Topics

500 series Calibration


Christopher Hilton-Johnson
 

hi Guys

Am spending the first few days of the newly instigated UK national lockdown calibrating several 500 series scopes – a 545B and a 547.

In each case there is an intriguing point where the manual, as part of the A and B timebase trigger level centering calibration asks you to:

for A Time Base Cal- ground the junction of R19 & R20 – both 545B (Change instructions) and 549 (manual)

for B Time Base Cal – ground the junction of R69 & R70 - both 545B (manual) and 549 (manual)

Now here is the issue. Finding and connecting to the required junctions can be/is hazardous particularly for those of us who have something of the shaky hand syndrome and a well developed sense of self preservation when working with high voltages in cramped spaces.

But wait: there appears to be a simple solution in every case. With the timebase trigger switch in the *Auto* position there is a direct path between those resistor junctions and chassis – the schematic says so and a simple continuity test with the scope off confirms it. Interestingly my version of the 545B manual uses this method in the manual, before changes brought in by the change information.

So am I missing something here? Does the suggested 'jumper lead' provide magic continuity properties? Is there some hidden feature not shown on the circuit diagram?

Any ideas why the obviously easy way is not followed, indeed is specifically disavowed it the case of the 545B change information.

Thanks in advance


Chuck Harris
 

Hi Christopher,

Fundamentally, I believe it is because there are a lot of
other circuits controlled by the many poles of switch
10B (DC, AC, AC LF REJECT, AUTO).

Check out Schematic #4 and #5's SW10B wafers.

The calibration specifies that TRIGGERING MODE control
should be in the AC position, and the STABILITY control
should be in the CW position.... that would cause SW110
to be in the position shown in the schematic, and would
put the wiper of the STABILITY control at -150V, and
connect it to the grid circuit of V125.

But if the TRIGGERING MODE switch was in the AUTO position,
the switches would connect the wiper of the PRESET ADJUST
trimmer to the grid circuit of V125.

My guess is that would affect the centering adjustment in
some way that isn't exactly repeatable.

-Chuck Harris


Christopher Hilton-Johnson wrote:

hi Guys

Am spending the first few days of the newly instigated UK national lockdown
calibrating several 500 series scopes – a 545B and a 547.

In each case there is an intriguing point where the manual, as part of the A and B
timebase trigger level centering calibration asks you to:

for A Time Base Cal- ground the junction of R19 & R20 – both 545B (Change
instructions) and 549 (manual)

for B Time Base Cal – ground the junction of R69 & R70 - both 545B (manual) and 549
(manual)

Now here is the issue. Finding and connecting to the required junctions can be/is
hazardous particularly for those of us who have something of the shaky hand syndrome
and a well developed sense of self preservation when working with high voltages in
cramped spaces.

But wait: there appears to be a simple solution in every case. With the timebase
trigger switch in the *Auto* position there is a direct path between those resistor
junctions and chassis – the schematic says so and a simple continuity test with the
scope off confirms it. Interestingly my version of the 545B manual uses this method
in the manual, before changes brought in by the change information.

So am I missing something here? Does the suggested 'jumper lead' provide magic
continuity properties? Is there some hidden feature not shown on the circuit diagram?

Any ideas why the obviously easy way is not followed, indeed is specifically
disavowed it the case of the 545B change information.

Thanks in advance







Dave Wise
 

?Disclaimers: (a) I own 545, 535A, and 547 but not 545B; and (b) my only 545B manual is the scan from BAMA whose last change is for S/N 2290 and A and B TRIGGER schematic pages drawn by CMD dated 565.


The 545, 545A, and 547 manuals all avoid AUTO, and the latter two employ a jumper. (The 545 procedure simply assumes that "0" yields 0V.)


AUTO has effects other than grounding Triggering Level, and using it to do so may result in incorrect calibration.


The Trigger Level cal procedure in my 545B manual is a self-contradicting mess. The B section tells you to set as in Table 5-1 except HORIZONTAL MODE B, but Table 5-1 sets TRIG A to AUTO and TRIG B to AC. At the end it says remove the jumper, without ever having told you to apply the jumper. Looks like some mistakes crept in when this manual was written. I don't have your change information, but I believe it corrects those mistakes.


