Date   
Re: 2465B SN 55xxx with TEST 05 FAIL 40

 

Option 46 is the designation for the military version of the scope (OS-288/G) that included option 10 IEEE-488 interface and 2 probes.

Manuel

Re: free - tek 453 scope manual printout

chuck
 

just confirmed my scope is pre "a" so the docs would need to be for the vanilla 453.
Thanks

Re: troubleshooting Tek453 Mod 210H

Fabio Trevisan
 

Hello Chuck,

On your finding of D940 opened, there is a screaming question... How did you tested it open?
H.V. diodes usually have a very large forward voltage drop (circa 20 volts), and they won't test right on a regular diode test.
Still, assuming your diagnostic is correct and D940 is indeed open, it's a Tek part number 152-0192-00, and the commercial part number is manufacturer specific, it's a VARO 7701-5X.
You can find its specs here:
http://w140.com/Tektronix_Xref_sm.pdf, page 12-2, line 8.
It's a 5kV diode, 50mA rated average forward current. and it has 15V forward voltage drop at the rated current.

Back in 2016, When I needed to diagnose a H.V. problem on my former 464, one of my first suspects were the H.V. diodes, and they're of this same vintage (not the same specs, but are also from VARO).
Back then, I sourced from a local electronics store, a few modern ESJA53-12. They are 12kV, low recovery time H.V. diodes, for currents up to 5mA and they worked fine on the 464, but the original parts on the 464 were 12kV 5mA (so the ESJA53-12 were a perfect match).

The ones on the 453, however, are 50mA, so I guess you will need to source different ones:
Either original parts (new old stock), and two reputable sources that users from Tekscopes group often resort to are:
Sphere: (http://www.sphere.bc.ca/) or...
QService: (https://www.qservice.tv/)...
(No affiliation though... just a happy customer)
Or you can try these folks here: http://hvstuff.com/
Never dealt with them, but they're almost the only source you can find on the net for H.V. oriented stuff.

Krgrds,

Fabio

On Wed, Oct 10, 2018 at 05:16 PM, chuck wrote:


hi folks,
Just confirmed this is a 453 pre A version.
Found D940 was open and when I looked at the two versions of this circuit
there is considerable differences.
D940 is the biggest diode I've ever seen so I guess a 1n911 is not going to do
the job. I haven't had a chance to look at the BOM but if any one knows the
commercial P/N would be appreciated. Also stray thought what blew the diode?
Everything else in the grid bias ckt seems to be alive and well. Any thoughts?
Thanks for your help been a great learning experience for me.
Chuck

Re: 2465B SN 55xxx with TEST 05 FAIL 40

Chuck Harris
 

Tektronix wrote high option numbers, like OPT46, to show things,
like including 4 probes, when they usually only included 2, or
including a carry pouch, or adding a Japanese mains power cord,
..., stuff like that.

Other options were mnemonic to what the option provided, like
OPT14 being for P14 phosphor on some scopes.

However, I don't see 46 listed in any of the literature I have.

-Chuck Harris

tekscopegroup@... wrote:

Right you are, only 4 SMD problem caps total. I need to have the board in front of me for facts to start falling in place. Definitively will carefully chop apart the caps before attempting removal. I did not intend to disturb any tantalums, unless really necessary. I've also read that the 20K trimmer pot near the DAC sometimes gets also damaged and needs to be replaced before the ref voltages are correct again. Maybe just order it too along the caps, just in case.

Your cleaning procedure makes a lot of sense, something I've not seen explained in detail anywhere else. Usually one would cringe at the idea of splashing water on a board like this, but now I am reassured it will be the best thing to do, even if corrosion damage appears to be light (due to fumes spreading on all nearby surfaces) its worth doing it right.

Do you by any chance know what Option 46 would be for this scope? Its the only field on the rear panel that has a punched hole in it.

Thanks.



Re: troubleshooting Tek453 Mod 210H

chuck
 

hi folks,
Just confirmed this is a 453 pre A version.
Found D940 was open and when I looked at the two versions of this circuit there is considerable differences.
D940 is the biggest diode I've ever seen so I guess a 1n911 is not going to do the job. I haven't had a chance to look at the BOM but if any one knows the commercial P/N would be appreciated. Also stray thought what blew the diode? Everything else in the grid bias ckt seems to be alive and well. Any thoughts?
Thanks for your help been a great learning experience for me.
Chuck

Re: 2445A calibration

Chuck Harris
 

R618 adjusts a balance between the two output sections of the
vertical amplifier. It will affect the overall gain of the output
amplifier, somewhat.

