Date   

Re: Bench mains supply - another attempt

 

An isolation transformer will only lower the short circuit current by raising
the wiring resistance. I think almost any low current breaker will do what you
want and prevent the larger breaker from tripping.

On Mon, 4 Nov 2013 08:41:24 +0100, you wrote:

Would the delay through a transformer be long enough for a breaker to
trip on the secondary side, pulling a breaker on the primary side
before the transient "makes it through" the isolation transformer?
Apparently the ABB breakers have 0.1 or 0.2 sec short-circuit
response, which is 6-12 cycles at 60 Hz. I'm assuming a typical
isolation transformer isn't resonant, so it doesn't store energy.

BTW - I'm not sure if I mentioned in the thread, but the breaker I'm
dealing with here is likely 30 Amps. Well at least it blew on 30A once
while it didn't with a 25A draw.

Cheers,
D.


Re: Bench mains supply - another attempt

 

On Mon, 4 Nov 2013 07:59:00 +0100, you wrote:

Hi David,

On Mon, Nov 4, 2013 at 2:54 AM, David <davidwhess@...> wrote:
On Sun, 03 Nov 2013 19:09:34 -0600, you wrote:

On 11/02/2013 01:30 PM, David wrote:
The simple thing to do might be to
just build an outlet extension that has its own small (5 amp?) short delay
circuit breaker

That too. I have some DIN rail ABB breakers in my junk store of 2A 4A 6A 8A 12A...

any of those would be fine for this kind of app.

I have a photo catalog of my attic and store room junk. Maybe I should put it on the web and consider offers...:-)
I found suitable and relatively inexpensive, less than $20, panel mount ones
from Newark but I had to spend time going through datasheets to do it. They
were panel mount toggle switch style hydraulic-magnetic breakers. I had to
check the datasheets to verify the delay curves.
What part have you found? Have you seen any rail-mounted ones as well?

Cheers,
D.
I was looking for panel mount and not rail mount breakers. Now I see that the
one I thought I found was not in stock anyway. :(


Re: Bench mains supply - another attempt

 

Would the delay through a transformer be long enough for a breaker to
trip on the secondary side, pulling a breaker on the primary side
before the transient "makes it through" the isolation transformer?
Apparently the ABB breakers have 0.1 or 0.2 sec short-circuit
response, which is 6-12 cycles at 60 Hz. I'm assuming a typical
isolation transformer isn't resonant, so it doesn't store energy.

BTW - I'm not sure if I mentioned in the thread, but the breaker I'm
dealing with here is likely 30 Amps. Well at least it blew on 30A once
while it didn't with a 25A draw.

Cheers,
D.


Re: Bench mains supply - another attempt

 

Hi David,

On Mon, Nov 4, 2013 at 2:54 AM, David <davidwhess@...> wrote:
On Sun, 03 Nov 2013 19:09:34 -0600, you wrote:

On 11/02/2013 01:30 PM, David wrote:
The simple thing to do might be to
just build an outlet extension that has its own small (5 amp?) short delay
circuit breaker

That too. I have some DIN rail ABB breakers in my junk store of 2A 4A 6A 8A 12A...

any of those would be fine for this kind of app.

I have a photo catalog of my attic and store room junk. Maybe I should put it on the web and consider offers...:-)
I found suitable and relatively inexpensive, less than $20, panel mount ones
from Newark but I had to spend time going through datasheets to do it. They
were panel mount toggle switch style hydraulic-magnetic breakers. I had to
check the datasheets to verify the delay curves.
What part have you found? Have you seen any rail-mounted ones as well?

Cheers,
D.


Re: Tek 2445B regulator C1072 voltage rating

 

I agree about film and ceramic capacitors back when it was designed but
Tektronix could have used tantalums.

The values are not critical so the voltage coefficient of capacitance of X7R
ceramics should not be a problem.

On 03 Nov 2013 21:07:30 -0800, you wrote:

My guess is that in the 80's there weren't many affordable ceramics in the 1-10uF range, and the film ones with such capacities were rather huge.

