Topics

453 calibrator

Brendan
 
Edited

This looks to be the final issue with my 453. There was no calibration signal at all. I Changed q1274 which gave me a perfect square wave but the voltage was high. Checking R1274 which is supposed to be a 2.19K precision resistor, was actually a 392ohm 1% installed by someone else. Installing a 2.19K ohm 1% resistor resulted in a reduction of voltage but it is still incorrect. Output from the calibration BNC is now .6V at the .1V setting and 6 volts at the 1V switch setting. This is a screen shot of the calibrator circuit. https://groups.io/g/TekScopes/photo/37195/15?p=Name,,,20,1,0,0 I have worked on this for many hours and can't figure this out.

 

Did you check R1275, 1276, and 1277? Is there continuity through the current loop to ground?

----- Original Message -----
From: "lop pol via Groups.Io" <the_infinite_penguin=yahoo.com@groups.io>
To: <TekScopes@groups.io>
Sent: Monday, May 07, 2018 11:39 PM
Subject: [TekScopes] 453 calibrator


[Edited Message Follows]

This looks to be the final issue with my 453. There was no calibration signal at all. I Changed q1274 which gave me a perfect square wave but the voltage was high. Checking R1274 which is supposed to be a 2.19K precision resistor, was actually a 392ohm 1% installed by someone else. Installing a 2.19K ohm 1% resistor resulted in a reduction of voltage but it is still incorrect. Output from the calibration BNC is now .6V at the .1V setting and 6 volts at the 1V switch setting. This is a screen shot of the calibrator circuit. https://groups.io/g/TekScopes/photo/37195/15?p=Name,,,20,1,0,0 I have worked on this for many hours and can't figure this out.

Mike Merigliano
 

Are you getting the correct voltage into the base of Q1274? The signal output at Q1274's collector should be about 12 volts, so your circuit is cutting it in half. Try lifting (disconnect) R1275, to isolate the 1-volt output from the current probe loop and the 0.1 volt part of the circuit. Maybe you have done this already, or just checked the resistor values. Maybe someone changed R1275 to R1277 (a voltage divider) along with R1274, or they tried to compensate for a problem here with the 392 R resistor, or they just wanted higher output for some reason.It seems like you should still get 1 volt if the switch is okay, even if R1275 etc. are wrong.

I have a 453, with a working calibrator, so I can do some measurements here for you to compare to. I have the <20000 and >20000 serial number manuals, although the calibrator circuit looks the same. The circuit description in the manual should be helpful.

I bet someone here can nail-down the problem for you, but I am not that experienced, so wanted to see how close I could come up with a solution with the information so far.

On 5/7/2018 9:39 PM, lop pol via Groups.Io wrote:
[Edited Message Follows]

This looks to be the final issue with my 453. There was no calibration signal at all. I Changed q1274 which gave me a perfect square wave but the voltage was high. Checking R1274 which is supposed to be a 2.19K precision resistor, was actually a 392ohm 1% installed by someone else. Installing a 2.19K ohm 1% resistor resulted in a reduction of voltage but it is still incorrect. Output from the calibration BNC is now .6V at the .1V setting and 6 volts at the 1V switch setting. This is a screen shot of the calibrator circuit. https://groups.io/g/TekScopes/photo/37195/15?p=Name,,,20,1,0,0 I have worked on this for many hours and can't figure this out.



 

On Mon, May 7, 2018 at 10:20 pm, Mike Merigliano wrote:


Try lifting (disconnect) R1275
That would open the return path for the collector of Q1274 which would result in that voltage stuck at the emitter voltage.

Someone obviously changed the resistors to modify the circuit but failed to take into account the current through Q 1274, which was bad when Lop got there. That would only be about 30 mA but maybe something else was afoot, like maybe not enough base current.

The combined resistance of R 1276 & 1277 is 20 ohms. With the 180 the 2.19 K is working into 200 ohms to get to spec in the high setting when loaded with 50 ohms. In the low setting it is 2.37 K working into 20 ohms. (60 and 30 in parallel) Of ocurse that will be slightly lower when you throw a 50 ohm load on it.

Those three resistors at the bottom must be high in value. Either burnt partly open or the last guy changed them. The transistor operates sort of saturated, effectively it is at that current level anyway.