C105 and 205 will affect the corner accuracy of the 1KHz calibration
waveform. They probably won't affect the overall CAL02 calibration.

It is good to do what they tell you to do. The code running in the
internal calibration routines is a black box, and I doubt anyone outside
of the tektronix engineers that wrote it knows exactly what it is doing.

-Chuck Harris

maxim.vlasov@... wrote:

Chuck,

Sorry for the typo:

not super symmetric: -1,236 for CCW and -1.265 for CW.
to be read as "not super symmetric: -1,236 for CCW and +1.265 for CW."

Also one more thing. Just realized that I have skipped the C105 and C205 adjustment together with R618. Could it cause the problem, what do you think?

Thanks again,

Maxim

Re: 2445A calibration

Chuck Harris
 

Ack!

A rule of thumb is that when calibrating, is you need to use references
that are a minimum of 10x more precise and accurate than what you are
calibrating.

The scope you are using to measure the Arbitrary Waveform Generator, is
likely no better than +/-1%, assuming it was recently calibrated.

To that end, the PG506 is specified to be within +/-0.25%, which is
not quite 10x more precise and accurate than the 2445A is capable, but
certainly a lot better than what you are doing.

Further, the PG506's output impedance, when in voltage calibration mode,
is not 50 ohms, it is about as close to zero ohms as was humanly possible
in its day. To wit, its specified accuracy is +/-.25% +/-1uV for loads
of 1M *and* of 50 ohms.

The AWG most likely has a near zero ohm source with an internal 50 ohm
series resistance, put there to prevent reflections, from reflections
at the load end of the cable.

If 0.5Vp-p is showing as 0.55Vp-p, something is very wrong.

As to the DAC swing, it is not supposed to be symmetric about ground.
It must be 2.500V +/-1mv swing when the DELTA control is turned from
the fully CW position to the fully CCW position.

-Chuck Harris



maxim.vlasov@... wrote:

Hello Chuck,

I have started from the beginning. Replaced 4 aluminum caps on the A5 board (checked the ESR and capacity and they were fine). Then borrowed two 6.5 digit Agilent multimeters (to make sure about the readings) and set the 10V reference voltage to 10.0001V (can't do any better, the resistor is crusty). To measure things I use the ground hole under the calibrator output for the banana plug and pointy probe to measure things on J119.
Then I've continued to set the DAC reference voltage. The whole band is 2.501 volt, however it's not super symmetric: -1,236 for CCW and -1.265 for CW.
Then without touching anything else and re-running the CAL01 I've jumped on CAL02. Unfortunately CAL02 fails in the same fashion -> LIMIT ERROR.
Also noticed, that the gain of the scope is a little bit higher. I.e. instead of getting 0.5V p-p for 500mV calibration signal I get 0.55V. I wonder if it needs some fixing before going to CAL02.

For the vertical calibration I don't have the calibrator module like PG506. I substitute for that the AWG. The signal is 1KHz 50% duty cycle. Low level is 0V, HIGH level is what menu asks for into 50 Ohm, i.e. for 500mV required the AWG is set to provide LO=0V HI=0.5V into 50 Ohm. The output was tested on the "reference" scopes terminated to 50 Ohm.

I'm a bit lost in what could go wrong. I'll try checking the voltage ripple at the output of the power rails.

I just wonder if CAL02 would be affected by bad CAL01?

Thank you!

Best wishes,

Maxim



Re: 2445A calibration

maxim.vlasov@...
 

Chuck,

Sorry for the typo:

not super symmetric: -1,236 for CCW and -1.265 for CW.
to be read as "not super symmetric: -1,236 for CCW and +1.265 for CW."

Also one more thing. Just realized that I have skipped the C105 and C205 adjustment together with R618. Could it cause the problem, what do you think?

Thanks again,

Maxim

Re: 2445A calibration

maxim.vlasov@...
 

