Date   

Pro technique for discharging an old Tektronix 5440 CRT?

Rick
 

Hi, I have an old Tektronix 5440 scope and would like to know what technique the pros use for discharging the CRT on this scope. The CRT is hidden behind a shroud so getting to the HV line right on the CRT is difficult. There is access under the HV component area. I know that the fact that I'm asking such a basic question is a red flag in itself. But I do want to know how others tackle this on this unit. Thanks, Rick


Re: Odd 485 behaviour in ALT and CHOP

 

Pah! I tried to upload them but neo's broken as usual.

The pictures are on my website:

<http://www.perdrix.co.uk/pix/Odd 485 behaviour in ALT and CHOP (3).JPG>

<http://www.perdrix.co.uk/pix/Odd 485 behaviour in ALT and CHOP (4).JPG>

Dave

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: 30 September 2016 17:19
To: TekScopes@...
Subject: [TekScopes] Odd 485 behaviour in ALT and CHOP

1) Using 1kHz cal signal as input to Channel 1, sweep 0.5mS/div, mode ALT,
trigger on Channel 1 all OK

2) As above but INT TRIG "Normal", sweep doesn't trigger on cal signal but
appear to be triggering on alternate sweeps

3) Using 1MHz cal signal to channel 1, sweep 0.5uS/Div, mode CHOP, INT TRIG
on Channel 1 all OK

4) As 3) but INT TRIG "Normal", I see a upper trace two lines broken at rep
rate of CHOP signal with gaps for the CHOP blanking and lower trace (Channel
2) single trace broken at CHOP blank rate but reverse of upper.

I'll put a couple of photos in the pictures area to show what I mean for 3)
and 4).

Dave





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Posted by: "David C. Partridge" <david.partridge@...>
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Yahoo Groups Links


Odd 485 behaviour in ALT and CHOP

 

1) Using 1kHz cal signal as input to Channel 1, sweep 0.5mS/div, mode ALT,
trigger on Channel 1 all OK

2) As above but INT TRIG "Normal", sweep doesn't trigger on cal signal but
appear to be triggering on alternate sweeps

3) Using 1MHz cal signal to channel 1, sweep 0.5uS/Div, mode CHOP, INT TRIG
on Channel 1 all OK

4) As 3) but INT TRIG "Normal", I see a upper trace two lines broken at rep
rate of CHOP signal with gaps for the CHOP blanking and lower trace (Channel
2) single trace broken at CHOP blank rate but reverse of upper.

I'll put a couple of photos in Album "Odd 485 behaviour in ALT and CHOP" to
show 3) and 4)

Puzzled

Dave


Odd 485 behaviour in ALT and CHOP

 

1) Using 1kHz cal signal as input to Channel 1, sweep 0.5mS/div, mode ALT,
trigger on Channel 1 all OK

2) As above but INT TRIG "Normal", sweep doesn't trigger on cal signal but
appear to be triggering on alternate sweeps

3) Using 1MHz cal signal to channel 1, sweep 0.5uS/Div, mode CHOP, INT TRIG
on Channel 1 all OK

4) As 3) but INT TRIG "Normal", I see a upper trace two lines broken at rep
rate of CHOP signal with gaps for the CHOP blanking and lower trace (Channel
2) single trace broken at CHOP blank rate but reverse of upper.

I'll put a couple of photos in the pictures area to show what I mean for 3)
and 4).

Dave


Re: Scope input capacitance

 

Tried with a "DER EE DE-5000" LCR meter, on a HM203-6 scope, no problems
measuring.
5mV range did need to be measured with scope powered to be at the specified
30pF, powered off it measured 1.2nF.

Paul


2016-09-29 23:35 GMT+02:00 colingherbert@... [TekScopes] <
TekScopes@...>:

Hi,
According to the datasheet for the 067-0538-00 Calibration fixture (input
normalizer 20pF), it is possible to measure the input capacitance of a
scope channel with a Tektronix type 130 L-C meter. Does anyone have any
idea of how this might be achieved and if any other L-C meter could be used?
I have tried just connecting the test-leads of two or three of my L-C
meters across the input BNCs while the scope is powered up to no avail. I
am puzzled.
Colin.