The fact that the output stays at 6 X the setting in either setting suggests that someone changed those resistors at the bottom to make the output they wanted. they would be the first thing I check. If they are not the problem then something very weird is going on.

Brendan
 

On Mon, May 7, 2018 at 11:21 pm, Jeff Urban wrote:


On Mon, May 7, 2018 at 10:20 pm, Mike Merigliano wrote:


Try lifting (disconnect) R1275
That would open the return path for the collector of Q1274 which would result
in that voltage stuck at the emitter voltage.

Someone obviously changed the resistors to modify the circuit but failed to
take into account the current through Q 1274, which was bad when Lop got
there. That would only be about 30 mA but maybe something else was afoot, like
maybe not enough base current.

The combined resistance of R 1276 & 1277 is 20 ohms. With the 180 the 2.19 K
is working into 200 ohms to get to spec in the high setting when loaded with
50 ohms. In the low setting it is 2.37 K working into 20 ohms. (60 and 30 in
parallel) Of ocurse that will be slightly lower when you throw a 50 ohm load
on it.

Those three resistors at the bottom must be high in value. Either burnt partly
open or the last guy changed them. The transistor operates sort of saturated,
effectively it is at that current level anyway.

The fact that the output stays at 6 X the setting in either setting suggests
that someone changed those resistors at the bottom to make the output they
wanted. they would be the first thing I check. If they are not the problem
then something very weird is going on.
tmillermdems
May 7 #147653

Did you check R1275, 1276, and 1277? Is there continuity through the current loop to ground?


R1277,R1276 and r1275 were all incorrect values. Replaced with the correct value and now all is good. All in all It was a fun repair. Replaced the fan,replaced the frozen variable time pot,tracked down a bad transistor in the Alt circuit, replaced a blown out 150V 3uf wet tantalum on the low voltage board and replaced the bad transistor and resistors in the calibrator circuit. Thanks for all the help!!

 

Don't you just love undocumented modifications ?

But still, have a pity party for people who work for ISO compliant companies. If they modify something they have a mountain of paperwork. I would just put a note inside and out but that ain't good enough apparently.

Actually I do understand why - it has to do with company value and how much trouble it would be to liquefy those "assets". But like everything they get ridiculous,

So, let's guess the resistor values our budding ex engineer used.

You get 6 X the output so I would assume the values of those 3 resistors at the bottom are approximately 6 X of the proper value, err the proper value for the rest of us that is. But they might have to be a bit higher than that. I doubt he was going into 50 ohms, he wouldn't get much. More that is.

Am I close ?

Brendan
 

On Tue, May 8, 2018 at 09:04 am, Jeff Urban wrote:


Don't you just love undocumented modifications ?

But still, have a pity party for people who work for ISO compliant companies.
If they modify something they have a mountain of paperwork. I would just put a
note inside and out but that ain't good enough apparently.

Actually I do understand why - it has to do with company value and how much
trouble it would be to liquefy those "assets". But like everything they get
ridiculous,

So, let's guess the resistor values our budding ex engineer used.

You get 6 X the output so I would assume the values of those 3 resistors at
the bottom are approximately 6 X of the proper value, err the proper value for
the rest of us that is. But they might have to be a bit higher than that. I
doubt he was going into 50 ohms, he wouldn't get much. More that is.

Am I close ?
What threw me off the most was.. I checked around there yesterday. R1275 is supposed to be 180ohm i checked it, it checked good 180ohm I started scratching my head. I checked it this morning and man did I goof up last night. It was 1.80K ohm. I need to learn to look at stuff correctly. I can't be mad about the modification seems they got what they wanted from the calibrator.

Göran Krusell
 

Hi, can anyone explain why this calibrator needs transformer T1255. Such a component should be expensive. Would it not be possible to have an oscillator/Schmitt trigger design and still get the same performance?
Göran

John Gord
 

Göran,
I think the tuned transformer was used to give better frequency accuracy than could be obtained with an RC based circuit.
These days a cheap crystal and digital divider would be used.
--John Gord

On Tue, May 8, 2018 at 11:02 am, Göran Krusell wrote:


Hi, can anyone explain why this calibrator needs transformer T1255. Such a
component should be expensive. Would it not be possible to have an
oscillator/Schmitt trigger design and still get the same performance?
Göran

 

These days the microprocessor makes the signal. Just takes a few lines of code.