Hello Chuck,

I have started from the beginning. Replaced 4 aluminum caps on the A5 board (checked the ESR and capacity and they were fine). Then borrowed two 6.5 digit Agilent multimeters (to make sure about the readings) and set the 10V reference voltage to 10.0001V (can't do any better, the resistor is crusty). To measure things I use the ground hole under the calibrator output for the banana plug and pointy probe to measure things on J119.
Then I've continued to set the DAC reference voltage. The whole band is 2.501 volt, however it's not super symmetric: -1,236 for CCW and -1.265 for CW.
Then without touching anything else and re-running the CAL01 I've jumped on CAL02. Unfortunately CAL02 fails in the same fashion -> LIMIT ERROR.
Also noticed, that the gain of the scope is a little bit higher. I.e. instead of getting 0.5V p-p for 500mV calibration signal I get 0.55V. I wonder if it needs some fixing before going to CAL02.

For the vertical calibration I don't have the calibrator module like PG506. I substitute for that the AWG. The signal is 1KHz 50% duty cycle. Low level is 0V, HIGH level is what menu asks for into 50 Ohm, i.e. for 500mV required the AWG is set to provide LO=0V HI=0.5V into 50 Ohm. The output was tested on the "reference" scopes terminated to 50 Ohm.

I'm a bit lost in what could go wrong. I'll try checking the voltage ripple at the output of the power rails.

I just wonder if CAL02 would be affected by bad CAL01?

Thank you!

Best wishes,

Maxim

Re: 2465B SN 55xxx with TEST 05 FAIL 40

Tom Gardner
 

My technique, which I used to replace the capacitors and one SMD resistor in the middle of the others, was:

* play a soldering station's hot air gun over the relevant component until the
solder melts and it blows away (do a few experiments to see which
temperature/velocity works best, and use a narrow nozzle)
* protect the surrounding components by loosely covering them with
kapton/polyimide adhesive tape, to deflect the hot air away
* clean the pads etc by any means you choose; I used IPA
* dab solder paste on the pads
* place replacement components, using solder paste as an "adhesive"
* use hot air gun to reflow that component
* remove polyimide tape

On 10/10/18 17:02, tekscopegroup@... wrote:
Right you are, only 4 SMD problem caps total. I need to have the board in front of me for facts to start falling in place. Definitively will carefully chop apart the caps before attempting removal. I did not intend to disturb any tantalums, unless really necessary. I've also read that the 20K trimmer pot near the DAC sometimes gets also damaged and needs to be replaced before the ref voltages are correct again. Maybe just order it too along the caps, just in case.

Your cleaning procedure makes a lot of sense, something I've not seen explained in detail anywhere else. Usually one would cringe at the idea of splashing water on a board like this, but now I am reassured it will be the best thing to do, even if corrosion damage appears to be light (due to fumes spreading on all nearby surfaces) its worth doing it right.

Do you by any chance know what Option 46 would be for this scope? Its the only field on the rear panel that has a punched hole in it.

Thanks.

Re: troubleshooting Tek453 Mod 210H

Dale H. Cook
 

At 11:53 AM 10/10/2018, chuck wrote:

Second serial number is 005652 so I guess this monster is pre A.
Do you have Nuvistors in the front end and on the trigger board? If so you need the early 453 manual (serials below 20,000). It is at TekWiki:

http://w140.com/mmm/tek-453.pdf

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

Re: troubleshooting Tek453 Mod 210H

Brendan
 

On Wed, Oct 10, 2018 at 08:55 AM, chuck wrote:

just bought a 453 and of course there are problems. The trace is fat! Using the 1Khz internal signal when I put it on either channel the trace is out of focus and really hi intensity. The focus knob works to an extent but the intensity knob does nothing.

Fabio,
Just thought of something.
So far I have yet to see a tube. Have only lifted the Z amp so far but
everything is Xstrs.
There will be two rectifier tubes inside the HV box unless someone has made mods, and if you have a below 20,000 serial # the other "tubes" will be nuvistors. The A version has a larger screen than the non-A version. I have 2 non-A 453s one nuvistor and the other is all transistor minus rectifier tubes, both have a screen size of 3 1/2 inches wide by 2 1/4 tall.

Re: 2465B SN 55xxx with TEST 05 FAIL 40

tekscopegroup@...
 

