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Notice the Regulated +55 Volts signal through the Zener VR1515 at the
bottom of the 110 Volt regulator circuit? It is believed the root
cause is 120 HZ noise on the +55 Regulated supply.




A careful inspection of the +5 volt regulator circuit reveals that
regulated +55V also supplies a voltage divider circuit (R1559 and
R1554) to provide a +5 voltage reference to OP amp U1554A, pin 9. If
the +55 V signal is noisy, the same noise will be reflected in the +5
volt signal with a ratio of approximately 1/10 amplitude of the +55
volt noise.

+5 volt ripple can propagate to the blanking circuit when the voltage
supplied by the intensity adjustment pot is not high enough to block a
noisy +5 volts signal via diode CR1463. The blanking input is
normally around 0.4 to 0.5 volts, so a little bit of ripple is all
that's required to cause a blanking issue.



The most likely caps needing replacement are C1512, C1513. The
schematic indicates +78 volt reading to ground between caps C1512 and
C1513. These affect the +110 V, +55 v and ultimately +5 volt regulated
supplies.

Noise on the +5 volt supply can affect blanking when the intensity
adjustment voltage is less than +5 volts and voltage limiting diode
CR1463 is allowed to conduct.

On my scope, the blanking issue goes away when the intensity is
increased high enough, adding additional weight to this theory.

Ron



"One experiment is worth a thousand calculations."







--- In TekScopes@..., "jordankersten" <jordankersten@>
wrote:

Ok, all voltages (regulated and unregulated) are fine except the

110V supply. I get 120V

unregulated, which I think is fine. I only get 100V regulated.

Also, the 110V unregulated

reads 25VAC and the 110V regulated reads 11VAC. All other supply

voltages (regulated

and unregulated) read 0 VAC. I would suspect the 550uf power supply

cap, but would that

explain why my regulated 110 voltage is 10V low?

--- In TekScopes@..., "jordankersten" <jordankersten@>

wrote:

Wow, how did I miss this: the 110 test point reads 100V DC and 11

volts AC. Something

is

up there.

--- In TekScopes@..., larrys@ wrote:

How's the +110?
-ls-

glydeck@ wrote:

Jordan,
I don't have a 465B manual with me, but 40 mv rms does sound a

little on the

high side. I believe that would be about 113 volts pp, [(RMS

x 1.414) x

2=P-P not exactly a sine wave but close enough]. Having a

scope to trouble

shoot the scope is always helpful, but in a case like this

I've used clip leads

to parallel an equivalent or larger capacitor across the

suspect power supply

filter caps in the circuit, and then observe the results on

screen. (Make

doubly sure the working voltage of the cap is high enough.)

This test doesn't

always work because the filter cap could be failing toward

short and not

failing toward open thereby negating the added capacitance.

Ron,
Nice picture, labels and all. I can even count on the

graticule 8 small

divisions between the start of each darkened portion. That

translates to an 8

ms period, or a frequency of 125 Hz. This would be well

within the margin of

error to be 120 Hz ripple from the full wave bridge in one of

the supplies.

I agree you have a similar problem with AC mains.

George



In a message dated 9/29/2008 8:17:21 P.M. Pacific Daylight Time,
jordankersten@ writes:

Just turned off the auto-ranging and took readings again.

They all read

about .003VAC
except the +55 rail. It reads .040VAC. Is that enough to cause

my problem?

I also have the same issue with my Tek 465 scope. A picture

was added

to your photo album:

_.<WBR

()

These are my settings:

1) Set Horizontal sweep to 5 milliseconds per division.
2) Set Vertical to Channel 1.
3) Set Channel 1 to Ground.
4) Center trace vertically.
5) Set Trigger Mode to NORM
6) Set Trigger Source to Line to synchronize to 60 HZ.
7) Reduce the intensity (counter-clockwise) to a bare

minimum to see the

trace.

I'm thinking +15V power supply is the culprit, but not sure.
Unfortunately, I don't have another scope to test this one.

Using the

scope to test itself is no good because the blanking circuit

blanks

it's own trace.

But, it's definitely caused by 60 HZ noise, somewhere...
Ron



****Looking for simple solutions to your real-life

financial

challenges? Check out WalletPop for the latest news and

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()

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How's the +110?
-ls-

glydeck@... wrote:

Jordan,
I don't have a 465B manual with me, but 40 mv rms does sound a little on the
high side. I believe that would be about 113 volts pp, [(RMS x 1.414) x
2=P-P not exactly a sine wave but close enough]. Having a scope to trouble
shoot the scope is always helpful, but in a case like this I've used clip leads
to parallel an equivalent or larger capacitor across the suspect power supply
filter caps in the circuit, and then observe the results on screen. (Make
doubly sure the working voltage of the cap is high enough.) This test doesn't
always work because the filter cap could be failing toward short and not
failing toward open thereby negating the added capacitance.

Ron,
Nice picture, labels and all. I can even count on the graticule 8 small
divisions between the start of each darkened portion. That translates to an 8
ms period, or a frequency of 125 Hz. This would be well within the margin of
error to be 120 Hz ripple from the full wave bridge in one of the supplies.
I agree you have a similar problem with AC mains.

George



In a message dated 9/29/2008 8:17:21 P.M. Pacific Daylight Time,
jordankersten@... writes:

Just turned off the auto-ranging and took readings again. They all read
about .003VAC
except the +55 rail. It reads .040VAC. Is that enough to cause my problem?