These days you can find inexpensive X7R ceramics covering this range. TDK has 1uF in both 50V and 100V rating, if you're scared about capacitance derating with DC bias go for the 100V version.

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

Maybe Tektronix used aluminum electrolytics because they preferred they fail
open. I probably would have used film or ceramic capacitors.


Re: Tek 2445B regulator capacitor polarity

vdonisa
 

Have a look here:


http://search.murata.co.jp/Ceramy/image/img/A01X/RDEEDCD1.gif


if you go for an 100V X7R, up to 10V there's no significant change of capacitance with DC bias.


Did I mention that ceramics are bipolar too? :-) :-) :-)





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

Davids advice caused me to recalculate a voltage but I reach the same conclusion as before and the same as David.  The voltage across C1291 could reach 7 volts and the older layout oriented polarized caps to accommodate the voltage.  But BIPOLAR remains the best answer for todays technology.

From: machine guy <machineguy59@...>
To: "TekScopes@..." <TekScopes@...>
Sent: Sunday, November 3, 2013 10:58 PM
Subject: Re: [TekScopes] Re: Tek 2445B regulator capacitor polarity
 
My schematics do not agree with this description so the precise numbers I use may be different than yours.  But my advice should still fit your case.  I will describe the difference, then why the answer fits both layouts. 
 
On my schematic there is no C1292.  On my schematics C1291 is 1 mfd 50 V electrolytic.  Also C1274 is a 1 mfd 50 V electrolytic.  C1291 connects between pins 8-9 of U1300.  C1274 connects between pins 8-9 of U1371.  Its possible but surprising to me. that other versions of these power supplies use different layouts with the exact same design.  For example, pins 12-13-14 of U1300 serve the same function as pins 10-9-8 (note the changed numerical order).  So I believe that there is a change in layout but NOT a change in functional requirements.  So I have addressed the circuit requirements to determine the needs for these two capacitors.
 
These two capacitors serve their circuits each in the same way and analysis is straight forward.  In each case, the 1 mfd capacitor provides feedback from the output of an operational amplifier to its inverting input.  For the operational amplifier connected to R1292 (10 V adjust) the voltage between these two points (across the capacitor) is less than 20 millivolts.  Polarity wont matter much to a 50 volt rating at this low voltage.  For the other operational amplifier the pins will be within 0.6 volt of each other unless the +5 Vd has begun to fail (sag).  Even then, the voltage is less than 3 0r 4 volts and the scope has other problems failing (we had a failed opto coupler here last month that presented this characteristic).  But, again, the voltage will be so low that polarity should not matter.
 
But, bottom line, THESE TWO CAPACITORS SHOULD BE BIPOLAR (marked BP, not NEG as polarized caps are marked).  You found BP caps installed, marked BP and the board has no polarity markings.  Even Tek is telling us these caps should be BIPOLAR ALUMINUM ELECTROLYTICS.  But older models of 24xx scopes got by using 50 V polarized because the applied voltage is low enough they survived until BIPOLAR (BP) became available.  

From: Rob Turk <r.turk@...>
To: TekScopes@...
Sent: Sunday, November 3, 2013 10:23 AM
Subject: [TekScopes] Re: Tek 2445B regulator capacitor polarity
 
It is a bit confusing to me. The capacitors do have the marking 'BP' on them which might mean Bi-polar. However, the 2465B schematics I found suggest that C1291 and C1292 have a well-defined polarity. On the schematics, the negative side of C1291 connects to U1300 pin 13 and a divider which will alway be between 0 and 10V, while the positive side connects to U1300 pin 14 (+10V ref). For C1292 the positive side connects to the gate of Q1290 and to +2.5V via a resistor, while the negative side goes to -15V unreg. C1270 has polarity on the schematics but is a regular non-polarized capacitor on the PCB. C1274 again shows polarity on the schematics, and it is an electrolytic version, but again marked 'BP' and no polarity indication. This is the only one I'd suspect to see both polarities. I could not find anything about these in the group history, does this mean that most people do not swap these out when re-capping their scope?
On 11/3/2013 4:48 PM, machine guy wrote:
 