Right you are, only 4 SMD problem caps total. I need to have the board in front of me for facts to start falling in place. Definitively will carefully chop apart the caps before attempting removal. I did not intend to disturb any tantalums, unless really necessary. I've also read that the 20K trimmer pot near the DAC sometimes gets also damaged and needs to be replaced before the ref voltages are correct again. Maybe just order it too along the caps, just in case.

Your cleaning procedure makes a lot of sense, something I've not seen explained in detail anywhere else. Usually one would cringe at the idea of splashing water on a board like this, but now I am reassured it will be the best thing to do, even if corrosion damage appears to be light (due to fumes spreading on all nearby surfaces) its worth doing it right.

Do you by any chance know what Option 46 would be for this scope? Its the only field on the rear panel that has a punched hole in it.

Thanks.

Re: troubleshooting Tek453 Mod 210H

chuck
 

Kevin,
Thanks for your tip. Will check these out once I get the courage to get into the CRT circuit. LOL

Re: troubleshooting Tek453 Mod 210H

chuck
 

Fabio,
Just thought of something.
So far I have yet to see a tube. Have only lifted the Z amp so far but everything is Xstrs.

Re: troubleshooting Tek453 Mod 210H

chuck
 

Fabio,
First thank you for your very specific help. I know what I'm doing today now. LOL Anyway yes I have the service manuals (pdf) howver I think I have the A version and need the non A I can find that on the web.
Second serial number is 005652 so I guess this monster is pre A.

Re: 2445A calibration

Chuck Harris
 

Hi Maxim,

Everything in the scope is referenced to the DAC voltage reference
adjustment, and it is referenced to the +10V power supply adjustment.

Setting the reference is tricky in that it must be exactly a 2.5V
difference between the DELTA CCW and DELTA CW readings. I wrote a little
program for the TI-84 calculator (a castoff from my son) that helps with
that.

Wat are you using for your calibration voltages when doing CAL02 ?

-Chuck Harris

Max Vlasov via Groups.Io wrote:

Hello Chuck,

Thank you for the great help. Looks like we are moving forward with 2445a, slowly but surely. I've recaptured the photo of the calibration CAL02 step 111:

https://groups.io/g/TekScopes/photo/74577/17?p=Name,,,20,1,0,0

Now it seems that the dots are round. The problem was with the faulty coax (BNC plug was a bit loose).

However, all the CAL02 and CAL03 tests with the external signal generator generate LIMIT error regardless the channel number. I have assumed that the LIMIT is detected by the peak detector circuit in U500 by altering the trigger level signal generated by the DAC.
Also I've checked following your advice whether the CAL/NCAL Voltage pot can be left where it was or placed into the detent position. In both cases LIMIT error is generated....

But good news are that after running CAL03, even though the LEVEL error was generated every time, I don't have a problem any more with AUTO LVL. So, when I press the AUTO LVL on channel 1/2/3/4 the scope automatically finds 50% voltage level of the selected trace. So, now it really works. IMHO, there is nothing wrong with U500. Also checked attenuators for CH1/2 in all the modes and all the V/DIV positions. They work properly, no problem (also I assumed that a film resistor is blown on channel 1, but can't find a fault).
By looking at the vertical trace levels when the external signal is applied, it seems like they are off by 1-2%, which is a small error (calibration should take care of that, but it doesn't).

Looks like the scope is fully functional...

Maybe the problem is with DAC and/or with the demultiplexer and sample&hold? I'll try checking the DAC reference. Also I wonder how symmetrical the DAC calibration should be (when judging by voltage measurements on J119). Also I wonder how precise the main voltage reference must be set (10.000V)? Likely I have omitted an important step somewhere, therefore the FW can't close the calibration loop.
I plan to re-check the power supply, DAC output voltages. I wonder if anybody else had anything similar to that....

Thank you again,

Best regards,

Maxim

Re: 2465B SN 55xxx with TEST 05 FAIL 40

Siggi
 

On Tue, 9 Oct 2018 at 22:20 <tekscopegroup@...> wrote:

I've been reading up on this A5 board bad caps situation and have found
similar good tips and information.
You should probably just change those SMD caps on sight. If you want to
conclusively trace the wandering traces to the DAC reference, you can do
that by measuring the 1.36 and -1.25 reference voltages on the A5 board.
Those should be spot-on and pure DC, if they wobble around as the traces
move, then you know the DAC reference is compromised.
If you don't see those wobble around with the traces, it means you have
other and/or additional problems.