Use the jumper. If you don't want to play "Operation"(TM) on a live instrument, install the jumper prior to powering on, and manipulate the grounded end as needed.?


Regards,

Dave Wise

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Christopher Hilton-Johnson via groups.io <chj=pchjhome.com@groups.io>
Sent: Wednesday, January 06, 2021 6:16 AM
To: TekScopes@groups.io
Subject: [TekScopes] 500 series Calibration

hi Guys

Am spending the first few days of the newly instigated UK national
lockdown calibrating several 500 series scopes - a 545B and a 547.

In each case there is an intriguing point where the manual, as part of
the A and B timebase trigger level centering calibration asks you to:

for A Time Base Cal- ground the junction of R19 & R20 - both 545B
(Change instructions) and 549 (manual)

for B Time Base Cal - ground the junction of R69 & R70 - both 545B
(manual) and 549 (manual)

Now here is the issue. Finding and connecting to the required junctions
can be/is hazardous particularly for those of us who have something of
the shaky hand syndrome and a well developed sense of self preservation
when working with high voltages in cramped spaces.

But wait: there appears to be a simple solution in every case. With the
timebase trigger switch in the *Auto* position there is a direct path
between those resistor junctions and chassis - the schematic says so and
a simple continuity test with the scope off confirms it. Interestingly
my version of the 545B manual uses this method in the manual, before
changes brought in by the change information.

So am I missing something here? Does the suggested 'jumper lead' provide
magic continuity properties? Is there some hidden feature not shown on
the circuit diagram?

Any ideas why the obviously easy way is not followed, indeed is
specifically disavowed it the case of the 545B change information.

Thanks in advance


Christopher Hilton-Johnson
 

Chuck

As ever you are correct - I had overlooked the sneeky addition to the SW10 switch on schematic page 5 of the 545B manual, which clearly connects V125 to the preset adjust pot when in the Auto position. Mea cupla!

Having said that discretion etc works for me - I calibrate to good functionality bu not necessarily to the absolute!

Even so the scopes (both 545B & 549) work well within their published performance specs - except perhaps the 549 whose tube is a bit tired, but then aren't we all!

Good to hear from you & thanks

Christopher

On 06/01/2021 16:20, Chuck Harris wrote:
Hi Christopher,

Fundamentally, I believe it is because there are a lot of
other circuits controlled by the many poles of switch
10B (DC, AC, AC LF REJECT, AUTO).

Check out Schematic #4 and #5's SW10B wafers.

The calibration specifies that TRIGGERING MODE control
should be in the AC position, and the STABILITY control
should be in the CW position.... that would cause SW110
to be in the position shown in the schematic, and would
put the wiper of the STABILITY control at -150V, and
connect it to the grid circuit of V125.

But if the TRIGGERING MODE switch was in the AUTO position,
the switches would connect the wiper of the PRESET ADJUST
trimmer to the grid circuit of V125.

My guess is that would affect the centering adjustment in
some way that isn't exactly repeatable.

-Chuck Harris


Christopher Hilton-Johnson wrote:
hi Guys

Am spending the first few days of the newly instigated UK national lockdown
calibrating several 500 series scopes – a 545B and a 547.

In each case there is an intriguing point where the manual, as part of the A and B
timebase trigger level centering calibration asks you to:

for A Time Base Cal- ground the junction of R19 & R20 – both 545B (Change
instructions) and 549 (manual)

for B Time Base Cal – ground the junction of R69 & R70 - both 545B (manual) and 549
(manual)

Now here is the issue. Finding and connecting to the required junctions can be/is
hazardous particularly for those of us who have something of the shaky hand syndrome
and a well developed sense of self preservation when working with high voltages in
cramped spaces.

But wait: there appears to be a simple solution in every case. With the timebase
trigger switch in the *Auto* position there is a direct path between those resistor
junctions and chassis – the schematic says so and a simple continuity test with the
scope off confirms it. Interestingly my version of the 545B manual uses this method
in the manual, before changes brought in by the change information.

