Re: Necessity of special calibration equipment vs. a good function generator
Which pieces of cal equip did the fun/sig gen and counter substitute for which calibration functions?
Thanks, Dave
-=-=-=- A function generator (or signal generator)?and frequency counter can do the same function. Tom
-=-=-=- The Tektronix manuals give procedures for using their calibration generator, leveled sine wave generator and time mark generator for checking and adjustment of a 2235. I don't know about the time mark generator, but is there any reason a good calibrated function generator cannot be used in place of these? And is there a substitute for a dedicated time mark generator? Philip
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Three articles related to Tek equipment
I recently found among my files three articles related to Tek equipment:
"IC connector assembly aids serviceability" (related to 7104 scope)
"Chip, CRT, and assembly automation bring in a new era of portable scopes" (about 2400 series scopes)
"Embedded microprocessor enhances an instrument's versatility" (about the 494/494P spectrum analyzer)
I've attached scans of these articles, in case someone finds them of interest.
Regards,
Carlos
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Re: Type 184 Time Mark Generator Transistor Question
Oh, and the 2N3251A transistors should work fine as well. The A versions are graded for higher voltage and higher gain. I suspect the leakage will only matter for Q114. The 2N3906 or 2N4403 would be cheaper unless you found a really good deal. On Tue, 15 Jan 2013 22:17:45 -0600, David <davidwhess@...> wrote: Based on the Tektronix parts catalog, I suspect the 151-0133-00 or
2N3251 transistors were graded for an Icbo (collector to base leakage
current) of 10nA or less although the test conditions are unclear.
Some of the other grades of the same transistor are shown as 10 times
worse.
I would be very surprised if a 2N2907, 2N3906, or 2N4403 did not make
a great substitute. They are almost exact matches.
On Wed, 16 Jan 2013 01:38:00 -0000, "andersen_bill@..."
<andersen_bill@...> wrote:
I am repairing a 184 that has had transistors removed from the countdown board.
I am looking at;
Q104
Q114
Q134
SM says "selected from 2N3251"
I can get 2N3251A's local.
I looked at the data sheets. Specs are close. Looks like the A has higher ratings.
Does anyone know if they will work or do I need the non A part?
|
Re: Type 184 Time Mark Generator Transistor Question
Based on the Tektronix parts catalog, I suspect the 151-0133-00 or 2N3251 transistors were graded for an Icbo (collector to base leakage current) of 10nA or less although the test conditions are unclear. Some of the other grades of the same transistor are shown as 10 times worse. I would be very surprised if a 2N2907, 2N3906, or 2N4403 did not make a great substitute. They are almost exact matches. On Wed, 16 Jan 2013 01:38:00 -0000, "andersen_bill@..." <andersen_bill@...> wrote: I am repairing a 184 that has had transistors removed from the countdown board.
I am looking at;
Q104
Q114
Q134
SM says "selected from 2N3251"
I can get 2N3251A's local.
I looked at the data sheets. Specs are close. Looks like the A has higher ratings.
Does anyone know if they will work or do I need the non A part?
|
Re: 465B Oscilloscope No -8V
There could also be a bad bridge. This is not a difficult supply to trouble
shoot, being completely linear and using an op-amp for the control loop. But we
are just going through the process of check most likely failure first. In most
of the cases where the -8 is very low, either a shorted tantalum cap is dragging
the supply down, the bulk capacitor is open, the bridge has opened one diode, or
the op-amp has failed. This assumes the +15 and +55 volt supplies are good, as
stated by the OP.
?
I am somewhat confused with the ESR and Capacitance readings reported as
they conflict. Of course this assumes the test equipment is good :).
?
?
Best,
Tom
?
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Show quoted text
----- Original Message -----
Sent: Tuesday, January 15, 2013 8:40
PM
Subject: RE: [TekScopes] Re: 465B
Oscilloscope No -8V
?
Given the
initial problem you described, I believe you¡¯re looking for capacitors that
check a consistent relatively low ohm with a standard ohm meter (i.e. do not
charge to show open or build towards open). Open or bad caps (high esr wise)
would cause you to have high ripple but not lack of DC.