In normal service these capacitors see very little voltage (less than 1 volt typ) but it can be in either polarity.  I would use bipolar electrolytics in these two bpositions.  But if you absolutely must use polarized, use 50 volt caps with the nebative terminal of C1270 connected to pin 9 of U1371, and the negative terminal of C1291 connected to pin 9 of U1300.  This gives the least likelihood of a reversed voltage.  But, again, it would be better if these were non-polarized capacitlors.  I thik that is why the polarities are not marked on the PCB.


Re: Tek 2445B regulator capacitor polarity

 

Davids advice caused me to recalculate a voltage but I reach the same conclusion as before and the same as David.  The voltage across C1291 could reach 7 volts and the older layout oriented polarized caps to accommodate the voltage.  But BIPOLAR remains the best answer for todays technology.

From: machine guy
To: "TekScopes@..." Sent: Sunday, November 3, 2013 10:58 PM
Subject: Re: [TekScopes] Re: Tek 2445B regulator capacitor polarity
 
My schematics do not agree with this description so the precise numbers I use may be different than yours.  But my advice should still fit your case.  I will describe the difference, then why the answer fits both layouts. 
 
On my schematic there is no C1292.  On my schematics C1291 is 1 mfd 50 V electrolytic.  Also C1274 is a 1 mfd 50 V electrolytic.  C1291 connects between pins 8-9 of U1300.  C1274 connects between pins 8-9 of U1371.  Its possible but surprising to me. that other versions of these power supplies use different layouts with the exact same design.  For example, pins 12-13-14 of U1300 serve the same function as pins 10-9-8 (note the changed numerical order).  So I believe that there is a change in layout but NOT a change in functional requirements.  So I have addressed the circuit requirements to determine the needs for these two capacitors.
 
These two capacitors serve their circuits each in the same way and analysis is straight forward.  In each case, the 1 mfd capacitor provides feedback from the output of an operational amplifier to its inverting input.  For the operational amplifier connected to R1292 (10 V adjust) the voltage between these two points (across the capacitor) is less than 20 millivolts.  Polarity wont matter much to a 50 volt rating at this low voltage.  For the other operational amplifier the pins will be within 0.6 volt of each other unless the +5 Vd has begun to fail (sag).  Even then, the voltage is less than 3 0r 4 volts and the scope has other problems failing (we had a failed opto coupler here last month that presented this characteristic).  But, again, the voltage will be so low that polarity should not matter.
 
But, bottom line, THESE TWO CAPACITORS SHOULD BE BIPOLAR (marked BP, not NEG as polarized caps are marked).  You found BP caps installed, marked BP and the board has no polarity markings.  Even Tek is telling us these caps should be BIPOLAR ALUMINUM ELECTROLYTICS.  But older models of 24xx scopes got by using 50 V polarized because the applied voltage is low enough they survived until BIPOLAR (BP) became available.  

From: Rob Turk
To: TekScopes@...
Sent: Sunday, November 3, 2013 10:23 AM
Subject: [TekScopes] Re: Tek 2445B regulator capacitor polarity
 
It is a bit confusing to me. The capacitors do have the marking 'BP' on them which might mean Bi-polar. However, the 2465B schematics I found suggest that C1291 and C1292 have a well-defined polarity. On the schematics, the negative side of C1291 connects to U1300 pin 13 and a divider which will alway be between 0 and 10V, while the positive side connects to U1300 pin 14 (+10V ref). For C1292 the positive side connects to the gate of Q1290 and to +2.5V via a resistor, while the negative side goes to -15V unreg.C1270 has polarity on the schematics but is a regular non-polarized capacitor on the PCB. C1274 again shows polarity on the schematics, and it is an electrolytic version, but again marked 'BP' and no polarity indication. This is the only one I'd suspect to see both polarities.I could not find anything about these in the group history, does this mean that most people do not swap these out when re-capping their scope?
On 11/3/2013 4:48 PM, machine guy wrote:
 
In normal service these capacitors see very little voltage (less than 1 volt typ) but it can be in either polarity.  I would use bipolar electrolytics in these two bpositions.  But if you absolutely must use polarized, use 50 volt caps with the nebative terminal of C1270 connected to pin 9 of U1371, and the negative terminal of C1291 connected to pin 9 of U1300.  This gives the least likelihood of a reversed voltage.  But, again, it would be better if these were non-polarized capacitlors.  I thik that is why the polarities are not marked on the PCB.