----- Original Message -----
From: "johncharlesgord" <johngord@...>
To: <TekScopes@groups.io>
Sent: Tuesday, May 08, 2018 2:39 PM
Subject: Re: [TekScopes] 453 calibrator


Göran,
I think the tuned transformer was used to give better frequency accuracy than could be obtained with an RC based circuit.
These days a cheap crystal and digital divider would be used.
--John Gord

On Tue, May 8, 2018 at 11:02 am, Göran Krusell wrote:


Hi, can anyone explain why this calibrator needs transformer T1255. Such a
component should be expensive. Would it not be possible to have an
oscillator/Schmitt trigger design and still get the same performance?
Göran

Mike Merigliano
 

Although lop pol fixed it by now, I wonder about something:

the schematic shows a DC voltage drop between the Q1274 emitter (5.9) and after R1274 (0.5 DC). With R1275 lifted, there is still a return to ground -- at or via connection BB. If R1274 is lifted, than I would expect the voltage to be about 6 volts at the emitter.

On 5/8/2018 12:21 AM, Jeff Urban wrote:
On Mon, May 7, 2018 at 10:20 pm, Mike Merigliano wrote:

Try lifting (disconnect) R1275
That would open the return path for the collector of Q1274 which would result in that voltage stuck at the emitter voltage.

 

On Tue, May 8, 2018 at 11:02 am, Göran Krusell wrote:


Hi, can anyone explain why this calibrator needs transformer T1255. Such a
component should be expensive.
Tektronix seems to like simple transformers. They have a propensity to just have a bifilar or trifilar winding around a toroid. About 5 turns they can make it oscillate at 200 KHz with practically no capacitance across it, so a few more turns and some capacitance a simple transformer would work fine for 1 KHz as long as they have a transistor with enough gain.

Not sure exactly of all the dynamics of it but that circuit looks like it is designed to assure a 50 % duty cycle. I think a simple astable multivibrator would do just fine but as johncharlesgord said they might have used the transformer for more stable frequency control.

 

On Tue, May 8, 2018 at 04:15 pm, Mike Merigliano wrote:


the schematic shows a DC voltage drop between the Q1274 emitter (5.9) and
after R1274 (0.5 DC). With R1275 lifted, there is still a return to ground --
at or via connection BB. If R1274 is lifted, than I would expect the voltage
to be about 6 volts at the emitter.
There must be some sort of error concerning the connection at BB. If it is as shown there would never be any output. It is either a mistake or they found a new way to use a symbol. I have run into alot of that in consumer, so much so that I always check, never trust. I have seen a line representing a wire or trace on a PC tht says 12 volts and about an inch away says 0 volts. I have seen mistakes that would pretty much turn the unit into a bomb. (almost wonder if they'e really mistakes...)

Richard Knoppow
 

I am working on a 453 right now so its easy enough for me to look at the actual wiring. Will do so tomorrow.
I have both the commercial and military versions of the handbook. The civilian one has some badly drawn places in the schematic, perhaps this is another. In the HV regulator circuit a dividing line for the circuit boards appears to be a connection. Maybe the same here.

On 5/8/2018 10:00 PM, Jeff Urban wrote:
On Tue, May 8, 2018 at 04:15 pm, Mike Merigliano wrote:


the schematic shows a DC voltage drop between the Q1274 emitter (5.9) and
after R1274 (0.5 DC). With R1275 lifted, there is still a return to ground --
at or via connection BB. If R1274 is lifted, than I would expect the voltage
to be about 6 volts at the emitter.
There must be some sort of error concerning the connection at BB. If it is as shown there would never be any output. It is either a mistake or they found a new way to use a symbol. I have run into alot of that in consumer, so much so that I always check, never trust. I have seen a line representing a wire or trace on a PC tht says 12 volts and about an inch away says 0 volts. I have seen mistakes that would pretty much turn the unit into a bomb. (almost wonder if they'e really mistakes...)
--
Richard Knoppow
dickburk@...
WB6KBL

Chuck Harris
 

This is a mistake many people make when they look at scanned
tektronix schematics.