It's also useful to measure those voltages after your repair to validate
that you've brought the DAC in spec.

Re: troubleshooting Tek453 Mod 210H

Fabio Trevisan
 

Hello Chuck,

When it comes to intensity control inoperative, and highly intense trace, I`m afraid that you're going to set your fears aside about the CRT circuit and playing around it (with all its indeed intimidating High Voltages)...
Still, a lot of those circuits can be troubleshoot on the "Low" side, and what can't, can be troubleshoot by rising one lead of the components and measuring them (with scope turned off).
The regular caution is advised though... To keep one hand in the pocket, to remember to discharge the H.V. points before poking around and, preferably, don't be isolated in the bunker with nobody around.

About the focus, I think you probably don't have a problem in that dept. The trace is fat and the focus can't tame it because it's too intense and the beam is "bloomed".

An inoperative intensity control can have many causes, from a short between grid (G1) and Cathode (K) of the CRT tube, to problems (mostly leakage currents) in the DC restorer circuitry, to defects around the CRT bias circuitry, which encompasses the Intensity control pot and the CRT bias control (usually a trimpot).

All that I`m saying above is general to CRTs and not exactly specific to the 453.

In order to get more specific, anyone in the group will ask you 2 things:
1. If you have a manual, whether in Paper or PDF form (which for the 453 vintage is simultaneously a user and service manual). Some options to download here:
http://w140.com/tekwiki/wiki/453
2. What is the serial number? And if it's really a plain 453, or if it's a 453A.

Please let us know... and we take from there.

Kindest Rgrds,

Fabio

On Wednesday, October 10, 2018, 2:38:26 AM PDT, chuck
<@chuckyorbalinda> wrote:

Folks,
just bought a 453 and of course there are problems. The trace is fat!
Using the 1Khz internal signal when I put it on either channel the trace is
out of focus and really hi intensity. The focus knob works to an extent but
the intensity knob does nothing. I traced the signal thru the z amp and it
behaves as it should as I adjust the knob the signal at the output stage
(prior to going into the CRT control circuit) changes. I'm intimidated by the
CRT circuitry and would love to get some feedback so that I'm not going in
blind. The Tek troubleshooting guide talks about Typical High Voltage problems
but does not really point me in a direction.
Any help would be appreciated. I have a couple of DVM's and a pocket
scope (Chinese knock off) to work with.
Chuck


Re: 2445A calibration

Max Vlasov
 

Hello Chuck,

Thank you for the great help. Looks like we are moving forward with 2445a, slowly but surely. I've recaptured the photo of the calibration CAL02 step 111:

https://groups.io/g/TekScopes/photo/74577/17?p=Name,,,20,1,0,0

Now it seems that the dots are round. The problem was with the faulty coax (BNC plug was a bit loose).

However, all the CAL02 and CAL03 tests with the external signal generator generate LIMIT error regardless the channel number. I have assumed that the LIMIT is detected by the peak detector circuit in U500 by altering the trigger level signal generated by the DAC.
Also I've checked following your advice whether the CAL/NCAL Voltage pot can be left where it was or placed into the detent position. In both cases LIMIT error is generated....

But good news are that after running CAL03, even though the LEVEL error was generated every time, I don't have a problem any more with AUTO LVL. So, when I press the AUTO LVL on channel 1/2/3/4 the scope automatically finds 50% voltage level of the selected trace. So, now it really works. IMHO, there is nothing wrong with U500. Also checked attenuators for CH1/2 in all the modes and all the V/DIV positions. They work properly, no problem (also I assumed that a film resistor is blown on channel 1, but can't find a fault).
By looking at the vertical trace levels when the external signal is applied, it seems like they are off by 1-2%, which is a small error (calibration should take care of that, but it doesn't).

Looks like the scope is fully functional...

Maybe the problem is with DAC and/or with the demultiplexer and sample&hold? I'll try checking the DAC reference. Also I wonder how symmetrical the DAC calibration should be (when judging by voltage measurements on J119). Also I wonder how precise the main voltage reference must be set (10.000V)? Likely I have omitted an important step somewhere, therefore the FW can't close the calibration loop.
I plan to re-check the power supply, DAC output voltages. I wonder if anybody else had anything similar to that....

Thank you again,

Best regards,

Maxim