positioning range and low vertical deflection means
low gain somewhere between the channel switch and vertical output. My
guess is that a gain resistor has drifted high in value.