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Posted by: colingherbert@...
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------------------------------------

Yahoo Groups Links




Re: 485 Chop mode not working

bobh@joba.com
 

I am often searching for articles on custom ICs. Analog Devices has some good articles and you can search by author which is sometimes helpful.

http://www.analog.com/library/analogDialogue/archives.html#ghi

Gilbert, Barrie

Leif's Teaser Number 1

Considering Multipliers (Part 1)

Noise Figure and Logarithmic Amplifiers

D-Day (continued)

D-Day

Oscar Stirs

The Fourth Dee: Turning Over a New Leif

The Four Dees of Analog, circa 2025

Accurate Gain/Phase Measurement at Radio Frequencies up to 2.5 GHz

Low-Distortion Mixer: +24 dBm 3rd-Order Intercept for Only —10 dBm LO Power

Low-Noise, Wideband Voltage-Controlled Amplifiers with "Linear-in-dB" Gain

Monolithic DC-to-120-MHz Log-Amp Is Stable and Accurate

High-Accuracy, Widest Bandwidth IC Analog Multiplier

Monolithic Analog Trigonometric Function Generator

Wideband 2-Channel Monolithic Analog Multiplier/Divider

Monolithic IC RMS-to-DC Converter

Accurate, Low-Cost, Easy-to-Use IC Multiplier

Versatile Monolithic V/F or I/F Converter

Current Inverter with Wide Dynamic Range



Thought this might be of interest to someone out there.

Bob.




From: 'David C. Partridge' david.partridge@... [TekScopes]
Sent: Friday, September 30, 2016 7:03 AM
To: TekScopes@...
Subject: RE: [TekScopes] 485 Chop mode not working


On re-checking the 7400 was sick, clearly not enough caffeine when I checked
earlier.

I'd still like to know more about the 155-0011-00 though if there is info
about it out there.

D.
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: 30 September 2016 12:06
To: TekScopes@...; TekScopes2@...
Subject: [TekScopes] 485 Chop mode not working

Alt mode works fine. Chop mode doesn't, but may end up on one or the other
channel. I initially thought that U1530 or U1580 were suspect, after
checking, I believe they are OK.

Pin 4 U1585 (155-0011-00) has what looks like it ought to be the chopping
signal, but is only 0.5V pp which feels wrong.

Does anyone have any information about that that IC?

Please could someone who has a 485 put it into chop mode and check that
signal for me?

Thanks
Dave





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


Re: DM501A problem

Tom Gardner
 

On 30/09/16 15:46, Sigur�ur �sgeirsson siggi@... [TekScopes] wrote:

On Fri, 30 Sep 2016 at 08:05 David davidwhess@... [TekScopes] <
TekScopes@...> wrote:

On the gripping hand (obscure?),
<OT>The Mote in God's eye - my all-time favorite SciFi book. Not at all
obscure, if you ask me.</OT>
Not for us greybeards anyway. My copy is signed by Niven, the only
time I've bothered to get an autograph (it was zero effort on my part,
so why not).

Other rather good "first contact" books are
"Childhood's End" by Arthur C Clarke (the recent TV movie somehow manages to avoid all sense-of-wonder),
"The Black Cloud" by Fred Hoyle (any novel containing calculus has to be worth reading),
"A For Andromeda" also by Fred Hoyle (shame the BBC lost Julie Christie's first performance)


Re: DM501A problem

Siggi
 

On Fri, 30 Sep 2016 at 08:05 David davidwhess@... [TekScopes] <
TekScopes@...> wrote:



On the gripping hand (obscure?),
<OT>The Mote in God's eye - my all-time favorite SciFi book. Not at all
obscure, if you ask me.</OT>


Re: 485 Chop mode not working

 

On re-checking the 7400 was sick, clearly not enough caffeine when I checked
earlier.

I'd still like to know more about the 155-0011-00 though if there is info
about it out there.

D.

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: 30 September 2016 12:06
To: TekScopes@...; TekScopes2@...
Subject: [TekScopes] 485 Chop mode not working

Alt mode works fine. Chop mode doesn't, but may end up on one or the other
channel. I initially thought that U1530 or U1580 were suspect, after
checking, I believe they are OK.

Pin 4 U1585 (155-0011-00) has what looks like it ought to be the chopping
signal, but is only 0.5V pp which feels wrong.

Does anyone have any information about that that IC?

Please could someone who has a 485 put it into chop mode and check that
signal for me?

Thanks
Dave


Re: DM501A problem

 

So motie it be ... :)

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...]
Sent: 30 September 2016 13:06
To: TekScopes@...
Subject: Re: [TekScopes] DM501A problem

On one hand, I have a DM501A with problems as well although not the same
problems. On the other hand, the service manual I have has split schematics
which are also not very good scans. On the gripping hand (obscure?), I will
be spending some time today fixing up the schematic scans (including the
LD120 and LD121 scans) and then make them available at which point I may be
able to make some more constructive suggestions.