Unless I
missed something along the way. Hopefully helpful
Rob
--- In TekScopes@...,
"rwdplz1" wrote:
>
> OK, I checked C4419, it is a 5000uF 35V
capacitor. ESR is 0.08, which should be about right. However, after
desoldering it from the board (which is a real pain with the two large
mounting legs), and measuring capacitance, one of my meters couldn't measure
it, and the other read 0.185 nano Farads. Both of these meters read the
capacitance of other small capacitors I have on hand perfectly, so the meters
are fine. ESR of the other large capacitors is about the same, but I'd rather
not desolder them from the board if I don't have to, to prevent damage to the
fragile traces.
>
> --- In TekScopes@..., "Tom
Miller" wrote:
> >
> > OK, good. I would think the next
thing to check is C-4419, a 5000 uF can capacitor.
> >
> >
Regards,
> > Tom
> >
> > ----- Original Message
-----
> > From: rwdplz1
> > To: TekScopes@...
> > Sent: Tuesday, January 15, 2013 2:40 AM
> > Subject:
[TekScopes] Re: 465B Oscilloscope No -8V
> >
> >
>
>
> > The resistance between the -8V test point and ground
(either a test point labeled ground on the board or the scope case) is 49.7
ohms.
> >
> > I replaced one tantalum, C4203, 33uF, with no
effect.
> >
> > --- In TekScopes@...,
"pdxareaid" wrote:
> > >
> > > you might want to check
for shorted tantalum caps in -8 circuits.
> > > see:
> >
>
>
> > phil
> > >
> > >
> > >
> > > --- In TekScopes@...,
"rwdplz1" wrote:
> > > >
> > > > Hello, I am
trying to fix my Tektronix 465B Oscilloscope. I have the service manual and
have been using it to try and figure out what's wrong. When turned on, there
is nothing on the screen, even when pressing and holding beam finder, and the
power light doesn't come on. The only control that seems to work is scale
illumination, which makes the screen glow orange when turned up.
> >
> >
> > > > I checked the voltages at the test points on
the main board A4 as described on page 4-24, and found all of them to be
within spec: +55, +15, +5, and +110, EXCEPT for the -8, which measures 0.2mV.
The power supply wiring diagram at the back of the manual shows two blue wires
from the transformer, going through a fuse F4501 (desoldered and removed from
board, it's good), then through a rectifier bridge CR4411, which is also good.
> > > >
> > > > So where do I go from here?
What voltage should I be seeing at the two blue wires, because I'm starting to
suspect that part of the transformer? Thank you
> > > >
>
> >
> >
>
|
Re: Necessity of special calibration equipment vs. a good function generator
A function generator (or signal generator)?and frequency counter can
do the same function.
?
Tom
?
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Show quoted text
----- Original Message -----
Sent: Tuesday, January 15, 2013 8:43
PM
Subject: [TekScopes] Necessity of special
calibration equipment vs. a good function generator
?
The Tektronix manuals give procedures for using their calibration
generator, leveled sine wave generator and time mark generator for checking
and adjustment of a 2235. I don't know about the time mark generator, but is
there any reason a good calibrated function generator cannot be used in place
of these? And is there a substitute for a dedicated time mark
generator?
|
Re: Necessity of special calibration equipment vs. a good function generator
I actually used a slightly overclocked PIC chip to generate the marks when I re-calibrated my 2465BDM. Set a port high...set it low..wait...do it again, or for wider pulses set it high..wait a little bit..set it low...wait more...do it again. With the correct crystal feeding the PIC you can get exact pulses that are perfect for this type of stuff. Shocked nobody has done this before. I guess a burst mode on a signal generator would do the same. Didn't have one at the time.
Jeff
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On 1/15/2013 7:16 PM, Tom Miller wrote:
A function generator (or signal generator) and frequency counter can do the same function.
Tom
----- Original Message -----
*From:* Philip <mailto:ndpmcintosh@...>
*To:* TekScopes@... <mailto:TekScopes@...>
*Sent:* Tuesday, January 15, 2013 8:43 PM
*Subject:* [TekScopes] Necessity of special calibration equipment
vs. a good function generator
The Tektronix manuals give procedures for using their calibration
generator, leveled sine wave generator and time mark generator for
checking and adjustment of a 2235. I don't know about the time
mark generator, but is there any reason a good calibrated function
generator cannot be used in place of these? And is there a
substitute for a dedicated time mark generator?
|
Re: 465B Oscilloscope No -8V
If the fuse F4501, the rectifier CR4411, the capacitors C4419
and C4203 and the test point TP4439 only shows a tiny voltage while showing 50
Ohms to ground in the off condition, it looks like something around U4206B,
Q4102, Q4105, and Q4106 has failed.