Re: Tek 2445B regulator C1072 voltage rating

vdonisa
 

My guess is that in the 80's there weren't many affordable ceramics in the 1-10uF range, and the film ones with such capacities were rather huge.


These days you can find inexpensive X7R ceramics covering this range. TDK has 1uF in both 50V and 100V rating, if you're scared about capacitance derating with DC bias go for the 100V version.



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

Maybe Tektronix used aluminum electrolytics because they preferred they fail
open. I probably would have used film or ceramic capacitors.


Re: Odd 7904 problem

 

When the 7904 won’t work in Chop Mode check for a missing Chop Drive Waveform which is on pin A5 and Chop Common which is on pin A6 of the interface board. Without it you can only alternate. Or try putting a desiccated chicken foot inside it to get rid of the evil spirits. J

 

Dennis

 

From: TekScopes@... [mailto:TekScopes@...] On Behalf Of ictjayhawk@...
Sent: Sunday, November 03, 2013 8:37 PM
To: TekScopes@...
Subject: [TekScopes] Odd 7904 problem

 



Picked up 2 7904's the other day. B15xxxx with a bad interface connector and FF in the calibrator circuit, and B25xxxx that is possessed.

No matter what vertical mode I selected I got Alternate. Except alternate, then it would sweep L1, L1, R1, R1,L2,L2,R2,R2 (alternate alternate??) I thought I had a logic board problem and swapped U215 (I think) and it was still misbehaving. Other than that and no readout on the R2 channel it all seemed to be OK.

So I went to try it before posting, it was still broken. Then it started working as advertised (except the R2 readout) and now it won't break again.

Any ideas/wags?



Re: Tek 2445B regulator capacitor polarity

 

My schematics do not agree with this description so the precise numbers I use may be different than yours.  But my advice should still fit your case.  I will describe the difference, then why the answer fits both layouts. 
 
On my schematic there is no C1292.  On my schematics C1291 is 1 mfd 50 V electrolytic.  Also C1274 is a 1 mfd 50 V electrolytic.  C1291 connects between pins 8-9 of U1300.  C1274 connects between pins 8-9 of U1371.  Its possible but surprising to me. that other versions of these power supplies use different layouts with the exact same design.  For example, pins 12-13-14 of U1300 serve the same function as pins 10-9-8 (note the changed numerical order).  So I believe that there is a change in layout but NOT a change in functional requirements.  So I have addressed the circuit requirements to determine the needs for these two capacitors.
 
These two capacitors serve their circuits each in the same way and analysis is straight forward.  In each case, the 1 mfd capacitor provides feedback from the output of an operational amplifier to its inverting input.  For the operational amplifier connected to R1292 (10 V adjust) the voltage between these two points (across the capacitor) is less than 20 millivolts.  Polarity wont matter much to a 50 volt rating at this low voltage.  For the other operational amplifier the pins will be within 0.6 volt of each other unless the +5 Vd has begun to fail (sag).  Even then, the voltage is less than 3 0r 4 volts and the scope has other problems failing (we had a failed opto coupler here last month that presented this characteristic).  But, again, the voltage will be so low that polarity should not matter.
 
But, bottom line, THESE TWO CAPACITORS SHOULD BE BIPOLAR (marked BP, not NEG as polarized caps are marked).  You found BP caps installed, marked BP and the board has no polarity markings.  Even Tek is telling us these caps should be BIPOLAR ALUMINUM ELECTROLYTICS.  But older models of 24xx scopes got by using 50 V polarized because the applied voltage is low enough they survived until BIPOLAR (BP) became available.  