So am I missing something here? Does the suggested 'jumper lead' provide magic
continuity properties? Is there some hidden feature not shown on the circuit diagram?

Any ideas why the obviously easy way is not followed, indeed is specifically
disavowed it the case of the 545B change information.

Thanks in advance








Christopher Hilton-Johnson
 

Dave

I too have the 547 and a 556, both of which work well (547 has the Chuck EHT transformer).

I like the 545B. Built like a tank, but beautifully constructed internally. As a measure I last calibrated it fully in 2002. When looking at it late last year its measured performance was pretty much spot on in most of its performance range. You are correct about the manual being a bit incoherent, but the change notes correct some of that.

I also have  another 545 Tek publication headed 'Calibration and Maintenance Procedure' with part number 070-282 first printed in March 1961 and selling for $2.00 with free shipping. It is different again from the Instruction manual in some respects.

I had always understood that when using or calibrating you had to wait 15 to 20 minutes from each switchon for the scope to stabilise/warm up , so that process slows everything down. It also concerns me about the more frequent startup/switchoff/warmup/cooldown cycles and stresses on 55yr old equipment.

I suppose the better way to do this is to attach all test wires/jumpers to all test points before startup, label and insulate everything and go through it all that way. I will go over those adjustments again - but very carefully!

Anyway thanks for the reply &, as usual, the useful help

Christopher

On 06/01/2021 16:55, Dave Wise wrote:
?Disclaimers: (a) I own 545, 535A, and 547 but not 545B; and (b) my only 545B manual is the scan from BAMA whose last change is for S/N 2290 and A and B TRIGGER schematic pages drawn by CMD dated 565.


The 545, 545A, and 547 manuals all avoid AUTO, and the latter two employ a jumper. (The 545 procedure simply assumes that "0" yields 0V.)


AUTO has effects other than grounding Triggering Level, and using it to do so may result in incorrect calibration.


The Trigger Level cal procedure in my 545B manual is a self-contradicting mess. The B section tells you to set as in Table 5-1 except HORIZONTAL MODE B, but Table 5-1 sets TRIG A to AUTO and TRIG B to AC. At the end it says remove the jumper, without ever having told you to apply the jumper. Looks like some mistakes crept in when this manual was written. I don't have your change information, but I believe it corrects those mistakes.


Use the jumper. If you don't want to play "Operation"(TM) on a live instrument, install the jumper prior to powering on, and manipulate the grounded end as needed.?


Regards,

Dave Wise

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Christopher Hilton-Johnson via groups.io <chj=pchjhome.com@groups.io>
Sent: Wednesday, January 06, 2021 6:16 AM
To: TekScopes@groups.io
Subject: [TekScopes] 500 series Calibration

hi Guys

Am spending the first few days of the newly instigated UK national
lockdown calibrating several 500 series scopes - a 545B and a 547.

In each case there is an intriguing point where the manual, as part of
the A and B timebase trigger level centering calibration asks you to:

for A Time Base Cal- ground the junction of R19 & R20 - both 545B
(Change instructions) and 549 (manual)

for B Time Base Cal - ground the junction of R69 & R70 - both 545B
(manual) and 549 (manual)

Now here is the issue. Finding and connecting to the required junctions
can be/is hazardous particularly for those of us who have something of
the shaky hand syndrome and a well developed sense of self preservation
when working with high voltages in cramped spaces.

But wait: there appears to be a simple solution in every case. With the
timebase trigger switch in the *Auto* position there is a direct path
between those resistor junctions and chassis - the schematic says so and
a simple continuity test with the scope off confirms it. Interestingly
my version of the 545B manual uses this method in the manual, before
changes brought in by the change information.

So am I missing something here? Does the suggested 'jumper lead' provide
magic continuity properties? Is there some hidden feature not shown on
the circuit diagram?

Any ideas why the obviously easy way is not followed, indeed is
specifically disavowed it the case of the 545B change information.

Thanks in advance