The schematic gives you some test voltages to check in that
area.
The last thing I would suspect is the transformer, but then
anything is possible.
Common sense is your best friend.
tom jobe...
?
?
?
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Show quoted text
----- Original Message -----
Sent: Tuesday, January 15, 2013 5:40
PM
Subject: RE: [TekScopes] Re: 465B
Oscilloscope No -8V
?
Given the
initial problem you described, I believe you¡¯re looking for capacitors that
check a consistent relatively low ohm with a standard ohm meter (i.e. do not
charge to show open or build towards open). Open or bad caps (high esr wise)
would cause you to have high ripple but not lack of DC.
Unless I
missed something along the way. Hopefully helpful
Rob
--- In TekScopes@...,
"rwdplz1" wrote:
>
> OK, I checked C4419, it is a 5000uF 35V
capacitor. ESR is 0.08, which should be about right. However, after
desoldering it from the board (which is a real pain with the two large
mounting legs), and measuring capacitance, one of my meters couldn't measure
it, and the other read 0.185 nano Farads. Both of these meters read the
capacitance of other small capacitors I have on hand perfectly, so the meters
are fine. ESR of the other large capacitors is about the same, but I'd rather
not desolder them from the board if I don't have to, to prevent damage to the
fragile traces.
>
> --- In TekScopes@..., "Tom
Miller" wrote:
> >
> > OK, good. I would think the next
thing to check is C-4419, a 5000 uF can capacitor.
> >
> >
Regards,
> > Tom
> >
> > ----- Original Message
-----
> > From: rwdplz1
> > To: TekScopes@...
> > Sent: Tuesday, January 15, 2013 2:40 AM
> > Subject:
[TekScopes] Re: 465B Oscilloscope No -8V
> >
> >
>
>
> > The resistance between the -8V test point and ground
(either a test point labeled ground on the board or the scope case) is 49.7
ohms.
> >
> > I replaced one tantalum, C4203, 33uF, with no
effect.
> >
> > --- In TekScopes@...,
"pdxareaid" wrote:
> > >
> > > you might want to check
for shorted tantalum caps in -8 circuits.
> > > see:
> >
>
>
> > phil
> > >
> > >
> > >
> > > --- In TekScopes@...,
"rwdplz1" wrote:
> > > >
> > > > Hello, I am
trying to fix my Tektronix 465B Oscilloscope. I have the service manual and
have been using it to try and figure out what's wrong. When turned on, there
is nothing on the screen, even when pressing and holding beam finder, and the
power light doesn't come on. The only control that seems to work is scale
illumination, which makes the screen glow orange when turned up.
> >
> >
> > > > I checked the voltages at the test points on
the main board A4 as described on page 4-24, and found all of them to be
within spec: +55, +15, +5, and +110, EXCEPT for the -8, which measures 0.2mV.
The power supply wiring diagram at the back of the manual shows two blue wires
from the transformer, going through a fuse F4501 (desoldered and removed from
board, it's good), then through a rectifier bridge CR4411, which is also good.
> > > >
> > > > So where do I go from here?
What voltage should I be seeing at the two blue wires, because I'm starting to
suspect that part of the transformer? Thank you
> > > >
>
> >
> >
>
|
Necessity of special calibration equipment vs. a good function generator
The Tektronix manuals give procedures for using their calibration generator, leveled sine wave generator and time mark generator for checking and adjustment of a 2235. I don't know about the time mark generator, but is there any reason a good calibrated function generator cannot be used in place of these? And is there a substitute for a dedicated time mark generator?