From: Rob Turk To: TekScopes@...
Sent: Sunday, November 3, 2013 10:23 AM
Subject: [TekScopes] Re: Tek 2445B regulator capacitor polarity
 
It is a bit confusing to me. The capacitors do have the marking 'BP' on them which might mean Bi-polar. However, the 2465B schematics I found suggest that C1291 and C1292 have a well-defined polarity.

On the schematics, the negative side of C1291 connects to U1300 pin 13 and a divider which will alway be between 0 and 10V, while the positive side connects to U1300 pin 14 (+10V ref).

For C1292 the positive side connects to the gate of Q1290 and to +2.5V via a resistor, while the negative side goes to -15V unreg.

C1270 has polarity on the schematics but is a regular non-polarized capacitor on the PCB. C1274 again shows polarity on the schematics, and it is an electrolytic version, but again marked 'BP' and no polarity indication. This is the only one I'd suspect to see both polarities.

I could not find anything about these in the group history, does this mean that most people do not swap these out when re-capping their scope?

On 11/3/2013 4:48 PM, machine guy wrote:
 
In normal service these capacitors see very little voltage (less than 1 volt typ) but it can be in either polarity.  I would use bipolar electrolytics in these two bpositions.  But if you absolutely must use polarized, use 50 volt caps with the nebative terminal of C1270 connected to pin 9 of U1371, and the negative terminal of C1291 connected to pin 9 of U1300.  This gives the least likelihood of a reversed voltage.  But, again, it would be better if these were non-polarized capacitlors.  I thik that is why the polarities are not marked on the PCB.


Re: Odd 7904 problem

 

I suspect connectors, sockets, and voodoo.

On 03 Nov 2013 20:37:06 -0800, you wrote:

Picked up 2 7904's the other day. B15xxxx with a bad interface connector and FF in the calibrator circuit, and B25xxxx that is possessed.

No matter what vertical mode I selected I got Alternate. Except alternate, then it would sweep L1, L1, R1, R1,L2,L2,R2,R2 (alternate alternate??) I thought I had a logic board problem and swapped U215 (I think) and it was still misbehaving. Other than that and no readout on the R2 channel it all seemed to be OK.

So I went to try it before posting, it was still broken. Then it started working as advertised (except the R2 readout) and now it won't break again.

Any ideas/wags?


Re: 453 follow-up

 

On Mon, 4 Nov 2013 04:25:58 +0100, you wrote:

On 04 Nov 2013, at 04:10, David <davidwhess@...> wrote:
1. When switching between normal/inverted modes on CH2, the zero line needs to be about half a division above the middle reticule in order for inverting to not move the line. I can "fix" that by tweaking the CH2 calibration settings, but not while also having proper vertical calibration as per the manual. Since there is no calibration procedure for this element, I am guessing that it might be normal, but is it?
The 454 added an adjustment (R334 in the middle of schematic 4) for the vertical
amplifier balance which could fix this. Tektronix apparently used it to prevent
position shift in ADD mode but I think it is effectively the same thing. You
could add a similar adjustment and calibrate out the channel 2 inverting mode
trace shift if it bothers you.
Ah, good to know. I will take a look at the 454 manual and maybe just find a fixed resistor value that gets it closer to zero.
If you use a trimmer potentiometer, then it will take 1 or more fixed resistors
to lower the sensitivity.

The 465 added separate adjustments for vertical amplifier balance and channel 2
inverting balance.

The 465 specification for inverting balance is 2 divisions so your 1/2 division
is well within the specification for later oscilloscopes. Typically I see it
shift a minor division at most on non 45x series oscilloscopes and it is
somewhat temperature sensitive.
On my 453 it seems reasonably constant. Step attenuation balance changes a fair bit with temperature, though, so maybe once inverting balance gets closer to zero, it becomes more noticeable.
The unbalanced Nuvistor front end does not have the best temperature stability.