BA, BB, and the like are terminus points for the calibrator's
circuit board. The drawn line that connects them was originally
blue, or grey, and has had its density, and color, mucked with by
the scanner until it appears black, like an ordinary wire. It is
not. It is simply a gray or blue line that depicts the boundary
between what is on the calibrator circuit board, and what is
elsewhere.

-Chuck Harris

Jeff Urban wrote:

On Tue, May 8, 2018 at 04:15 pm, Mike Merigliano wrote:


the schematic shows a DC voltage drop between the Q1274 emitter (5.9) and
after R1274 (0.5 DC). With R1275 lifted, there is still a return to ground --
at or via connection BB. If R1274 is lifted, than I would expect the voltage
to be about 6 volts at the emitter.
There must be some sort of error concerning the connection at BB. If it is as shown there would never be any output. It is either a mistake or they found a new way to use a symbol. I have run into alot of that in consumer, so much so that I always check, never trust. I have seen a line representing a wire or trace on a PC tht says 12 volts and about an inch away says 0 volts. I have seen mistakes that would pretty much turn the unit into a bomb. (almost wonder if they'e really mistakes...)

Dale H. Cook
 

At 09:49 AM 5/9/2018, Chuck Harris wrote:

The drawn line that connects them was originally blue, or grey, and has had its density, and color, mucked with by the scanner until it appears black, like an ordinary wire.
That is one reason why my 453 (Serial 20,000+) scan at BAMA has those prints scanned in color.

Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcity/radios/index.html

Mike Merigliano
 

To check the schematic, I opened up my 453 (>20000). There is no error here; BB is a ground point, and the emitter of Q1274 goes to it via R1274 in series. Even if the line denoting the edge of the board, labeled as "Partial A Sweep Board", and blue on original schematic (see Dale Cook's reproduction for >20000 serial number units) is mistaken for a wire/trace, the connection is the same. Why would Q1274, with about 6 volt DC emitter voltage "blow up" with a 2.19K resistor in series to ground?

On 5/8/2018 11:00 PM, Jeff Urban wrote:
There must be some sort of error concerning the connection at BB. If it is as shown there would never be any output. It is either a mistake or they found a new way to use a symbol. I have run into alot of that in consumer, so much so that I always check, never trust. I have seen a line representing a wire or trace on a PC tht says 12 volts and about an inch away says 0 volts. I have seen mistakes that would pretty much turn the unit into a bomb. (almost wonder if they'e really mistakes...)

ArtekManuals
 

Dale
[REPLY OFF LIST]

Unless I missed something it appears to me that the 453 manual on Bama is part # 070-0478-00 which is for serial #'s below 20000. The manual for the higher serial numbers is 070-0755-00

-DC
manuals@...

On 5/9/2018 10:07 AM, Dale H. Cook wrote:
At 09:49 AM 5/9/2018, Chuck Harris wrote:

The drawn line that connects them was originally blue, or grey, and has had its density, and color, mucked with by the scanner until it appears black, like an ordinary wire.
That is one reason why my 453 (Serial 20,000+) scan at BAMA has those prints scanned in color.

Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcity/radios/index.html



--
Dave
Manuals@...
www.ArtekManuals.com

ArtekManuals
 

Ooooops

Well I meant to reply OFF LIST Still getting userd to Groups.IO
-DC

On 5/9/2018 11:39 AM, Artekmedia wrote:
Dale
[REPLY OFF LIST]

Unless I missed something it appears to me that the 453 manual on Bama is part # 070-0478-00 which is for serial #'s below 20000. The manual for the higher serial numbers is 070-0755-00

-DC
manuals@...

On 5/9/2018 10:07 AM, Dale H. Cook wrote:
At 09:49 AM 5/9/2018, Chuck Harris wrote:

The drawn line that connects them was originally blue, or grey, and has had its density, and color, mucked with by the scanner until it appears black, like an ordinary wire.
That is one reason why my 453 (Serial 20,000+) scan at BAMA has those prints scanned in color.

Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcity/radios/index.html




--
Dave
Manuals@...
www.ArtekManuals.com

 

On Wed, May 9, 2018 at 08:13 am, Mike Merigliano wrote:


There is no error here; BB is a ground point, and the emitter of Q1274 goes to
it via R1274 in series.
Then there can be no output at the calibrator terminal unless the whole thing floats and has a separately isolated power supply. The signal would forever be shorted to ground.