Mine almost works after cleaning all of the mechanical switches. They may
need even more cleaning.

My DM501A has those terrible Texas Instruments edge wipe sockets. Have you
tried reseating all of the ICs? Pay particular attention to any which feel
loose.

I may end up preemptively replacing the sockets and aluminum electrolytic
capacitors in mine and then cleaning the boards in my ultrasonic cleaner.

On 30 Sep 2016 04:07:57 -0700, you wrote:

Hi,

Thanks. I did check them, they are OK. The power supply seems to be OK. So
I'll continue looking at the AD and associated circuitry.

Szabolcs

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Posted by: David <davidwhess@...>
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------------------------------------

Yahoo Groups Links


Re: DM501A problem

 

On 30 Sep 2016 05:34:17 -0700, you wrote:

...

I also checked the reed relays for the 2V/200mV rage change, and that the input voltage appears at the input of the AD. So this is why I'm now concentrating on the AD, as the input there seems to be fine and the segment drivers work. I actually get consistent, but false reading for various inputs.
That threw me off for a bit. My first thought was that the input
protection circuits are leaking do to damage but I looked at the
schematic long enough to see that input protection relies on R1613
(560k) and whatever internal arrangements U1601 (LD120) has. Saying
LD120 is bad is not very satisfactory because I would prefer something
easier to fix or replace.

What I do not understand is why the zero adjustments do not do
anything and again, that points to a bad LD120 and I would still
prefer some other problem.

Next is to check the waveforms for LD120/121 on the scope,then to check all passives around the AD, like the integrator capacitor, etc.
The LD120/121 datasheet will be invaluable here to understand what is
suppose to be going on. I am hoping that the problem is something
like failure of the integration capacitor or autozero storage
capacitor.

The various other functions, like ohms also seem to work, as there is voltage/current on the inputs,but the reading is false. But there is no point in looking at the other functions, until the voltage reading works.

Szabolcs
Exactly, fix the 200mV and 2V DC ranges first.


Re: TM500 'specials' & OEMs

 

On Fri, 30 Sep 2016 12:43:54 +0100, you wrote:

from Tim P (UK)

I saw the two 'specials' on Christian's website - the ZIG-T is interesting
in that ultra-high impedance amplifiers have application in Cell Physiology
for use with micro-electrodes. I'd love to see the schematic.

...

Tim
The input amplifier will be about what one would expect; The ZIG-T was
recent enough to use JFET or MOSFET inputs without a shunt resistor.
See the 7A13, 7A22, and DM502 schematics for examples where the input
shunt resistor can be disconnect.

It is easy to get into the 10s of gigohms range and much higher today
using a JFET or MOSFET input operational amplifier. Check out the
common mode input resistance specification on an operational amplifier
datasheet which applies to the non-inverting input; for an LMC6081, it
is greater than 10 teraohms (10 mega megohms) typical. DIP parts have
an advantage here over surface mount because the non-inverting input
pin can be bent up away from the printed circuit board and wired in
the air which is an excellent insulator.

Close attention needs to be paid to input leakage from other sources
including input protection circuits.


Re: DM501A problem

Szabolcs Szigeti
 

Thanks. Yeah, those scans are not very good. I ended up printing them and just taping the pages together. Fortunately they are scanned with some overlap, so it is easy to glue them into one.

So far I have checked the power supplies, reseated the sockets, cleaned the swithes a bit. I really do really not wish to take it apart, seems like I'd need to de-solder all the switches to remove the upper panel. Not a very good design...
I also checked the reed relays for the 2V/200mV rage change, and that the input voltage appears at the input of the AD. So this is why I'm now concentrating on the AD, as the input there seems to be fine and the segment drivers work. I actually get consistent, but false reading for various inputs.

Next is to check the waveforms for LD120/121 on the scope,then to check all passives around the AD, like the integrator capacitor, etc.

The various other functions, like ohms also seem to work, as there is voltage/current on the inputs,but the reading is false. But there is no point in looking at the other functions, until the voltage reading works.

Szabolcs


Re: DM501A problem

 

On one hand, I have a DM501A with problems as well although not the
same problems. On the other hand, the service manual I have has split
schematics which are also not very good scans. On the gripping hand
(obscure?), I will be spending some time today fixing up the schematic
scans (including the LD120 and LD121 scans) and then make them
available at which point I may be able to make some more constructive
suggestions.