2. More importantly and annoyingly, when switching from A/A-with-B to B sweep, the horisontal position moves about 3.5 division to the left. This happens at all sweep speeds and settings. I have tried to follow the circuit description, but I am only a humble software guy, so no joy as yet. Any suggestions?
I would take a look at the sweep start adjustments starting on page 6-45 of the
service manual. Before I decided something was wrong though, I would do a
complete horizontal calibration.
I already did a full calibration. The A sweep start adjustment R758 moves A and B horizontal positions equally, so the offset stays the same.
It looks like there could be an offset problem in either the A sweep (D543,
Q543, D545, Q544) or B sweep (D753, Q753, D754, Q754) differential amplifiers
which control the sweep integrator starting voltages. Either one is low or the
other is high. With some cleverness I think you could measure the difference in
start voltages with the oscilloscope set to normal mode and no trigger.

Besides further measurements to determine the exact problem, if I was going to
try and fix that I might:

1. Grade some suitable replacement transistors and diodes for best offset
voltage match and swap out the 4 parts in each differential amplifier. Or pick
just one diode or transistor and start swapping it with replacements to see if
you can find one that moves the sweeps back into alignment. Or swap one part at
a time between the differential amplifiers to match their offset voltages.

2. Add an offset voltage trim to one of the sweep differential amplifiers to
adjust the start voltage so it matches the other sweep.

3. Duplicate the sweep start adjustment for the A sweep with a new R757, R758,
and R759. The offset trim fix (2) would be easier to calibrate though.


Odd 7904 problem

ictjayhawk@...
 

Picked up 2 7904's the other day. B15xxxx with a bad interface connector and FF in the calibrator circuit, and B25xxxx that is possessed.

No matter what vertical mode I selected I got Alternate. Except alternate, then it would sweep L1, L1, R1, R1,L2,L2,R2,R2 (alternate alternate??) I thought I had a logic board problem and swapped U215 (I think) and it was still misbehaving. Other than that and no readout on the R2 channel it all seemed to be OK.

So I went to try it before posting, it was still broken. Then it started working as advertised (except the R2 readout) and now it won't break again.

Any ideas/wags?


Re: Tek 2445B regulator C1072 voltage rating

 

I usually reverse engineer from the schematic to decide what part would be best.

C1291 and C1292 may be polarized but should be low leakage. They operate with a
voltage of 7.5 volts across C1291 and 17.5 volts across C1292.

There is some failsafe stuff going on with C1291 but I doubt that would drive it
with reverse polarity and if it did nothing would be damaged. U1300C is a
backup circuit that makes sure the 10 volt output never rises above 10.83 volts.
The other two inputs pull the 10 volt reference down pulling other supply
voltages down if either the +87V or +42V power supply outputs sag for whatever
reason.

C1272 could be driven into reverse polarity if the +5VD output tried to sag or
the optocoupler was insensitive requiring more drive from U1371C but the
impedance is high and it would not be damaged.

Maybe Tektronix used aluminum electrolytics because they preferred they fail
open. I probably would have used film or ceramic capacitors.

On 03 Nov 2013 16:39:55 -0800, you wrote:

Hi Rob,

Assuming that your power supply was working correctly prior to the recapping, then you should replace with the same capacitor types that you find installed in the unit and ignore the Tek service manual schematic and the parts list.

I had found bipolar caps in one power supply but not another, both installed in 246xA scopes produced in 1988. This is why I had earlier posted that one cannot place 100% faith in a capacitor list found either in the service manual or on this website.

Patrick Wong AK6C

---In tekscopes@..., <r.turk@...> wrote:

It is a bit confusing to me. The capacitors do have the marking 'BP' on them which might mean Bi-polar. However, the 2465B schematics I found suggest that C1291 and C1292 have a well-defined polarity.

On the schematics, the negative side of C1291 connects to U1300 pin 13 and a divider which will alway be between 0 and 10V, while the positive side connects to U1300 pin 14 (+10V ref).