|
Re: 465B Oscilloscope No -8V
Given the initial problem you described, I believe you¡¯re looking for capacitors that check a consistent relatively low ohm with a standard ohm meter (i.e. do not charge to show open or build towards open). Open or bad caps (high esr wise) would cause you to have high ripple but not lack of DC. ? Unless I missed something along the way. Hopefully helpful Rob
toggle quoted message
Show quoted text
--- In TekScopes@..., "rwdplz1" wrote: > > OK, I checked C4419, it is a 5000uF 35V capacitor. ESR is 0.08, which should be about right. However, after desoldering it from the board (which is a real pain with the two large mounting legs), and measuring capacitance, one of my meters couldn't measure it, and the other read 0.185 nano Farads. Both of these meters read the capacitance of other small capacitors I have on hand perfectly, so the meters are fine. ESR of the other large capacitors is about the same, but I'd rather not desolder them from the board if I don't have to, to prevent damage to the fragile traces. > > --- In TekScopes@..., "Tom Miller" wrote: > > > > OK, good. I would think the next thing to check is C-4419, a 5000 uF can capacitor. > > > > Regards, > > Tom > > > > ----- Original Message ----- > > From: rwdplz1 > > To: TekScopes@... > > Sent: Tuesday, January 15, 2013 2:40 AM > > Subject: [TekScopes] Re: 465B Oscilloscope No -8V > > > > > > > > The resistance between the -8V test point and ground (either a test point labeled ground on the board or the scope case) is 49.7 ohms. > > > > I replaced one tantalum, C4203, 33uF, with no effect. > > > > --- In TekScopes@..., "pdxareaid" wrote: > > > > > > you might want to check for shorted tantalum caps in -8 circuits. > > > see: > > > > > > phil > > > > > > > > > > > > --- In TekScopes@..., "rwdplz1" wrote: > > > > > > > > Hello, I am trying to fix my Tektronix 465B Oscilloscope. I have the service manual and have been using it to try and figure out what's wrong. When turned on, there is nothing on the screen, even when pressing and holding beam finder, and the power light doesn't come on. The only control that seems to work is scale illumination, which makes the screen glow orange when turned up. > > > > > > > > I checked the voltages at the test points on the main board A4 as described on page 4-24, and found all of them to be within spec: +55, +15, +5, and +110, EXCEPT for the -8, which measures 0.2mV. The power supply wiring diagram at the back of the manual shows two blue wires from the transformer, going through a fuse F4501 (desoldered and removed from board, it's good), then through a rectifier bridge CR4411, which is also good. > > > > > > > > So where do I go from here? What voltage should I be seeing at the two blue wires, because I'm starting to suspect that part of the transformer? Thank you > > > > > > > > > >
|
Type 184 Time Mark Generator Transistor Question
I am repairing a 184 that has had transistors removed from the countdown board.
I am looking at;
Q104
Q114
Q134
SM says "selected from 2N3251"
I can get 2N3251A's local.
I looked at the data sheets. Specs are close. Looks like the A has higher ratings.
Does anyone know if they will work or do I need the non A part?
TIA
B
|
7313 and 7504 manuals are at w140.com (tekwiki).
Dave Wise
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-----Original Message----- From: TekScopes@... [mailto:TekScopes@...] On Behalf Of larrys@... Sent: Tuesday, January 15, 2013 4:50 PM To: TekScopes@... Subject: Re: [TekScopes] 7514 info jerry massengale <j_massengale@...> wrote:
Hi,
I just stumbled onto a 7514. I know nothing about 75xx stuff. It has a
broken knob but looks good otherwise. Seller makes no claim for
condition. I believe it is a 90mhz scope but cannot find a free
manual. I would be grateful for advice.
Jerry Massengale
Should be roughly a 7504, with bistable storage added. The 75XX's didn't stay in the catalog very long.... -ls-
|
Re: Bench Built Isolation Transformer
Transformers do have a max input voltage related to the core flux of the transformer.
Typical off the shelf transformers run about 15-16K (close to the limit of M6 steel) Gauss at 120VAC per primary winding. Typical variac can produce greater than 135VAC if the lower tap is used. At 135VAC, the transformer core flux may be higher than the core material? will be happy with..
Another reason to put the iso-transformer before the variac.
Bernice
|
--- On Tue, 1/15/13, Stefan Trethan wrote:
From: Stefan Trethan
Subject: Re: [TekScopes] Re: Bench Built Isolation Transformer
To:
TekScopes@...
Date: Tuesday, January 15, 2013, 8:26 PM
?
Are you worried about the top end overvoltage, or is there any negative effect at lower voltages?
(I am asking because I had to do it the other way around in one situation, where the output did not reach the desired voltage the "usual" way around).
ST
On Tue, Jan 15, 2013 at 9:13 PM, Geoff Blake <geoff@...> wrote:
The reason to place the variac after the isolation transformer is that the latter will (presumably) be working at its design voltage..
Yes, I am aware of isolated variable voltage transformers.....
Geoff
|
Re: 465B Oscilloscope No -8V
I'm thinking the cap is NOT bad, and your meters simply cannot measure large caps. Try measuring a know-good 4700uF or so cap with it. Did you discharge it before measuring? My Fluke 87 III will not measure large uF caps. Not sure what the spec on it is, but I'm thinking anything above 10 uF won't measure.