Mine almost works after cleaning all of the mechanical switches. They
may need even more cleaning.

My DM501A has those terrible Texas Instruments edge wipe sockets. Have
you tried reseating all of the ICs? Pay particular attention to any
which feel loose.

I may end up preemptively replacing the sockets and aluminum
electrolytic capacitors in mine and then cleaning the boards in my
ultrasonic cleaner.

On 30 Sep 2016 04:07:57 -0700, you wrote:

Hi,

Thanks. I did check them, they are OK. The power supply seems to be OK. So I'll continue looking at the AD and associated circuitry.

Szabolcs


TM500 'specials' & OEMs

Tim Phillips <tim@...>
 

from Tim P (UK)
I saw the two 'specials' on Christian's website - the ZIG-T is interesting in that ultra-high impedance amplifiers have application in Cell Physiology for use with micro-electrodes. I'd love to see the schematic.

Also, I was intrigued by the Ball Screw Test Fixture, although that's probably just my puerile sense of humour !! <g>

Tim


Re: DM501A problem

Szabolcs Szigeti
 

Hi,

Thanks. I did check them, they are OK. The power supply seems to be OK. So I'll continue looking at the AD and associated circuitry.

Szabolcs


485 Chop mode not working

 

Alt mode works fine. Chop mode doesn't, but may end up on one or the other
channel. I initially thought that U1530 or U1580 were suspect, after
checking, I believe they are OK.

Pin 4 U1585 (155-0011-00) has what looks like it ought to be the chopping
signal, but is only 0.5V pp which feels wrong.

Does anyone have any information about that that IC?

Please could someone who has a 485 put it into chop mode and check that
signal for me?

Thanks
Dave


Re: New user with 465 needs help

 

A change from 1.000 megohms to 0.993 megohms is not significant so
maybe the input capacitance and compensation just needs to be
adjusted.

On Fri, 30 Sep 2016 00:06:07 +0000 (UTC), you wrote:

I tested the inputs with ohm meter. Channel with 307-1014-01 attenuator is 1M ohm all voltage settings. Channel with suspect 307-1014-02 attenuator is 1M ohm thru .2V/div, all higher voltage settings show .993M ohm. 7K ohm difference. Doesn't matter which channel it is in, reads the same. The 307-1014-02 is correct part in part list,


Re: Scope input capacitance

 

I was not able to make these measurement with my 1 kHz ESI 250DA
impedance bridge; the 1 megohm shunt resistance across such a small
capacitance moved the dissipation out of range. An external variable
reference resistance could be used with the impedance bridge but it is
a lot more trouble and I do not have one handy.

The Tektronix 130 manual makes a point of saying that the 130 is
specifically suitable for making these measurements.

On 29 Sep 2016 20:57:39 -0700, you wrote:

You can measure the dead (disconnected from power and signal cables) scope input capacitance with a low frequency bridge if the low side of the bridge has low enough impedance to drive the scope's chassis against its capacitance to everything else around without upsetting the measurement.

However, the input capacitance may be a little different when the circuits are powered up. The best way to measure it is with power on, and a ground-referenced C-meter like the Tek 130, or fix the bridge measurement setup with a balun to allow one side to be grounded.

I know that in the case of the 130, it can handle the shunt 1 meg input R OK, although some meters may have issues with it. At common test frequencies the C current should dominate the result. If you use a bridge and very low frequency to avoid the chassis loading effects, the R becomes more of a factor.

I wouldn't worry too much about measuring or tweaking the input C unless you've made significant changes or repairs to the front-end.

Ed


Re: Scope input capacitance

Ed Breya
 

You can measure the dead (disconnected from power and signal cables) scope input capacitance with a low frequency bridge if the low side of the bridge has low enough impedance to drive the scope's chassis against its capacitance to everything else around without upsetting the measurement.

However, the input capacitance may be a little different when the circuits are powered up. The best way to measure it is with power on, and a ground-referenced C-meter like the Tek 130, or fix the bridge measurement setup with a balun to allow one side to be grounded.

I know that in the case of the 130, it can handle the shunt 1 meg input R OK, although some meters may have issues with it. At common test frequencies the C current should dominate the result. If you use a bridge and very low frequency to avoid the chassis loading effects, the R becomes more of a factor.

I wouldn't worry too much about measuring or tweaking the input C unless you've made significant changes or repairs to the front-end.

Ed

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