For C1292 the positive side connects to the gate of Q1290 and to +2.5V via a resistor, while the negative side goes to -15V unreg.

C1270 has polarity on the schematics but is a regular non-polarized capacitor on the PCB. C1274 again shows polarity on the schematics, and it is an electrolytic version, but again marked 'BP' and no polarity indication. This is the only one I'd suspect to see both polarities.

I could not find anything about these in the group history, does this mean that most people do not swap these out when re-capping their scope?


Re: 453 follow-up

 

On 04 Nov 2013, at 04:10, David <davidwhess@...> wrote:
1. When switching between normal/inverted modes on CH2, the zero line needs to be about half a division above the middle reticule in order for inverting to not move the line. I can "fix" that by tweaking the CH2 calibration settings, but not while also having proper vertical calibration as per the manual. Since there is no calibration procedure for this element, I am guessing that it might be normal, but is it?
The 454 added an adjustment (R334 in the middle of schematic 4) for the vertical
amplifier balance which could fix this. Tektronix apparently used it to prevent
position shift in ADD mode but I think it is effectively the same thing. You
could add a similar adjustment and calibrate out the channel 2 inverting mode
trace shift if it bothers you.
Ah, good to know. I will take a look at the 454 manual and maybe just find a fixed resistor value that gets it closer to zero.

The 465 added separate adjustments for vertical amplifier balance and channel 2
inverting balance.

The 465 specification for inverting balance is 2 divisions so your 1/2 division
is well within the specification for later oscilloscopes. Typically I see it
shift a minor division at most on non 45x series oscilloscopes and it is
somewhat temperature sensitive.
On my 453 it seems reasonably constant. Step attenuation balance changes a fair bit with temperature, though, so maybe once inverting balance gets closer to zero, it becomes more noticeable.

2. More importantly and annoyingly, when switching from A/A-with-B to B sweep, the horisontal position moves about 3.5 division to the left. This happens at all sweep speeds and settings. I have tried to follow the circuit description, but I am only a humble software guy, so no joy as yet. Any suggestions?
I would take a look at the sweep start adjustments starting on page 6-45 of the
service manual. Before I decided something was wrong though, I would do a
complete horizontal calibration.
I already did a full calibration. The A sweep start adjustment R758 moves A and B horizontal positions equally, so the offset stays the same.


--
Soren


Re: 453 follow-up

 

On Mon, 4 Nov 2013 01:55:49 +0100, you wrote:

. . .

However, there are a couple of minor functional failings left that I'd like to address.

1. When switching between normal/inverted modes on CH2, the zero line needs to be about half a division above the middle reticule in order for inverting to not move the line. I can "fix" that by tweaking the CH2 calibration settings, but not while also having proper vertical calibration as per the manual. Since there is no calibration procedure for this element, I am guessing that it might be normal, but is it?
The 454 added an adjustment (R334 in the middle of schematic 4) for the vertical
amplifier balance which could fix this. Tektronix apparently used it to prevent
position shift in ADD mode but I think it is effectively the same thing. You
could add a similar adjustment and calibrate out the channel 2 inverting mode
trace shift if it bothers you.

The 465 added separate adjustments for vertical amplifier balance and channel 2
inverting balance.

The 465 specification for inverting balance is 2 divisions so your 1/2 division
is well within the specification for later oscilloscopes. Typically I see it
shift a minor division at most on non 45x series oscilloscopes and it is
somewhat temperature sensitive.

2. More importantly and annoyingly, when switching from A/A-with-B to B sweep, the horisontal position moves about 3.5 division to the left. This happens at all sweep speeds and settings. I have tried to follow the circuit description, but I am only a humble software guy, so no joy as yet. Any suggestions?
I would take a look at the sweep start adjustments starting on page 6-45 of the
service manual. Before I decided something was wrong though, I would do a
complete horizontal calibration.