Why don't you troubleshoot by checking voltages with the scope turned on. That's the best way sometimes. For example, what's the unregulated Vdc (i.e, the volts DC across C4419) when you get one re-installed?
Jimmy
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Show quoted text
--- In TekScopes@..., "rwdplz1" wrote:
OK, I checked C4419, it is a 5000uF 35V capacitor. ESR is 0.08, which should be about right. However, after desoldering it from the board (which is a real pain with the two large mounting legs), and measuring capacitance, one of my meters couldn't measure it, and the other read 0.185 nano Farads. Both of these meters read the capacitance of other small capacitors I have on hand perfectly, so the meters are fine. ESR of the other large capacitors is about the same, but I'd rather not desolder them from the board if I don't have to, to prevent damage to the fragile traces.
--- In TekScopes@..., "Tom Miller" wrote:
OK, good. I would think the next thing to check is C-4419, a 5000 uF can capacitor.
Regards,
Tom
----- Original Message -----
From: rwdplz1
To: TekScopes@...
Sent: Tuesday, January 15, 2013 2:40 AM
Subject: [TekScopes] Re: 465B Oscilloscope No -8V
The resistance between the -8V test point and ground (either a test point labeled ground on the board or the scope case) is 49.7 ohms.
I replaced one tantalum, C4203, 33uF, with no effect.
--- In TekScopes@..., "pdxareaid" wrote:
>
> you might want to check for shorted tantalum caps in -8 circuits.
> see:
>
> phil
>
>
>
> --- In TekScopes@..., "rwdplz1" wrote:
> >
> > Hello, I am trying to fix my Tektronix 465B Oscilloscope. I have the service manual and have been using it to try and figure out what's wrong. When turned on, there is nothing on the screen, even when pressing and holding beam finder, and the power light doesn't come on. The only control that seems to work is scale illumination, which makes the screen glow orange when turned up.
> >
> > I checked the voltages at the test points on the main board A4 as described on page 4-24, and found all of them to be within spec: +55, +15, +5, and +110, EXCEPT for the -8, which measures 0.2mV. The power supply wiring diagram at the back of the manual shows two blue wires from the transformer, going through a fuse F4501 (desoldered and removed from board, it's good), then through a rectifier bridge CR4411, which is also good.
> >
> > So where do I go from here? What voltage should I be seeing at the two blue wires, because I'm starting to suspect that part of the transformer? Thank you
> >
>
|
Re: Tek 2247a big problems
Hi Richard,
Any 224x manual would get you started, but Shannon Hill has
the 2247A manual at:
You are required to log into Yahoo Groups to get it, but then
you have to have a Yahoo Groups login to belong to Tekscopes.
Great scope that 2247A!
Start with the low voltages, if they are not right, nothing
will work properly.
tom jobe...
?
toggle quoted message
Show quoted text
----- Original Message -----
Sent: Tuesday, January 15, 2013 4:31
PM
Subject: [TekScopes] Tek 2247a big
problems
?
????? Has
anyone had experience with repairing a 2247a , where there is a screen lit,
logic works 100% on all switches. No intensity adjustment no sweep changing,
no digital readout. Any help would immensly be appreciated and or a schematic
location would also help.
?
?? All The Best, Rich
D.
|
jerry massengale <j_massengale@...> wrote:
Hi,
I just stumbled onto a 7514. I know nothing about 75xx stuff. It has a
broken knob but looks good otherwise. Seller makes no claim for
condition. I believe it is a 90mhz scope but cannot find a free
manual. I would be grateful for advice.
Jerry Massengale
Should be roughly a 7504, with bistable storage added. The 75XX's didn't stay in the catalog very long.... -ls-
|
????? Has anyone had experience with repairing a 2247a , where there is a screen lit, logic works 100% on all switches. No intensity adjustment no sweep changing, no digital readout. Any help would immensly be appreciated and or a schematic location would also help.
?
?? All The Best, Rich D.
|
Hi,
I just stumbled onto a 7514. I know nothing about 75xx stuff. It has a broken knob but looks good otherwise. Seller makes no claim for condition. I believe it is a 90mhz scope but cannot find a free manual. I would be grateful for advice.
Jerry Massengale
|
Re: Bench Built Isolation Transformer
It's not quite true that you can ground any one point in the floating circuit - you can ground any low impedance point such as a DC bus or circuit common. If you ground a signal or a high impedance node it may upset the circuit operation.