I also have the same issue with my Tek 465 scope. A picture was added
to your photo album:
_.<WBR
()

These are my settings:

1) Set Horizontal sweep to 5 milliseconds per division.
2) Set Vertical to Channel 1.
3) Set Channel 1 to Ground.
4) Center trace vertically.
5) Set Trigger Mode to NORM
6) Set Trigger Source to Line to synchronize to 60 HZ.
7) Reduce the intensity (counter-clockwise) to a bare minimum to see the
trace.

I'm thinking +15V power supply is the culprit, but not sure.
Unfortunately, I don't have another scope to test this one. Using the
scope to test itself is no good because the blanking circuit blanks
it's own trace.

But, it's definitely caused by 60 HZ noise, somewhere...
Ron



****Looking for simple solutions to your real-life financial
challenges? Check out WalletPop for the latest news and information, tips and
calculators. ()


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


------------------------------------

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Jordan,
I don't have a 465B manual with me, but 40 mv rms does sound a little on the
high side. I believe that would be about 113 volts pp, [(RMS x 1.414) x
2=P-P not exactly a sine wave but close enough]. Having a scope to trouble
shoot the scope is always helpful, but in a case like this I've used clip leads
to parallel an equivalent or larger capacitor across the suspect power supply
filter caps in the circuit, and then observe the results on screen. (Make
doubly sure the working voltage of the cap is high enough.) This test doesn't
always work because the filter cap could be failing toward short and not
failing toward open thereby negating the added capacitance.

Ron,
Nice picture, labels and all. I can even count on the graticule 8 small
divisions between the start of each darkened portion. That translates to an 8
ms period, or a frequency of 125 Hz. This would be well within the margin of
error to be 120 Hz ripple from the full wave bridge in one of the supplies.
I agree you have a similar problem with AC mains.

George



In a message dated 9/29/2008 8:17:21 P.M. Pacific Daylight Time,
jordankersten@... writes:

Just turned off the auto-ranging and took readings again. They all read
about .003VAC
except the +55 rail. It reads .040VAC. Is that enough to cause my problem?


I also have the same issue with my Tek 465 scope. A picture was added
to your photo album:
_.<WBR
()

These are my settings:

1) Set Horizontal sweep to 5 milliseconds per division.
2) Set Vertical to Channel 1.
3) Set Channel 1 to Ground.
4) Center trace vertically.
5) Set Trigger Mode to NORM
6) Set Trigger Source to Line to synchronize to 60 HZ.
7) Reduce the intensity (counter-clockwise) to a bare minimum to see the
trace.

I'm thinking +15V power supply is the culprit, but not sure.
Unfortunately, I don't have another scope to test this one. Using the
scope to test itself is no good because the blanking circuit blanks
it's own trace.

But, it's definitely caused by 60 HZ noise, somewhere...
Ron



****Looking for simple solutions to your real-life financial
challenges? Check out WalletPop for the latest news and information, tips and
calculators. ()





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1) Set Horizontal sweep to 5 milliseconds per division.
2) Set Vertical to Channel 1.
3) Set Channel 1 to Ground.
4) Center trace vertically.
5) Set Trigger Mode to NORM
6) Set Trigger Source to Line to synchronize to 60 HZ.
7) Reduce the intensity (counter-clockwise) to a bare minimum to see the
trace.

I also have the same issue with my Tek 465 scope. A picture was added
to your photo album:


These are my settings:

1) Set Horizontal sweep to 5 milliseconds per division.
2) Set Vertical to Channel 1.
3) Set Channel 1 to Ground.
4) Center trace vertically.
5) Set Trigger Mode to NORM
6) Set Trigger Source to Line to synchronize to 60 HZ.
7) Reduce the intensity (counter-clockwise) to a bare minimum to see the
trace.

I'm thinking +15V power supply is the culprit, but not sure.
Unfortunately, I don't have another scope to test this one. Using the
scope to test itself is no good because the blanking circuit blanks
it's own trace.

But, it's definitely caused by 60 HZ noise, somewhere...
Ron





--- In TekScopes@..., glydeck@ wrote:

Jordan,
Absolutely. If your triggering off of the mains, and the dashes

are in sync

with the mains it pretty much proves that the Z modulation is most

likely

supply hum. I would agree with your assessment of the power supply

caps being

suspect. That was the root cause when I fixed my 533A. Your 465

is truly a

great scope that you will enjoy when you get it all tuned up.

Good luck,

George



In a message dated 9/29/2008 4:45:05 P.M. Pacific Daylight Time,
jordankersten@ writes:

Also, the dashes in the lines move along the trace...if the trigger

is set

to Line, the dashes stop and the trigger led lights. Would this be

a sign that

it's AC line hum? If so, would power supply caps be the likely cause?

~Jordan~







****Looking for simple solutions to your real-life financial
challenges? Check out WalletPop for the latest news and

information, tips and

calculators. ()


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I have to retract my recommendation for esssurplus. I visited today, and the store is pretty much cleared out. Looks like they are moving exclusively to eBay. There is still some very vintage equipment in the store, but not much of value. Coincidentally their eBay listings now have a lot more small items listed.

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Ahh...Good point. Forgot the part where it's a full wave bridge. -- George

In a message dated 9/29/2008 4:36:56 P.M. Pacific Daylight Time,
larrys@... writes:

He said 2 mS, but that's the culprit. ~8 mS period is roughly
120 Hz. There will be much hum on at least one test point.






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