Re: Bench mains supply - another attempt

Don Black <donald_black@...>
 

I'd use a halogen or projector lamp rather than a fuser lamp. They should run with a much higher filament temperature and have a greater cold/hot resistance change. It should be only a couple of ohms when cold (depending on the operating voltage) up to the calculated resistance from power/voltage at full brightness. Since it's reasonable to assume the house fuse can handle using a projector without blowing, the lamp should provide complete protection. Worst case is  a dead shorted load in which case it's the same as just using the lamp.

Don Black.

On 04-Nov-13 12:05 PM, John Griessen wrote:
 

On 11/02/2013 01:24 PM, edbreya@... wrote:
> Another option if you have enough junk laser printers available, is to use the fuser lamps fromthem - typically around 750-1000W.
> They have nice ceramic mounts, but are kind of long, so trickier to mount and cool within a piece of equipment.

Unless you leave them in the fuser....or just mounted in the fuser roller...

I have an obsolete HP 8550 fuser for sale on craigslist. Maybe I'll keep it instead...:-)



Re: Bench mains supply - another attempt

 

On Sun, 03 Nov 2013 19:09:34 -0600, you wrote:

On 11/02/2013 01:30 PM, David wrote:
The simple thing to do might be to
just build an outlet extension that has its own small (5 amp?) short delay
circuit breaker

That too. I have some DIN rail ABB breakers in my junk store of 2A 4A 6A 8A 12A...

any of those would be fine for this kind of app.

I have a photo catalog of my attic and store room junk. Maybe I should put it on the web and consider offers...:-)
I found suitable and relatively inexpensive, less than $20, panel mount ones
from Newark but I had to spend time going through datasheets to do it. They
were panel mount toggle switch style hydraulic-magnetic breakers. I had to
check the datasheets to verify the delay curves.


Re: Tek 2445B regulator C1072 voltage rating

vdonisa
 

As long as one observes the max rated ripple current and voltage, there's no harm done through replacing polarized caps with non-polarized (bipolar) ones. So if in doubt use BP and live happy.

 



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

Hi Rob,


Assuming that your power supply was working correctly prior to the recapping, then you should replace with the same capacitor types that you find installed in the unit and ignore the Tek service manual schematic and the parts list.


I had found bipolar caps in one power supply but not another, both installed in 246xA scopes produced in 1988.  This is why I had earlier posted that one cannot place 100% faith in a capacitor list found either in the service manual or on this website. 


Patrick Wong AK6C



---In tekscopes@..., <r.turk@...> wrote:

It is a bit confusing to me. The capacitors do have the marking 'BP' on them which might mean Bi-polar. However, the 2465B schematics I found suggest that C1291 and C1292 have a well-defined polarity.

On the schematics, the negative side of C1291 connects to U1300 pin 13 and a divider which will alway be between 0 and 10V, while the positive side connects to U1300 pin 14 (+10V ref).

For C1292 the positive side connects to the gate of Q1290 and to +2.5V via a resistor, while the negative side goes to -15V unreg.

C1270 has polarity on the schematics but is a regular non-polarized capacitor on the PCB. C1274 again shows polarity on the schematics, and it is an electrolytic version, but again marked 'BP' and no polarity indication. This is the only one I'd suspect to see both polarities.

I could not find anything about these in the group history, does this mean that most people do not swap these out when re-capping their scope?


Re: Tek 2445B regulator C1072 voltage rating

vdonisa
 

 There are quite a lot of 3.3uF/400V available from digikey, mouser and newark. If you're looking for the longest life, the Rubycon LLE (digikey has stock) is the one. Take care there are 2 versions in 3.5mm and 5mm lead spacing, IIRC you want the 5mm but since you have the scope disassembled you may want to measure first.



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

I'm re-capping my Tek 2445B scope. One of the capacitors on the A2 low voltage regulator board (C1072) is 3.3uF 350V. My supplier happens to not have this one in stock. Looking at the schematics I can't see why this capacitor should be rated for such a high voltage. It has low voltages all around it.

Since the scope is disassembled I do not have the option to switch it on and measure what's across that capacitor. Can anyone with this scope measure it, or perhaps confirm that a lower rated capacitor can be used as a substitute?

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