Ed
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--- In TekScopes@..., "Mover" wrote:
I went through a similar exercise recently - my experience may be helpful to others. My apologies if the following is too obvious to more experienced folks on this group.
A GFCI on the primary side of an isolation transformer is of little use other than protecting you from a ground fault in the transformer primary winding. Rather, I use 40/60/100 watt bulbs on the secondary side in series with the equipment under test to protect from a short in the equipment. The bulbs limits secondary current to about 0.3A/0.5A/1.0A, sufficient for most testing.
On the secondary side driving an SMPS, it should be completely safe to ground or touch ANY ONE point in the SMPS floating ground circuit. It is NOT OK to ground one point and then ground or touch another point at a different place in the SMPS - that will be fatal. Being super cautious, I don't get near anything that is not grounded - period.
Priya.
--- In TekScopes@..., "tubesnthings@" wrote:
Dave;
I see your point; the iso-xfrmr would keep the GFCI from "seeing" a fault on the load side...
B
Sent from my Verizon Wireless Droid
-----Original message-----
From: DaveC
To: "TekScopes@..."
Sent: Tue, Jan 15, 2013 17:22:37 GMT+00:00
Subject: Re: [TekScopes] Re: Bench Built Isolation Transformer
Bernd,
If I understand this correctly, your proposed configurarion will not porotect you if you touch power in the isolated supply (ie, in the DUT.)
The GFCI will protect you only when inatalled in the supply side (as you propose), and only if you touch power in the supply side of the isolator.
Dave
-=-=-=-
On Jan 15, 2013, at 8:38 AM, "tubesnthings@" wrote:
Ed;
Hadn't thought about min voltage for GFCI?€?thx.
Guess pre-variac (and iso-xfrmr) is the place for it?€?
Bernd
Sent from my Verizon Wireless Droid
-----Original message-----
From: Ed Breya
To: TekScopes@...
Sent: Tue, Jan 15, 2013 04:19:35 GMT+00:00
Subject: [TekScopes] Re: Bench Built Isolation Transformer
You can put GFCIs on normal-voltage outlets, but they won't work on variable ones that go below a certain point. The GFCI circuit needs a minimum line voltage to work properly since it has to be able to fire a solenoid plunger that trips the disconnect.
You can probably modify them to work, or find special industrial type ones that can operate over any range, but regular ones as-are will likely not work below a certain line voltage - perhaps one-half the normal amount. It shouldn't hurt the GFCI to run at any lower voltage, but be aware that it may not trip.
Ed
--- In TekScopes@..., tubesnthings@ wrote:
Thank
|
Re: 7623a with cracked crt. Any hope at all?
--- In TekScopes@..., "empr1o" wrote:
Thanks Steve,
You are right that I'm not familiar with all the terms. Some hope introduced here.
Turns out that the one that is smashed has a smashed getter! The remainder of what I write is about the other---the one that has a hairline crack in the getter.
Turns out, I guess, that I don't know if it is the crt that's cracked after all. From my reading all I can see outside of the big case is the getter.
I have seen something of a sign of life along the way. A dot marking in a small circle in the top left corner. It didn't respond to anything, and didn't seem all that healthy.
Tonight, (Eastern) I'll take another look at this getter business. Like I said, I've got all these parts and I'm not sure if any or all are in order.
One other thing---I don't have any probes yet, as I'm not sure I have a scope to connect them too! Will I be able to determine viability without a probe?
A probe is convenient for testing a scope, but not essential. A paper clip can serve the purpose as well. If you have a probe or a BNC cable that brings out the center conductor to a bare wire, you can use it to connect from the vertical input connector to the scope's calibrator signal. This will allow you to see a square wave if the V/div and Time/Div controls are set properly. To use a paper clip, bend the end of the wire to allow it to stick out so you can touch the center of the vertical input BNC connector. With the V/div set to a low setting like 10 mV/div or so, and the time base set to 5 ms/div or so, you should see deflection in the trace synced to power line frequency. Basically your body is acting as an antenna. If you switch to LINE trigger on the time base, note that the waveform remains stable. Note that this technique only works with high impedance (1 M ohm) inputs. Plug-ins with 50 ohm input impedance such as the 7A24, 7A19 or 7A29 will not likely see any signal as the input load is too great acting on the antenna coupling your body is providing ¨C basically the scope is shorting your body to ground ¨C the same as touching the ground connection of the BNC connector. - Steve
|
David Hess